I purchased a GMPP ZZ430 (clone) this past summer for my 68. I have had it in the car now for a couple of months, and i am somewhat disappointed in the performance. I have done some tuning, but it has been a trial and error process and I have not found anything that I am happy with. This is what I have done to the engine so far:

-750cfm Holley w/ Vacuum Secondaries (stock settings "feels" the best so far)
-MSD pro-billet distributer (Mech advance) with 6AL ignition box. Timing is at 11deg, and the advance is set to the slowest setting so that the total timing comes in at 4000 w/ 34deg total timing.
-8mm Accel plug wires
-Plugs are set at 0.045 right now, started at 0.035"
-Hooker headers with 2.5" exhaust and flowmasters (sounds great)
-Wide ratio 4speed (purchasing keisler with CF group purchase) with 3.55 rear end gears

I used a G-tech the other day, and it said that I was making 235HP, and 285ft-lbs. I know this will read lower than the HP at the crank, but this seems excessivly low. Any ideas on something to try? I want to go to a dyno, but most places I have asked won't tune for liability reasons. I seem to get goofy plug readings, in some cases all of the plugs will read "fat" tan to black, but one or two will read clean. I check the valve lash and all of them were close. Any suggestions will be welcome.

Thanks for your help
Matt
68 vette

Pic of engine before install
http://www.picturejudge.com/memberpi.../P10100661.JPG

 

My $0.02. Your advance is way too slow. I picked up quite a it a power by rate of advance. According to Lars' tech paper, you want 36 degrees mechanical all in by 2500-2800 rpm. You may be better off with 34 total with the Fast-Burn heads but you definitely need to bring it in quicker. I run 34 mechanical, all in by 2600 rpm which gives me about 16 at idle but I never drive at idle anyway.

For more info, go to www.corvettefaq.com and get Lars' tuning papers.

 

Good lookin motor. Did you degree the cam before installing the motor? I've heard and read several bad stories of the cam not installed properly, pistons installed backwards, ect, ect. It isn't the first place I'd look of course, just something to be aware of.

 

No, I did not degree the cam. It was mostly a plug and play operation.

The instructions that came with the motor called for the total timing and when it should come in. I thought is sounded like it came in too late, but I went with it at least for the break in period. Maybe GM is consertitive to keep people from damaging these crate engines. I will have to check out Lar's papers.

Matt

 

I adjusted my timing this way and have found that my car is much more responsive and seems to have a little more power.

 

Do you have the specs on the motor, cam, heads compressin ratio etc.

Are you saying that because of the frequency people sue other people around there you can't get your car dyno tuned, that's pretty bad if it's true

 

I'd change the vacuum secondary carb to a Holley 750 HP series double pumper with mech. secondaries.. That should make a nice difference.. Also adjust yout total timing to around 36 - 38 degrees...

 

i agree get the timing to come in faster and at 36-38 degrees.

 

I'm also running a clone of a ZZ430 except I'm using a Q-jet and very happy with the way it runs.A couple of thing to check. First are you using headers designed for fast burn heads, the intakes and exhaust posts are both raised about 1/8 of an inch so if you use standard headers they will bolt up fine but restrict the flow. I had Sanderson make mine a couple of years ago but I see several companys are now making fast burn headers.
You might try going leaner on the jetting, according to GM the stock 750 Holley jetting is to rich and you will lose a lot of power. There is a lot of info on the GM performance dealers webb sites covering jetting.
As far as timing, bring in the full advance by 2500 rpms. Standard GM heads run best with 36 to 38 degrees advance but you will start losing power with anything over 33 degrees with fast burn, because they burn the fuel faster they don't need as much advance. GM says 32 and my 1/4 times start slowing down over 33, over rich jetting will need more advance.I hope this helps.

 

It looks like I have a good starting point for the spring, and I have a lot of reading to do. I thought about the headers not fitting correctly, but I had them from my previous engine.

Anybody have any insight about plug gap? Thanks for all of the input so far!!

74ZZ430: Looks like we are only about an hour apart. I lived in Toledo until about 93'.

 

That plug gap should should be fine for either a HEI system or if you are running a MSD type box.

 

Matt,

I originally purchased my 68 with a new ZZ430. The original owner could never get the engine to perform well after initial installation. He spent about 8 months and a great deal of time on the engine (and he was a skilled military airplane mechanic). He had used a 600cfm Deamon carb on the car and reused the existing headers. After many attempts I was able to make the car perform well. I replaced the intake manifold (I found that the original was not planed flat from the factory - leaving a slight vacuum leak under the carb), and adjust the timing to the updated ZZ430 timing specs on the SDPC-2000 web site - the orginal supplied specs were incorrect. The car now preforms beyond my expectations. I do not seem to have any issue with the use of a non D port style header.

 

74ZZ430: You said that there are several GM perfomance web sites that have a lot of info about Holley jetting. Could you give me a couple of these addresses? I have check several, and have not found much info. Maybe I am not looking in the right place?

65LS6C4:You said that the SCPC web site has updated timing specs, but I was not able to find them. The site said that they no longer carry that engine. Do you rember what these specs are.

I did do some investigation in my instruction manual and it said that the included distributer had the following mechanical advance:
1100RPM 0.0 deg
1600RPM 12.0 deg
2400RPM 16.0 deg
4600RPM 22.0 deg

But is sounds like full advance does not come in at 2600-2800. It did have vacuum advance (20deg at 7.5"hg and 0deg at 3.0"hg) so maybe that is the difference.

Looks like it is going to be somewhat nice this week, so I will have to try some spring changes.

 

You want 34 degrees of mechanical advance at 2600 rpm.

Vaccum advance works under light load conditions only such as cruising. Most small blocks like about 54 degrees total (mechanical plus vacuum) under light load.

All you need to do is swap in some lighter springs so that your mechanical advance is all in by 2600 rpm.