OK...ARRRRRRRGH!
I put new AFR 190 Street heads on my ZZ4.
It has an Edelbrock RPM intake & a 750 Holley double pump. All brand new parts.
new GM HEI Dist. Set with a mechanical advance to 36 degrees at 2,000 rpm's

Intake is port matched by a professional. All was done right.

Vacuum at idle is aroung 16.

My Dyno today which I WAS excited about revealed I have about the SAME horse as I did with my stock ZZ4 heads & intake.

No matter what we did with the jetting it only made 10 horsepower differences???
Went fron 70 to 74 primary 78 to 84 secondary...

Primaries are at 74 with secondaries at 82 currently.
It does hold the horse to higher rpms than before with stock ZZ4 heads & Intake but thats it.

Its a smooth picture perfect curve and runs out of breath at about 5,800 rpm's then begins to drop off in horsepower where as befor it ran out of breath at about 5,200 rpm's with ZZ4 heads & intake.

Does it sound like the carb isnt doing it's job...since jet changes make no meaningful differences???

I'm lost on this one. The engine sounds awsome, Doesn't break up at all at any rpm but I should have much more horse than before.

It's also the same carb I used on the stock ZZ4 heads & Intake that made the 282 rear wheel horse before.

I can fax the dyno sheet to whom ever thinks they can see something but what can I check next. plugs are clean, no Vacuum leaks, good fuel pressure etc...

New Wires and super coil etc...
Help.
Thanks, Vin


[This message has been edited by 81ZZ4 (edited 07-27-2001).]

 

Did you have the AFR's milled to 58cc chambers to keep the compression ratio the same?

Did you play around with timing? AFR's usually like 2-4 degrees more than L98 heads.

What kind of exhaust are you running?

If the above issues are ok then it sounds like you're running out of cam. The AFR's won't do much over a set of L98 heads until 4000 rpm and then you need more cam to really take advantage of the flow potential. The 190's have broadened the RPM range significantly and even though the peak HP and TQ are about the same, I bet you would run significantly quicker with that extra 600 rpm. The extension of the HP range without an increase in peak HP is typical of a motor with small cam when switching to higher flowing heads.

 

Sounds like there is a restriction other than the heads. Like previously mentioned, it could be the cam.

 

I have the GM Hot Cam with the 1.6 Roller rockers. This combo yields .525 lift, forget what the duration is...maybee 220 or so...

I thought this was enough? No?
Exhaust is 2.5" True Duals with 3 chamber flow masters. Headers are Hooker super comps.

While researching the up grade to the ZZ4 I spoke with AFR. They projected 450 to 480 horse with my combo. Their Comp Cam has a little more overlap and duration with 110 degree lobe seperation. Nothing my better headers and higher compression shouldn't offset.

Heads are milled to 58 cc chamber for 10:1 CR

What am I missing here??? Think I need a bigger cam better cam?

Now I understand the longer horsepower range pulling the car better. It is faster but I thought the Horsepower would be higher.

Anything else I should check for restrictions?
As far as timing goes I'm at 12 degrees initial timing...I did notice the heads like more advance. Should I try 38 Dergees in my curve kit?
Thanks Guys!


[This message has been edited by 81ZZ4 (edited 07-27-2001).]

[This message has been edited by 81ZZ4 (edited 07-27-2001).]

 

I thought you still had the ZZ4 cam - the hot cam should be sufficient so scratch that idea. I'm a little stumped as to why you aren't making more HP now.

I would try changing the timing to 38 degrees total and see if that helps but I doubt it will be more than a 10hp difference. The AFR's should be making at least 30-45 hp more than unported L98 castings. Does the dyno shop have the capability to monitor your air/fuel ratio?

 

Try to post your dyno results, so we can see them, what were your numbers?

 

Ihave a scanner but not a clue on how to post what I scanned

Unfortunatley no air/fuel ratio...
I'm wondering if I should try another dyno shop just to be sure...

Should the AFR's give me the 30 to 45 more horse at the wheels? Thats what I was hoping for. I thought I would hit 320 to 340 rear wheel.

[This message has been edited by 81ZZ4 (edited 07-28-2001).]

 

Do you have room to put a 1"-2" open holed spacer under the carb? It should raise the RPM limits of the dual plane into a higher RPM range,,just a thought and cheap at that.

 

Thanks for any suggestion you post...
The RPM intake is rated to 6,500 rpm.
We brought the car to 6,400 just to see what's up...power went down around 6,000

The more I look at the graph & talk with you guys the more I learn as usual.

Now I understand and see how the larger heads make a broader hi rpm peak horsepower range. It should be a higher output though.

Hopefully some more posts from you all and others will lead me in a direction to help figure this out.

I'm going to do a compression test just for a back to basics approach and process of elimination. Ohm out the plug wires etc. Check what there is to check.

 

More info....
Spoke to my friend Richie who is soooo good with building race engines. As soon as I began to explain results he basically finished my sentances with answers as to what we will do next.

his suspisions thus far are wrong power valve enrichening too soon throughout the power curve and jetting along with more advance needed in total timing.

I'll keep my fellow gear heads updated. Any other suggestions are certainly welcome and much appreciated.

After some more jet work we are up to 400 at the crank with much more to tweak out of this sucker
I'm feeling a bit better now. Sheeeeesh.
That sucked after all the careful work and time.

 

Just wondering if you changed the valve springs when you did the cam change?

Where are you in NY? It would be nice to get some A/F readings with your carb tuning. Are you getting enough fuel pressure?

Not to knock the person who did the work, but these days I never fully trust "professionals".

I had a "professional" build my 383 the 1st time and then a Professional built it right the 2nd time. The 1st 383 made 347hp at the wheels and the 2nd made 445hp, same heads,intake, cam & block!

Good luck and let us know how you make out.

 

Sting Ray,
What were the differences you found when you built it the second time?

I gave the spring specs to my friend that I had received from AFR. I remember him saying he liked the pressures and so on.

That was also another new one for me. This stuff is very involved. Just when I think I know a good amount I learn soooo much more.

Now I'm learning there should be between o to three threads of the plug going into the chamber.

I also found that a new plug wire in my new set from MSD had a bad end on it! The steel end going over the top of the plug for the connection was bent over never clipping on to the plug. Just touching against it.

It doesn't take much to ruin engine performance.

 

Hmmm, where do i begin...let's see I had a solid roller cam matched with hyd roller lifters!!! 2 bent rods, flywheel not balanced, valve springs too weak, heads & intake not ported enough, the motor had excessive blowby from day 1...etc. I wound up getting new pistons and moving up to 6" rods. I'm happy now.

 

OK,OK...HERE WE GO.

I dropped the power valve from an 8.5 to a 6.5 even though the formula for power valve selection came out to an 8.5

Re-jetted. Now the 4 corner circut adjusters respond on the Holley...before it really made little difference when attempting to adjust for best vacuum.

Now it's out sideways in 1st when I hit it
Full posi and screaming with my sticky Eagle GT 2's
YES

More tweaking to come.