500+hp w/ 3650 in OD?

[Boone]

Car is an '05GT with a new 5.3L. I currently have a 3650 backup up with a 4.10 rear gear, and top speed in 4th is around 130. I expect straight speeds to increase with the new mill (140-145 mph), so now I'm sweating the tranny.

What kind of trouble am I asking for putting a 3650 into 5th gear while on an uphill straight on a road course (back straight at VIR)?

Do I need to change my rear gear to handle my top track speed in 4th gear?

Do I just loose a little time with the shift, or am I headed for a failure?

 

[Department Of Boost]

You need a trans cooler.

 

[eighty6gt]

Install 3.55's or something.

 

[Department Of Boost]

Install 3.55's or something.

Another good plan.

 

[RazorbackMustang]

Install 3.55's or something.

This. With 500+ you don't need 4.10 gears on a road course.

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[Boone]

I know the norm is to put 3.55 or 3.31 gears in. I have to admit I enjoy exiting corners in 3rd at 45 mph and being able to wind up at 100 mph without a shift.

Until I change the rear gear... If I load the 3650 in 5th, is it stressing more, or do I just need to avoid being too aggressive on the shift? I don't want to drop a tranny and have the world tell me how stupid I was.

Does my next mod need to be a catch can? I have an Eaton Trutrac, so I would think that will keep Temps down compared to the stock clutches.

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[eighty6gt]

If the 3650 is anything like the T5's I've been into, 5th is not on the countershaft and is cantilevered off of the back of the case. The gear was smaller and had more teeth than the main 1-4 gears. It did not seem to me to be built for heavy loads.

You could just trial it and run the 3650 until it blows up. A used one is very cheap compared to the cost of open track racing.

 

[Pentalab]

I have an Eaton tru trac. I also added the Bob's autosports rear axle catch can. Otherwise you will end up with fluid all over the ground, and there is not much in there to begin with. Tru-tracs + dino oil won't heat up vs clutch plates.

Is your 500 hp NA or a blower? The story I got was the 5th gear OD is bad news when a blower is used. It puts a lot of stress on the OD. A 27" tall rear tire + 3.31 rear gear = 150 mph @ 6 krpm..... in 4th gear ( 1:1). ( 165 mph @ 6600 rpm). If a 3.55 gear was used, and 6.6 krpm, and a 27" tall tire, then it's maxed out at 154 mph...( 148 with a 26" tire). . A 3.73 rear would equate to 146 mph @ 6.6 krpm..again, with a 27" tall tire. (140 mph with a 26" tire)

But you would have to carefully factor in the rear tire height. With anything much less than 27" tall, the 3.73 would be a dud. Then factor in how much stress there is on everything with sustained high rpm.

 

[Boone]

Is your 500 hp NA or a blower?

I am NA.

3.55 rear gear and 26.25" (305/30R19) tire gives me 150mph @ 6800rpm in 4th (1:1).

3.31 rear gear and 26.25" (305/30R19) tire gives me 160mph @ 6800rpm in 4th (1:1).

It looks like I'm going to end up with a 3.31 so I can get more use of 2nd gear on track. Corner exit speeds of 41mph correspond to 3500rpm in 2nd gear. Driving VIR Full in only 3rd and 4th with the 4.10s did help me focus on the line as a total noob. I guess I'm just going to have to learn how to drive the car. No shortcuts.

 

[Pentalab]

I am NA.

3.55 rear gear and 26.25" (305/30R19) tire gives me 150mph @ 6800rpm in 4th (1:1).

3.31 rear gear and 26.25" (305/30R19) tire gives me 160mph @ 6800rpm in 4th (1:1).

It looks like I'm going to end up with a 3.31 so I can get more use of 2nd gear on track. Corner exit speeds of 41mph correspond to 3500rpm in 2nd gear. Driving VIR Full in only 3rd and 4th with the 4.10s did help me focus on the line as a total noob. I guess I'm just going to have to learn how to drive the car. No shortcuts.

Go with 3.31 You will get more out of 2nd...and 3rd gear. Still plenty of tq in 4th gear...and less stress on the eng. You also might end up not having to do a 3-4 shift in some places on some tracks, since it will be fast in 3rd gear..@ 6.8 k rpm.

 

[Boone]

So I've analyzed the speeds and gears for corners and straights at the tracks I'm going to run, At VIR, I'm going to go from 8 gear changes per lap to 12 gear changes per lap. At CMP I'll go from 4 gear changes to 6 gear changes per lap.

What would be the mechanical ramifications of putting in a 4.56 rear gear and using 3rd, 4th, and 5th while on track instead of 2-3-4? This setup would also help with larger and faster autox courses where you can drop it into 2nd and forget about it. It would also help acceleration from a standing start. A true three sport athlete.

I don't want to know what "everybody does," I want to know the cons and mechanical risks of running 3-4-5 on a road course or going to 5th at the drag strip. Would this make for an early and certain death for my 3650?

 

[NUTCASE]

I would stick with 2-3-4. The ratios between 2-3-4 and 3-4-5 are close, however 2-3-4 is an easier shift pattern IMO. Also with the taller rear gears you will spin the DS slower saving some energy.

1st 3.38
2nd 2
3rd 1.32
4th 1
5th .68

2-3 34% drop
3-4 24% drop
4-5 32% drop

 

[DiMora]

Shifting into 5 will be a pain. Stick with 2-3-4