Power loss through a C4 trans

A friend sent me an email today about some dyno numbers.

90 degrees F
323HP, 349TQ @ 4200rpm RWHP & TQ

Builder figures 435HP at the engine based on a 23% loss of HP through the C4 transmission.

What do ya think? 112HP loss through a C4?

Sounds a bit high. I'm thinking high 30's to mid 40's for Hp loss through a C-4. I've seen a few posted numbers in the 40-45 range.

I think percentage losses may be flawed and probably aren't the most
accurate way of looking at things.

Thanks. Seems a bit high to me too, like the builder is trying to make the engine sound more impressive than it really is.

Originally Posted by BrianS

A friend sent me an email today about some dyno numbers.

90 degrees F
323HP, 349TQ @ 4200rpm RWHP & TQ

Builder figures 435HP at the engine based on a 23% loss of HP through the C4 transmission.

What do ya think? 112HP loss through a C4?

90 degrees F implies those are uncorrected numbers. What were the SAE corrected numbers.

My car was 313 RWHP with a C4 and 335 RWHP with a T5z. Both numbers were SAE corrected. Best estimate was the old engine was about 395 HP at the flywheel. 23% could be not that far off depending on the rest of the drivetrain. HP is getting used up due to friction, gear efficiency and inertia...not just friction or heat.

i think years ago tci published est hp to drive different auto trans. c4 & pg were about 25 hp IIRC.

"90 degrees F implies those are uncorrected numbers. What were the SAE corrected numbers."

Yes, it implies it but if I know the builder...323/349 were the SAE corrected numbers. He takes every advantage. He also said a C6 was a 25% estimated loss. If the C4 and C6 are only 2% apart, why bother?

I checked and the calculation was done wrong anyway. 323/.77=419HP. That's still a 96HP loss. And BTW, the engine is a 408/351C stroker with fully ported 4V heads and a custom cam. The bill was about $9K. Such a deal!

Using SAE corrected does not always net an advantage, but at 90 degrees F it may. In my case, the dyno was performed at about 65 or 70 degrees F. Uncorrected was 345 RWHP and SAE corrected was 335 RWHP. Torque was the same way...346 RWTQ uncorrected and 337 RWTQ SAE corrected.

Originally Posted by BrianS

"90 degrees F implies those are uncorrected numbers. What were the SAE corrected numbers."

Yes, it implies it but if I know the builder...323/349 were the SAE corrected numbers. He takes every advantage. He also said a C6 was a 25% estimated loss. If the C4 and C6 are only 2% apart, why bother?

I checked and the calculation was done wrong anyway. 323/.77=419HP. That's still a 96HP loss. And BTW, the engine is a 408/351C stroker with fully ported 4V heads and a custom cam. The bill was about $9K. Such a deal!

and tci felt that the c6, t400, & 727 ate about 50 hp, give or take a touch.

The info i have seen on power loss in trannies listed the C4 at about 23-25 hp. I think 125 hp is way too high.
The same info lists the PG at 18hp.

I have read/been told that the converter plays a big part in this as well. Is there a chance that a miss matched converter could cause low HP #'s?