High Compression 390

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I would not "overestimate" the effect of the lower air density at higher altitudes here in CO, that lower density's effect on gas engines and detonation is offset by our super low humidity and high summer air temps. I had chronic pinging issues in my old 360 until it finally busted a ring land and cracked a cylinder; it was a 1975 360 LA block bored .060" over with KB flat-tops at zero deck, stock crank and rods, stock Magnum heads and rockers, Lunati Voodoo 256/262 adv. duration hydraulic FT cam (too small), Air-Gap intake, shorty headers... It measured out to 10.42:1 SCR and I had cranking compression only around 160 psi but on hot summer days even with fresh premium 91 in the tank and total mechanical advance of 32* it would ping like a mf'er if I opened up the secondaries in 2nd or 3rd gear (904 trans with 2.94 rear gears). This was when I lived in Denver, then the first year or 2 I lived in Fort Collins so the elevation was usually 5000-6000'.

After that experience I decided I would only go through the effort of a full rebuild for a race car or something really special; having blueprinted high compression and all the associated machine work for the short block just isn't worth it in a vehicle that gets driven all the time with lots of street duty IMO. The satisfaction of having custom-built the engine to my own personal specs wore off after a while especially after seeing so many successful low-compression/junkyard builds on FABO that made more power than my combo. I would have given up 20 HP just to get rid of that damn pinging, the engine would probably still be running today; in hindsight I should have NEVER put that tiny cam in it and just gone with proper duration from the beginning but the high compression still wasn't worth the trouble. Now I'm going with a junkyard 5.9L Magnum and some new top-end parts but no machining to the short block, just because I want to DRIVE the thing. I'd also rather put the money for machining an SBM wedge into the G3 5.7L Hemi swap I will eventually be doing to my Duster.

Since it sounds like this engine will be working pretty hard and get used a lot I would go for lower compression and just use a slightly smaller cam to suit. If it was going in a weekend-warrior type A-body I'd say go for it but 11:1 in a farm truck seems like a gamble to me IMO.
 
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I do not know where we are on this but
too bad there are no heads between 3 and 30 cc (est)
I don't mind 10.5 with 87 or 11 with 91 at altitude but I'd build for 87 and run 91 with a load or if going flatland
I do think the quench at .050 + .010 is way more than I'd like to see
and no way with the open chamber heads
you can open the chamber around the intake with the valve guide machine and pick up 5 cc
put the heads on the bare block and scribe the bores then open to the bore the flow prefers a match - do make the chamber larger than the bore but sometimes they are that way already (thinking big block here) if the chamber overhangs the bore chamfer the top of the block
keep working with Lunati you are close depending on which way the compression comes out
 
I would say farm truck is a stretch . But yes it has a np435 in it right now. It doesn’t do work, but it also is not a strip truck either. It’s a driver, it gets driven, whether is to the store or a car show or to my job. so I am back to thinking .038 head gaskets and maybe try to get the heads to 65cc by enlarging the chamber on the edge of the bore. Maybe jump up to a 276 Lunati.
 
stumblinhorse said:
I would say farm truck is a stretch . But yes it has a np435 in it right now. It doesn’t do work, but it also is not a strip truck either. It’s a driver, it gets driven, whether is to the store or a car show or to my job. so I am back to thinking .038 head gaskets and maybe try to get the heads to 65cc by enlarging the chamber on the edge of the bore. Maybe jump up to a 276 Lunati.
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Just play with a dynamic compression calculator on int close for an idea...and hopefully the grinder gets you a cam that captures 180-190 psi dynamic. If you ever dip into sea level... you might stand a chance.
 
@nm9stheham and @AJ/FormS last question, for today :lol:. Better to get the bigger Cam, Lunati 276, and keep a 1.5 rocker ratio or get the smaller Cam, Lunati 268, and get 1.6 rocker ratio? I think with the 276 cam and 1.6 ratio I am right under the limit for the stock edelbrock springs.
 
stumblinhorse said:
@nm9stheham and @AJ/FormS last question, for today :lol:. Better to get the bigger Cam, Lunati 276, and keep a 1.5 rocker ratio or get the smaller Cam, Lunati 268, and get 1.6 rocker ratio? I think with the 276 cam and 1.6 ratio I am right under the limit for the stock edelbrock springs.
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That's a question you should be asking the cam grinder. That's why I told you to call several cam grinders and see who you get along with the best, and then do what they say.

Of all the relationships I have in this crap business, my relationship with my cam grinder was most important. When you are getting 100 or more cams a year, you have flow bench and dyno data it becomes very easy to get the exact cam the first time.
 
It's all about torque fall off when you shift
calculate the % rpm drop 2-3 and 3-4
me if these are forged pistons I'd send em to Texas and have them dished (I'd do it myself)
see if whoever is going to tune up the heads (check the guides for tight and maybe give them a better concentric valve job ) can open up the chambers
use the thinner gasket- anyone else used another but Edlebrock's gasket- and since Edelbrock does not make gaskets whose is the cheapest gasket they were able to find?
I'd rather have a little more compression and a lot tighter quench - but that's me
My gut tells me the 268 Lunati cam with the 1.6 rockers on the intakes only would be max for that truck trading broad torque band for a little top end HP
If it was me I'd call Rick Jones at Controlled Induction and see how much he would charge to run the numbers for you- have your head flows handy, see how he adjusts for altitude and the other things that make your build sorta special- like the 3 speed
any chance on running a sft?
cheers
let me know what he says
 
Wyrmrider said:
It's all about torque fall off when you shift
calculate the % rpm drop 2-3 and 3-4
me if these are forged pistons I'd send em to Texas and have them dished (I'd do it myself)
see if whoever is going to tune up the heads (check the guides for tight and maybe give them a better concentric valve job ) can open up the chambers
use the thinner gasket- anyone else used another but Edlebrock's gasket- and since Edelbrock does not make gaskets whose is the cheapest gasket they were able to find?
I'd rather have a little more compression and a lot tighter quench - but that's me
My gut tells me the 268 Lunati cam with the 1.6 rockers on the intakes only would be max for that truck trading broad torque band for a little top end HP
If it was me I'd call Rick Jones at Controlled Induction and see how much he would charge to run the numbers for you- have your head flows handy, see how he adjusts for altitude and the other things that make your build sorta special- like the 3 speed
any chance on running a sft?
cheers
let me know what he says
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If everything comes in at the right spec, the SCR would be 11.27:1 from wallace calculator. For another $100 I could have the pistons made custom to bring me to about 10.5:1. But is my 7000 ft altitude just canceling out the need for the extra $100 on a custom dish? So save the hundred for better rockers? From Wallace DCR
Static compression ratio of 11.27:1.
Effective stroke is 3.25 inches.
Your dynamic compression ratio is 9.34:1 .
Your dynamic cranking pressure is 161.95 PSI.
Your effective boost compression ratio is 7.94 :1.
V/P (Volume to Pressure Index) is 154

Where I am at is the 268 lunati with 1.6 rockers on the edelbrock 63CC will be a great combination. If I get some pinging at 5000 ft above see level, I will just pull the heads and take a cc or 2 off around the edge of the bore.
 
sounds good
I don't remember but does the Wallace calculator work off .050 or advertised?
one of the calculators does not consider intensity (shows factory slow cam closing earlier than it really does and shows faster aftermarket closing later that they really do
 
Wym, the Wallace calculator works with an entered value of ICA, so I think the answer to your question is no, it just uses that as the termination point for pressure release via the intake. I think you may be thinking of the Comp calculator, which IIRC works from .050" and makes some assumptions of how much later the valve effective closes. FWIW: For the Wallace and Pat Kelley calculators, I typically put in advertised unless it is for a solid, where I adjust from advertised to try to account for lash.

I personally agree very strongly with the tighter quench gap. And I like the 1.6 rockers but my hesitation of putting them with a Lunati Voodoo cam is that you are putting more force on the valvetrain with an already fast slope cam. Where I really hesitate is at the lifter/lobe interface. I bet peak pressures on the lifters and lobes will go up by >10% or more, with the 1.6 rockers. You get a mildly exponential increase since the force is related not just to the lift ratio, but is also increased by the increased valvetrain velocities. That same applies to the Voodoo and XE types cams: the valvetrain force goes up more than many folks may realize.

We put 1.6 rockers in my son's 340 but it was with a milder ramped Crane 268 cam.
 
MOPEkidD-3 said:
I would not "overestimate" the effect of the lower air density at higher altitudes here in CO, that lower density's effect on gas engines and detonation is offset by our super low humidity and high summer air temps. I had chronic pinging issues in my old 360 until it finally busted a ring land and cracked a cylinder; it was a 1975 360 LA block bored .060" over with KB flat-tops at zero deck, stock crank and rods, stock Magnum heads and rockers, Lunati Voodoo 256/262 adv. duration hydraulic FT cam (too small), Air-Gap intake, shorty headers... It measured out to 10.42:1 SCR and I had cranking compression only around 160 psi but on hot summer days even with fresh premium 91 in the tank and total mechanical advance of 32* it would ping like a mf'er if I opened up the secondaries in 2nd or 3rd gear (904 trans with 2.94 rear gears). This was when I lived in Denver, then the first year or 2 I lived in Fort Collins so the elevation was usually 5000-6000'.
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Which is perplexing.... 'cuz I had a 10+ SCR at 160 psi cranking pressure (at 1000') iron headed 351C that I ran at 1000-2500' all the time, and no issues. DCR worked out in the 8.2 or so range, higher than yours.
Now that engine DID have quench, and polished chambers to help fight detonation. I did not go high on ignition advance either or I would run into pinging.... could not tell you where it actually ended up. Another difference was in the cam; the .050" intake duration was something like 194.... really and truly, but it had long, slooow ramps, unlike your Voodoo cam.. .and a 114 LSA. Oh, and 3.08 rear gears in a 3300 lb Ranchero; Torker intake and headers. No problems....

Your story makes me wonder again about 91 octane..... others have reported issues with it with SCR/DCR numbers that in my experience, would not be an issue.

The differences are:
  • 93 vs 91 octane
  • quench versus none and open chambers
  • polished chambers very
  • probably 2-4 degrees later ICA for mine
  • perhaps cam ramp effects
  • MAYBE humidity (which does indeed have a strong effect) but cool fall days in the VA mountains are very dry too
  • Ford SB vs Mopar SB....????
 
I spoke to Racer Brown about a cam today. Jim also agreed that with the right quench, 11.25:1 wouldn’t be a problem. He is going to think about a cam with the right amount of lift and duration for the altitude.
 
stumblinhorse said:
I spoke to Racer Brown about a cam today. Jim also agreed that with the right quench, 11.25:1 wouldn’t be a problem. He is going to think about a cam with the right amount of lift and duration for the altitude.
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Damn good decision. I promise you'll be much happier with the end product if you talk to the cam grinder first. I don't care if it's Lunati or who you chose. At least call the first.

I like the smaller grinders the best because I always get to talk to the same guy. And I know they aren't going to sell me a grind off the shelf just because it's sitting there.
 
stumblinhorse said:
I spoke to Racer Brown about a cam today. Jim also agreed that with the right quench, 11.25:1 wouldn’t be a problem. He is going to think about a cam with the right amount of lift and duration for the altitude.
Click to expand...

Nice, I think I'll call him for my cam too, that's reassuring he says it will work. I wouldn't be surprised if the quench was off the mark in my past build, I used .039" head gaskets but didn't go through the full process of making sure each piston came up to zero deck. I only measured #1 and it was still .003-.005" below, the rest may have been more or less as my machinist said the block had already been decked but not square-decked. Also I later checked the accuracy of my Harbor Freight compression tester with my air compressor and it was definitely reading low by maybe 20 psi at 150 on the compressor gauge so I think the actual compression was higher. @nm9stheham the Voodoo cam I had not only has 'fast' ramps but is ground 4 degrees advanced from the factory and is advertised as being intended for smaller-displacement engines with stock/lower compression. I first bought the cam for the stock 318 the car came with, I was dumb and wanted to save a couple hundred bucks so I reused it (with lifters of course) in the 360. Sure had a sh**load of torque on the bottom end at least and it lasted maybe 20k miles even with all the pinging.
 
nm9stheham said:
Wym, the Wallace calculator works with an entered value of ICA, so I think the answer to your question is no, it just uses that as the termination point for pressure release via the intake. I think you may be thinking of the Comp calculator, which IIRC works from .050" and makes some assumptions of how much later the valve effective closes. FWIW: For the Wallace and Pat Kelley calculators, I typically put in advertised unless it is for a solid, where I adjust from advertised to try to account for lash.

I personally agree very strongly with the tighter quench gap. And I like the 1.6 rockers but my hesitation of putting them with a Lunati Voodoo cam is that you are putting more force on the valvetrain with an already fast slope cam. Where I really hesitate is at the lifter/lobe interface. I bet peak pressures on the lifters and lobes will go up by >10% or more, with the 1.6 rockers. You get a mildly exponential increase since the force is related not just to the lift ratio, but is also increased by the increased valvetrain velocities. That same applies to the Voodoo and XE types cams: the valvetrain force goes up more than many folks may realize.

We put 1.6 rockers in my son's 340 but it was with a milder ramped Crane 268 cam.
Click to expand...

I'm posting 3 sorted by duration lists of cams
one for .008 for Factory and DC and Engle
one at .006 for Comp, lunati, howard
and one at .004 for Edelbrock, summit, melling, Sealed Power, Elgin, Wolverine, CRANE TRW, etc
users can use to help determine intake close
take the intake centerline (here 106) and subtract from 180 to get the degrees to BDC (180-106 = 94 then take half the duration (say 284/2 142) and subtract the degrees to BDC number 142-96 = and what's left is the 46 ABDC intake close estimate-- fudge for asymetrical grinds, adjust for checking height and "intensity" when does it really close
you can also calculate "intensity" ( which will be different for each checking height for the same cam)
 
MOPEkidD-3 said:
Nice, I think I'll call him for my cam too, that's reassuring he says it will work. I wouldn't be surprised if the quench was off the mark in my past build, I used .039" head gaskets but didn't go through the full process of making sure each piston came up to zero deck. I only measured #1 and it was still .003-.005" below, the rest may have been more or less as my machinist said the block had already been decked but not square-decked. Also I later checked the accuracy of my Harbor Freight compression tester with my air compressor and it was definitely reading low by maybe 20 psi at 150 on the compressor gauge so I think the actual compression was higher. @nm9stheham the Voodoo cam I had not only has 'fast' ramps but is ground 4 degrees advanced from the factory and is advertised as being intended for smaller-displacement engines with stock/lower compression. I first bought the cam for the stock 318 the car came with, I was dumb and wanted to save a couple hundred bucks so I reused it (with lifters of course) in the 360. Sure had a sh**load of torque on the bottom end at least and it lasted maybe 20k miles even with all the pinging.
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I did not realize your quench was that good.... .043 or so is decent.

OK, yeah, if that gauge was that far off, then at 170-180 psi, you were reeeealy up there in DCR with that short of a cam duration. But I bet the low end torque was sumpthin' !

One other thought: Your Voodoo cam profile had the potential for better cylinder filling than the slooow ramp cam that I used. So that may be another factor; better cylinder filling, or 'area under the curve', should push up effective DCR, like being at a lower altitude.
 
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stumblinhorse said:
I spoke to Racer Brown about a cam today. Jim also agreed that with the right quench, 11.25:1 wouldn’t be a problem. He is going to think about a cam with the right amount of lift and duration for the altitude.
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Sound very promising. I'd like to hear about the specs and the ramps in particular.

And just remember, you have some easy to implement 'outs' to keep this under control.

Working that 2:1 gear step is a challenge, but if you can conquer that with good torque all across the RPM range, it will be pretty cool.
 
Have you ever considered a turbo? Wide torque curves are its specialty. You could shift at 5000 bringing it down to 2500 and immediately have full boost.
 
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