I got my 1990 L98 6-speed. Right now it has:

-350 bored .040 over
-1.6 roller rockers
-Hooker long tube headers
-No pre-cats
-high flow main cat
-Flowmaster 40 series mufflers
-Custom burned chip (from one of the members of the forum)
-Holley AFPR
-cut air lid
-K&N filter
-air foil (it was free!)
-ported plenum
-siamesed (1" deep, 1/2" high) base
-TB bypass
-frisbee removed
-180 degree t-stat

I dynoed it bone stock minus the bored motor. It ran 235hp to the wheels when it was 78 degrees out. I took it to the local Millersville car show, and had it dynoed with all the mods listed. This time it put down 240hp. Obviously 5hp for everything there is a load of crap. However the guy there (a Corvette tuner company from Ohio that brought the portable dyno), said I was running way lean. In the area of 17:1 instead of 13:1.

So looked at my AFPR, and the screw was turned in almost all the way. Only about a turn to a turn and a half was left. The prom is calibrated for the headers and everything else. I was wondering how else I could adjust the A/F ratio to get it close to where I need it? I also wondered how to accurately test the A/F ratio. Me and my dad are mechanics, but we don't own a A/F meter, and our computer only tells if it runs rich or lean, it doesn't give numbers.

Also, roughly how much HP am I loosing with the numbers being off like this? Am I going to see a substantial difference (25+ Hp) or just like, 10?

So, if anyone could help, it'd be greatly appreaciated!

 

A 17:1 A/F doesn't seems right. Looks like his a/f meter might have been off. I would have it tested somewhere else. At 17:1 you would lean out and blow the engine.

If you were really running 17:1 A/F and went down to 13:1, you'de probably lose horspower. Leaner usually makes more power.

 

who was the forum member that burned your chip? if he didn't fuel your VE tables, that would go a long way in explaining it. you need a fair amount of adjustments there, as you've opened up your exhaust, and your intake to a degree -- and with SD its likely your ecm isn't up to the task......its up the chip. JMHO

 

Did you pull a few spark plugs after the dyno run to verify that the engine is actually running lean? Either way, definitely pull a few today to analyze.

 

I'll definately pull a plug or two, and check them.

The chip was tuned for the car after the exhaust and intake work. He's from central PA area, but for the life of me, I can't remember who it was. And I don't feel like taking off the computer to see the name on the sticker.

They did say it was knocking, I couldn't really hear it though.

 

A significant lean condition at WOT (17:1) would likely result in engine knock, which would cause the ECM to retard timing, which probably explains why the engine wasn't able to put down a lot of power on that dyno run.

I'd bet that the porcelain insulators are bone white, which would indicate lean. If that's the case, definitely start troubleshooting the lean condition (and fix it) before going full throttle again.

 

Sounds like Jesse "ski_dwn_it".

 

I just purchased FAST Air and Fuel Meter. It cost around $400 for single sensor. You can buy one with 2 sensors too or later on upgrade to 2 sensors.
It is very acurate ( +/- 0.1). You can purchase one from www.asscracing.com. That's where I got mine.
I was testing my car (carbureted) and it's very easy to use.
Ziggy

 

Bingo! It was ski_down_it. I knew if I heard the name, I'd remember it.

Yeah, 400 bucks though...thats more money than I'm willing to spend to use once or twice. Especially being the broke *** college kid I currently am.

 

Did you switch cams? Also, are the pistons running the same compression ratio as your old ones?

Edit to say sent PM.

 

Do you at least have a fuel pressure gauge? I wouldn't even drive the thing until you get the fuel pressure set right at least.

 

Oh yeah, we have a bunch of crap...my dad is a mechanic. Just don't have a A/F meter...since we never had the need for one.

The fuel pressure is around 42psi.

Same cam, same compression.

 

He did the same to me.. Just about fried/melted my new motor on my 91' Vette. Not enough fuel in the VE tables running way lean. Luckly I found a local tuner through some Vette guys and he made some adjustments to the tuning. You can't do a mail order tune on a speed density pcm car and get it right. 17 to 1 will destroy your motor. Find a local tuner....

 

Here's a good read for ya...

http://forums.corvetteforum.com/show...highlight=tune

 

So, should I go with a chip, from say, pcmforless, or get it custom tuned locally? If I should get it tuned (I know I should, I mean, will it make a ton of difference?) does anyone know of any local C4 tuners in the Allentown/Philadelphia/Harrisburg/Lancaster/York region?

I really want to get this corrected now. I'm also pissed I dropped money on basically nothing.

 

You're luckier than I, I lost $5k in engine damage over it.

I went with Alvin at pcmforless.com. who did a fantastic tune for me. I can tell you he was 180* difference from the other tuner. PM me for details.

 

[QUOTE=1990dtgL98]So, should I go with a chip, from say, pcmforless, or get it custom tuned locally? QUOTE]


I did both, the mail order (from pcmforless) and latter got it dyno tuned by pcmforless. Actually pcmforless did a great job on my mail order tune. I picked up a little with the dyno but not much. Keep in mind I have speed density as well. IMO one of the main advantages in dyno tuning is seeing the car run they may spot other problems besides just the tune.
By the way, I was the center of the argument in the above referenced post. I too spent about $400.00 for what turned out to be fan changes etc, but nothing to the fuel tables or timing tables. I spent $400.00 for the chip, dyno time to send scans back and forth, several test and tune times, shipping on at least 3 retrys, and lots of personal time. In other words a lot more then just $400.00 but at least I didnt blow my motor like some did.
But I did learn a lesson. Do research on who you consider using. Tuners are like mechanics or any other profession. Some are good and some just dont know what they are doing. If you were to hire a mechanic to work on your car would you pick one who only had about 1-2 years experience? And that was mostly on their own car and friends?
Sorry for all the ranting and raving, it still ticks me off.
But back to your car. Have you tried reinstalling the stock chip to see how it runs? Looking at your mods you really have not done a lot to change the basic tune and especially to the point of going so lean (17to 1). I mean unless I am missing something here, it is basicially .040 overbore, 1.6 rockers, headers and exhaust work. Usually switching cams, compression, and displacement is what really makes the need for a chip change necessary.