Dope

iTrader: (2)

Here's my dilemma.

I have a 99 FRC vette. Stock gears. 410rwhp. Runs through the traps at 120-122mph (never ran better than 122.5).

Car shouldn't ever have much more power than it does now. Maybe 10-20rwhp TOPS.

I want to add gears. Drag radials will be 25.7" tall. With 4.10s, I will be hitting redline (6600rpm) at 123-124mph. Is this too close for comfort? I am willing to raise my rev limiter to maybe 6700 (125mph), but that's it. When you trap at 122, are you really crossing the traps at 122, or is it slightly faster? From what I understand, the trap speed is calculated by your average speed across the last 60' of the track.

So how fast will I really be going? I doubt I will ever be trapping over 123mph, so 4.10s would be juuuust right. However, if I'll actually be going faster, 3.90s might be a better idea. That's 130mph at 6600rpm, so I'll have room to spare.

Keep in mind, the car is more of a daily driver and part time road racer, than a drag racer. It would just be nice to not have to shift into OD 50' from the finish line.

Oh yeah, my power peaks somewhere around 6200-6300 (T1 cam) if you were curious. Doesn't really FALL off right away, but it does start dropping. Should I aim to be hitting power peak at the traps or redline?

Dope

WicketMike

iTrader: (13)

im not sure what your tranny you have, but it think from reading that your have a A4, if you do go with 3.73's. if you have a M6 go with 4.10's for sure and you should really raise your limiter to 6700-6800 and you should be trying to get your shift points around 6500-6600 and you will pick up a good .2 and 2mph.

Dope

iTrader: (2)

Sorry, it's an M6, the only tranny the FRC vette ever came with.

Reason I don't want to raise my rev limiter is I'm afraid of breaking a rod bolt. I'd like to keep it as low as possible. I shift at 6400-6500 usually.

Dope

Colonel

Your actual speed across the line will be a couple MPH higher than what your time slip reads. For a 123 MPH trap, I'd calculate 125 MPH. That comes out to 6700 RPM.

Dope

iTrader: (2)

Thanks Colonel. What about my question regarding where in the power band I want to be through the traps? With 3.90s, 6600rpm is 130mph, which means I would be trapping right at my power peak or so (6200-6300rpm is like 122-123mph).

Plus I won't be beating the **** out of my motor by hitting 6700-6800rpm every pass.

Hmph. I wish I had better tire selection for drag radials, some 27" tall tires would be great

Dope

Colonel

That cam has a 112 LSA which means your power drops off just a tad quicker than with a 114. Taking that into consideration, ideally, I'd want to be shifting about 6500 and crossing the line no more than about 6700ish.

Take your pick. It's borderline either way and it's really not going to make much difference in your ET either way. It's so close that we're kinda nitpicking here.

Me? I'd take the 3.90 to give me a little growing room in the MPH department. You say no more than 123 now but I've heard that one before. This time next year you'll be saying "no more than 130."

Dope

iTrader: (2)

Good thinking, Colonel. I think 3.90s is the wise choice too. Even just based on the fact that I won't be beating the **** out of my motor on every pass. Stock bottom end + 6700-6800rpm rev limiter passes every run makes me cringe. Letting off at 6400-6500 (~125mph) makes me feel better. Plus, like you said, room for improvement.

Thanks for helping sway my decision.

Dope

Colonel

You're making the right choice. Glad to help.