Winter Project...Engine Build

[Its Just Me]

I hope this is the right forum, Modifiers may be better.

 

I’m looking for some advice or recommendations on intake and torque converter selection.

 

Here’s the supporting data: 1971 Monte Carlo SS, air conditioning, .030 over Mark IV 454 (460 c.i.), TH400 trans w/shift improver kit, 3.31 rear gears w/posi, 255/60-15 rear tires. I’m running 1-3/4” long tube headers into 2-1/2” Flowmaster dual exhaust, h-pipe and rear bumper exit.

 

So far, this is the engine configuration I have:

 

Engine has estimated 8.75:1 compression w/forged flat top pistons, 2-bolt mains, stock valve configuration 781 heads (I wish I had the bigger valves, but that’s another story), a GM ZZ502 hydraulic roller cam (.527/.544 lift, 224/234 duration, 112d separation), I’m using the ZZ502 valve springs to match the cam, but shimmed to give consistant 140 psi closed pressure (Sidebar: does anyone know what installed height should be?). GM suggests max 5800 rpm on cam. I’ll be running Howards Max Effort hydraulic retro roller lifters and Comp Cams Ultra Pro Magnum roller rockers. A Holley 750 cfm vacuum secondary, square bore carb, MSD Street-Fire HEI distributor and a Holley mechanical fuel pump.

 

This car is not a daily driver, but it is our cruiser. The intention is to have a very reliable, (and gutsy) road tripper. I want to be able to take it cross country if the desire hits, but don’t want to build it strictly for that purpose. The majority of the driving is day trips or weekend runs with my wife & gear head pals and their cars, and a show of power is a good thing on these events. We’re also considering the Eastern meet next year which is 11 hrs away.

 

So, on to my questions: I have an Edelbrock Performer 2.0 intake (0-5500 rpm) and an Edelbrock Performer RPM Air-Gap intake(1500-6500 rpm), both waiting to be called to duty. Which intake would give me the best bang for the buck in my application? And with that thought, I’m thinking a slight stall converter to get the engine into power. Maybe 2500 flash max? Edelbrock recommends a min 3000 stall with the RPM intake, but I’m afraid that may slip too much with my 3.31 gears on my longer trips. Will a 2200-2500 stall be worth the money or will it be mostly insignificant?

 

Any suggestions, recommendations or questions?

 

Scott

[Sam (Bones)]

throw away the 2.0 intake, the air gap is way better, with your combo I wouldn't go to larger valves, you should have a very torquey engine there

[LIL' Mac]

IMO Sam is absolutly correct. You are MUCH better off with the airgap. The 2200-2500 stahl should work nice for your situation too, I would think. That is just the right amount of stahl for the street as far as I am concerned. I would have thought the flattops would have made more ratio? Like maybe 10:1 ? I am more familiar with SBC builds though.

[LIL' Mac]

I just remembered you said 781 castings. Those are open chamber heads, like 118CC I think. If they have been milled and gasket thickness can also determine comp ratio too. I do see where you got your data from now though.

[Sam (Bones)]

I'm willing to bet your compression ratio is closer to 8.0:1

depending on your deck height, head gasket thickness and I know your heads have at least 118cc chambers or larger unless they have been milled

 

my +.030 454, has 049's that have been milled to 110cc's, L2399F pistons with a 13.8cc dome, .041 thick gaskets and .020 deck height is a 9.6:1 compression

 

but anyway, the 2.0 intakes are terrible, airgaps make great torque, even with a 2000 stall you'll be ok with the cam you are using

[wallaby]

Mine is set up almost the same as yours. I went with the 2.0 intake and it was terrible. The stock iron intake was far better. That 2.0 wouldn't flow enough air to even open my Q-jet secondaries, and it fell flat closer to 4500 rpm...like that was all it had. I thought it would be better at making low-end torque, but when it wouldn't let me run on all 4 barrels, it wasn't even good at that.

 

The performer RPM fixed all that. I didn't go with the airgap, but it's the same otherwise. Don't expect miracles, the RPM performs a tad better than stock, but it weighs a LOT less...it's also better suited for a square bore carb, and has no downside traits.

 

I made the story long, but the point is that the RPM intake is what you want.