I have a 2140 pound Vega running 6.00 in the 1/8 mile. 383 small block. I have a 5.13 in the car now and thinkng about 4.88 or 4.56.Right now the car is crossing at 7100. I think that is to much.I am thinking about a 4.56. What everybody think. Converter flash to 6400. Thanks

quote:

Originally posted by blowerman:
I have a 2140 pound Vega running 6.00 in the 1/8 mile. 383 small block. I have a 5.13 in the car now and thinkng about 4.88 or 4.56.Right now the car is crossing at 7100. I think that is to much.I am thinking about a 4.56. What everybody think. Converter flash to 6400. Thanks

I don't know which finishline RPM your engine might prefer, but I'd have to assume your valvesprings might last longer with something lower. I'd try the 4.88 and see how you like that. Bear in mind, the gear change is going to make the converter flash slightly higher. Just one opinion. Take care. Tom Worthington

RPM Calculator & Tom is right the converter will flash higher.

http://www.wallaceracing.com/c....php#google_vignette

I’m 2000 lbs running mid 5.60s with a MT 14x32 and 4.88, flash to 6200 and go through at 6900. I think you might need the 4.56 but don’t know how much you’re trying to take out of it.

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Right now the car is crossing at 7100. I think that is to much.I am thinking about a 4.56. What everybody think

I think your 1/8 mile combination is very good based on the 6400 converter flash, 5.13 gear and crossing at “only” 7100. I wouldn’t install anything less than 5.00 if it were me.

In door car gearing I want 5.14, 5.00, 4.86, 4.57 because all these are 7 tooth pinion ratios.

If you have FB watch this video, and then watch it 2x more. This guy is Spot On with his analysis imho.


J Lamb

Knowing some other things about your car could help one’s choices. What size/ type tire are you presently using? Do you have a dyno sheet or DA photo of run to post? If not, then what CR, fuel, induction on engine?

I think the 4.88 will get you to 6900 with no other changes. If the car is good, I wouldn't drop to the 4.56 without consulting your converter supplier.

Are you running a spragless converter?

If not, 4.56 and a spragless would probably be my move.

Conventional 23 degree head 383 / 406 engines rarely benefit from more than 6500 RPM's.

The converter is spragless and the car has 14x32 M/t. Car is good I just want to lower the finish line RPM.Thanks

quote:

Originally posted by markemark:
If you have FB watch this video, and then watch it 2x more. This guy is Spot On with his analysis imho.


J Lamb

Justin Lamb & his resume speaks for itself; he's one of the best in drag racing, in multiple classes!

I race against Justin, his cars are fast, deadly & consistent. I'm sure I left some things out. I have learned a bunch from him from observing & competing against him.

2BKING

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Justin Lamb & his resume speaks for itself; his cars are fast, deadly & consistent.

Agreed, and those DC are 3 speeds!

We made a rear gear change at the beginning of 2025. It was for the same basic reasons as the OP. Our combo is totally different than Blowerman's.

Our Camaro is 3100 lbs. & was going through the traps 1/4 mile around 7,400 with a 30" radial. Anyway, we decided to switch from the 3.89 to a 3.55. We lost around 300 rpm & we gained 300-400 rpm in converter stall.

This was one of the best changes we did with this combo/race program. More to come in a different thread.

2BKING

6 yrs ago when I stopped 1/4 mile racing I went from a 4.40 to 5.14 and picked up just over 600 finish line rpm in the 1/8 @ 7250+ now. 2850#, 32x14, 388

Blowerman, what is your MPH at the 7100 crossing RPM?

My MPH is 113.70 1/8 mile.

I don't know where your cam and heads run out of breath, but your car is light enough and with good MPH, so I am thinking a 4.88 would not hurt your performance at all, might even help. It would probably run very well with a 4.56 too. Either option would likely keep your valve train happy for a longer time.

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Car is good I just want to lower the finish line RPM.

Then 4.57 would be an excellent choice as finish line will be lower and it’ll improve your SLR with a car as light as yours. I’ll assume the car uses wheelie bars.

Without the HP and TQ numbers of the engine. (see my signature)

Ill be the first to bet that it will slow down and your good weather to bad weather swing will open up. I bet you lose 60 and mph. The 5.14 gear is the only thing keeping that 6400 stall happy. 6600/6700 and less gear will be more slip, most likely. If you can make 500 passes on valvesprings, i wouldnt worry about it. jmo

quote:

Originally posted by blowerman:
I have a 2140 pound Vega running 6.00 in the 1/8 mile. 383 small block. I have a 5.13 in the car now and thinkng about 4.88 or 4.56.Right now the car is crossing at 7100. I think that is to much.I am thinking about a 4.56. What everybody think. Converter flash to 6400. Thanks

My sons S10 weighs 2550 with him in it and it runs 6.30s with a 5:13 gear and his converter flashes 5500 and he shifts at 6200 and hits the stripe around 6400.
Your converter flashes higher than my Greg Slack converter in my truck and I have a 436 running 5.50s at 2700lbs.

It depends on so many factors.

I have 4.86 gears in my car. Switched to 4.56 gears for a weekend and the car hated them. Went back to 4.86 and the car loved them. Didn't change anything else. Car just didn't like that ratio. Wish I could try something like 5.13 just to see if there is any difference.

I shift at 7400 and can easily go to 8000.

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Wish I could try something like 5.13 just to see if there is any difference. I shift at 7400 and can easily go to 8000.

Here’s a method to consider if going 5.14 that would require an extra ratio change. With 5.14, change the glide planetary to 1.69 (Coan) keeping the same SLR as with 4.86/ 1.80.
With my 5.14 I’m using a 1.56 planetary gear.