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I switched from a T5 to a C4 and lost lost 1/10th and 2 mph. The car still has a stock NA longblock and was running 13.4 @ 100.98 MPH for the most part. Now it is 13.5 @ 98. I can deal with the 13.5 but for some reason it just bugs me to be under 100 MPH. I am running a 26 inch tall tire with 3.73's. I am at 14 degrees of timing. I am going to bump that up a little. Is anyone running 18 degrees initial on a stock engine? Any suggestions to squeeze a couple MPH's out? I had the interior out of it at the end of last year and was running 12.9 @ 103. (That was in late October in ideal weather. The car was running 13.1 at the beginning of this year with no interior.) I really don't want to gut it again, but I will if I have to.
 

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At your power level a 4.10 gear would prob give you back what you lost and maby a tenth faster. 1st gear is higher so you need more gear to get it moving.
 

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going from 5 speed to auto, you are going to lose a little mph with all other things being equal. A C4 converter does not lock up like a 5 speed does, so you have some slippage there. Are you sure your ET loss isn't due to a change in weather?
 

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I hate to say it, but at your power level I wouldn't expect much et gain when you get everything sorted out.

You are making roughly 250-260rwhp with the c4 . . . which isn't enough to see a huge advantage like if you were running 10s or so or a turbo car.

I went the other way with an old falcon I had awhile back.
I got tired of the no overdrive and the best it went with a c4 was an 8.03 at 87mph in the 1/8. Changed to a t5 with nothing else and it went a 7.93 at 89.

made 264rwhp with the c4 and 301rwhp with the t5 just for reference.
 

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In a stock setup like yours I could see you loosing some e.t. Now if you had a more drag type car a C-4 would do you some justice. I would keep the T-5!!
 

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Converter converter. A good one will cost you $1000.
Tim
 

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at the power level your at with the stock motor it seems that most of the 5 speed cars are running a little faster than a decent c4 set up.

when i was running low 13's the car went fastest leaving off idle and flashing the converter.
 

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Another vote for the convertor. It you are running some street/strip 3000 rpm stall convertor, thats slowing you down.

If its a limited use street car, go with the 4.10's as well.
 
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