LT4 Shift point on LT4

[Skant]

What's the best shift point on an LT4?

I've vaguely heard some numbers from 5600 to 6000. I've been using 5800 at the drag strip. But looking at a dyno curve for the LT4, I'm thinking 6000 is the right spot.

- Skant

 

[B17Crew]

Skant,
This is a great question... I have seen the same kind of RPM shift points (5600 to 6000) mentioned here in the forum and the ETs and trap speeds are pretty impressive.

I would’ve thought running up to about 6,300 RPM would’ve produced the best scenario by using the LT4s higher RPM, but I have read too many positive comments about shifting at or below 6,000.

If I may add to your post; can you guys who respond to Skants question tell us what gear you are in as you complete your run. I had once read about a stock LT4 running the 1/4 and finishing it in third gear. Is this possible?

B17Crew

 

[CKA_Racing]

In my area here, factory Stock LT4's go thru the traps in third gear with the rev limiter kicking a few feet from the traps or just past the traps. My best run of 12.9@110mph was done in 4th gear over the traps. I hit the limiter in third just before the trap and then shifted into 4th a split second before the traps. I shift by feel so I can't tell ya what rpm's I shift at.

 

[twiget]

Correct me if I'm wrong, but since the tach is analog, isnt there some slop, or lag in what the tach reads what the engine is actually at? Especially at full acceleration. Combine that with the reaction time for the shift it's self, isnt it possible the rev's will be at 6,300 rpm by the time the shift is intiated?

Jason

 

[stumpy]

I've been shifting just before the rev limiter, at least I try to, and cross the line in 3rd just before hitting the rev limiter. I never tried shifting before 6,000 as it seems to have plenty of power left past there. Smeone said to shift around 200 RPM past peak HP, although I've never dyno'd the car and haven't a clue where that might be. I just started racing this car a few weeks ago.

 

[Louis Bartay]

I shift at 6300 RPM and my rev. limiter is at 6400 RPM I had it at 6600 but I now have 60,000 miles on the stock clutch and the LT4 engine so I am trying to be a little less abusive. My friend thinks I should lower the Rev Limiter to 6000 RPM for safety sake.
Good ET for a stock LT4.:cool

 

[FX GS]

If you do have dyno numbers, should'nt the best shift point be at the rpm point where the graph shows where you are making peak hp & torque numbers, that is where the hp & torque lines intersect?

 

[Louis Bartay]

I have never had the Vette on a Dyno, Yet. But after racing several LS1 fbodys on the open hiway I have found that shifting at 6300 RPM that I stayed Just a little ahead of my neighbors 1997 C5 Auto that is bone stock. If I sfift at 6000 and do not Power Shift he stays even with me Ouch.
Louis

 

[cgtarga1]

>If you do have dyno numbers, should'nt the best shift point be at the rpm point where the graph shows where you are making peak hp & torque numbers, that is where the hp & torque lines intersect?

They always intersect at 5250, regardless of where your peak HP is.

 

[cgtarga1]

shifting from 3rd to 4th around 6000 (stock 3.45 gears), what's the lowest rpm 4th hits? In other words from 3rd to 4th, how far do the rpms drop? Looking at a stock dyno, you should be able to take the difference in rpm and 'roll' it around the peak area to find the optimal shift point.

 

[froggy47]

Mine is sweet at 6000. Feels right. Not less than 6000.