yeah craig, i was tol 340/400 bhp, i did have pics of it, the guy who bought the engine sent me some on my old pc, it had graham walker on it in big block letters.

back to the original question, 2.5 inch should be big enough for 300bhp, the difference in size from 2.5 inch to 3 inch will change how and where you get the power really

Thats the one! i have soem techie pics and half a dozen of the engien bay i will post tomorrow.

Danny
for packaging reasons 2.5 would suit me better, can you elaborate on the differences in delivery? also any idea on the differnce in noise levels between the two as we have to meet static noise tests at every vent and drive by at some too. i was trying to get away without running a silencer you see, altho the exh will be longer than i cuurently use as it wille xit out of the rear of the car

going for a slightly smaller bore should give you a little better off boost response . The 2.5 inch system on Lou's s12 has a single silencer and is seriously loud, probably louder than a blitz NUR. I doubt you'll pass scrutineering without any silencers, you'll probably need a cherrybomb style middle box and a sensible backbox at the very least

i currently have a 2.5" system with a single Jetex medium length oval silencer which exits thru rear of passenger door. That runs static at tested rpm 4350(suppossedly 2/3rds of max ;) ) at between 98 and 102Dbs. variance is generally how up to temp engine is and how good the testing equipment is. Ironically although it registers apprx 100Db static, its quieter on track than some of the mildly modified V6s that register 89-96Db. The turbo does a great job of chopping up the sound pulses when under load. Im gonna lag the system from manifold all the way to tail pipe which will help a bit (and stop cooking me!)
Whaddya reckon?

I thought most tracks made you be under 96db now?, lagging should help, the tubular manifold will make it quite a bit louder. I'd run that Jetex box in the middle and a 3 inch tail pipe silencer personally. If you make it from Mild steel it will be a nicer sound too

no sprint hillclimb regs are 105Dbs except where thats over ruled by the venue, but i can only really think of Castle Combe which is 102. Think its summat to do with the fact most venues have planning permission for so many days a year at higher levels, but all the other dates such as track days etc come under normal planning noise restrictions.
Thanks for the suggestions re exh. I was gonna use mild due to it being a bit lighter and bit more ductile than SS. should as you say, take the crackle of the exh note too.