Compression Ratio On a 748BP
 

I gather that the 748 sps has a number differences to the standard BP, one of which being a slightly high compression ratio. I was wondering if increasing the compression ratio on 748BP was possible and what the power gains might be..?

There would only be about 2 BHP differance between the BP and the SPS on a 748 according to the MCN data performance sheet. 4D

Differences.

higher compression pistons and a different set of cams (more lift & duration)
Different exhaust valves
Titanium Con Rods & 45/50 Termi system with chip to match.

You can fit the higher comp pistons in a bip £££'s

I'm waiting for my Bip-SPS conversion to be setup on the dyno, then I can let you know how much more power it gives.

But,
I got the parts V. cheap.
I was having the topend rebuilt anyway
I fitted vernier pulleys had the cam timing done
I'm retaining my 45mm system
The chip's being mapped on the dyno.


SPS dynochart on sigma's site

http://www.sigmaperformance.com/dyno1lbig.jpg

Bip V SPS Chart
http://www.sigmaperformance.com/dyno2-3hp-big.jpg

The article
http://www.sigmaperformance.com/748spstech.htm

[Edited on 8-3-2005 by Mr_S]

It will be interesting to see what power gains you get from the conversion.

It's been on the dyno today...

The numbers.

99.1 BHP
59.5 ftlbs

Not bad for a '97 748
We did get 100.4 on the last run, so with a few miles on it, it should get consistently higher that the ton :D :D

Just waiting on the MOT now.

AVI of one of this afternoons runs, taken just before I arrived

http://www.chathamclose.com/pics/dyno.avi

The dyno chart

http://www.chathamclose.com/pics/dyno-sp.jpg

Not bad at all...! I suspect fitting 50mm end cans would give a couple of extra bhp as well.

Have you got a power commander fitted...?

No I have a FIM Ultimap chip.