Fg Xr6 Turbo

[Trent0]

On my e85 tune the limiter is 6750rpm.

 

I thought 7k on a built engine was the norm but because these engines have a long stroke higher isn't advisable  (althought Jet066 ran up and over 8k and I believe kent battle did too for drags and burnouts)

 

I make peak power at 5800rpm so I guess 7k isn't really needed either?

[k31th]

Depends how big your turbo is, too, with regard to peak/rising-top-end power.

 

A strong engine can handle the 8k rpm that qik1 and others have done, but is on the expensive end of the built engine market.

[jacobmitchell92]

I have no doubt mine can handle 8k no problems. But Iv been avoiding changing into 5th gear at the drags as it puts a fair amount of load on the gearbox. I think my limiter is set at 7500rpm now. But I never touch the limiter.

[k31th]

Yep, you're doing the right thing, don't change into 5th. It's better to over-rev 4th a little.

[MattyP]

Why's that?

How does it add load

[k31th]

Turns out that's a good question with a reasonably complex answer... I didn't know the answer fully (and probably still don't! haha probably have to ask a gearbox engineer for clarification)

 

From what I know (could be wrong), over-drive gears (anything with a ratio of <1:1) aren't meant to be changed into or accelerated in under extreme load because the driven wheels are running at a higher rotational speed to the engine with over-driven gear ratio's... This means the engine is trying to apply it's current torque (near maximum if at red-line in previous gear) to a gearset that is needing to increase torque to be able to push the bigger gear on the output, which means torque is multiplied at the connection of the gears and anything in between (clutches/synchro's/gear-teeth etc) may be prone to failure at the higher torque levels. This obviously depends on the strength of the parts in question... but as far as I know, gearboxes are deliberately weaker in these areas because those gears are very rarely used for maximum RPM and power application (due to the ridiculous road speeds required in these instances) to save money on parts at the manufacturing level. From my own experience, a lot of automatic gearboxes have a safety feature that prevents shifting into over-driven gears at WOT to save the gearbox from destroying it's own parts... hopefully that helps?

 

Somebody please tell me if I'm way off base

[discostig]

Oh so that's what they mean by overdrive gears, I thought it meant they were "fake cogs" or something and that's why they were weaker.

[k31th]

The term "overdrive" can be used in a few different ways, but yes, when talking about multiple gearsets, it's either under-driven or over-driven (or parity, of course, that'd be the same gear on each side 1:1 ratio). Under-driven is (greater than 1):1 and over-driven is (less than 1):1.

[jacobmitchell92]

I could be completely wrong but I thought it had something to do with the amount of clutch packs in 5th gear etc

[Elusivef6]

@jacobmitchell92 what wheels were you running on this?

Were you still using the 4 pot brembo's with the slick setup ?