The V8 Owners Forum -

Getting to the exhaust stage of the engine build. I have (came with the engine ) a pair of cast dual outlet manifolds ,how good are these .....just that building a set of headers is a bit of a wriggle . I have big valve heads, ported stage 3ish and will have a fast road cam kent m228 . Are the cast manifolds going to cost me lots of hp or are they not to bad . I have already built 2 complete sets of headers for this car that have now been discarded coz I keep changing other things (mostly my mind )4-2-1 or 4-1 and then to big primaries and I just cant be arsed making another set if I dont really have to . Any body getting 225 ish hp with these manifolds ?

The SD1 type with the exits at the back are said to be a pretty good design. Apart from the weight, of course.

With the LR 3.9, the view of those in the know is that there is little to be gained with aftermarket extractors over the standard exhaust manifolds. Gains are to be made in opening the system downstream from the exhaust manifolds.

Garry

Thanks garrycol and DaveEFI , I guess the thing to do is match the port to manifold as best as one can and go for a bigger bore system after that. Makes me think tho ,not so good pic of the exhausts (engine is a 3.5 I have parked in favour of the 3.9 serp motor ) but I had decided to discard these because the primaries are to small but they are ,at a rough measure up , bigger cross section than the cast stock ones , they are def bigger that the port opening on the heads . But the cast ones are tidier...