GO4BROKE

To set the baseline for my experimenting I specked out my stock 97 454 Mag carbs in the dyno program. I used head flow info from the website linked to in the other thread and cam specs from Dennis Moores Big Block Chevy Marine Performance book (great book by the way). Switching between seat to seat cam specs and .050" specs produces VERY different results. The instructions say the seat to seat specs are the accurate ones, and that makes sense. After getting all the engine specs in the only variable left is exhaust. As there are no marine exhaust options in the program I experimented until I had the HP right. With "H.P. Manifolds And Mufflers" selected it came up with 364 hp at 5000 rpm's, seems right to me. The problem I have is that switching the exhaust to " Small Tube Headers Open Exhaust" adds 75 hp! Thats WAY too much, and a suspiciously round number, but I don't see where I've entered bad data. Any ideas?

cobra marty

Your 364hp is pretty poor-- .8hp/CID so the HP increase with headers is not too unreasonable. What you can't do is individual long tube headers except a few so figure an exhaust with 2-21/4" diameter and 15" length open or thru hub? Also it's crank no accessory HP.

GO4BROKE

Cobra Marty, I certianly agree that .8hp per inch is pretty lame! Merc rated this motor at 365 hp, so I figured when I hit that number I had all the right specs in the simulator (meaning the right exhaust option). I just have a hard time believing that the stock exhaust is that restrictive. It is the same as used on the 502 mag which is 440 cshp, 415 pshp, seems it should flow well enough not to choke off a mild 454.

GO4BROKE

I was just on the CP performance site, Lightning headers says a 45hp gain for a 365, time for more simulator experiments!

KAAMA

I have and use the Desk Top Dyno as well. I have found it to be very accurate at times when comparing it to a real dyno and then sometimes I'm not real sure. It can be interesting to use it as a reference point and it's kind of fun just to horse around with the different combinations, etc. I have also read in the instructions that it is better to use the "Seat to Seat" cam duration as well.

Crazyhorse

I agree with KAAMA. Based on real-time dyno numbers on SuperV's 454 as compared with the Desktop Dyno numbers, the two were closer than 1%. Right KAAMA? You were there.

KAAMA

Yep!

Crazyhorse

KAAMA has spent more time with Desktop Dyno than anyone I know, so I'd value his opinion on it. KAAMA, how did your cam specs for the cams you have now compare with the boat's performance as related to rpm's? What did DTD say your top rpm's would be?