High Compression 390

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Thanks for informing me on the 390. The car in my picture is my after racing car/engine. It is 10:1 410 with aluminum W2 heads. I too was concerned about compression. I live at 4000' and have no ping problems. I run 3.23's with a 28" tire. Your truck should be a torque monster. My cam is an hydraulic flat tappet. With aluminum heads you should have no problems unless it's hot an try to bring it up in 4th gear from 10 mph.As far as a cam is concerned, too much duration is the biggest problem as in no low end torque. The cam specs you show will work. The only suggestion is to install it 4 degrees advanced. Unless you just like a rumpty rump sound, too little is way better than too much cam. Go have fun and don't over think your build. I am not an expert just been building Mopars since 1963 The car runs 12.30 's and 108 at Las Vegas
 
do not change rockers- you have to change pushrods too and go through the rocker arm geometry procedure all over again- best to do that on the engine stand
you have a wide ratio 4 speed so do not want a torque drop when you shift
Pick your RPM range- where do you want your torque drive-ability or high rev hot rod- be honest- I won't tell
that will determine your cam duration
then pick the compression to go with the cam duration doing compression first is backward
low compression and big cam is a stocker race build- a dog around town
high compression and a short cam will detonate into oblivion even at your altitude
you need to work together
.050 can be way off as far as picking seat timing
Mike Jones is best for the lower compression short cam combination with a HT or any compression with a HR
Comp, Erson, Isky, have nothing in the range you are looking for in MOPAR
Try working with Lunati- perhaps or Crower lurker will chime in but would have to be custom- nothing in the catalog- same with ENGLE but most of their catalog mopar cams have been custom anyway, also Howard
 
What yellow rose said
Get the rockers you want to run, the call B3 racing engines and have Mike get your geometry correct.
And no, I don't care what name is on the rockers, they won't have the correct geometry. Read this again
Edelbrock requiring some certain head gasket-- I call BS they also want you to run their CRAP cams
You can go Cometic if you have the block decked to their spec- or the .028 will work
what's the compression work out to with the thin gasket, 63 cc head and larger dish in the piston? keeping the 0 deck
remember that that 4 speed is really a 3 speed- are you not taking off in second most of the time? big gear drop
figure it out Car 4 speed or Auto trans can hide a bog
I have a truck with a truck 4 speed also and it had a 3 speed column shift- had an earlier one with a 270 Isky which is like a 280 most anyone elses
If you did not rev it up in 2ed it would be flat when you hit third
 
Once the OP calls the grinder.... none of this will be a question anymore.

Tell him everything about the motor , trans, gear, tire, weight, head flow, header/exhaust system and what your main driving habbits/conditions/aspirations...
"what you're doing with it"..
 
stumblinhorse said:
Wow, thanks... I guess I am asking for opinions from people that might have more experience in this than I do. Not sure what a forum is for if not that. After I do this I will be glad share my experience with people. But at this point I have never built a 390 stroker 11:1 motor.

For the CR, there are not a lot of choices out there for pistons. So right off the bat I was thinking that 11:1 was too high for what I was building. But it is right on the cusp of ok at 7000 ft of elevation with AL Heads. I can build a 9.6 CR motor with cast iron heads and call it good, but wasn't sure I was selling the motor short at that point.
Click to expand...

It's just a warm nudge.
You were mentioning these tiny cams amidst the 'assumed' fact "11.1 compression"
 
Just everyone keep in mind that the OP is going to be at 5000' elevation MINIMUM. 9.6:1 is LOW SCR at those altitudes, because the low pressure makes EFFECTIVE DCR even lower. His atmospheric pressure is going to be almost 8"lower than standard at 7000'.

Think of altitude as 'negative turbocharging'.... when you turbocharge, you lower SCR. So with 'negative turbocharging', you raise SCR. A lot of what gets learned for typical use goes out the window at theses altitudes.

9.6 SCR with a 58 degree ICA (a smallish cam) gives you an effective DCR of 6.7 at 7000'.....that is less than most stock 318's. Cranking pressure is 130 psi with that combo... again, stock 318 territory.

The 11:1 is an actual combination with certain SCAT stoker/piston package and Edelbrock heads. So no assumptions on that matter...
 
It’s a shame they don’t offer E85 in Elbert, you could run higher cr and any cam.

I still think you’d have better luck rebuilding the 318 with well machined heads, nice rockers, the right cam for the remainder of the drivetrain and going EFI. Stock bores and pistons if the math adds up. You would trade off displacement and some power but you’d gain driveabily, start ability, fuel efficiency, and performance over a carb and a simple ignition system. And you won’t have a high-altitude-only truck.

Plus if you play it right, you could get this close, maybe under your budget.
 
the NP 435 is a farm-truck trans. It is a 3 plus granny. And granny is unsynchronized IIRC. I cannot recall that granny ratio but I seem to remember there were a couple available, with ratios between about 5 and 7, to 1, (and I seem to remember one at close to 10/1). In either case, with a 3.55 rear your starter gear is as good as useless at between 16 and 25 to 1, and there is no way to downshift into it. That leaves you with three wide ratio, slow-shifting, high enertia, gears, All suited to a farm-truck or a low-rpm engine. IMO get rid of it.
>At 7000ft and with aluminum heads, you can run almost any Scr and cam you want to, on skunk pee. Just keep the Q in the zone. And I would shoot for high pressure with a cam that suits your application and personal goals.
But
If you run the pressure up,you cannot drive that engine down to sealevel. If you optimize for sealevel, it's gonna be soft at altitude. I'm not saying you cannot drive it down the mountain. I am saying, if the pressure is optimized for 7000ft., then at sealevel, you cannot give her full throttle down there.
And once built,you only have;the ICA to work with, and, if you build it right, the head gasket thickness.
There is about a 30psi change in cylinder pressure between 7000ft and 1000ft.
So it is possible to optimize at 1000ft having a small-cam torque monster,beast of an engine, which at 7000 becomes an average-joe engine.
Or you can set it up with minimum Q at 7000, and maximum Q at 1000, with just a gasket change. 2.5cc doesn't sound like much, but it's still .3 of a point in Scr.
But if the engine will be staying at 7000, and for your stated useage in post #1, then if it was me, I would get the pressure up and probably throw that small carb away.
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My aluminum headed 367 at 10.9 and with a 230*HFT is incredibly docile with a 750DP on it.And once I had the bugs worked out of it, it has never required anything but regular oil-changes. Oh and yes, it still burns 87E10.
If you have to keep that NP trans, You are gonna be starting in second gear about,All the time. You are gonna need torque to get you thru those other wide-ratio gears to top gear. Pressure and cubes are your torque makers. Your 390 will have enough grunt at 7000ft even with pressure down at 160, in which case you could easily run iron closed chamber heads. The question is why would you cheat yourself out of another 25 or 30 psi, if you already have the aluminums?
Jus my opinion
 
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1st is 6.68 and 2nd is 3.34, 3rd is 1.66, easy to remember ratios. It is a farm truck! But west of the Kansas state line they are called “ranches”. I get horse feed with it. Lol. Trucks are hot right now . Don’t you watch Barrett Jackson? Lol.

I run ethanol free 87. Which is available in my county. And the truck will prolly never go less 5000 feet above sea level. And will go to 9000 more than 5000.

But all of these opinions is why I am struggling, some say 11:1 is no problem. Some say I will need a really big cam and some say don’t build it at all.
 
The problem with most camgrinders is that they do not understand MOPAR or long rod motors
it's not just the lifter diameter
a 4" stroke SBC spends more time around BDC so when the intake closes or exhaust opens is not quite as important as it is to a MOPAR- you have more leeway with a SBC and you need it because the lifter is smaller
On the top of the stroke you have longer with the long rod engine- you do not have to open the intake as early and you can close the exhaust earlier- you want less overlap and shorter duration (and with the smaller lifter you have to have longer durations and more overlap to get the valve moving to match the cylinder demand
does that make sense?
so look at your camgrinders catalog
If they recommend the same grinds and timing, LCA etc for a 1.5 rocker SBC and MOPAR they are obviously not doing the MOPAR any favor
and since many do not know what they are doing then you, the mopar professional, have to spec
or use a program like the Controlled Induction software
very few shelf cams for Mopars- sorry
I've posted up a couple of MOPAR cam lists from my database
one is for Factory and Direct Connection/ Mopar Performance cams - in duration order
Direct Connection Cams
the second I called B/RB cams but it basically a lobe list so the lobes are available for SBM also
There are sections that compare with CRANE and the BIg Detroit grinders that use the SAE- .004 advertised notation
and another that compares with the popular .006 method (Comp, Lunati, Howards etc
The DC page uses .008 which approximates the factory method
B/RB Standard Cams

The drill is to pick your rpm range - which gives you a target duration and target dynamic compression then pick an intake close and mechanical compression ratio
If you already have pistons and a fixed mechanical compression ratio you can use the list to maximize your torque
 
So do I understand this right; the truck will be running from 5000 to 9000 feet altitude?
If yes, 11/1plus is peanuts for a small cam and aluminums, which is what you need to haul stuff with.

From 5000 to 9000 your cylinder pressure will drop about 20psi, a huge drop. In fact, with 11.3SCR, your pressure may fall to just 150psi from just 170, with an ICA of 62*,a small cam of say 262/112
So you can already see that 11.3 is a necessity with that cam, not an option, cuz at 150psi, your 390 is already being strained. If you're hauling a load, she's gonna feel it.
So in your case you need a 20psi range, and you might as well run it up to 185psi at 5000, so it only drops to 165 at 9000.
Using that same 262 cam, this would require about 11.8scr at 9000 to get 163psi; which would increase to 185psi at 5000ft
The ICA becomes somewhat critical. Therefore to make power you are gonna need the fastest ramps around, which points to a solid lifter cam.
That 262 cam in a HFT will be about 216 at .050.
A 262solid FT might get you a [email protected]; about 70% of the next bigger cam.If you get a proper 4speed, you can tighten up the LSA to say 108, and then you can run another size bigger cam say and maybe get about [email protected]., still with the 60/62 ICA. That would be 11* bigger but the overlap jumps from 41 to 56, a very significant increase.

On the flipside, you could run a smaller SFT for a smaller ICA and then you could give up some Scr.
Say you were happy with a [email protected]. This could be a 258/266/108 cam with an ICA of 55*. Ok that would take an SCR of 11.4 to make 163psi at 9000ft. Now at 5000, that same 11.4 would make 184psi.
But the 108 cam will not play nice with the NP435 wide ratios. Those 50% splits means if you run the tach up to 5400 say, at the shift, the Rs will drop to 2700, so you have a powerband requirement of 2700rpm. That will take an automatic type cam to cover, like a 115 to 112 LSA. Whereas the A833 will have a powerband requirement of just 1500. So you can run a 108 or even down to a 104Lsa with that..... and that would decrease the ICA again, which would allow a lesser Sca.And if you wanted to, now you could go back to a hydraulicFt cam.
Bottom line is.... IMO..... to get rid of that NP435, and get you an A833, that has splits of about 72%, instead of 50%. That is the whole point I'm trying to hammer home here.
 
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Bypass the 'don't build it at all' for the moment; that is more of an economics position IMO than whether the 390 will work or not. Focus on what will work for this higher CR 390 design, and once you get where you are comfortable, THEN look at the cost and decide if you want to stroke it or not.

I did not realize that this had the NP trans in it, was used for load hauling, and you used 87. So that leads to the following observations:
- A 3:1 usable torque RPM range is highly desirable...actually necessary. I raced in a car with a <2:1 usable torque range and a 1.6 ratio step between 2nd and 3rd. That 2-3 gear step could be miserable when going uphill as you just weren't far enough up on the torque curve when trying to jump up into 3rd. So with your 2-3 gear step of 2:1. you had darned well better have a solid 3:1 torque band..... which absolutely means keep that CR up there. That speaks to your desire to have a smaller cam and higher SCR... both keep the lower end of the torque range alive. OR... AJ's suggestion for a trans change.... but the NP with the granny gear makes it a proper TRUCK so you really can't take it out, right? LOL (Besides, if you are on the farm...err, ranch.... a granny gear does come in handy.)
- The load hauling tends to make detonation a bit more likely. But a lot of that has to do with heat and getting the heads hot. So a good cooling system is a must and also goes along with a higher CR engine, because the combustion temps are higher with higher CR.
- The 87 octane makes things harder with higher CR. So that's working against you. 160-165 psi cranking pressure at the lowest altitude would be my limit, and for sure go with AL heads for ease of making it work. Also make sure you try for an effective quench gap; the .050" head gasket makes that less effective.

I KNOW I'd go with 11:1 kit without hesitation for your 5000'-9000' and have in my arsenal:
  • ignition timing work
  • changing head gaskets
  • adjusting cam timing
to bring it together. BTDT on this type of build a coupla times in my life. The wide torque range is why.
 
I like and agree with nm9..... except;
stumblinhorse said:
Np435 4 speed. Hydraulic FT. Used for fun, no towing or work.
Click to expand...

So I still advise to ditch that slow-performance 3+1 trans.


the D100 is about 3600 pounds right. Make that 3500 with an A833, Make that 3400 with aluminum heads and intake.
At 3400 with a 390@ 185psi..... you are gonna have a lotta,LOTTA, fun, no matter what the rear gear is. Plan on installing a traction-aider real soon. And then you will have to figure out what to do about the violent wheel-hop, because if those chebby-type springs back there, and no pinion snubber,and no weight on the tires. ...... lol. Even a 318 does that; been there done that!
 
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So I might think about a tranny swap later. But for now I am sticking with the NP. That swap is done a lot to these trucks. And since the tranny works great I need to focus on the engine this year.

I can run 91 no problem and is actually about the same $ than E free 87.
 
The 91 is just another 'arrow in your quiver' to make this work out.

This type of engine in a truck with a granny gear will be very strange, at least to me. I always associate a granny gear with the 1960 F350 that I used as my 1st race car hauler with the low compression 292..... 45 mph in 3rd gear up the WV hills on I-64 and in the PA mountain was all it would do. But you shoulda seen the folks scatter and cars scoot out of the way when it was headed downhill LOL....
 
Not too strange to me... I have 2 other trucks that have granny gears that have a lot more TQ than a 390 will have.

So I guess flat tops pistons with Edelbrock AL heads is back on the plan. Any suggestions on where to research open up the chambers to about 65cc?
 
I'd still be shooting for max compression,and no way would I put open chamber aluminums on, not a chance.

But if you gotta have 'em, there is a guy on here that recently acquired a pair, and wants to sell them. Try the for sale section.
 
AJ/FormS said:
I'd still be shooting for max compression,and no way would I put open chamber aluminums on, not a chance.

But if you gotta have 'em, there is a guy on here that recently acquired a pair, and wants to sell them. Try the for sale section.
Click to expand...

Don’t have to have them. Are you saying don’t get the open chamber version 60179? That isn’t what I am saying, I am saying get the closed version 60779, and add a couple of cc to the chamber. Or are you saying get something else’s?
 
Yes I read your post wrong, I did jump to open chamber heads, my bad.
I'm saying the magic of 185 psi and tight Q is phenomenal at 1000 ft, at 7000 it would be just as phenomenal, but the Scr to achieve it will be far greater than at 1000, so I think you're jumping the gun about lowering your STATIC compression. At altitude the TIGHT-Q will be even more important.
Now
The 390 at 3.94x4.00 is 799.177swept
To make 185psi at 5000ft, with a small-cam ICA of say 56* requires an Scr of 11.5.. A bigger cam would require even more Scr.... to make 185psi.
To make 11.5 with the above swept requires a total chamber volume of 799.177/10.5=76.11.
Ok then, 76.11 less 63+8.8 =4.3 in the decks and piston tops. If the pistons have 5cc pockets, then you are already .7 cc in deficit and .010 decks will add another 2cc putting you at 2.7cc deficit. You can't afford to give up 2 more in the heads.
But if the pistons come in at .010 down then you can run the .028(6.3cc) gasket, for a total of .038Q. This will get your total chamber volume back down to 63+6.3+5+2=76.3(with pistons .010 down) and now you are in the ballpark with no deckwork. (799.177+76.3)/76.3=11.47, close enough.
Now as to the 58* ICA, this is a pretty small cam. It could be something like 258/266/110 in at 109. Could be. With a 390 at 185 psi, the Wallace say it makes a VP of 181.That is really really big; so it's a torque monster. You will never ever need the granny gear. After the first time you stuff it in there, just to see, the only time you will ever use it again is for parades.Because 800 rpm will be about 2.8 mph.
OK now at 9000 ft your cylinder pressure might drop to 158 psi, and the VP to 158, which would be normal at sealevel with iron heads.
The beauty of this combo, is that if you want more power, you can slam any cam in there you want to, with a corresponding loss of pressure. But at 5000 ft this is no big deal cuz you have so much of it! of course at 9000 ft, the picture is a lil less rosy.
Ok so say you wanted to get 30 more hp at 5000ft. This is just about 2 cam sizes away, so lets work it out with a 272/280/110. In at 108, the ICA would be 64*. Your pressure would fall to maybe 171psi and VP is still 157; so at 5000 ft you still have monster low-rpm power, and now high-rpm power as well.
Unfortunately at 9000, your pressure is down to 150 and VP down to 138. However this still doesn't make it a dog. 138VP is about what a stock 360 Magnum would make at 1000ft.And your 272 cam is still gonna make plenty of power once winding up...... which you will need with that trans,lol.
One more thing; with the bigger cam, at 1000ft the pressure rises to 193/177VP, so you can still run WOT down there on pump gas. And with a VP of 177now, you can twist your driveshaft up pulling semis out of the ditch.

So bottom line I think is to get the short block built and see what the deck heights come in at, before worrying about the 2 cc in the head you are asking about. As long as you stay with aluminum heads, you cannot, I say cannot, go wrong.

This is an excellent engine combo with a lot of adjustability built right in, at an affordable entry point.
 
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@AJ/FormS that sounds great. My only misunderstanding is when you use ICA of 56*. I think of ICA as installed centerline angle. The cam I am looking at is this spec; Cam Spec Card :: Lunati Power I think the ICA is 106 or am I missing something? Intake closes at 39* abdc. Not sure where to get 56*.
 
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ICA is IntakeClosingAngle
I like that cam for this combo, if you need to run down at 1000.
The ICA is
Intake duration/2 less the installed centerline(ICL), add 360 then subtract the intake duration. The number you get, you then subtract from 180 to get the ICA.

Ok so 268/2 less 106 is 28. Then add 360, and subtract 268 is 120. Subtracting that from 180 yields an ICA of 60*, and that is close to perfect.
Plugging that into the Wallace at 11.5Scr, we get 178psi@169VP at 5000ft, and falling to 156psi@149VP by 9000, and rising to 200psi/190VP at 1000.
Now 200psi is about the limit for pumpgas and aluminum heads; and in the stroker, the 106ICL is not needed obviously, so you could install it at say 109, for an ICA of 63* and that would pull the pressure back to 194psi@180VP at 1000ft, and so now you are good to go WOT at 1000ft.
Now check this out
At 9000 you can run 87 gas.
At 5000 I still run 87, you might start out with 89
At 1000 she's gonna want 91 or better,
depending in the tune. With the .038 Q and aluminums, and if you have a proper cooling system, Ima thinking she will run 32 to 34 degrees power-timing, which is all aluminum heads and tight-Q usually ask for. In any case with that 268 cam and 390 cubes,194psi, and at 1000ft ; you will have a real honey of a stump puller and a pretty good race truck, if it had an A833. With the NP435 shifting at 6500 is gonna be exciting; make sure you have a rev-limiter. The synchros in that trans were built for about half that rpm. The friggin cluster weighs about what my wife did when I met her. The gears are brutishly heavy, and the synchros are built inside out. Get a soft clutch disc with plenty of spring in the hub cuz those heavy gears are gonna want to tear it up if you're not easy on the pedal.
Oh wait, yur not gonna have traction anyway so any old clutch will do,so long as it doesn't slip when you lay on the throttle,lol.
On paper this looks dynomite.
 
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ICA is Intake Closing Angle.... the crank angle after BDC when the valve is closed 'enough' so that no more pressure can escape and the charge can be compressed. ICL is what you are thinking of with the 106.

I assume you want to open up the standard 63 cc Edelbrocks a couple of cc's to get to 65 cc? I'd just do some light cleanup work around the sides by the valve pockets and smoothing things out...which will help prevent detonation... 2 cc's will come out very quickly. (Try taking out 8 cc's (like I did once); that is a lot more serious work.)

Buuut....I'd go for 1 step bigger cam myself.

2.8 mph in the granny gear at idle would be perfect for moving cows around LOL
 
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