Hypothetical build questions…

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rumblefish360 said:
I don’t think it’s that much of a RPM drop and no cam covers that range in a way you could call good. Also, 3K isn’t screaming. You’re just used to new rides that cruise at 70 mph @ 1500 rpm. That’s todays rpm. Yesteryears rpm was an easy 2500 - 3000.

If you’re thinking 3.23’s, your (yet unknown) tire size has a play in a camshaft selection. You said you don’t care about mileage but do not want to travel at 3K rpm. OK….

Your first gear, 3.09 X 3.23 = 9.98 (Excellent for hot rods)
In overdrive, .73 (?) X 3.23 = 2.35 (Not so good for hot rods)
The problem here is a hot rod cam takes advantage and feels best with the first gear final ratio while the OD ratio is so high it’s stifling power and mileage. And the flip side of a small cam….
You get the idea.

If I suggest a cam to try and bridge both the ability to help provide power on take off and be reasonable enough for decent mileage, it can not really be done very well. I know you said you don’t care but here’s the rub, mileage will tank with to large of a cam, a small cam cuts power turning the first gear take off power to a crappy level. A cam between 210 - 218 @050 is what I’d look at myself.


With the Purple cam you have now, I’d use that and tune that carb to be a lean runner on cruise. Fatten the secondary side as needed. Just send it. It’ll be fine enough.

The thing with the OD transmission is the 1-2 & the 3-OD shift has a big drop. You’ll have to rev the engine a bit higher and call it normal. That is just simply how it is going to be. IMO, you can try really hard from here to get the perfect set up with one of the most difficult transmissions and be upset or just not worry about it. You’ll never get to a modern day level, the car lacks all of the equipment that makes it possible except cubic inches and probably a very reasonable car weight.

The old tech is limited. Even if you try and band aid the cam with Rhodes lifters, grab more lift with 1.6 rockers, use new heads custom ported to take advantage of the cam and in the direction you want, it’ll never get to the new car point where you have great power and a double OD for great V8 mileage. Just do the best you can and enjoy it.
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100% FACT^^^^^^

These engines were designed with a cruise RPM exactly where RF says it is.

Thats not screaming RPM. Forcing these engines to cruise at lower than 2000 RPM (and that’s awful low) just kills them. They get dirty. You give up a ton of power because you have to reduce your overlap.

3000 isn’t screaming for these engines.
 
vntned said:
The intent for the car would not be fuel mileage. I don’t care what anybody here says, you are not gonna get good fuel mileage with a modified smallblock. 12-14mpg around town is fine by me.

The intent for the car would be able to drive at modern interstate speeds, 70+mph, without screaming at 3000+rpm’s.

I just took my old D100 on the PowerTour and with 3.23s, an A727 and 28” tall tires out back, it was turning 3000+rpm the entire time.

Not that I will be on the interstate everyday, but I want the capability.


I’m really thinking 3.23s with the overdrive are gonna get me what I want as far as hwy mph/rpm.

The question left to answer is what cam would provide a broad enough power band to cover that 3000rpm drop from 1st-2nd with the overdrive?
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28 in with 3.23 gear at 3000 rpm = 77 mph.

2800 rpm would be 70 mph.

You were speeding.

28in with .73 od and 3.91 gear is 85 mph at 3000.
At 2500 rpm with the 3.91 is 70mph.
 
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They might have been designed for those RPM's but that was back when 55 mph was the general speed limit. And even then, a 3.23 gear and 205/70R14 (E70-14) was only spinning at 2575 rpm at 60 (5 over).

I have a '91 Dakota w/ a 318 TBI motor, A500 and 3.55 gears and it cruises at just over 2K rpm's at 60-65 mph and jumps to 3K when it kicks down to 3rd to pull a hill (gutless motor, 5.9 Magnum swap in the works). Going back and forth makes it pretty apparent that 3K suck, no thanks. Not to say I haven't killed OD for a long hill and then forgotten to turn it back on and not noticed. So certainly you can get used to it, but when sampled back to back, the lower rpm is much nicer.

I run an A833OD in my Duster with a 3.21 rear gear and 25.7" tires. Runs at 2k rpm at 65, pulls the hills without needing to shift down, works well on the highway. Even fun to drive on the side streets, pulls hard enough.

From about '92 or '93 until '98 I drove my Duster as my daily with about the same setup, 3.21/A833OD, but with a slightly taller 26.1" tire. This was with a low compression 360, Isky Mega 270, TQ, HP exhaust manifolds. Worked great, probably a touch more fun that how it is now since the current cam in the car is kind of on the smaller side.

If it were me, I'd run the Purple Shaft cam, maybe find a way to tone down the compression, use the A833OD with some 3.23 gears and enjoy the car for what it is. Should make for a fun all around car.
 
@dgc333 hasn't been on in a couple of years (I think he bought a Focus ST and walked away from here), but he build a really similar setup:

www.forabodiesonly.com

Magnum 360 heads "best" for my build?

So I have a set of Magnum heads ready to bolt on. After some careful consideration looks like I can do about a .510 lift with the right springs. Considering the XE268H cam http://www.summitracing.com/parts/CCA-20-223-3/ Block is a .030 over '99 magnum. Will be going into a '71 Scamp in place...
www.forabodiesonly.com www.forabodiesonly.com
 
Jadaharabi said:
28 in with 3.23 gear at 3000 rpm = 77 mph.

2800 rpm would be 70 mph.

You were speeding.

28in with .73 od and 3.91 gear is 85 mph at 3000.
At 2500 rpm with the 3.91 is 70mph.
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Yes, I was speeding. That’s why I put “70mph+” in my post. Highway speeds are regularly in the 75-80mph range where I live, and I’m not trying to poke along in the slow lane all day at 65mph.

Good job with your math though.
 
The pistons are 10.5:1 is the engine gonna be?

If shifting at 5500-6000 rpm drops to 2500-3000 rpms power just not gonna be to high there.
Plus hp as a % of torque at that rpm range is 48 to 58 % so 20ibs-ft cam difference is 9.6-11.6 hp difference.
 
A 10.5, 340 with 2.02 intake valves and a 284 480 lift cam with 3.91s or 4.10 gears was a 350-396 *** kicker back in the 70s.
 
DionR said:
They might have been designed for those RPM's but that was back when 55 mph was the general speed limit. And even then, a 3.23 gear and 205/70R14 (E70-14) was only spinning at 2575 rpm at 60 (5 over).

I have a '91 Dakota w/ a 318 TBI motor, A500 and 3.55 gears and it cruises at just over 2K rpm's at 60-65 mph and jumps to 3K when it kicks down to 3rd to pull a hill (gutless motor, 5.9 Magnum swap in the works). Going back and forth makes it pretty apparent that 3K suck, no thanks. Not to say I haven't killed OD for a long hill and then forgotten to turn it back on and not noticed. So certainly you can get used to it, but when sampled back to back, the lower rpm is much nicer.

I run an A833OD in my Duster with a 3.21 rear gear and 25.7" tires. Runs at 2k rpm at 65, pulls the hills without needing to shift down, works well on the highway. Even fun to drive on the side streets, pulls hard enough.

From about '92 or '93 until '98 I drove my Duster as my daily with about the same setup, 3.21/A833OD, but with a slightly taller 26.1" tire. This was with a low compression 360, Isky Mega 270, TQ, HP exhaust manifolds. Worked great, probably a touch more fun that how it is now since the current cam in the car is kind of on the smaller side.

If it were me, I'd run the Purple Shaft cam, maybe find a way to tone down the compression, use the A833OD with some 3.23 gears and enjoy the car for what it is. Should make for a fun all around car.
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Really? The speed limit didn’t drop until the Carter administration and national disgrace didn’t start until 1977.
 
Rat Bastid said:
Really? The speed limit didn’t drop until the Carter administration and national disgrace didn’t start until 1977.
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"On January 2, 1974, President Richard M. Nixon signs the Emergency Highway Energy Conservation Act, setting a new national maximum speed limit."

President Nixon signs national speed limit into law

On January 2, 1974, President Richard M. Nixon signs the Emergency Highway Energy Conservation Act, setting a new national maximum speed limit. Prior to 1974, individual states set speed limits within their boundaries and highway speed limits across the country ranged from 40 mph to 80 mph. The...
www.history.com www.history.com

Found one comment that Congress enacted a national 55mph speed limit in '72. Not sure what the difference was.

Later than I thought, no idea if or what the speed limits was before then. But not '77 either.

Just my gut, but I have doubts that people regularly traveled at 65-70 mph prior to the 55 speed limit. But just a guess.

Besides, the world was different then and the highways weren't even completed.

www.roadandtrack.com

The Cars of 1960 Explain Why Your Grandparents Drive Differently

The 1960 Ford Falcon is dog slow today. But it was perfect in 1960. Let Mr. Regular explain...
www.roadandtrack.com www.roadandtrack.com
 
LOL!!!
Rat Bastid said:
Really? The speed limit didn’t drop until the Carter administration and national disgrace didn’t start until 1977.
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Yeah, all the great engines were built, sold, & disco'd by the time the Nat'l gyped-t-five speed limit & 85mph speedos were forced on us. The great thing about the Mopar digital dashes in the '80's was if You pulled out the cluster, there was a little slide switch on the back marked "US" & "Export", slide it on over to "Export" and the mph kept climbing past 85. My '84 LaserXE TurboI went 114mph BTW.
 
DionR said:
"On January 2, 1974, President Richard M. Nixon signs the Emergency Highway Energy Conservation Act, setting a new national maximum speed limit."

[/URL]

Found one comment that Congress enacted a national 55mph speed limit in '72. Not sure what the difference was.

Later than I thought, no idea if or what the speed limits was before then. But not '77 either.

Just my gut, but I have doubts that people regularly traveled at 65-70 mph prior to the 55 speed limit. But just a guess.

Besides, the world was different then and the highways weren't even completed.

[/URL]
Click to expand...


Yup, Nixon passed it and Carter enforced it by threatening to take away some **** I can’t remember. I lived through it. I know exactly how it happened
 
DionR said:
"On January 2, 1974, President Richard M. Nixon signs the Emergency Highway Energy Conservation Act, setting a new national maximum speed limit."

[/URL]

Found one comment that Congress enacted a national 55mph speed limit in '72. Not sure what the difference was.

Later than I thought, no idea if or what the speed limits was before then. But not '77 either.

Just my gut, but I have doubts that people regularly traveled at 65-70 mph prior to the 55 speed limit. But just a guess.

Besides, the world was different then and the highways weren't even completed.

[/URL]
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Dude, You haven't got a clue, most people went that fast on every road they could. They did just as they do Today, drive over the limit by at least 5mph, & those inclined a lot more anywhere they figured they'd get away with it.
What are You talking about? The highways are STILL not completed, I remember when some of the local major Interstate links were completed, but stuff like the Mon-Valley expressway started & stopped so many times, street racers used part of it for a while, and a section of overpass sat there stopped in mid-span like a Kenievel jump begging for a taker. Took 2 decades before it got kick-started again. A lot has been completed now, (almost another 2 decades), but it still ain't finished.
Your "gut tells You" what You read on the web, & I don't give a **** who wrote it, the avg American just wasn't, & still isn't afraid of speed. The Interstates were designed for cars of the '50's to "safely travel at 70mph", as most rural 2-lane roads routinely had 50mph speed limits, 70mph & no stoplights or signs were a major improvement. And yes, We know the concern over the ability to move equipment & goods besides relying on the rails after WW2 was the real intial impetus, not Your vacation plans.
 
Rat Bastid said:
Yup, Nixon passed it and Carter enforced it by threatening to take away some **** I can’t remember. I lived through it. I know exactly how it happened
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Hwy funding among other funding areas. New York was under the same gun again years later. The first Gov. Cuomo decided to adapt California emission standards but he was met with resistance in a big way, he backed down. Until the President threatened to withhold A LOT of money for our Hwy. and other things in the hundreds of millions. He flipped back to the Cali standards. Everyone was pissed at the Gov. a bit but really really pissed at the President.

What sucked for us car guys was a visual inspection for the cars cats. Also, the cars had to be run on rollers to simulate driving down the road. The rollers would detect weight, tire speed and levels of tail pipe pollutants @ the laws 55 mph speeds. To add insult to injury for the car owner, a live camera feed was installed to make sure the computer inputs were for the car being testers and NO shenanigans were taking place.

So, at the time, I was putting together my first ‘79 Magnum and used twin high flow cats off the exhaust manifolds. Thankfully it wasn’t a big deal for the daily driver where power was wallet limited to basic bolt on parts. Not even a cam for the ‘79-360-2bbl engine.

It scooted along well enough and got 20 mpg’s. Work was 25 miles one way, so it was good. She passed emissions as a later F.I. car could. Very clean burning.
 
273 said:
The pistons are 10.5:1 is the engine gonna be?

If shifting at 5500-6000 rpm drops to 2500-3000 rpms power just not gonna be to high there.
Plus hp as a % of torque at that rpm range is 48 to 58 % so 20ibs-ft cam difference is 9.6-11.6 hp difference.
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This is “The Rub” I was talking about in gear shift changes.
Luckily, the Purple cam isn’t to bad at that low 2500 rpm. But it could certainly be better. If you could drop 10*’s of intake duration @.050, that would cover it well.
 
This thread has digressed. Can an admin please go ahead and shut it down?

Thanks for the help guys, there is some good advice in this thread.
 
vntned said:
This thread has digressed. Can an admin please go ahead and shut it down?

Thanks for the help guys, there is some good advice in this thread.
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Agreed, & I'm guilty of starting to participate in the side-track, keep Us updated on the project & best of luck with it.
 
IDK, I think it’s going well.
You got whatcha need.
 
To clarify what meant about power in the 1000-2500 ish rpm range is that mainly decided by displacement then cr. Not saying cam and top end has no effect though but also power is less sensitive to change in torque at those rpms.


Thread seems fairly on track with one off shoot debate, stanard, you got to be like a sheep herder after a page or two if not it's just gonna turn into an open discussion and if you already got what cha need seems ok to me.
 
273 said:
To clarify what meant about power in the 1000-2500 ish rpm range is that mainly decided by displacement then cr.
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I hate to ask but please explain this.
 
rumblefish360 said:
I hate to ask but please explain this.
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Well, 1st we know to gain hp at any one rpm, is with a gain in torque.
2nd the main/easiest way to gain torque is displacement the other is efficiency, cr is a big part of that. 3rd VE is second part of that it's hard to improve down low over stock, most mods will make peak torque gains in a higher mid rpms, torque has frown curve. 4th each rpm has a hp% of torque, we all know 5252 rpm is 100% double rpm same torque 200% hp and half rpm 50% hp, but at 1000 rpm is 19% and 2500 rpm is 48%, 3000 rpm is 58% etc... so if you move torque say by 20 lbs-ft with different cams thats 4-12 hp, not saying so it doesn't matter and or what happens down low, so throw any cam into her it just a little extra info.

Oh ya :) So my overall point to the OP was the majority of hp where 2 gear drops to has already been mostly decided by displacement and cr etc... the cam obviously have some effect on torque there but that torque will have a smaller effect on power at these rpms. To make a decent gain in power you would need a huge increase in torque at these rpms.
 
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My friend John runs that exact Purple Stripe cam in this 385" small block and it absolutely a blast to drive. Go with it advanced 4 degrees.

Tom
 
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