Converter comparison question

[79rustbucket79]

I'm currently running a N/A 408 small block in a 3550 pound 1979 Camaro with a 9 inch converter that stalls to 5300 RPM at my track (200 to 300 more at sea level) in a car that runs 11.2's/11.3's with an upper 1.5 60' time. By going with an eqivalent stall 8 inch converter will I gain anywhere on the time slip, justifying the expense? Current slippage works out in the 12 to 13 percentile range assuming 1/2" of tire growth. If it matters, Converter is a custom build by TCS in British Columbia (originally for a lower power 327), trans is a manual shift TH350, 4.10 gears, spool, M/T ET Street 12.5x28, soon to be changed to 9x29.5 ET Drag slicks. Trap RPM is currently 6500, peak engine torque is 4700, horsepower at 6400 but doesn't fall off by more than 15 HP at 6800.

Thanks for any suggestions,

Doug

[Hutch]

The gains would be in question. There are a few different 9" converters being used today and all can have different results based on similar internal designs. To get the stall speed that you require would need to have a 9" converter with a negative vein angle or neutral (straight) with a very restricted stator design. The only time I have ever seen this faster is in lightweight vehicles with glides. The 8" will be a more agressive fin angle with the std 8" race stator.
I would think an 8" converter would be better and may help down track efficiency. Also because you have a 3 speed the weight of the 8" will greatly reduce the moment of inertia due to the fact that you need to spin it 3 times/pass.
Im by far NO converter expert but I can only tell you what results I have had in the past that worked for me. TCS is a very reputable company, no problems with their products.

Hope this helps, Hutch

[79rustbucket79]

Thanks for the quick reply Hutch.
You are correct about my 9" TCS, it is a negative fin angle but that's all I could afford when I bought it about 10 years ago for my 327. No doubt it's a quality piece, I finally had it opened up 2 winters ago, all in top shape other than clutch material filling it up. I had considered having them change it at that time, but I didn't want to kill what the car currently does. When the track is there, my car's 60' times are within .015 second. I strictly bracket race this car, so consistancy is paramount.
On a related note, in a quest to improve the car's hook on the crappier tracks (ours included most of the time :) ) I'm going from 28 to 29.5 inch slicks, and wondering if a gear change would be a good idea, or am I chasing my tail by working the tires harder? Currently 4.10's, thinking 4.56's

[Hutch]

Try the new tires first and see what the trap rpm changes to then if you need to ,change to a 4.30 axle to give you the same effective ratio as what you have now if you were happy with it the way it was.
If you need more trap rpm go with the 4.56 and it is possible that you may not have any change in trap rpm and the converter will just be more efficient at the top due to the decrease in load.

Let me know how you make out ,Hutch

[79rustbucket79]

Thanks again for the reply Hutch, we'll see whether or not my ET's take a dump with the taller tires, possibly in a couple of weeks. I would consider the 4.30's, however I'm not aware of any company that makes that ratio for a 10 bolt GM (8.5 inch). A gearset is going to cost about half what a converter will be, so I may look into that first for next season, and get another year out of my current converter. I like the idea of taking the load off the converter, and thinking back I chose this gear set due to running 26's at the time, then came the quest for more traction, etc.

Best regards,

Doug