I recently did some dyno tuning on the ZZ430 crate engine that I installed last summer. I was hoping to get around 360 HP at the wheels (~15% loss) and ended up with 325HP. I definitly think that there is some room for improvement from the testing that I did but I wanted to get some opinions. Here is how the engine is set up currently.

Carb: Holley 750CFM w/ Vaccum Secondaries
- Main Jetting set a 72 (AFR of 14:1 when cruising at 2700RPM in 4th)
- Idle set for an AFR of 13:1
- No change to Acclerator pump or squirter nozzle (#31)
- Yellow Secondary Springs (lightest)
- Power Valve at 6.5 (Stock)
Distributer: MSD Pro-Billet w/ Mechanical Advance and 6AL ignition
- Initial timing set at 9.5deg
- Total timing set at 31deg (Fastburn aluminum heads)
- Total timing in around 2400RPM
Plug Gap: 0.045"
Plug Wires: 8.8mm Accel wires
Exhaust: Hooker headers w/ 2.5" exhaust and Flowmaster mufflers

We started off the testing with a baseline run with the carb set the same as from the factory and got 290HP. We then ran the car at 2700RPM in 4th to see how the main jets were. From this we lowered the main jets from 74 to 72. We also increased the redline of the motor from 5800 to 6200 based on the power curve. With these changes we got 320HP, but it still appeared to be running too rich (around 11:1 AFR). After several more pulls, we found we had a problem with the secondary diaphram, so we put a quick change kit on and replaced the diaphram. Once this was done we tried the lightest and stiffest secondary springs with not much change in the AFR. This leads me to believe that I need to try different secondary metering plates, but at 20 bucks a pop it will get expensive to try these.

The way we had the Dyno set up, I would "floor" the gas and the dyno would hold the engine at 2000RPM for about 5 sec (you can hear this on the video). I would think that by this point the acclerator pump circuit would be out of the picture and the vaccum was down to 0 so the power valve should not be a factor (it should be open the whole time). Again this is why I think that it is in the secondary metering plates.

Problems during dyno:
1. I checked the adjustment for the rockers on the pass side and forgot to set the poly locks. During the first pull one of the rockers loosened up and beat the **** out of the roller tip. I repaired it, but need to keep an eye on it.
2. In dash tach needs to be calibrated
3. Problem with the secondary diaphram
4. I found out I do not have the rear end gear I though I did since my tach was off. I actually have a 3.73 instead of a 3.55. (I still question this since a 3.73 was not offered and would have to be aftermarket)

I have not tried anything since the dyno and the car seems to drive fine. I have not really got on it since I just installed a new 5 speed and am breaking it in.

If anyone has any suggestions or needs some information, please don't hesitate to respond. I have never tuned on a dyno or with an O2 sensor, so I may be going about it all wrong.

Thanks
Matt

http://forums.corvetteforum.com/phot...shot-thumb.JPG If you click on "My Corvette Photos" it will show a larger picture

Dyno video
Click here to watch Vette-Dyno1

 

Those are pretty darn good numbers to the rear wheels.

Here is a bump for you.

 

What gear did you do the dyno run in ?

Anyway what are your secondary jets and you might want to try a mechanical secondary carb like the 4779 or similar so you know the secondary is opeing up for sure. Also have you ever checked to see if when you floor it all four throttle blades are completly vertical, commonly overlooked problem.

And finally, a zz4 rated at 350HP? usually gets about 260 -280RWHP in a C3 from what I have seen, now if you take 270RWHP for the zz4 and apply the same ratio to the zz430 you get 332RWHP

 

What's your exhaust? My 430 had similar numbers off the dyno with the same carb (changed the plate to a secondary system so I could change jets) and went with primaries at 70 and secondaries at 73 - still a bit fat all the way, but better fat than lean). Did 10 horse improvement by improving the exhaust, ended up @ 330 rhhp by "Y" ing in a second system, have 2.5" sidepipes and 2" down the center exhaust). A decent undercar system will equal or beat this, but I like the sidepipes, and this dual system, while unconventional, has a great sound, too.
Have you done much with the timing? - cause my car with fastburns tolerates 38 degrees total with 93 octane at 800' altitude and never a sign of preignition. Every suggestion I've seen is that 12 degree initial and 32 degrees at 3000 is the gospel, but mine tolerates 38 total, try some advance if your motor will agree.
Daffy

 

I think you got a few ponies left on the table...i'd go with a Mechanical Secondaries carb, 5.5PV and turn up your timing to 34 and go from there. Your not far from getting the most out of that engine. I seen a Fastburn 385 put down 308rwhp, so those heads have potential for more hp on your setup.

 

Daffy, you have not read Lars papers on tuning then. His experience shows most GM motors (and some Fords ) work best with 36 degrees mechanical advance all in by 3000 RPM with another 12(?) from the vacuum advance for cruising. The only variable may be the fast burn heads but by the sound of it they require the same specs.

 

Yea baby!

 

I follow the advice from Lars - he really knows his stuff. I got to the advance I'm at by dialing in 2 degrees at a time and a lot of driving in between. This motor just prefers more than most. My previous motor was a zz3 and loved 34 total mech., didn't want any more. Both motors set up with advance all in at 2800 and both with 10 degree cans (GM# 1973682). Both with manifold vacuum to the can.
A note: if you don't occasionally clean the pins that the mech. advance springs pivot on, the drag will start to slow that all in point from the 2800-3000 that you want. Only takes a couple of minutes to do, I learned this on a bench with a mittfull of springs and a trigger pull gage.

The 430 would be stouter with a 750 DP as suggested above (I think that's what GMPP uses when they developed them), but I've got good street manners now. BTW, I know my secondaries don't open all the way, most never do, but they are close. I either saw or dreamed up a little goathorn thingy that is on my carb so I can check the secondary opening. A DP opens all the way everytime. Interestingly, about half of the cars that I help people with have the linkage so poorly setup that the carb. never gets full open at all.
I am interested in why the 5.5 PV is suggested above. I've seen a couple of different thoughts on how to determine the valve needed and with my idle vac. at 15"-16" the 5.5 valve seems to be low. Always eager to learn...

Daffy

 

Sorry it has taken so long to reply... who would have thought that kids would take up so much time!

First some corrections to my original post:
1. Total timing is coming in around 2800RPM (Not 2400)
2. I am at 70 for primary jet size like Daffy2 (I started at 72)

Second, responses to questions:
1. All dyno passes were in 4th
2. Throttle blades are opening all the way with the pedal
3. I did not play with the timing, I had a short amount of time and wanted to get the carb tuned in as best as possible with the adjustments I had.
4. I have though of replacing the meteing plate with a secondary system, but it is a pretty new carb and I just bought and Aeroquip fuel rail that I don't really want to modify. This would probably require me to reset my idle mixture (I may have to do this with a new metering plate as well), and I was hoping that I could get some suggestions for metering plates.

I do have a couple of questions hopefully someone can help me with.
1. The metering plate I have (134-21)has a main hole of 0.081 and an Idle hole of 0.040. Would this be equivalent to having two 81 jets in the secondary? In other words, if I put a secondary system on, could I put 81 jets in and be at the same point?

2. If a carb is not touched but the timing is increased would that changed the O2 sensor reading (richer or leaner)? I would think that with the same amount of fuel and air the AFR reading would be the same. There would just be a point at which your are igniting the charge too quickly (not running too lean) causing detonation.

Thanks for everyones help and opinions
Cheers
Matt

 

YUP, kids are a challenge and a joy. Got one boy at 38 and another at 18, quite a trick.

This post made me remember that when I changed the metering plate to a jettable plate I found a lot of casting flash and particles in the carb. The change may be worth doing just to be sure everythings right inside. Please try more timing, I know that the Gospel is 32-34 total but mine is sweet at 38. Also, I asked about exhaust - got a good system?
I'm suprised that your secondaries go full open with a yellow spring, is it the short or long yellow spring?

Daffy

 

I should clarify, the primaries are opening fully with pedal WOT. I do not know about the secondarys - yet.

I tore the carb completely apart a couple of years ago when I was still at school and cleaned it in an ultrasonic cleaner in the lab. (I paid for it : ) )

I am going to try and play with the timing in the next couple of weeks and see what it likes. Hopefully I can make it to the drag strip as well.

The exhaust is Hooker headers which I port matched to the Fastburn heads since the port shapes are not quite the same. With a 2.5" system back to a pair of Flowmaster 40series delta mufflers.

20 years apart - that's pretty impressive. You know what they say "Practice makes perfect"

Matt

 

You say on the 3.73 gears where not available on your car. A 3.70 set was used. The stock gears were 3.08, 3.36, 3.55, 3.70, 4.11, and some 4.56s were used.