I have been hearing for quite some time this is not a good thing. Why?

 

i believe its because of the load it puts on the drivetrain.4th gear is typicaly a 1to 1 ratio meaning the engine spins once and so does the rest of the drivetrain anything more multplies the load on the drivetrain which will eventually break something due to stress it puts on the drivetrain.

 

How do the guys with 4.10 gears do it with no issues?

 

i have never sprayed in 5th, as far as gear ratio, it is still 1:1 as far as trans is concerned? does that make sense? lol! i hope so

 

Fourth gear is a 1:1 gear, not 5th gear.


Some try to say it's OK to spray 5th gear with 4.10 gears under this justification.

If a car has stock 3.42 gearing and it's in 4th gear, the overall gearing (3.42*1.00)= 3.42

If a car has aftermarket 4.10 gearing and it's in 5th gear, the overall gearing (4.10*.74)= 3.03 That is still semi close to stock and puts less of a load on your engine.

Try 5th gear with stock gearing, and you have (3.42*.74)= 2.53....the taller overall gearing would then put an even greater load on your engine in it's attempt to accelerate.

 

like these other guys have said it must have something to do with putting less load on the motor,


I myself will never spray in 5th gear but if I was going to I would make sure I had something to monitor a/f and knock live that is easily readable during the runs. This way you can shut down at the slightest hint of trouble.

 

Ive sprayed a light shot in 5th twice now with no issues. I have done some research on this, and the concensus seems to be the main stress point will be the clutch. I can sit here and say "ohh I'll never spray in 5th...." but the first time i race someone and the race goes 120+, I will DEFINITLY spray in 5th.

 

thats simply because their willing to push the limits on the drivetrain.maybe they got bigger ***** than me or they dont give a f---. some people do it with no problems .I wont recommend it but it your choice!

 

Supra guys spray in 5th all the time. The reason they get away with it...and with big HP and smaller CI motors ...is because they always run with something like C16. Have enough octane to cover the detonation issue under the high load of 5th gear and you will be fine.

 

N2o likes the higher rpms right, so when you hit fifth watch the tach, you start lugging the motor. But, I have no room to talk as I have run 125hp in fourth (auto/273 gears) upto about 135/140mph for much more than a 1/4 mile. A little pinging but didn't hurt anything, I was probably lucky though.

 

So the higher rpm's are better? Most of the time we do not go below 5krpm when racing..

 

With 4.10, if you make the 4th to 5th shift in a T56 at say 6200 or 6500 rpm at 100 to 110 mph, the motor will only drop down to around 4000 rpm in 5th, which should be no problem on the juice. Anything above 3200 rpm in 5th should be Ok to spray.

 

You say should be?

 

The higher the rpm's the less cylinder pressure builds up on the bottle, but it's still putting all the other high rpm stress on the motor it normally would.

 

Robert56 Is right about the lugging in overdrive.

In theroy an engine that spins 6000 rpms can handle twice the nitrous flow that it could at 3000rpm. That does not mean put 300hp in the car and hit it at 6000 rpms. The engine is just moving twice the amount of air. When you are racing the rpms stay up there will above 4000. but going into overdrive the engine calms down and start to lug. It is the same reason you do not spry off idle. The engines air flow is not able to handle the nitrous injections flow, air speed stalls(or bogs) lugs the engine and start detenation.
Ricky

 

I used to spray in 5th all the time with 4.10 gears. It will be fine. I put 200 bottles through that motor on a 1/4 track and another 200 through it on a 1/8 mile track and it is still running in a friends car to this day. LOL

 

Same here, but I will admit I have never sprayed the motor below 3200 or in 6th.

 

Me too........that would be crazy and just asking for trouble.

 

So spray it to the top of 4th and be happy with 3.42's. That is what I am hearing...

 

Well, again, I have sprayed to the top of 5th gear, which with my setup and 4.10, is around 140 mph(?).