Changing Cylinder Heads should I change my cam too?

[rhart]

Hi all,

I put my car on the dyno and was somewhat disappointed. My 1969 351W only put 255 Max RWHP and 307 Max RWTrq. The funny thing is that the HP begins to fall off at 4400RPM.

I recurved the Distributor and that seemed to help wake the Sluggish 351w up from 2500RPM up to 6000RPM. I went to the Drag strip and ran 104@13.3 1/4mile. I could not hook on street tires.

The motor has an Edelbrock Performer Intake and slightly ported heads, Flat top Pistons and a Reed Racing Solid Lift Cam with 290 Duration and .490 Lift, 750 Demon(not so happy with the Demon) with MSD and Mallor Unilight.

I was going to buy some Edelbrock RPM heads to improve things but I also thought I may go to a hydraulic Lift Cam. I love the sound of my car(it beats the ground as they say) and would want a hydraulic cam with similar sound and but better performance. I have a 3.73 gear and want to run the motor in tthe 2000 - 6000 RPM range.


Any cam recommendations are appreciated.

[Dennis Kelley]

Call Comp Cams. I went to small on my cam and it cost me some power. Good luck.

[TerrysSPF]

Check out the AFR heads. 185 or 205's would wake it up. Victor Jr. intake, and (as Dennis said) call comp cams. Have you considered a stroker kit? Check out DSS. www.dssracing.com
Reasonable prices and quality stuff.

[Jack21]

Motor out of breath by 4,400, eh? Performer not designed to do much better than that, and stock iron heads are boat anchors. Don't blame the Demon just yet.

Get a pair of AFR185's, or TFS TW Street heads. Then bolt on a Performer RPM or Air Gap intake. Put the Demon back on, and then tell us what you think.

Definately hang on to the Demon 750 if you go the 393W stroker.

I have a Demon 650 on a 351W and love it.

[auto10x]

Get AFR 185's.
auto10x
Bill

[newBDR]

I'm no expert but I think that carb's too big also. I saw a good calculator once to figure what size carb you really need (forget where, maybe on this site). I was surprised at how small the recommendations came out to be. But a lot of comments from people with more know-how than me indicated that it was right on. Just something to look into.

[cleggy]

I like Jacks answer, AFRs, RPM manifold, the performer is not a high rpm manifold, by the way I assume the engine is basically sound, before you start adding hipo parts, make sure your compression is where it should be, the timing is right etc.

[Curt C.]

Ditto to Jacks response. Try the AFR 185 heads with the RPM air gap. You will definately be surprised.

[relaxinrob]

The right cam is important to match to the heads because if your new heads flow well and there isn't enough lift or duration to accomodate the flow, then you've wasted time and money. Talk to the guys at Comp Cams and tell them what you have or what you're getting and they will match you up with the proper cam.

[cuda66273]

You curved the distributor?

So now you have about 22-24 Initial and 35 total at about 28-2900 RPM all mechanical advance no vacuum unit...right?

Not Happy with the 750 Demon???

Your 750 Mighty Demon should be tunable although a 650 Mighty Demon would work allot better on that little motor.

You do have the Mighty Demon right?

A 290 advertised duration is about a 244-46 at .050, that's a race cam or at least a stout bracket car. It will make it's power from about 3000 to 7000 RPM.

Your Performer manifold can't breath enough to handle the cam which really wants a single plane large plenum intake and a good set of heads with at least a 2.02 valve.

Of course when you add manifold volume the velocity decreases and the bottom end falls off even worse although the top end 3500 to 7000 the thing will be trying to turn itself inside out.

So what we have here is a typical imbalance of components and it's maybe time to make some decisions on how you want the car to perform.

If you want street manners and canyon carving smooth performance then you should look at a smaller cam to match the manifold, compression ratio and head flow that you already have...look at a Racer Brown SSH 24.

Nice Hydralic cam, ground pounding sound, good low end tork, works good with the Performer Manifold and will carry 6000 RPM without any problem and maintain reasonable street manners.

If you want that all out asphalt ripping neck snapping dragster type power then you need to make some changes to match that cam.....single plane manifold, better heads, more compression (at least 11.5:1 on Al heads and 10.5 on steel) you'll need to run additive or mixed race gas, maybe even some more gear and be prepared to let it rip to about 6500 to real let it work. You might be able to live with the 750 as long as it is a Mighty Demon.

So where do you want to go and maybe I can help you get there?

Don

[cuda66273]

Her's some links to my site with the information that may help you understand more:

Carb CFM calculator for Demon Carbs
http://www.4secondsflat.com/Carb_CFM_Calculator.html

Racer Bown cam specs and combination suggestions:
http://www.4secondsflat.com/Racer_Brown_Cam_Specs.html

You may find this article of interest also:
http://www.4secondsflat.com/Cam_Design.html

[rhart]

Thanks for all the input.

I worked on the motor this week and found that the timing marks were way off. I able to advance the timing several degrees. And I also change the Demon 750 to Holley 650 DP. The engine feels much more responsive and pulls much harder.

I agree that the AFR or TFS heads would make guite a change with another intake. That may happen later this spring.

Rick

[cuda66273]

The Demon was not the issue the size and series of the Demon was the problem.

IMO....you stepped down in Carburetor technology and performance level.

But..if works for you then you made the right choice.

[cuda66273]