I am trying to determine what my optimum shift points would be based on the dyno charts. I searched on here and didn't really find much. According to some stuff I read elsewhere, you basically need to keep the engine in a range where it makes the most "average power" after the shift. So I guess I need to go drive it and make some logs and see where the RPM drops to at the 1-2 and 2-3 shift now. I have it set up to lock the verter in 3rd so that will obiviously make the rpms lower after the shift than they would be otherwise. Is experimentation and trial/error just the best way?

My home track is 1/8th mile but I am going to be running 1/4 in a couple weeks so I will be getting into 3rd gear and I want to have the tune as good as can be by then. Any suggestions?

 

Post up a dyno chart, that will be a start. My setup peaks around 6200 but I shift around 6600-6800 because it carries well to almost 7000.

 

I couldn't get scanner to work so I took a pic of the screen, best I can do right now. Peak torque was like 421 and peak horsepower was like 349 I think so the line where the hp peaks is the 350 mark and the next one up is 400. I have it shifting at 5500 now, almost thinking it needs to be lower the way the power falls off.

 

Id shift at 5400-5600.. Your dying up top... your limiter shouldn't even go past 5800

 

Which vehicle does this graph belong to? Any Ls1 should peak way above this... this looks like a graph for some old big block with restrictive heads...

 

This is my 94 truck-bone stock 99 model LS1 with a 67mm front mount turbo. The turbo came from a STS kit so it has a .81 exhaust housing and I know that is a big restriction. Only running 5 psi, have been on the phone with Precision turbo and they say my turbo is too small for a stock LS1 but I know there are other people running 67's, arent there??

 

The truck weighs 5000 lbs and has 3.08 gears yet it went 8.34 in the 1/8th at 84 mph this past Friday. I guess the 400lbs of torque down low is why it runs as good as it does with such low HP.

 

Dude.. I really wasnt going to get into your lack of high rpm powerband since you said you only wanted to know where you should shift.

That turbo cant flow the lbs/min of air you need. You need a larger turbo, IMHO that dyno sheet looks like crap. You should be peak at 5600-6000 with a stock cam.. Not 5000 with a Nose dive after 5500.

 

i find 500 rpm over peak hp output is a nice starting poiint,then take it to the track,it tells all.

 

So I did a little logging and I ended up lowering the 1-2 shift to 5400rpm which drops it to about 4300 at the beginning of 2nd then I am shifting into 3rd at 5200rpm which drops it to about 4300 again. The 2-3 shift is happening about 95 mph and I estimate the truck is going to run 105 or so in the quarter.

So the question is, will it like the 5200rpm shift into third at 95mph and then carry the rest of the track in 3rd, crossing the line around 4800rpm or would it just be better to hold it in 2nd thru the traps and be out of power turning 5800 or so and avoid the extra shift? The seat of the pants dyno says it runs better just winding it out in 2nd....

 

If your content and having fun etc then great , but im still not convinced things are right... It's getting choked higher in the rpms a TON!

 

And looking at the graph again, it aint smooth... At all...

 

Whats up with that graph....

 

I am having fun but I am not content. I wouldnt be content if I had 3000hp at the wheels and was getting 50 miles to the gallon lol. I know it is choked, and I am convinced it is the turbo. I have a bigger one ready to go on but I am not going to change anything til after the "fest" It runs smooth the way it is and it is getting 20 mpg, but I know things aren't "right"

So what would cause the graph to be all jagged like that? I have the Dynojet software on my puter and I am trying to learn a little about it. The graph I posted is with the smoothing turned up all the way to 5. It is really jagged with it turned off !!

 

****, if that graph has smoothing turned all the way up... I would honestly stop driving the truck. You have MAJOR tune issues.

 

You have KR from 4000 till redline. Bad in some spots.

 

No KR til 5000rpm then it shows 1.7degr. Immediately starts tapering down til it gets to .4 at 6300 then spikes back to 1.7 about the time I got out of the throttle.

The AF is 11.7 at 3900rpm going richer til it hits about 11.1 at 4900 then it climbs back to 11.7 at the end of the run. Timing was about 18 at the hit then settled down to around 14 or 15 for the rest of the pull.

 

That 67mm is killing your top end with backpressure. 67mm is ok for a rear mount but a lil small for a front mount

 

Not only is it a 67, its a 67 with a .81 exhaust housing !

 

Graph says otherwise. Look at all the dynos in this forum... look at yours.. Could also be compressor surge.