Depends on many variables.

1st. What is your RPM when you go through the traps? What RPM are you shifting at?

 

What's your mph? Are you already in 4th near the end? Do you happen to have any dyno data to show the power curve (crate engine, chassis dyno run?)

 

Car runs through the lights at at 5700 and I shift at 5700. Tried all the way to 6200 but it didn’t make any difference. The engine is a vortec. 350/330 ho from gm with a lunatic voodoo 268 cam and 9:1 compression. I don’t have any dyno data with this cam. I may change to a 383 or 400 next year. Probably from blueprint.

 

Before you responded, I was going to say, it probably won't make a significant difference going from 4.10s to 3.73s in 1/4 mile, but it also won't do much to improve highway. If you're going to bother do anything, you'd want the 3.55s.

So the Autogearset is: 2.98-1st, 2.04-2nd,1.46-3rd, 1:1-4th correct? That'll drop your 1st gear multiplier from 12.2:1 to 10.6:1. That's still a great takeoff gear.

One thing you mentioned is the lack of difference shifting 5700 vs. 6200rpm. This may change with the slightly milder 3.55s. I think if you do the swap, maybe experiment different launch rpms and shift (even try varying it 2-3 vs. 3-4) and you'll probably get most of it back. At least it's not requiring you to use another gear you previously weren't, as that would be more time lost due to the gear-shift time. Plus the 3.55s will probably work better later on with the extra torque of the 383 if you go down that route later.

 

Many variables to consider OP. I suspect you will lose .01+ in 60' times which generally = .02+ loss at the big end.

The Drag Tour guys run gear vendor behind their trans to resolve the drag use vs hwy RPM thing

Or a T56 for the win. 4:10's in 6th.....29xx RPM at 80mph. I hit the big end in 4th at 5500 ish RPM using a 26 x10 on a 15" rim MT slick.

 

Put a 5 speed in the car. It fits the tunnel tremec tkx

 

I'd like to put a 5 speed in it but rear end is leaking and needs attention first. My trans gears are 1st-2.559,2nd-1.752,3rd-1.366,4th-1.0,. If i go 3.55 I need to buy a new carrier since mine is a series 4 but I can run 3.73 thin gears per driveline shop. The Mph is usually 105 to 107 with a 1.85 to 2.0 60'. Car never really 60's even with a 3500 rpm launch. Thanks everyone for you help.

 

With what you have go with 3.55. You may lose 3-5 tenths ET.

 

Thinner ring gear, high RPM clutch dumps while running a tire often = BOOM.

Rear end leak is either pinon seal or diff cover, no need to disassemble rear end to replace either

Give the TKX some more thought...

 

Here is what us old guys used to use:

 

How about getting your leak fixed, toss on some 28" tall tires for the street and keep the 26s for the track ?

That should drop your RPMs around 500-700

 

Eventually I will go 5 speed but for now I need to buy other parts. I thought of the gear vendors but figured the tkx5 speed would fit better. I had forgotten about the Moroso calculator. I’ll have to order one. I thought of putting a 275/60 on the back but wasn’t sure if I could get it to fit. Looks like I’ll start with the pinion seal. It’s only been in there for about 5 years but is definitely leaking. Thanks everyone

 

Free calculator

Engine RPM Calculator | Spicer Parts

 

Although I had a 406" SBC (torque motor) TH350, 3000 stall (I think it was), and 2.73's out back... it was a solid high 13's car, 2.0 60's all day long, only using first, and second (hitting drive at the stripe. Went to 3.73's, everything else the same, and mid 13's.

So, I agree with the above and it slowing down maybe .5-ish

 

Thank you. I was afraid it may be that high. I’ll have to fix pinion seal and get a new set of tires and see how that goes.

 

IMHO, tires for the drags should be specific to that use vs "drag radials". I run MT ET Street which are a slick with just 2 narrow tread groves (DOT). 26 x 10 on a 15" rim, tube.

 

I need to buy both. I run m/t 235/60 15 at the track. They work well at my power level and there not too bad to drive there. Still trying to decide on a taller tire like DougG suggested for the street.

 

Still trying to decide on a taller tire like DougG suggested for the street.

enter size of tire (diameter) you are considering and rear gear to see RPM at X MPH

Engine RPM Calculator | Spicer Parts

 

Thank you. The big decision is if I stay with 15 inch rim or go larger. If I stick with 15s I can get a 27 on it. Researching to see if a 28 will fit in wheel well. Prefer the 28 to drop rpm more.

 

Going from a 26" to a 28" tire only drops the rpm 265 rpm at 70 mph. Going from 4.11s to 3.55s drops 500 rpm at 70 mph

Owned SBC 1st Gens with 3.55s is a very good compromise until you're ready to spend 3-4k on a TKX. If you don't often drive over 65-70 mph you don't really need to go OD.

That said I put ODs in every 1st Gen I've owned as well as my C2 Corvettes. But I often drive in the 70 - 80 pph range.

 

1969 Wheel and Tire Combo's... | Team Camaro Tech

To see what others have used...but MEASURE, MEASURE, MEASURE !!!

I made a cardboard template of the size I was looking at (like a giant C shape) to check clearances.

 

Thank you Vega&69 those are the same numbers I got when I ran it. Thats why I wanted to go to 3.73 and use a 27 inch tire. The gear swap alone doesn't make enough difference unless I go 3.55. It basically puts at the same spot as having 3.55's with a 26 inch tire and rpm shift indicators show I may stil be able to use 4 the gear with a 26 inch tire if I shift a little higher. I've been researching the tires in the tire forum like DougG suggested and I need to measure to see if I can fit a 275/60/15. I know I can fit a M/t 255/60/15 Drag radial and a Bfg 255/60/15. Since I have run both of these tires before. I need to pull the rear cover to check the gears and replace the pinion seal first. Then buy some tires. Unfortunately nobody sells anything decent in 15 inch rim and drag radials pick p too many rocks. Thanks Everyone.

 

Do you happen to have any dyno data to show the power curve (crate engine, chassis dyno run?)

Speed Test​

 

Unfortunately I don’t. I’d like to dyno it to tune the sniper Efi.

 

Decided to keep the 4:10s for now and run a 27 inch tire. It won’t help much on the highway but it helps on back roads.