MAF, MAF, MAF, MAF, ADV, MAF

[padgett]

Just had a visit from Greg and his s/c 5-speed that coincided with a week at home in Orlando and we programmed a mess of PROMs (despite a very cranky burner or possibly the first two bad PROMs I've seen.

This nudged me into disassembling the AXTP proms he sent earlier. These are designed for the '92 Park Ave with s/c series I 3800. The most evident was the gutted advance curve. Greg had been seeing some knock counts despite a wired open bypass (like a waste gate in a turbo) and I suspected the n/a advance is too aggressive for a s/c engine anyway so we tried it.

Now Greg has several thousand miles on the s/c engine now and had not grenaded yet so is pretty robust. Of course he has a crate engine that is apparently the same crate as used for the s/c version so has a robust bottom end. This is born out by the 70+ psi oil pressure he was showing at speed.

We tried one run with the 92 s/c advance curve grafted onto the 88 updated program and while there was no knock, it also felt much softer above 3000 so the current trial is a stock 88 advance curve with about 10% reduction at load (LV8 which is a cobination of MAF and RPM above 1800 rpm). At cruise it is the same as stock.

Now one of the changes in the ECM for the s/c engine is a "bypass control" line designed to open the bypass valve at idle and in reverse. Since Greg has a 5-spd we altered the TCC profile to close above 7 mph and with coolant above 20C (is already tied to closed loop operation). This may allow use of full boost though will need to get some readings of what that is. Since we do not have a MAP sensor, some of this is going to have the be by ear.

At any rate, he now has two PROMS, both with the TCC alteration, one with the s/c advance table and the other with the slightly reduced advance curve. Next stop: what happens with full boost.

Does anyone know what the stock compression ratio is for the 92-93 L-67 engine (supercharged 3800) ?

[Guest EDBS0]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Does anyone know what the stock compression ratio is for the 92-93 L-67 engine (supercharged 3800) ?

</div></div>Hi guys; The piston, wrist pin and connecting rod are what differ between a normally aspirated 3800 (L36) and the supercharged short block (L67), as the supercharged ones are much heavier and stronger. The resulting compression ratio subsequently differs between the L36 (9.4:1) and the L67 (8.5:1) That's right, you can't just bolt a blower on a naturally aspirated 3800 and expect to get a L67! Heads, rods, and pistons (including wrist pins) need to be changed.

From Thrasher

[2seater]

It sounds like Greg's engine has relatively high compression ratio, a little higher than mine actually, but both are probably too high for full boosting. Can you get a read on the knock retard? A couple of degrees of retard are probably acceptable as long as it is in a narrow window, such as at a shift point. If there is no knock at all, it will probably feel soft, as it had been running on the edge before, which is good for response (longevity is another question). Did you have any luck expanding the MAF tables?

[padgett]

a) performance felt very soft with the L-67 advance curve & Greg said he was getting some knock with the bypass partly open and the stock curve so using the stock 88 as base I left the low load area alone and dialed back the top end about 10% (3-4 degrees). That seems good for now and no knock was showing in limited testing.

He also has the PROM with the stock L-67 settings (about 10 degree less advance at load than 88) and will try that when he gets the full boost going.

c) Don't forget, he does not have a stock engine anymore but a remaned crate from GM with '92 specs. He said the same part number was showing for both the N/A and S/C engines so maybe it already has the good stuff. It certainly has the later oiling system (70 psi at speed).

d) wish he had a manifold pressure guage but that is still in the future, at least the exhaust system hasn't shown any signs of melting.

e) MAF is going to take more study. Used the 91 N/A table but that still tops out at 170 (Are in power enrichment above so should be rich enough). The L-67 changed the entire table structure (added a two byte offset) so cannot just graft one table on the other, need isolate the using suboutine and modify. If I just change the scalars, the ECM will think it is flowing more than is reality but top out at the same time.

f) Just made a run to Gainesville for a 213.6 mile loop, mostly at 2200 rpm cruise with a/c on 8*) about 5% city. BCM showed 23.5 mpg ave. with a high of 24.5 entering Gainesville. Filled up before and after same way at same pump and actual was 8.93 gal or 23.9 mpg. This was with my mostly stock 88 and 2 aboard & moderate traffic (& some real yo-yos 8*( plus a C-type Jag at chat 8*). Haven't diddled with spark or a/f. Just a data point.

[NYBobP]

I admire you guys. I read your posts and to me its like reading Korean, Mandarin or Swahili. If I have a problem, I take it to a local mechanic,who says "that's $710", and I say "OK, I'll put it on a credit card. Its either that, or the Reatta doesn't run. Wish I had your expertise. Nice going. It's too late for me to study brain surgery as well.

[padgett]

A Reatta is not just a car, it is an investment (didn't say it was a good one 8*), a hobby, a pet, and a lifestyle. I also cannot afford to make dealer's boat payments so have to fix my own.

[Guest]

And Im just sitting in the back waiting for the whole thing to be setup and then Im gonna ceize the moment and use what they know and make it happen. Right now though, Ive got my brothers 98 V6 Mustang to tinker with. Thats keeping me busy until the 4 Brains (EDSO, Hal, Greg, and Pag) get things dialed in.

[Guest EDBS0]

If you are waiting on me it could be the next millennium , too much other stuff going on here, the other 3 are the real gurus. I am but a humble apprentice standing in awe at the sidelines. Will be putting the Reatta away for another winter in a week or two.

[2seater]

Hey, thanks Padgett. My crude formula shows 170 gm/sec is good for about 224hp, although the only way to validate that would be a dyno run. I guess I shouldn't be surprised that they used the same scale which should cover even the Series II N/A engine. If he still has the bypass open, maybe the performance will pick up when it is fully operational? I wish he had a pressure gauge too. I estimate my turbo setup would need 1-2psi more boost to cancel the increased backpressure in the exhaust side, but then again I don't have the parasitic load of the S/C.

If I understand point "E", the situation would get worse with the MAF air flow sensing unless you invent a new subroutine? I, for one, really appreciate the time and effort you and Greg put into this. The programming side of this is well over my head (see learning brain surgery ) and I appreciate putting this in laymens terms.