Living with a 2.21....

[bschubarg]

I titled this thread, "Living with a 2.21" in reference to the gear ratio I have in my 7 1/4 rear.

THE CAR:

Yeah, I know. The car is a '87 Chrysler Fifth Ave. Not an A-Body. But it is has similar drivetrain and a hood ornament.


The curb weight of "Moby" ( I call her that...) is 3750 lbs. After the diet I put on Moby, she sits at 3470 lbs. I know this 'cause I weighed her at one of those Cat scales.

THE ENGINE:

I have authored several threads here on FABO documenting my trials and tribulations about the lowly 318 Roller LA motor. If you did a search you will find I have ported 302 heads with 1.88/1.60 valves I performed my self.

I notched the intake walls of the cylinders and Flex-Honed the bores.

Replace the rings with Chrome Moly and installed new rod and main bearings.

The ignition is interesting. GM HEI but using the MSD Digital 6 ignition controller. It has Start Retard, Variable RPM Limiter and a Two Step should I go with NO2.

The camshaft is the quintessential 20-212-2 from Comp Cams. 218 @ .050 - .454 Lift Single pattern with the appropriate springs.

The highly regarded Edelbrock RPM AirGap serves as the intake. The center divider notched about 1/2".

670 CFM Holley Street Avenger Vacuum Secondary carburetor with 72/74 jets and the lightest spring I have. Short Yellow one I think.

Your typical 1 5/8" chassis headers that merge into a single 3" exhaust.

Average cylinder pressure is 130 psi and with all the cutting and porting to the chambers I would guess static compression around 8.8 since the car was 9.0 from the factory and all I did was flex-hone. No boring the cylinders here.

I'd say the tweener makes 275-300HP.

QUESTION:

But wait you say; why the hell are you running only 2.21 when the 318 with it's 3.31 stroke screams RPMs.

ANSWER:

The car originally came with the 7.25 with the 2.21 gears and I did had every intention of replacing it. As went so far as purchasing a B-Body 8 3/4 with 3.90 gears.
I drive Moby daily and 95% is all highway. She has been running now after I solved all the little "issues" for a month. I'm averaging 19.2 MPG... WOW....

From a stand still, she won't spin the tires unless I'm making a left or right turn.

But...after 20 MPH she will accelerate and accelerate and accelerate.... passing cars isn't a problem and 75 MPH is the sweet spot. Engine goes into some sort of harmonic rhythm and with the single 3" exhaust it is hardly audible.

So would I change all the positives in exchange for lower MPGs, louder exhaust notes and 75 MPH at 3600 or so RPM I'de get with 3.90s......

In a heart beat.....

 

[273]

Could swap an OD trany into with the rear end have the best of both worlds.

 

[gliderider06]

I would think 2.76 gears would do it much better and get better milage. A slightly higher stall converter as well. The motor wiuldnt have to work as hard to get it moving. If it were me, i would drop down a few jet sizes on the primaries and a stiffer secondary spring. The HEI is good stuff, but what is the advance curve?

 

[540slant6]

Wow, put a 3.23 in that bad boy and It'll be a different animal! I run 3.90s in my D100 and it's really too steep to consider streetable. I think 3.23 is a good middle of the road gear. I run 318's as well and they turn 6,500 RPM all day long.

 

[toolmanmike]

Yep, sounds like you built a nice Teen, now do yourself and car a favor and put a 3:23 under that thing! You'll be happy and still get almost 20 mpg hwy. You probably have a lock up 904 transmission. That is a plus.

 

[rustycowll69]

2.94 might be an option. It might be easier to find and cheaper to buy, if you go 8-3/4.

 

[bschubarg]

I would think 2.76 gears would do it much better and get better milage. A slightly higher stall converter as well. The motor wiuldnt have to work as hard to get it moving. If it were me, i would drop down a few jet sizes on the primaries and a stiffer secondary spring. The HEI is good stuff, but what is the advance curve?

Excellent idea about the TQ. Right now it has one of those lock-up converters so I don't know if any aftermarket TQs are offered. As for the jet sizes: I fiddled around with different sizes for an entire afternoon and found those which are in now, 72/74 work the best. Same goes for the spring. But great idea about the TQ...

 

[bschubarg]

2.94 might be an option. It might be easier to find and cheaper to buy, if you go 8-3/4.

The current 8 3/4 I have sitting in my garage already has a 2.94 in it. Do you think it would make much of a difference between the two?

 

[bschubarg]

Yep, sounds like you built a nice Teen, now do yourself and car a favor and put a 3:23 under that thing! You'll be happy and still get almost 20 mpg hwy. You probably have a lock up 904 transmission. That is a plus.

You gave me an idea ToolmanMike... maybe I will start a new thread asking for suggestions on a gear ratio for my 8 3/4 rear for the 3470lb White Whale ....

 

[jos51700]

Drop the rear gear to a 3:55 and add add-in overdrive automatic from a Dakota.

 

[89.Fifth]

Everybody saying to swap in an overdrive... yeah. That's a LOT of work. Not saying it's not worthwhile, but it's a big project.

I would get 2.71 gears with the sure grip. I would also swap the intake for a ported SP2P with the long skinny runners. Your intake has a relatively big plenum volume and runner cross section for that engine. It puts your power band much higher in the rev range than your gearing will allow.

I have a 4bbl factory ported intake and 600cfm Edelbrock and I think that's really overkill.

Hook up a Tach and watch how much RPM you're turning when accelerating and when cruising down the highway. I bet it's not even 3000rpm. Hell my 5th Ave with 2.21 gears barely breaks 2000rpm. Then go ahead and punch in your numbers here:

Wallace Racing - Intake CFM Requirement

Tell me how many CFM you really need.

What you really need is port velocity. I'm willing to bet a high flowing intake like that has got some really lazy ports on this combination. It would be different if you were turning 4000 or 5000rpm but that's not the case, it ain't a manual transmission 1/4 mile car, it's a slow revving cruiser. Gotta design the combination to match that.

 

[toolmanmike]

I titled this thread, "Living with a 2.21" in reference to the gear ratio I have in my 7 1/4 rear.

THE CAR:

Yeah, I know. The car is a '87 Chrysler Fifth Ave. Not an A-Body. But it is has similar drivetrain and a hood ornament.


The curb weight of "Moby" ( I call her that...) is 3750 lbs. After the diet I put on Moby, she sits at 3470 lbs. I know this 'cause I weighed her at one of those Cat scales.

THE ENGINE:

I have authored several threads here on FABO documenting my trials and tribulations about the lowly 318 Roller LA motor. If you did a search you will find I have ported 302 heads with 1.88/1.60 valves I performed my self.

I notched the intake walls of the cylinders and Flex-Honed the bores.

Replace the rings with Chrome Moly and installed new rod and main bearings.

The ignition is interesting. GM HEI but using the MSD Digital 6 ignition controller. It has Start Retard, Variable RPM Limiter and a Two Step should I go with NO2.

The camshaft is the quintessential 20-212-2 from Comp Cams. 218 @ .050 - .454 Lift Single pattern with the appropriate springs.

The highly regarded Edelbrock RPM AirGap serves as the intake. The center divider notched about 1/2".

670 CFM Holley Street Avenger Vacuum Secondary carburetor with 72/74 jets and the lightest spring I have. Short Yellow one I think.

Your typical 1 5/8" chassis headers that merge into a single 3" exhaust.

Average cylinder pressure is 130 psi and with all the cutting and porting to the chambers I would guess static compression around 8.8 since the car was 9.0 from the factory and all I did was flex-hone. No boring the cylinders here.

I'd say the tweener makes 275-300HP.

QUESTION:

But wait you say; why the hell are you running only 2.21 when the 318 with it's 3.31 stroke screams RPMs.

ANSWER:

The car originally came with the 7.25 with the 2.21 gears and I did had every intention of replacing it. As went so far as purchasing a B-Body 8 3/4 with 3.90 gears.
I drive Moby daily and 95% is all highway. She has been running now after I solved all the little "issues" for a month. I'm averaging 19.2 MPG... WOW....

From a stand still, she won't spin the tires unless I'm making a left or right turn.

But...after 20 MPH she will accelerate and accelerate and accelerate.... passing cars isn't a problem and 75 MPH is the sweet spot. Engine goes into some sort of harmonic rhythm and with the single 3" exhaust it is hardly audible.

So would I change all the positives in exchange for lower MPGs, louder exhaust notes and 75 MPH at 3600 or so RPM I'de get with 3.90s......

In a heart beat.....

View attachment 1715176732

I have a teen in my 70 Swinger. No 4 barrell or cam but no headers or fancy ignition either. I get almost 20 mpg @ 65 with my 3:23's. I mentioned before that your 904 probably is a lock up. A bonus if it is. Yes a A500 overdrive would be a bonus for sure. You built a nice engine. too bad you can't enjoy it more performance wise.

 

[MopaR&D]

I had a 1988 Fifth Avenue for a while, I swapped the rear end for an 8-1/4" out of a Jeep Cherokee XJ (direct fit, all it needs is the spring hangers flipped and moved and the shock mounts cut off) with 3.07 gears (open of course), that made a HUGE difference in the acceleration with that mod alone and it would still cruise at 3000 RPM at 80 MPH (typical freeway speed around here). At the time the engine did have homemade 2-1/4" duals but still the stock 2-bbl Holley with the Lean-Burn system and the difference was obvious; once I converted to 4-bbl that thing really screamed compared to when it was bone stock. The guy I sold it to lives about a half-hour from me and we're friends on FB so I see his updates on the car; he's either going to rebuild the 318 or swap in a hot 360 and most likely do an O/D trans although I don't think he understands how much work that is lol.

Oh yeah and it was getting around 18 MPG mixed 60/40 hwy/city with an old semi-worn-out ThermoQuad, the current owner put on a brand-new 600 cfm Edelbrock and claims he's getting 20 now. I'm sure it would be higher with taller gears since where he lives is mostly open country roads but he and I both like the acceleration the way it is.

 

[AJ/FormS]

I am shocked that you can make 19.2mpg USG, at 75mph, with that combo at 130psi.
As to the horsepower, that 268 probably peaks at around 5000, which in first gear will be around 63mph, with the 2.74 low gear,lol.
I like the 3-2 downshift at 60mph tho; right at about 3900 where the teener is swollen with torque.
3.55s are to 2.21s sorta what one more gear in the trans would be.
That is to say, the 3.55s will multiply your first gear torque by 3.55/2.21=plus 61%.
And the A500od will drop the cruise Rs of the 3.55s from 65= 2930 back to to 1730, or 59%.
But 3.91s are a better fit for the A500, dropping the cruize Rs from 65=3220 to 65=2220................. And the new starter gear of 3.91x2.74=10.71 will really wake the teener up,especially off-the-line.

But I just gotta say, if all you are after is a lil more giddy-up off the line, a lot more compression, or a lot earlier ICA, is the answer. Failing that, a looser TC is the way to go.Of course the compression will fatten up the power everywhere.

And I agree that if you are running a PV, your 72/74 jets would normally be considered way too big ,and the stagger way too small.Typically the frt/rr stagger with a well matched PV is 8 sizes.In all likelyhood the PV is coming in too late if at all, and the 72 is in there to compensate.
When I tune, I ballpark the timing with the T-port sync dialed in and the power-timing ballparked in the 32 to 36 range, coming in somewhere in the 2800 to 3400 range,depending on how tight the TC is.
Then I disable the secondaries, and plug the PV. Then stick a too-small MJ in there and go for a ride. I want to cruize on the top of that MJ, so if you cruize at 2200, I want that MJ to hit at least 2200, before leaning out. Jet up as may be required. Then start on the PV
I might consider doing a LeakDown test.
Just to compare; I run 72/78s on a 750DP fueling my 367HO@400 plus hp streeter.
I also agree that the mighty AG is probably not the best intake for your combo.hat's probably another reason for the 72s, or possibly THE reason.

 

[nm9stheham]

OP, your actual SCR is in the low 8's, not the high 8's. The 130 cranking pressure says that. You're just in the RPM's, at low speeds, of the engine dropping off of the low end of the torque curve, with that lower compression and the cam. The chronic stock 318 issue.....

As above, more compression is the best answer for the 'low RPM torque blues'. You can do a bit with advancing the cam (the earlier ICA mentioned above) but it is going to be more limited of a help at the low RPM's. But more compression means new pistons and going into the engine again.

The higher TC stall is one answer, to let the engine rev up from a stop to a better spot on the torque curve. But if you are driving over the road 95% of the time, there goes your locking TC and the better fuel mileage. I wonder if there is a locking TC with a higher stall that you can get.....??

 

[toolmanmike]

OP, your actual SCR is in the low 8's, not the high 8's. The 130 cranking pressure says that. You're just in the RPM's, at low speeds, of the engine dropping off of the low end of the torque curve, with that lower compression and the cam. The chronic stock 318 issue.....

As above, more compression is the best answer for the 'low RPM torque blues'. You can do a bit with advancing the cam (the earlier ICA mentioned above) but it is going to be more limited of a help at the low RPM's. But more compression means new pistons and going into the engine again.

The higher TC stall is one answer, to let the engine rev up from a stop to a better spot on the torque curve. But if you are driving over the road 95% of the time, there goes your locking TC and the better fuel mileage. I wonder if there is a locking TC with a higher stall that you can get.....??

These guys can. Precision of New Hampton | Torque Converters, Transmission

 

[AJ/FormS]

OP, your actual SCR is in the low 8's, not the high 8's. The 130 cranking pressure says that. You're just in the RPM's, at low speeds, of the engine dropping off of the low end of the torque curve, with that lower compression and the cam. The chronic stock 318 issue.....

As above, more compression is the best answer for the 'low RPM torque blues'. You can do a bit with advancing the cam (the earlier ICA mentioned above) but it is going to be more limited of a help at the low RPM's. But more compression means new pistons and going into the engine again.

The higher TC stall is one answer, to let the engine rev up from a stop to a better spot on the torque curve. But if you are driving over the road 95% of the time, there goes your locking TC and the better fuel mileage. I wonder if there is a locking TC with a higher stall that you can get.....??

As to the Scr I back-calculated the 130psi to; 8.5@ 1000ft, at in ICA of 60*, and 8.3 @ sealevel which yields a VP of100....... at least 33 points below a stock teener (133 for 1969), and 15 points higher than a slanty (85 for 1969). Both at sealevel, and both the highest compression oem examples.
I, probably as most of you, don't want to flat-out call this a bad combo, cuz in this application it's not. The saving graces are 1) it is 95% for a hiway cruiser, and 2) you gotta love the 3-2 downshift at 65 mph!
I built a similar combo back in the 80s, and it was a worse combo......... cuz it was a DD city car, with 2.73s. I had the same results; namely gutless on take-off but getting better with rpm , then back to being a dog on the 1-2 upshift, but a fantastic 3-2 downshift at 50/55 for passing. I put a 2800 in it and that was no big help. That was a low-compression 1973 block with 340 top end and cam. But when I put the 318 cam and heads back on it, then that 2800 was pretty sweet. And 3.55s completed the transformation.
That engine was also pretty sweet with the TTI's and 4.30s and a stick. I still have it, lo these several decades later.

 

[bschubarg]

As to the Scr I back-calculated the 130psi to; 8.5@ 1000ft, at in ICA of 60*, and 8.3 @ sealevel which yields a VP of100....... at least 33 points below a stock teener (133 for 1969), and 15 points higher than a slanty (85 for 1969). Both at sealevel, and both the highest compression oem examples.
I, probably as most of you, don't want to flat-out call this a bad combo, cuz in this application it's not. The saving graces are 1) it is 95% for a hiway cruiser, and 2) you gotta love the 3-2 downshift at 65 mph!
I built a similar combo back in the 80s, and it was a worse combo......... cuz it was a DD city car, with 2.73s. I had the same results; namely gutless on take-off but getting better with rpm , then back to being a dog on the 1-2 upshift, but a fantastic 3-2 downshift at 50/55 for passing. I put a 2800 in it and that was no big help. That was a low-compression 1973 block with 340 top end and cam. But when I put the 318 cam and heads back on it, then that 2800 was pretty sweet. And 3.55s completed the transformation.
That engine was also pretty sweet with the TTI's and 4.30s and a stick. I still have it, lo these several decades later.

There are some ppl here on the FABO forum that I look forward to hear from and their intelligent advice that is tempered yet straight to the point. Your thoughtful replies come with hard data that support your claims and not just biased commentary with hands off experience. You have replied to virtually every Post I placed. All with a perspective that is hard to refute. I welcome your expertise despite you're Canadian. You see, my first wife was from Fredericton, NB Canada. Lasted less than a year and to this day I hate her with every fiber of my being.... But that is another story for another day...

This build is a DD with 95% Highway as you stated and I enjoy the performance and MPG at highway as I built it for highway driving.

If you read the last line of my original post... this is going to change....

As I compose this reply I am looking at the 8 3/4 rear housing that will find it's way behind Moby.

One of your replies to another post of mine gave me hard data that recommended the use of 3.90 in the rear for my current engine configuration. I agreed as that is exactly what I came up with.

But how will I address the highway driving? I have that figured out too. You'll have to wait and see. It won't be the conventional OD...

My Canadian Friend, I wish you well....

 

[AJ/FormS]

Don't be thinking a 2-chunk system. I tried that and it got old in a hurry. It's about an hour and a quarter each time.
Don't be thinking tall tire short tire either, the range is too small. I tried that too. The range is about 10%, but it's the wrong way for traction.
The other choice is a winters QC . I was thinking about it but the GVOD was an easy G cheaper.
IMO, the best idea is to boost the power at lower rpms, and be happy with an intermediate gear like a 3.23/3.55
There is a program for performance WITH economy.
................... First for economy..............Second for performance
compression ..lots...........................................lots
overlap; .......as little as possible,<40*............. lots; >60
extraction...... lots,like >120* ........................ <110*,mostly don't care
TC.................low stall/loc-up......................... hi stall
cruise revs......low ........................................ don't care
Starter gear.... whatever ................................ >10,<13
weight........... light ....................................... light
aerodrag ....... low ........................................ under 65mph don't care

So check out the commons; lots of compression,and light weight.

But for you,IMO, the A833od is a a reasonable solution , but I would ditch that cam if I did that.
I might run it with 3.23s for 75=2150rpm, and a starter = 9.98,and 32mph=2150 in second; and that's where your 268* cam hits a wall. With just 130 psi and VP of just 100;there is no performance with those numbers. To run that 3+1 manual trans with it's very wide 1-2 split(.54) the engine needs to make a ton of torque below 3600 where most of your running is gonna be. That 3.23x1.67=5.39 second gear will make 60=about 4000rpm, so you need a power peak just under that, say 3800.Well that is not gonna be real impressive. You would need more cubes to liven that up; or supercharging.
But the next rear gear 3.55 is plus 9.9%. That would certainly liven up the zero to 60 mph. Lets work it out;
With 3.55s now 75=2400, the starter gear is 10.97 awesome, and 32mph is now 2360. Ok you are still gonna have to dump that cam. And 60mph in second will be 4420rpm so that's looking up. This cam should peak at 4200ish for low ET. That's pretty close to the stocker, maybe plus one size.
Now you say you have a roller motor, but the cam you listed is a FTH.
So I'm guessing you have a 9.2 Scr engine.
If that's true and exact, then I would run a solid FTH, at 248/256/110+2
For about 207/214 [email protected]. That is 11* less than the current 218/or about a size and a half. or 20/25hp or so.
Here's the thing about this smaller cam; The cylinder pressure pops up to near 160, which is plus 30psi over your currentcombo. And the VP pops up to 130, also plus 30 numbers, or plus 30%; this is like a turbo on the bottom. So it will have way more power below about 3000/3500 than the current cam.Your current cam peaks in first gear at around 5000rpm/63mpg. Second gear is outta sight at 113mph. Now this smaller cam will peak at a lesser power number, but; on it's way to 60mph,it will pass thru the power peak twice, once at about 4400=32mph and the second time at 4400=60mph. So even tho it gives up 20/25hp, it will be quicker from zero to 60 mph; less is more in this case.
The 248* cam, as a 110LSA has 32* of overlap,compared to the 48 of your current cam. It has 128* of compression, compared to the 120 of your current cam. It has 120* of extraction compared to the 112 of your current cam. It makes 160psi, compared to your current 130. And the VP is 30% better with the smaller cam. The smaller cam is better for your combo in every way...except it sacrifices absolute power, to get all those pluses.
So finally we come to economy.
You said you were making 19.2mpgs with your current cam, idling along at about 75mph=2060rpm.
Now you will be running at 75=2400, or plus 16.5%, so that could be a loss of mpgs of about; 16.5/2 =8.25% or less 1.56mpgs. But with the smaller cam, and waaay more efficient 160psi, and extra 8* extraction, and manual trans, I'm pretty sure those factors will increase your mpgs back to the former 19.2, and possibly 2mpgs beyond. now you are up to 21mpgs
So then as a two-gear, 0to60, car with a 10.97 starter gear, I wouldn't be afraid to tighten up the LSA to 108 or even 106.
Ok so; the 108LSA will pop the pressure up to 162 and VP back to the stock number of 133. The overlap increases to 36* and both compression and extraction are increases another 2 degrees. On the hiway your mpgs might increase a fraction, and around town she might use a tad more gas. The powerpeak will go up a few rpm maybe 50, but again the bottom-end is back to stock........ but you now have TM of 10.97, versus 6.06 plus TC as a stocker. So your off-the-line would be vastly superior now.
The 106LSA cam would increase the powerpeak perhaps another 50rpm, the VP would pop up to 136, and the pressure is maxed out for iron heads and pumpgas, at 165psi. On the hiway you could theoretically run 87 gas, but at max load it will want best guess.
'Course if you were willing to go to a 106LSA, solid, then you might as well get a 252/260/106+2... which drops the pressure back to 162@133VP..... and now you are up to a net211/[email protected], just one cam size down from the current cam, with no loss in low-rpm performance, compared to the stock 318; and the potential to make a bit more hi-way mpgs and a lot more city mpgs compared to the current engine and combo,and of course a much stronger 2-gear,0 to 60,ET.
BTW, this is about the only way to optimally use that A833 box. The more cam you run with her, the worse the 1-2 split Feels. The more torque your engine makes, the sooner you can hit second gear.
Above is an example of how to take a 318 with a 268 cam,and a weak-azz 100VP, and boost the VP back to stock (130plus) yet move the power-peak back to within about a half cam-size of the 268. That's power with economy, and we never touched the Scr.

Ok so that's all I got. Pretty UN conventional
Thanks for the blessing, and right back atcha.

 

[bschubarg]

You think I should run a SOLID FLAT TAPPET CAM at 248/256/110+2 or did you mean a FTH Cam....lost in translation a bit....

 

[AJ/FormS]

You think I should run a SOLID FLAT TAPPET CAM at 248/256/110+2 or did you mean a FTH Cam....lost in translation a bit....

In this case the only reason to run a solid FT is to restore the cylinder pressure, so the low-rpm performance is at least as good as the stock engine. I don't think any body makes a SolidFT in that 248 advertised size. The solid is about one cam size bigger at .050 than a similarly advertised hydro, because of the faster acceleration ramps.
I know you like your 268/268, but you only ever get to feel the power once below 100 mph, with those 2.21s. In the around town situation a smaller cam with a bigger reargear can and or will be way more fun because the engine is always spinning higher, closer to where the power is.
Here is another exercise
Say your current combo peaks at 5000/63mph. The torque peak usually falls at about 75% of the peak so say 3750, but you only have a VP of barely 100 so the bottom end is gonna be pretty lazy. Neverthless, the cam is waking up at 3750/47mph. Did you catch that?.....47 mph..... in 2.74 first gear.
That means the car is slooooow from zero to 47 mph, then waking up, and on the power by say 4500/57mph, peaking at 5000/63mph, and done by 5500/69mph. Then you put it into SECOND 1.54 ratio and the Rs fall to 4450 and you are back on the climbing part of the power curve to 75mph/4840 rpm;and into cruize-mode.
The next smaller cam
might peak at 200 rpm lower, and so give up maybe 15/20 hp, but with over 80% more TM with the 3.55x3.09=10.97, versus 2.21x2.74=6.06, it will flat out waste the current combo.......... in first gear.
Going two cam sizes smaller,
the engine might peak another 200 rpm lower, but again with 3.09/3.55 combo, the TM will more than make up for the loss of absolute power. Then when the manual combo peaks at say 4600 (5000 of the 268*, less 400), the speed in first will be just 34 mph, instead of 47. But the torque peak might be at 4600x75% so say 3450. That is 300rpm sooner, and the VP is up around 30% higher so that car is gonna be really moving, comparatively speaking. But it doesn't end there.
Running the tach up to 400 past the power peak, say 5000, and then dropping it into second/1.67 ratio, the Rs will drop to 2700 where with the current combo (2700=61mph in second gear), there is no power. But with this smaller SolidFT with its tight LSA,and now at 34mph there is plenty of power. But wait, that smaller tight-LSA cam actually power-peaks an easy 100rpm higher than expected..... and your ported heads are gonna stretch the Rs out maybe another easy 300 rpm, so now your peak might be around 4800/5000 and the shift point might be 5400, and that would be 40mph into second and the Rs now are 2950 in second gear. That's still a bit low, but again, the 130VP will slingshot you to the torque peak at say 75% of say 4800=3600 and the car is moving again.... all the way to 73 mph, for two full trips thru the power peak. And then you put it into overdrive and 75=2410rpm.
Now; this smaller cam with it's higher cylinder pressure, and way less overlap will be right at home at 75mph and passing many filling stations that you were used to stopping at.
This is just an exercise in using increased cylinder pressure by closing the intake so much sooner; 50* versus your current 60*.

The proper way to get the pressure up, is with a greater Scr;meaning hi-compression pistons. In your application,the engine doesn't much care which way you get the pressure, but you should. The more that you have to start with, the bigger the cam that you can run, before the bottom-end goes lazy.
With increased cylinder pressure, your engine/combo could be set up to run your 268/268/110, but I see no reason to. Your application calls for two gears for performance from zero to 60 mph to have a blast with, and a cruiser gear. As such the combo is limited to 3.55s and .73odx3.55=2.59 final drive. There is no reason to have a high rpm cam in that combo. It is just a bottom-end destroyer and a gas-burner on the hiway. I know you were impressed with the 19.2mpg, as am I,but imagine what it could do with an optimized tune.
And yes, you can keep the loc-up automatic, with the right tune, but you won't get BOTH equal performance and equal economy; to the 833od/3.55s. It will have to be biased a bit one way or another.
That's HotRodding.
_______________________________________
If I had your application, the first thing I would do is dump that 268 cam. Well that's maybe not true, the first thing to go might be the 2.21s. Ok maybe the cam,lol.
Then I'd decide on automatic trans or manual trans, and I would choose manual, cuz it's about an instant 2 mpg advantage, with all other things being equal.
Then I'd decide at what speed that's mph, I want the power to be at, and get the gears to put it there.
Then I'd decide solid or hydro, and I'd go solid, cuz I know how hard/expensive it is to get a 318 into the pressure zone, and the solid just makes it easier/cheaper.
Then I'd decide on how much torque to put at what rpm to optimally use those new gears, so I can pick a cam. And finally I would set the Scr to optimally use that new cam.
And finally, I wouldn't give a rat's behind about how much power it is or isn't making, cuz it will be smoking the hiway tires most of the way thru two gears anyway, so who cares about the absolute number.
_____________________________________
Your application is a natural for that 833od trans, one of the few combos I have seen like it. (early on, mine was another). But conversion ain't cheap. It would take several years to break even on gas savings before you start saving money.In the meantime tho, you would be having a blast around town.

If you decide to go 833od, I do have a spare complete set-up taking up space around here, less the floor hump. You would have to engineer where to put the outboard Z-bar anchor and the downrod, The pedal kit is out of a 68 Dart, so not sure if it will fit your FMJ chassis. There are guys on FMJ-body that have converted Dippys, and such, so you won't be alone. Just trying to be helpful, not pushing product..
Happy HotRodding

 

[bschubarg]

In this case the only reason to run a solid FT is to restore the cylinder pressure, so the low-rpm performance is at least as good as the stock engine. I don't think any body makes a SolidFT in that 248 advertised size. The solid is about one cam size bigger at .050 than a similarly advertised hydro, because of the faster acceleration ramps.
I know you like your 268/268, but you only ever get to feel the power once below 100 mph, with those 2.21s. In the around town situation a smaller cam with a bigger reargear can and or will be way more fun because the engine is always spinning higher, closer to where the power is.
Here is another exercise
Say your current combo peaks at 5000/63mph. The torque peak usually falls at about 75% of the peak so say 3750, but you only have a VP of barely 100 so the bottom end is gonna be pretty lazy. Neverthless, the cam is waking up at 3750/47mph. Did you catch that?.....47 mph..... in 2.74 first gear.
That means the car is slooooow from zero to 47 mph, then waking up, and on the power by say 4500/57mph, peaking at 5000/63mph, and done by 5500/69mph. Then you put it into SECOND 1.54 ratio and the Rs fall to 4450 and you are back on the climbing part of the power curve to 75mph/4840 rpm;and into cruize-mode.
The next smaller cam
might peak at 200 rpm lower, and so give up maybe 15/20 hp, but with over 80% more TM with the 3.55x3.09=10.97, versus 2.21x2.74=6.06, it will flat out waste the current combo.......... in first gear.
Going two cam sizes smaller,
the engine might peak another 200 rpm lower, but again with 3.09/3.55 combo, the TM will more than make up for the loss of absolute power. Then when the manual combo peaks at say 4600 (5000 of the 268*, less 400), the speed in first will be just 34 mph, instead of 47. But the torque peak might be at 4600x75% so say 3450. That is 300rpm sooner, and the VP is up around 30% higher so that car is gonna be really moving, comparatively speaking. But it doesn't end there.
Running the tach up to 400 past the power peak, say 5000, and then dropping it into second/1.67 ratio, the Rs will drop to 2700 where with the current combo (2700=61mph in second gear), there is no power. But with this smaller SolidFT with its tight LSA,and now at 34mph there is plenty of power. But wait, that smaller tight-LSA cam actually power-peaks an easy 100rpm higher than expected..... and your ported heads are gonna stretch the Rs out maybe another easy 300 rpm, so now your peak might be around 4800/5000 and the shift point might be 5400, and that would be 40mph into second and the Rs now are 2950 in second gear. That's still a bit low, but again, the 130VP will slingshot you to the torque peak at say 75% of say 4800=3600 and the car is moving again.... all the way to 73 mph, for two full trips thru the power peak. And then you put it into overdrive and 75=2410rpm.
Now; this smaller cam with it's higher cylinder pressure, and way less overlap will be right at home at 75mph and passing many filling stations that you were used to stopping at.
This is just an exercise in using increased cylinder pressure by closing the intake so much sooner; 50* versus your current 60*.

The proper way to get the pressure up, is with a greater Scr;meaning hi-compression pistons. In your application,the engine doesn't much care which way you get the pressure, but you should. The more that you have to start with, the bigger the cam that you can run, before the bottom-end goes lazy.
With increased cylinder pressure, your engine/combo could be set up to run your 268/268/110, but I see no reason to. Your application calls for two gears for performance from zero to 60 mph to have a blast with, and a cruiser gear. As such the combo is limited to 3.55s and .73odx3.55=2.59 final drive. There is no reason to have a high rpm cam in that combo. It is just a bottom-end destroyer and a gas-burner on the hiway. I know you were impressed with the 19.2mpg, as am I,but imagine what it could do with an optimized tune.
And yes, you can keep the loc-up automatic, with the right tune, but you won't get BOTH equal performance and equal economy; to the 833od/3.55s. It will have to be biased a bit one way or another.
That's HotRodding.
_______________________________________
If I had your application, the first thing I would do is dump that 268 cam. Well that's maybe not true, the first thing to go might be the 2.21s. Ok maybe the cam,lol.
Then I'd decide on automatic trans or manual trans, and I would choose manual, cuz it's about an instant 2 mpg advantage, with all other things being equal.
Then I'd decide at what speed that's mph, I want the power to be at, and get the gears to put it there.
Then I'd decide solid or hydro, and I'd go solid, cuz I know how hard/expensive it is to get a 318 into the pressure zone, and the solid just makes it easier/cheaper.
Then I'd decide on how much torque to put at what rpm to optimally use those new gears, so I can pick a cam. And finally I would set the Scr to optimally use that new cam.
And finally, I wouldn't give a rat's behind about how much power it is or isn't making, cuz it will be smoking the hiway tires most of the way thru two gears anyway, so who cares about the absolute number.
_____________________________________
Your application is a natural for that 833od trans, one of the few combos I have seen like it. (early on, mine was another). But conversion ain't cheap. It would take several years to break even on gas savings before you start saving money.In the meantime tho, you would be having a blast around town.

If you decide to go 833od, I do have a spare complete set-up taking up space around here, less the floor hump. You would have to engineer where to put the outboard Z-bar anchor and the downrod, The pedal kit is out of a 68 Dart, so not sure if it will fit your FMJ chassis. There are guys on FMJ-body that have converted Dippys, and such, so you won't be alone. Just trying to be helpful, not pushing product..
Happy HotRodding

God... I think I love you.....Can you cook?

 

[AJ/FormS]

I got married for a couple of reasons; she's a great cook.

 

[thesiren74]

Keep doing burnouts around corners and you won't have to worry about that gearing anymore.

 

[66jim]

had a similar combo with a cam a little too big, I would advance the cam, install thin head gaskets and put in Rhodes
lifters. Low cost weekend project. I think the main reason
people are turned off by Rhodes is they lose some of the
lumpy idle sound ( for the cruise night posers). The also
make mechanical sound that some don't like (like music to me) but they do everything as advertised