Is shrouding enough to make 10% more HP?

Danglerb · Post by **Danglerb** » Thu Jul 12, 2007 3:47 am

I'm still poking around issues with the old Porsche 928 16v V8, and trying to make sense of various bits of empirical data. The Euro S head is a 2V design with a 40/45 mm exh/int valve and its used unchanged on several different short blocks, 4.5L, 4.7L, 5.0L, and even a few 5.4L, same stroke with a piston size of 95, 97, 100, and 103 mm.

Comparing the HP on the 4.5L vs the 4.7L its about what I would expect around 245 rwhp vs 260 rwhp. What has me puzzled is that 5.0L seems to run about 285 to 295 rwhp. Could that be from the 100mm piston size and less shrouding with the 45mm intake valve?

bobqzzi · Post by **bobqzzi** » Fri Jul 13, 2007 9:33 pm

I'd think it is much more likely to be an increase in compression and management changes.

Unkl Ian · Post by **Unkl Ian** » Fri Jul 13, 2007 9:45 pm

Did they all run the same cam and exhaust ?

Danglerb · Post by **Danglerb** » Sat Jul 14, 2007 5:43 am

Same ECU, same cam, the whole top end, heads, cam towers, intakes, throttle, start on either a 4.5L or 4.7L and get swapped around between them and also used on the 5.0L short block (that started life as a 85/86 32v motor). Compression is 10.4:1 on the 4.7L version and closer to 10:1 on 5.0L that seems to be making more power than 300 cc's would suggest.

Could just be the general difficulty in finding accurate HP numbers for anything you don't personally own. I'm thinking of building one of each just to know for sure whats going on.

FordManVT · Post by **FordManVT** » Sat Jul 14, 2007 4:39 pm

I'd say yes. I have a pair of heads ( ford 4.6 2v v8 ) where the intake valve was moved 2mm to the center of the cylinder, and it outflows similar head by 10%. Head makes about 290rwhp vs 260rwhp on the stock cam.

Intake valve is 46.83mm, exhaust 35.88mm in a 90.2mm bore

edit: made a emoticon on accident