Aftermarket heads on a smogger 400?

[XCELLR8]

How much horesepower do you think one would get by putting on a set of stealth heads on a smogger 400? You should see about a one point increase in C/R with the stealths being a 80CC head. I'm putting in a hughes whiplash cam and was thinking about putting on a set of heads while I was in there. I do not want to remove the engine, so a rebuild is not going to happen at this time.

 

[WileE]

Only a dyno knows for sure. Somebody did a head comparo recently.But, seriously, raising the CR on a smog/low CR engine is a good idea. I'm not familiar with those heads. Talk to Hughes about your combo, they'll recommend a proper cam.

 

[XCELLR8]

Only a dyno knows for sure. Somebody did a head comparo recently.But, seriously, raising the CR on a smog/low CR engine is a good idea. I'm not familiar with those heads. Talk to Hughes about your combo, they'll recommend a proper cam.

Do you know who did the comparison?

 

[WileE]

Do you know who did the comparison?

One of the Mopar mags.

 

[IQ52]

How much horesepower do you think one would get by putting on a set of stealth heads on a smogger 400? You should see about a one point increase in C/R with the stealths being a 80CC head. I'm putting in a hughes whiplash cam and was thinking about putting on a set of heads while I was in there. I do not want to remove the engine, so a rebuild is not going to happen at this time.

If you send the Stealth heads out and have them checked and prepared, use a stock cast iron 4-bbl intake and change ONLY the heads, you would gain about 20-25 HP. Change the heads and put on a good intake manifold and you would see about a 40-50 HP gain. We just tested a low compression 1971 383 and changed the heads and intake, retained the stock camshaft and 4-bbl carburetor and got those results on our engine dyno.

The stock iron manifold will make more torque than the aftermarket manifold to about 3500 rpm and then fall off rapidly.

 

[451Mopar]

If you send the Stealth heads out and have them checked and prepared, use a stock cast iron 4-bbl intake and change ONLY the heads, you would gain about 20-25 HP. Change the heads and put on a good intake manifold and you would see about a 40-50 HP gain. We just tested a low compression 1971 383 and changed the heads and intake, retained the stock camshaft and 4-bbl carburetor and got those results on our engine dyno.

The stock iron manifold will make more torque than the aftermarket manifold to about 3500 rpm and then fall off rapidly.

IQ52, I'd be interested how changing to 1.7:1 rocker arms with the stock cam would work out with the heads and intake swap?

 

[IQ52]

IQ52, I'd be interested how changing to 1.7:1 rocker arms with the stock cam would work out with the heads and intake swap?

Some day we may be able to tell you, but I'm not too inclined to attempt 1.7 rockers on the Stealth heads, there are enough pushrod clearance issue with the 1.6 rockers and 3/8 diameter pushrods.

 

[YY1]

Can't you swap the cam for 1/2 or less the cost of 1.7 rockers?

 

[XCELLR8]

If you send the Stealth heads out and have them checked and prepared, use a stock cast iron 4-bbl intake and change ONLY the heads, you would gain about 20-25 HP. Change the heads and put on a good intake manifold and you would see about a 40-50 HP gain. We just tested a low compression 1971 383 and changed the heads and intake, retained the stock camshaft and 4-bbl carburetor and got those results on our engine dyno.

The stock iron manifold will make more torque than the aftermarket manifold to about 3500 rpm and then fall off rapidly.

Thank you. I'm looking to put in a Hughes whiplash cam, Stealth heads, edy 383 intake, 800 cfm carb, and 1 3/4 headers back to 2 1/2 duels.

 

[Meep-Meep]

Thank you. I'm looking to put in a Hughes whiplash cam, Stealth heads, edy 383 intake, 800 cfm carb, and 1 3/4 headers back to 2 1/2 duels.

This doesn't make much sense to me. I suspect you have a smogger 400 with the original cast pistons and lower end. I have nothing against cast pistons, and have tortured a set on a mild 383 and they never complained, but why do all that high RPM power stuff and keep the same bottom end? Is this for a street car? Then this even makes less sense. My approach would be to build an engine that optimizes power from off idle to 5500 and preserve drivability. Maybe the Hughes cam is magic and will keep the cylinder pressure and idle vacuum up, but typical big cam / low compression situations make for a pretty lazy low end combo. They also throw all the factory carb seting out the window along with the advance curve. I'd forget about max HP and focus on more average power in the low to mid range if this will be a street car. That's not to say a set of better heads won't help, but tread lightly on the cam.

 

[XCELLR8]

This doesn't make much sense to me. I suspect you have a smogger 400 with the original cast pistons and lower end. I have nothing against cast pistons, and have tortured a set on a mild 383 and they never complained, but why do all that high RPM power stuff and keep the same bottom end? Is this for a street car? Then this even makes less sense. My approach would be to build an engine that optimizes power from off idle to 5500 and preserve drivability. Maybe the Hughes cam is magic and will keep the cylinder pressure and idle vacuum up, but typical big cam / low compression situations make for a pretty lazy low end combo. They also throw all the factory carb seting out the window along with the advance curve. I'd forget about max HP and focus on more average power in the low to mid range if this will be a street car. That's not to say a set of better heads won't help, but tread lightly on the cam.

Outside of the cam and heads, the rest is spare parts that came off of the engine that I am building a stroker 451 out of. The motor was supposed to be "built", but when I tore it down, it was just bolt-ons. The whiplash cam is designed for low compression motors, its good for 8.2 to 9.2 C/R, so they say. I was going to put the heads on while I was putting the cam in, as the heads will end up on the stroker motor when its done. Plus it will bump up the compression without pulling the motor. I'm still on the fence with the heads.

 

[451Mopar]

Some day we may be able to tell you, but I'm not too inclined to attempt 1.7 rockers on the Stealth heads, there are enough pushrod clearance issue with the 1.6 rockers and 3/8 diameter pushrods.

Asking because I bought the old CAT stainless steel 1.7:1 rockers on closeout for $199/set. Had to grind the valve stem locating tangs off so they would not hit the valve spring retainers, then I annealed the adjusters to try prevent any breakage of the adjusters. My plan was to install them on my stock 1970 440 HP engine to see if they made much difference, but that engine blew a head gasket before I got to try the rocker arms on the engine. The rocker arms got used on my 505" stroked 440 with stealth heads. I clearanced the pushrod holes, but used Smith Brothers 5/16" pushrods because the spring pressures are not too high. Just running the Comp XR286HR-10 hydraulic roller cam (0.617"/0.614" lift with the 1.7:1 rockers), with the ISKY 8005A valve springs pressure should be about 375# @ 0.600" lift.

I plan to pull the valve covers tomorrow and inspect the rocker arms. They have about 500 miles on them so far.

 

[IQ52]

Thank you. I'm looking to put in a Hughes whiplash cam, Stealth heads, edy 383 intake, 800 cfm carb, and 1 3/4 headers back to 2 1/2 duels.

Eveything I see here would be of benefit to a smogger 400. You might not need a 800 cfm carb but I don't believe it would hurt a thing. I hope you can get a good distributor to get things lit off right.

 

[Kern Dog]

Some people do not have the space or the interest in pulling the engine. I remember how nervous i was when I pulled my first engine for a rebuild.
The OP is doing something I can relate to. He wants to do what he can with the resources he has. We can offer advice, but lets not get mad at the guy if he doesn't follow everyones advice to the letter.