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Old 08-04-2009, 08:11 PM
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Help on Tuning Please..

I am having a hard time tuning my engine. I am starting to wonder if one of the components is throwing everything off.

400Ci Pontiac
380HP
750CFM edelbrock
High flow fuel pump 6-8 PSI
MSD pro billet distributor(mech, no hook up for vacuum)
MSD 6al and blaster 2 coil

Timing is set for 33 at 3000

Had Dist sent to a tuner to be curved to the cam spec sheet. From that he got a setting for 34 at 3000. I attached the spec sheet for what my engine guy sent me bellow...for some reason it looks like the timing is different then what the curve is set for my Dist. Could I be reading it wrong?? Was the Dist curved improperly?

Here is what I am running into with my current settings:

-Cold start is instantaneous, no hesitation from the engine
-Warm start is difficult, but fires after a few turns
-I can hear misfire sometimes at lower RPMs but none at higher RPMs
-Seems to be a bit jumpy/Hesitant from a stop but picks up fine after I get the throttle open more.
-Starts pinging decently at 200-210 degrees engine temp(210 is what she maxes out at for temp) Usually pings when opening the throttle up a decent amount. From a slow start it usually wont ping.


I pulled the plugs and they look decent. Adjusted the timing a couple times but got similar results. I am a bit lost, as this is my first venture into aftermarket parts. Everything is brand new, so I am trying to get everything into a good sync.
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Old 08-04-2009, 08:43 PM
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With out knowing more about your engine, I haven't got a clue. What is the actual compression ratio, iron heads or aluminum, the cam duration @ .050" lift and where is it installed? The chart showed your peak horsepower at only 4500. That sounds low to me. The bottom end stumble could be a lack of accellerator pump shot.
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Old 08-04-2009, 11:07 PM
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I owe you some beer creech with how much you have been helpin me. Thanks! I hope to learn enough to help the next guy out.


-10:1
-Iron heads off of a 1968 GTO

I need to get my cam spec sheet from my shop. Ill grab it and post back as soon as I can.

As for the stumble, I think I know what an accellerator pump shot is but what is it exactly?

Also, would it be good for me to buy a fuel pres regulator?
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Old 08-05-2009, 12:20 AM
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You may well need a colder plug, along w/fattening up the pump shot. You might try jetting up a bit on the mains, too.
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Old 08-05-2009, 11:02 PM
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I actually just put some NGK Iridium plugs in...I emailed NGK, told them my specs and they sent me the recommended plugs. It was the XR4IX, which was cooler then the ones that I was using. The NGK people told me that as a rule of thumb(with them) for every 100 additional(from stock) HP you can go one step cooler.

Moving to the cooler plugs did help a noticeable amount.

Would jetting help with the pinging? I actually thought that it might be pumping too much fuel, as was the reason for getting the regulator. That was speculation though. I do get a strong odor of gas sometimes when I open the hood after running the engine and shutting it down. A bit more then I used to with my old engine.

I still need to pic up my cam spec sheet
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Old 08-06-2009, 12:57 AM
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"-10:1
-Iron heads off of a 1968 GTO"

There's your problem. Too much compression! To verify, get your tank almost empty and put in 5 gallons of 110 octane race gas, drive it for awhile, and then tell us how it runs. The only solutions that I see are, dished pistons or heads with larger combustion chambers. That is, probably, part of your temperature problem, too. pump gas and compression just don't mix!

Last edited by WDCreech; 08-06-2009 at 01:25 AM.
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Old 08-06-2009, 05:04 AM
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Quote:
Originally Posted by 66Ponty
Moving to the cooler plugs did help a noticeable amount.

Would jetting help with the pinging? I actually thought that it might be pumping too much fuel, as was the reason for getting the regulator. That was speculation though. I do get a strong odor of gas sometimes when I open the hood after running the engine and shutting it down. A bit more then I used to with my old engine.

I still need to pic up my cam spec sheet
Don't confuse fuel pressure with jetting. Jetting will allow more fuel into the fuel/air mixture that enters the engine to make power, totally different than fuel pressure that supplies the carb's float bowl, although excessive fuel pressure can cause the fuel level to become too high in some cases, and this will cause the engine to run rich- but for different reasons than larger jets. You really need a gage to determine what the pressure is, not arbitrary numbers on the regulator that have no correlation w/any real PSI figure.

When you mention heads from a '68 GTO, what you need to say is what "number" the heads are (the number is found cast onto the center exhaust port, will be 16, 31, 96, etc.). For '68, for instance, a GTO could have had several different heads, depending. But they all will have combustion chambers around 72cc, give or take.

If you don't want to change heads or pistons to lower the CR, you will need to tailor the advance curve, total timing and carb tune, as well as run the best available pump gas, 92 octane or whatever premium is in your area.

A cam change could help matters, if the CR is too high to work with- like if the heads have been excessively milled, or are being used w/domed pistons for some unknown reason (Pontiacs from the factory used combustion chamber volume to change the CR).

The cam timing has something to do w/how the engine will tolerate pump gas, too. You need to find the spec's on the cam.
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Old 08-09-2009, 07:48 PM
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I specified to the engine guy when he was building it that I was going to run it off of pump gas. I only put 92 in. He said that it should run fine off of pump gas, just that I need to get the timing down to a T.

I have the heating problem under control. It never gets above 210 now. Usually runs at 200-205. I have a few more small things I need to do to get it down more.

I will have the spec sheet soon...I still havnt had the time to drive over to get it. Vegas Trip this weekend dominated my time...

Thanks for the help guys! I will get those specs asap.
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Old 08-10-2009, 11:50 PM
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Solved the pinging problem. I worked with a helper this time and was able to rev it up to 3000 to set the timing, instead of working with it at idle. I tuned it down to 32 degrees and it is running like a champ.


Now on to jetting the carb.

Thanks again guys. You made things a lot easier!!
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