StreetSilverado

iTrader: (17)

Well Going to a TH400 and T-Brake, I'm a little curious as to which gears would be better. I'm stuck between a 3.70 or 4.11.

Anyone have any input as to why which gear you would perfer?

Setup is for the 1/4 with a Neal Chance 4200 nitrous converter 9.5" and a 370ci. setup for a 150-200 shot. The car will be bracket raced every weekend. Hoping to get around 3300-3400 race weight.

Or will there not be much difference between the two?

Mikey 97Z M6

iTrader: (37)

Kinda depends where your engine makes peak power, tire height, estimated trap speed (mph) etc... I would try to estimate your trap speed, then use an online calculator to play around with the ratios.

FWIW, I ran the times in my sig with some 3.89 gears and 26" tires, going through the traps around 6400. This next season will have a much higher winding cam, taller tires and 4.30 gears.

Mike

JL ws-6

iTrader: (50)

Being that your power level and car weight are about the same as mine was before I started digging into it again.. I can tell you I had 4.10's and went to a 3.73, and I don't think the 3.73 helped it. Honestly, the car still went on the bumper with the gear change... I changed ratio's because I swapped a spool in and it seemed like the right time to do it.

If I were in the same situation again, I'd have put a 3.90 in the 12 bolt. Just to drop the rpm's a couple hundred... I think the car with that gear, at the level you're at is about the best compromise, and will keep it in the right spot rpm wise for as much of the run as possible.

fwiw, my dyno sheet is in my photo album, if yours looks similar, I'd go with a 3.90.

StreetSilverado

iTrader: (17)

Engine makes Peak HP right at 5050-5100, 28" 10.5 Et Drag, and hoping around 137-138 MHP on the spray. Rev. limit should be set at 7000.

I'm thinking the 4.11's should be pretty close, but I was just wanting some more input between the two gears before I change my 4.30's out today.

Mine won't make the 1/4 on the bottle with 4.30s

JL ws-6

iTrader: (50)

I think I could make it on a 4.30, but I'd be spinning the thing to 7800 to do it I'd guess.

With the 3.73's, I have the shift light at 6900 and it doesn't come on thru the traps. if your converter is effecient enough you should have no problems making it on a 4.10 or lower, just depends how much lighter/more power you want to put to it before having to change the gearset again.

StreetSilverado

iTrader: (17)

So did you see any lose between the 4.11's and 3.73's? I don't plan to make any HP wise changes until next season, I hope to make it a 408 .

I'm wanting to keep the RPMs around the 6500 range perferably so thats why I was looking at the 3.70's that I have if they don't net me a good loss.

Since the 4.11's I have are some cheaper geras and the 3.70's are richmond I'd rather use the better quality gears without going and buying a new set of 3.90. Economy man.....economy.

JL ws-6

iTrader: (50)

I didn't lose anything so to speak, the car did seem to lose about .1 to the 1/8th but picked it back up in the back 1/2.... then I swapped the converter, lost another .1 to the 1/8th and gained .2 and 3 mph in the back 1/2

Again.... if I could do it again I'd have either left the 4.10 in the car, or put a 3.90 in. I had the rear apart to change from an eaton to a spool so I figured why not throw some new bearings and gears in it while it's apart and try something while I was at it.

Now with the car weighing 400 lbs less I'm sure that the 3.73, if it hurt it out of the gate will now be evened out, hell I'm at the point now that a glide will work and probably just pick up everywhere, car won't even lose anything even in the 60/300 foot times with this much weight out, nevermind another 100 motor hp and double the nitrous.

Mikey 97Z M6

iTrader: (37)

Did you mean it peaks at 6050-6100?

This brings up an interesting topic though. I've always understood that it's best to get the car to go through the traps within a couple hundred rpm of where your engine makes peak hp, depending how quick/slow the hp starts to drop off after peak. So in other words, if yours is peaking at 6100 and the hp levels out or falls off very slowly to 6700, then you'd want to go through the traps somewhere between 6100-6700. But, if your hp peaks and then falls off very quickly, then you'd want to go through the traps at a rpm closer to peak hp (like 6100-6200) to keep the car from nosing over through the traps. Someone please correct me if my logic is screwed up here.

BTW, your current setup is close to what mine will be in a month or two. Forged 370 w/ hand ported L92's, eventually want to spray it, eventually will make it a 408 etc....

Mike

JL ws-6

iTrader: (50)

Your theory is correct, usually. But, take a look at the dyno graph in my photo albums.. where do you think that likes to be shifted? I already know, curious what it tells ya though.

camscam02

iTrader: (21)

Ill tell you this, I go 140 and cross the traps at 6500 rpms with a 28inch tire and 3.89s in my 9inch. Seems like it might also be the perfect gear for you. Thats with 5-6% converter slip.

JL ws-6

iTrader: (50)

Sounds like your converter's about as effecient as mine.... I was seeing about 6600 rpm @ 143.

StreetSilverado

iTrader: (17)

Thanks guys, right now I'm having to go with the 3.70's since I don't have the coin to buy some 3.89's.

Looks like I'll be getting them once I get the money though

Mikey 97Z M6

iTrader: (37)

That is one broad hp curve up top. I would say that it probably isn't too picky on shift points lol....

Way back in 2001 when I still had the LT1 in this car I had an old Comp Cam grind with some first generation XER lobes and that cam was the peakiest cam I've ever seen. The cam peaked at 6100 and was down 35hp by 6300 and falling fast lol.... That was a tough cam to run consistent ET's with because it was so picky on shift rpm, but it made great street power/torque.

Mike

Mikey 97Z M6

iTrader: (37)

Man, I just sold my 3.89's too.

Mike

JL ws-6

iTrader: (50)

Funny thing is that is on an xer lobe.

I find, and this seems odd... but if I pull 2nd at about 6900, then pull 3rd at about 7200 it runs the best.

I've got alot of passes under my belt and this, is how it's the happiest. I pull the 1-2 right at the shift light that's on @ 6900 and then when it comes on for the 2-3 I give it a 1 count then pull it.

Just seems to work out.

Whole motor's or sale too Slug it in and hit it with a 65 jet and go make 9 second passes.

JRracing

iTrader: (35)

^^ My car seems to run a little better by shifting it like this.

My car is 2830# with me in it, 4500-5K stall/th400, 28" tire and it had a 4.56 in it. It would cross the line at 7500 rpm's. I took that out and put a 4.10 in it and it went through at 7K rpm's. This T rex cam did not make any more power past 7K. So it helped a lot. It didn't really seem to pick up ET but did pick up a few mph and is crossing while still in the power.

I'm putting a custom n2o cam in this year with a 100-250 plate kit. I may have to go up to a 3.73. But this cam will make power a little higher.

Reboot

iTrader: (5)

Like Camscam02, I go through the traps at 139-140 at exactly 6600 rpms with 3.91 gears and 28 inch tire. I will prolly go with 4.10's once I swap to an intake that makes power above 6300 rpms.