4l60e guys, questions on shift points
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4l60e guys, questions on shift points What: My Chevelle with the ls1, 230/224 cam, FAST 90/90, longtubes, SS3600 stall, and 3.42 12 bolt on 325/50r15 MT ET radials.
Cliffs: Do you have shifts the same on the 1-2 as the 2-3? Has anyone had better luck short shifting 3rd a tad if your cam falls off peak quickly?
Why I ask:
My peak power is at 6000rpm and begins to fall off pretty quickly past that point (not a downward spike, but immediate arch).
I used to race mostly 1/8th mile so I was barely getting into 3rd if at all at the stripe where the car would trap 90mph in 1840+ DA with a weight of approx 3700lbs. This is with the shifts occurring right at the rev limit of 6600rpm. Basically I kept bumping the 1-2 and it kept picking up small amounts of MPH. I'm thinking this was due to the huge 1-2 gear split and my stall/gear size.
At the 1/4 mile track, I am only trapping 110-111 in the 1/4 in the same DA. I think the car should gain a little more on the backhalf than that. Not much...but a little. (Or maybe it's just the aero taking effect vs a similar fbody car). The 2-3 is occurring right on the 6600rpm limiter and I'm thinking of trying a lower shift on the 2-3. I'm thinking I might fall into a better part of the power band VS the power past peak on that shift since the gear split isn't so great.
Or am I thinking about this backwards? Has anyone tried this with a cam that falls off quickly past peak rpm? Either way I need to adjust it a touch because the car will barely kiss the rev limit on the 2-3 at the track (doesn't do this on my street tires which are a tad shorter). Just wondering if anyone has experience with losing mph from getting too aggressive on the RPMs in 2nd.
Cliffs: Do you have shifts the same on the 1-2 as the 2-3? Has anyone had better luck short shifting 3rd a tad if your cam falls off peak quickly?
Why I ask:
My peak power is at 6000rpm and begins to fall off pretty quickly past that point (not a downward spike, but immediate arch).
I used to race mostly 1/8th mile so I was barely getting into 3rd if at all at the stripe where the car would trap 90mph in 1840+ DA with a weight of approx 3700lbs. This is with the shifts occurring right at the rev limit of 6600rpm. Basically I kept bumping the 1-2 and it kept picking up small amounts of MPH. I'm thinking this was due to the huge 1-2 gear split and my stall/gear size.
At the 1/4 mile track, I am only trapping 110-111 in the 1/4 in the same DA. I think the car should gain a little more on the backhalf than that. Not much...but a little. (Or maybe it's just the aero taking effect vs a similar fbody car). The 2-3 is occurring right on the 6600rpm limiter and I'm thinking of trying a lower shift on the 2-3. I'm thinking I might fall into a better part of the power band VS the power past peak on that shift since the gear split isn't so great.
Or am I thinking about this backwards? Has anyone tried this with a cam that falls off quickly past peak rpm? Either way I need to adjust it a touch because the car will barely kiss the rev limit on the 2-3 at the track (doesn't do this on my street tires which are a tad shorter). Just wondering if anyone has experience with losing mph from getting too aggressive on the RPMs in 2nd.
Guess the bigger question is what RPM are you seeing in 3rd in a 1/4 mi track. It has always been my understanding is that you want to be as close to peak power or useable power @ the 1/4 mi mark. Having a car set up for the 1/8th vs the 1/4 are generally 2 different setups and no one would be optimal for both. So I would not expect a huge return on a 1/8th mi car running the 1/4.
Depending on how far back the RPM drop from 2-3 and how much you get back up is a big question and remember, in a 1/4mi run you start dealing with things such asdrag coefficent and its not like this is a Fbody with smooth curves.
What is exactly the power drop from 6,000 to the limiter??
I could be wrong, but these are the things that stick out to me.
Depending on how far back the RPM drop from 2-3 and how much you get back up is a big question and remember, in a 1/4mi run you start dealing with things such asdrag coefficent and its not like this is a Fbody with smooth curves.
What is exactly the power drop from 6,000 to the limiter??
I could be wrong, but these are the things that stick out to me.
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I will see if I can find my dyno sheet. Appears I never scanned it. Wasn't exactly proud of it.
Not sure about RPM crossing the stripe, but a gear change is out of the question anyway. I will be going back to a shorter tire once these burn up, but that's the best I can do there.
Not sure about RPM crossing the stripe, but a gear change is out of the question anyway. I will be going back to a shorter tire once these burn up, but that's the best I can do there.
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Looking at this, I am fairly certain not only am I overrevving, but I might be getting valve float.
Going to try dropping shifts to 6000 unless I find some reason power should carry higher and longer.
Opinions?
Going to try dropping shifts to 6000 unless I find some reason power should carry higher and longer.
Opinions?
that looks to be a heavy valvetrain to drop off like that ^^^
some instability...
but to the question at hand I short shift my 2-3 about 100 rpm due to the shift extension being smaller on the 2-3
some instability...
but to the question at hand I short shift my 2-3 about 100 rpm due to the shift extension being smaller on the 2-3
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I was expecting it to carry more as well. But the valvetrain is all stock type things (stock rockers/valves, pac spings, comp pushrods, etc).
I had put the combo together shooting for more. But I can't seem to find anything wrong so I'm not sure what could cause the car to underperform but still run so well for so long.
That graph is over a year old and the car was on the road for 1.5 years before that as a daily driver. Perhaps by then the springs were just too weak? I didn't expect it to be an issue with such low lift on the cam.
I had put the combo together shooting for more. But I can't seem to find anything wrong so I'm not sure what could cause the car to underperform but still run so well for so long.
That graph is over a year old and the car was on the road for 1.5 years before that as a daily driver. Perhaps by then the springs were just too weak? I didn't expect it to be an issue with such low lift on the cam.
