Performer RPM

[-RootS-]

I'm looking for a new set of head on my 351 windsor, i currently have 1969 heads and they are my bottleneck, I made 350 hp on motor and 430 hp on a 125 hp nitrous shot. I was thinkinh about the performer rpm because they are relatively cheap to buy. How much hp will I gain with those heads, I have a performer rpm intake, 9.5:1 compression.

[Technick]

A conservetive estimate would be 50 H.P. Depending on cam, exhaust, and carb could be over 75 H.P. improvement. You also have the benifit of a 50 lb. drop in weight on the nose of the car by going with the aluminum heads.

[BilLster]

well actually maybe none. if your running 350 hp with 9.5 com your heads arent flowing that bad. if they have been ported and polished it may be your cam.

because with the n2o heads wouldnt cause the 80 hp gain from a 125 shot now this 125 is it from the kit or from using the jet's size on a 351 engine instead of a 302 (if the kit is designed for one engine power levels arent compareable for other engine sizes.)a 125 shot on a 302 = 107 on a 351 Flow and fill

69-70 heads have a fuge flow potential and if ported and set up right will flow with any entery level aluminum head.

I'm looking at replacing mine with AFR 205's mainly for weight and to improve flow.

have you used a vacum gauge to determine where your bottle neck is .PKRWUD posted a real good discription on how to test vacum on the intake maf throttle body ant then heads do a search and try it to see if the heads are in fact your bottle neck.

[jruppert]

sounds interesting.. how would i go about finding this post??

[Stang951]

This is from a post that I searched from Chris:

As far as tests with a vacuum gauge, where do I begin...

The vacuum that is created in a normaly aspirated engine (one that is not blown or turboed) gives you a great tool for diagnosing engine problems. Just about any internal engine problem can be identified with a vacuum gauge !!! I'll teach you some of the basics:

1) A steady reading of between 17" and 22" is considered normal for a stock engine.
2) A low but steady reading between 10" and 15" would be caused by retarded ignition or valve timing, or low compression.
3) A very low reading between 4" and 9" means you have a vacuum leak.
4) If the needle fluctuates as you increase the engine speed, you have either an ignition miss, a blown head gasket, a leaking valve or a weak valve spring.
5) A gradual drop in reading at idle means you have excessive back pressure or partial blockage in the exhaust system.
6) An intermittent fluctuation at idle means you have either an ignition miss or a sticking valve.
7) A reading where the gauge needle drifts anywhere between 12" and 22" indicates that your idle mixture is unstable. This is more common on carbureted motors.
8) A high and steady reading indicates that the ignition timing is too far advanced.
9) If, when you quickly close the throttle after running at 2000 rpm for ten seconds or more, the gauge needle DOES NOT jump two or more inches above what it is at idle, your piston rings are shot.
10) If the reading at idle is lower than normal, but the gauge needle fluctuates three inches on both sides of normal, your valve guides are excessively worn.
These are but only a few of the things you can learn about the condition of your engine with a vacuum gauge. Keep in mind that a blower or a turbo will create a false reading because the boost they create offsets the vacuum reading.

The following is the way to find out if you have an internal vacuum leak from a defective intake gasket:

1) Hook up a vacuum gauge to the intake manifold.
2) Fully close the throttle plate by backing out the idle screw all the way.
3) Plug up the PCV valve opening.
4) Disconnect and plug any vacuum hoses attached directly to the intake manifold.
5) Disconnect the wire to the positive side of the coil.
6) Crank the engine and observe the vacuum gauge. From 3" to 7" of vacuum (at a minimum of 250 cranking rpm) is normal. A defective intake manifold gasket will give, in most cases, a zero reading.

With a vacuum gauge, there are two easy tests you can run to determine if your exhaust is restricted (cats clogged).

First test:
1) Attach vacuum gauge to manifold vacuum source.
2) Observe vacuum at idle.
3) Snap throttle to WOT and release, while watching the gauge.

The vacuum gauge should drop to almost zero when you hit WOT. When the throttle snaps closed immediately after, the vacuum should read 4" to 6" higher than what it did at idle. It should then settle back at the same reading it was at idle before the WOT snap. This whole exchange should go from idle reading to idle reading in 2-3 seconds, tops. If it takes longer for the gauge to return to the same idle reading, your exhaust is restricted. The longer it takes, the worse the restriction.

Second test:
1) Attach vacuum gauge to manifold vacuum source.
2) Warm up engine.
3) Observe vacuum at idle.
4) Leave engine idling for 10 minutes. Do not touch anything on the car during this time. In fact, go inside and fix some coffee.
5) After 10 minutes, observe the vacuum.

If the vacuum is the same or higher, you don't have any resctrictions. If the vacuum gauge has dropped, you do have a restriction. The more it drops, the greater the restriction. If it drops 1" or more, you have a serious restriction. 2" or more and you might as well have the exhaust welded shut. Keep in mind that a rich exhaust will clog up cats in a hurry.