mike89z

I was just curious about when a motor should receive the max timing under WOT. Any other thoughts about timing are also welcome. I know that every engine is different and I am not looking for exact figures or anything. Just wanted to start a discussion on it.

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89 IROC-Z 355 10:1 , AFR 190 heads, LT4 HOT cam w/ 1.6 roller rockers, complete Superram intake, 58mm BBK TB, 24# svo injectors, screens out of MAF, MAT relocated, March underdrive pulleys, Streetdampner, Crane HI-6 ignition, 160 thermostat, K&Ns, TES headers(Jet hot coated), 3" Random Tech cat, Mufflex 4" cat back, B&M shift Kit, 2500 converter, 3.27s, and 4-wheel disc. Chip is custom(doing it myself). 2 1/2 Harwood and just painted.

Grumpy

Somewhere in the nieghborhood of 3K rpm. 2,400 to 3,200 are generally accpeted as where an engine is most deonation prone, and where the K/S are often tuned for.
With automatics converter stall speed will also play into that variable.

You might add a few degrees per thousand rpm over that.

So the short answer is you want max timing at peak HP, and for it to start at peak torque. the biggest factor is going to be the cam and when you start being able to have it artifically boost your VE.

700R4 trannies just really make it hard to get the timing right. With 1st gear being so darned high, and with a loose converter, you just about have to run really retarded timing or you just wind up smoking the tires, which is good for show, but really slow.

Depending on the torque curve of the engine, you also want the recovery rpm after a shift to be low enough so that you don't detonate during the end of a gear change. That's also why Stall Converters can be so much faster. You can have trace detonation at that point, and when in detonation an engine doesn't make as much power. Converter stall and flash speeds can really dicate what the timing will be.

HTH

Scott 88 GTA

I'll beat Grumpy to this one: The engine should receive max timing in WOT whenever IT wants it. Seriously, the best way to find out is to start with all of the values low and slowly increase them until you notice that you've gone past the peak performance or encounter knock. After you do this for all of the points of the WOT spark curve you'll know where your engine should have the highest spark.

Edit: Dang it, he barely beat me.

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Black 88 GTA L98
261 RWHP, 345 RWTQ
13.406 @ 103.72 MPH
ZZ4 bottom end, Edelbrock 6085 heads, LT4 HOT cam, GMPP 1.6 RR's, ported stock TPI, SLP 1 3/4" headers, no cat, Dynomax cat-back, Stock PROM
E.T.F.A Member #11

[This message has been edited by Scott 88 GTA (edited August 21, 2001).]

leirch

From past experience, do you run the SAME amount of timing at WOT?
I am currently, it seems to pull pretty good and at certain rpms it almost "quits", I may need more fuel or some taken away to resolve some of that problem but say i'm running 28.6 degrees of timing the entire time at wot, should there be some sort of curve at all?

Brendan

Grumpy

In general, you'll want the timing to be right at max from peak torque to peak HP.
One problem is that engines are mostly likely to detonate in the 2,400-3,200 range so sometimes you have to delay when it kicks in.
Stall speed of the converter can play havic too. The stall speed-flash speed, of the converter with the 700R is a real wierd combo.. You can run alot of timing in first since their is so much gear multiplication. Down side is you roast the tires so bad your actually slowing the car down. Easy to get to the point of making too much HP in first.
On my Cross fired 84, I wound up using very little timing below the stall speed of the converter. But, with junk TAs ran 2.0 60 foot times, and the didn't matter on what surface (well other then wet).
On my GN I run 17d form 2,400 rpm up. On the Bird, a total of 28d starting at 3,200. Yes the FBod had a looser converter.

Grumpy

Plugs showing any signs of detonation.
Sory for the double post, but it took a day for it to show up here, weird.....