New Converter, Different Shift Points?

S/ST 3040 · 06-27-2016, 04:33 PM

First of all, I do not race S/ST, as my screen name would imply. It was the number on my car when I bought it 15 years ago. I don't race SS either although, I've always been impressed with their performance.

My car is a back-halved 67 Barracuda. It weighs 2620 lbs. with me in it. The engine is +.060" 340 w/9.24:1 compression, OEM 596 castings w/1.88" IN valve, roller cam, Victor 340 manifold and Holley 950 carburetor. I run an aluminum drum, 904 transmission w/2.45 1st gear and trans-brake. Dana 60 w/5.57 gear. Either 31.2" or 32.6" tire.

I have been using an 8" ATI converter that hits about 6250 RPM on the brake and it has worked pretty well for the last few years. In an effort to find more MPH and shave some ET, I thought I'd try a little taller tire. It wasn't a horrible move in ET or MPH, except I was running towards the end of the year and was also getting into better air. On my last outing for the year, I was driving into a quartering headwind which, naturally cost me a little MPH but, I realized I was blowing a lot more RPM into the converter.

Fast forward to this year, I decided to swap to a tighter 8" converter and it hits about 5800 RPM on the brake. I take it out to the track, in 2400'-3000' DA air and the 60 ft. is hurting a little and the MPH is down 1 in the 1/8th mile and probably 1.5 MPH in the 1/4. Amazingly, my split times are better to the 330' by .019 sec. and .015 sec. to the 660' and ETs are pretty close.

So, I'm thinking, "Try the shorter tire!" Well, the track prep was awesome and my 60 fts picked up huge but, MPH is still down and my split times are worse.

Anyway, here's my question: Is it typical to have to alter your shift points after swapping to a "better" converter?

Thanks, in advance.

06-27-2016, 04:33 PM	#1
S/ST 3040 Junior Member Join Date: Jan 2015 Posts: 41 Likes: 4 Liked 1 Time in 1 Post	New Converter, Different Shift Points? First of all, I do not race S/ST, as my screen name would imply. It was the number on my car when I bought it 15 years ago. I don't race SS either although, I've always been impressed with their performance. My car is a back-halved 67 Barracuda. It weighs 2620 lbs. with me in it. The engine is +.060" 340 w/9.24:1 compression, OEM 596 castings w/1.88" IN valve, roller cam, Victor 340 manifold and Holley 950 carburetor. I run an aluminum drum, 904 transmission w/2.45 1st gear and trans-brake. Dana 60 w/5.57 gear. Either 31.2" or 32.6" tire. I have been using an 8" ATI converter that hits about 6250 RPM on the brake and it has worked pretty well for the last few years. In an effort to find more MPH and shave some ET, I thought I'd try a little taller tire. It wasn't a horrible move in ET or MPH, except I was running towards the end of the year and was also getting into better air. On my last outing for the year, I was driving into a quartering headwind which, naturally cost me a little MPH but, I realized I was blowing a lot more RPM into the converter. Fast forward to this year, I decided to swap to a tighter 8" converter and it hits about 5800 RPM on the brake. I take it out to the track, in 2400'-3000' DA air and the 60 ft. is hurting a little and the MPH is down 1 in the 1/8th mile and probably 1.5 MPH in the 1/4. Amazingly, my split times are better to the 330' by .019 sec. and .015 sec. to the 660' and ETs are pretty close. So, I'm thinking, "Try the shorter tire!" Well, the track prep was awesome and my 60 fts picked up huge but, MPH is still down and my split times are worse. Anyway, here's my question: Is it typical to have to alter your shift points after swapping to a "better" converter? Thanks, in advance.