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Discussion Starter · #1 ·
autocrossed at Salina this weekend with a mostly healthy '04. I think the struts could use some refreshing, but the brakes, wheel bearings and clutch are all rock solid. And I get my a$$ handed to me on a platter by the hot shoe in the '89 corvette and the s2K. My best time is three seconds behind theirs.

Yet I felt like I ran pretty good. I really needed third gear though and a lot. The course was tight, but the concrete and the A6s were sticking together pretty darn good. I still have trouble finding third when the car gets thrown around. On the last run I just left it in second and held the pedal to the metal and rode the rev limiter the entire length of the back half of the course. The course designer said the fast(er) A-stock cars were hitting the mid-sixties on both halves of the course. With slightly undersize A6s, I'm unlikley to be going much over 50 mph at the rev limit.

I think I'd like change the rev limiter to 8k, or put different gears in the tranny. I know changing gears would move me into SM. Anyone have an opinion on removing the rev-limiter? and how?

btw, I know our engine is running out of power at 7k, but the engineer in me sez that all I need is more power than the wheels are sucking up to go faster. 8k would get me about 60 mph, and it only takes 10-20 HP to go that fast
 

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as an engineer Im shocked you are even asking this. The limiter is there as a safety, you can remove it but at your own consequences. It saved my butt and the block more than once for me....
 

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Discussion Starter · #3 ·
2fas4u said:
as an engineer Im shocked you are even asking this. The limiter is there as a safety, you can remove it but at your own consequences. It saved my butt and the block more than once for me....
You won't be 2fas4me if this werx ;-)

hmmm, so do we know the limits of our engine?

The cobb AP with Street tuner lets one adjust the rev limiter. So being the engineer, I see I can test and discern. I know the honda boys are running stock somewhere in the 9k range, I'm willing to push the envelope a little. I'd sure like to balance the block first, but I'm willing to run a little higher and see what happens.
 

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thunderbird said:
You won't be 2fas4me if this werx ;-)

hmmm, so do we know the limits of our engine?
Ya, 7,000rpm

thunderbird said:
I know the honda boys are running stock somewhere in the 9k range,..
perfect. our motors are exactly the same as a high reving honda. :confused:
 

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Discussion Starter · #6 ·
MadMan77 said:
Won't that put you into the STU class though?

I'm heading for BSP. I can't give up r-compound tires :)

I should just learn how to shift, but the course was short ~ 35 second, and fast, and I needed to shift to third going out, downshift at the apex and then shift back to third.

I just don't see any amount of handling improvements or power improvements making much difference on that course. I was riding the rev limiter part of the out course, through a slalom no less, and then riding the rev limiter almost the entire length of the "slow" side of the course coming back to the exit.
 

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phil @ element has a sti with the stock valvetrain and drivetrain and he says that it says 8k all the time. it was somewhere on nabisco before.
 

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There is more than just the rev limiter. Yes, the rev limit is enabled at 7000rpms and removed at 6900. However, at 7000rpms the electronically controlled throttle will shut down to 20%, IIRC. So, you must change both things.

However, with all of that said, the rev limit on the engine is mostly about the valvetrain. I'm surprised nobody has mentioned this. In NO WAY would I ever contemplate pushing our motors to 8000rpms on a normal basis with the stock valve springs. The bottom end can take it. The valvetrain cannot. The springs are not spec'd for that type of abuse. They just aren't strong enough (lb/in rating). You definitely need stiffer springs if you want to rev the motor that high normally.

t
 

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Well, 8000rpm allows a pretty meaningful increase in what 2nd gear tops out at- 6mph or so. This would be unquestionably adventageous, but getting near the limitations of the valve springs scares me.
 

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Discussion Starter · #11 · (Edited)
nandanrp said:
Bingo. Easy solution to your problem, and you don't have to **** up your engine...



**** up things is just an excuse to upgrade ;-)
 

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there are things out there to help you find third easier. In fact, they started because of your exact problem.

Taller tires will help the final drive to keep you in gear longer. Yeah, the weight is gonna hurt, but you've got the torque to compensate.
 

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Turninconcepts.com said:
Taller tires will help the final drive to keep you in gear longer. Yeah, the weight is gonna hurt, but you've got the torque to compensate.
what i was gonna say, get some 245/45's and you wont have to worry about 3rd as much, raising the rev limiter is just plain stupid
 

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Discussion Starter · #14 ·
kessler89 said:
what i was gonna say, get some 245/45's and you wont have to worry about 3rd as much, raising the rev limiter is just plain stupid
I must drive the car harder than you guys. I'm already rubbing like crazy in the wheelwell. New struts and springs, or coilovers are on the horizon and may fix that, after I drop a two or three (or four) grand on the suspension. I was putting a serious scary groove in the middle of my 245-45/17 kumho V710s. I switched to 245-40/17 A6s and I'm still rubbing under hard braking, but at least its only the inside shoulder now. Plus the difference in 2nd gear top speed between the two is about 4 percent or 2 mph (25.4 dia for the V710 vs 24.5 dia for the A6).
 

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2fas4u said:
as an engineer Im shocked you are even asking this. The limiter is there as a safety, you can remove it but at your own consequences. It saved my butt and the block more than once for me....
+1, revving higher than factory limitations often requires re-doing the internals. (valves, retainers, rings, springs etc.)
 

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Discussion Starter · #17 ·
Peleg said:
+1, revving higher than factory limitations often requires re-doing the internals. (valves, retainers, rings, springs etc.)

or break them first by trying. Thanks to all for their input. Cobb AP is ordered and 7500 rpm will be dialed in as soon as I can figure out how to do it.

According to auto-x rulebook, for Street Prepared Classes. 15.10.R allows the engine to be "balanced" but 15.10.y seems to indicate that I have to use "stock" cam and related components. It looks like higher rate valve springs are out. It could be interesting.

BTW, I don't really even like revvinging at 7k, so I don't know how often I'll ever cross into the higher rpms. On my old Jensen Healey, with no rev limiter, one knew when to shift from how the engine sang. I accidentally revved itbeyond its 7k redline only once, in that particular case, way beyond the 7k redline. Nothing broke. I promise to be careful on how I use the extra rev range and I promise to shift as soon as I can tell that the engine doesn't like it.

The biggest issue will be first gear launches. I really don't want to miss the 7k shift limit in first.
 

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The Max bhp is achieved at 6000, unless there are modifications/tuning and the powerband changes.

Why not just rev to 6000....

* I personally wouldn't rev to 7500 to see if something breaks and then beef it up, but that's just me.
 

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Discussion Starter · #19 ·
Peleg said:
The Max bhp is achieved at 6000, unless there are modifications/tuning and the powerband changes.

Why not just rev to 6000....

* I personally wouldn't rev to 7500 to see if something breaks and then beef it up, but that's just me.


Its just to solve a simple problem. At most of the local autocrosses, I usually hit the rev-limiter, sooner or later, and usually for only a very brief amount of time, like less than two seconds.

But at the last autocross, I rode the rev-limiter for most of the second half of the course. I didn't need more power and I didn't need more handling, I needed to go faster. Bigger tires ride under hard braking and new gears moves me into SM. I didn't think there was enough time to shift up to third, back to second and then back to third, so I ended up running WOT at the rev-limiter. I think having a few more mph in second gear will help me be more competitive with the '89 corvettes that can run 70 mph in second gear.
 
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