When to replace a converter?

One of the most critical areas of a automatic race car

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vegahigh
Posts: 4
Joined: Tue Sep 09, 2008 12:07 pm

When to replace a converter?

#1 Post by vegahigh » Tue Oct 12, 2010 4:29 pm

I have a SBC chevy vega. It is a typical mid 10 car, turbo 400, 4.88 gears, 3060 lbs with me in the car. ( tires 31.25 tall)

The attached image is the datalog session of the last run, 10.80 @ 125. I have had a best of 10.60 @ 132. The current log is with a new t-ram and carbs, and it was pretty fat on this run. Anyhow, The ET seems poor for the mph. It Has an old hand me down 8" coan converter, whose history I don't know.

Is there anything to be learned by the rpm plots?

355 SBC 4340 crank, 4340 h beam rods (6.000)
Probe pistons (12.5 cc dome, should yield 12.5 ish compression.)

Sportsman II heads by Chapman head service
64CC chambers
Intake Exhaust
Lift CFM CFM
0.200 130 101
0.300 177 133
0.400 194 140
0.500 233 141
0.550 260 159
0.600 270 169
0.650 290 179
0.700 290 179

Victor Ram 2 holley 660's,,


Solid Roller)
.630 /.630 lift @ 1.5 , 1.6 Erson rockers used
252/260 duration @.050 lift
cam is straight up, 106 degree lobe centerline.
Crane stud girdles

1-3/4” headers hooker super comps, open exhaust
MSD 6AL, MSD dist. 36deg total timing.
Turbo 400 w/ reverse pattern valve body, trans brake.
4.88 gears,
ladder bar suspension, 90/10 shocks, line loc, M/T 31.25/12.2-15W tires
Et-cetera

vegahigh
Posts: 4
Joined: Tue Sep 09, 2008 12:07 pm

Re: When to replace a converter?

#2 Post by vegahigh » Tue Oct 12, 2010 4:34 pm

Sorry, here is the attachment.
Attachments
10.80-run.jpg
datalog 10.80

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Marty Chance
Posts: 193
Joined: Fri Sep 19, 2008 6:34 am
Location: Cheney, KS

Re: When to replace a converter?

#3 Post by Marty Chance » Tue Oct 12, 2010 5:47 pm

the converter looks pretty good actually. And coming from a guy who wants to sell you a converter , i think the converter is not the first place to start tuning this combo. how much timing are you launching on ? are you pulling timing on the launch and ramping it in? You may want to tune those carbs or even try a good single carb and intake and the car may come around and surprise you.
Neal Chance Racing Converters
Home of the World's Fastest Automatic Doorslammers!
www.racingconverters.com

vegahigh
Posts: 4
Joined: Tue Sep 09, 2008 12:07 pm

Re: When to replace a converter?

#4 Post by vegahigh » Thu Oct 14, 2010 9:27 am

Marty,

Thanks for the input.

I have been playing with street cars for years, this is my first "real" race car. I always thought the horsepower was the hardest part to come up with, I have learned that the first 60' makes or breaks the run , ET wise.

I don't understand what you are refering to with moving the timing around though, can you explain?. I was just setting the timing based on the best MPH performance.

I'll keep at it

Joe

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Marty Chance
Posts: 193
Joined: Fri Sep 19, 2008 6:34 am
Location: Cheney, KS

Re: When to replace a converter?

#5 Post by Marty Chance » Thu Oct 14, 2010 10:23 am

i meant if you are pulling out timing on the launch to calm it down , then you can add some timing back in and it will cleanup the graph in the first 1.5 seconds of the run. And you mentioned the carbs were alittle "fat" , if you are running rich on fuel mix that will slow the car down
Neal Chance Racing Converters
Home of the World's Fastest Automatic Doorslammers!
www.racingconverters.com

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