The V8 Owners Forum -

Hi all, ive got a rimmers stainless sport exhaust system on the sd1,engine will soon be a 4.6 with nitrous. Manifold 4 into 1 with 1 1/2" primary pipes to a 2" outlet, at Y-piece end is 2 1/2" ,free flow ,tailpipe is 3". Would i be loosing some power with small primarys and 2" outlet ??. All advice welcome, rich

i too am looking at what size primaries my 4.6 needs,
i also have 1.5" primaries, 4 into 1 that goes out via a twin 2" system with 'X' pipe.

Ive read 1.5" are ok for std heads,but if modified then min should be 1 5/8". But not sure if mine are 1.5" i.d or o.d , . rich

Not sure rich,
im running V8D stg3 heads, crower 50233 cam, 4.0 pistons on 4.6 rods.

Hi
1 1/2 inch primaries should be ok for N/A engine up to and including about 400 bhp total output including NOS, for what Tony is looking at with the blower then 1 5/8 would be better but I wouldn't go over that with a full exhaust system. I will be using 2" on the chevy, but that is with just primaries, no collector or system and on methanol and in 2013 it will have a 6-71 on to of it (I think I may have gon mad by the way)
Best regards
Mike

Well Tony it looks like we both need to change the manifolds. Im looking for atleast 450 bhp with nos min to achieve the time im after. . And as of yet i havent found any bigger manifolds. Cheers Mike rich

Hi Rich
you could always modify the ones you have to stepped manifolds, have the first 8-10 inches ( until just after the first bend) in 1 1/2 tube then step them out to 1 5/8 and into a larger collector and system, you would ba able to use the existing ones as patterns, the smaller diamiter top end of the headers would help low end torque and you would still have the flow advantage of the bigger tubes.
Best regards
Mike

All I can say is mine made good power with 1.5/8" primaries, as you know where they came from Rich!

Hi Tom
with a blower motor you can easily go up 1 size on primarys with no real down side, NA and nitrous you are having to compromise more as the engine spends 99% of it's time without the giggle gas and there is no forward boost to help keep the exhaust going out the pipes. Tony's engine will be interesting as it will only produce more than a couple of pounds of boost at the top half of the rev range.
Best regards
Mke

kiwicar wrote:Hi Tom
with a blower motor you can easily go up 1 size on primarys with no real down side, NA and nitrous you are having to compromise more as the engine spends 99% of it's time without the giggle gas and there is no forward boost to help keep the exhaust going out the pipes. Tony's engine will be interesting as it will only produce more than a couple of pounds of boost at the top half of the rev range.
Best regards
Mke

hopefully

Ive taken the manifolds off and measured them up. Primarys 1 3/8" i.d , collector 1 3/4" i.d , Y-piece 2" o.d pipe to a 2 1/2" o.d single pipe which goes to the back of car. It seems a tad small,any advice welcome. rich . Also when you say for ex; 1 5/8" is that o.d or i.d. ??

looks like i have the 1-5/8 pipe sorted for mine now, and it fits the flanges caprisport have had laser cut perfectly.
caprisport said once ready they will lend me the templates they have for the manifolds they made on my car to take to ARRC so they can bend the pipes up for me,

Some more ?????. with nitrous am looking at 500ish. Have read that for that power and a single exhaust it should be 3 to 4" if dual then 2 1/2 to 3", any ideas. I cant go dual because of fuel tank, side pipes could be an option, but how important is the balance pipe ??. all advice welcome, rich

Hi
If you are going for that much BHP then a ballance pipe or an X pipe is needed for a twin exhaust, if you are going single pipe then forget the ballance pipe ! If it is a single exhaust set up you probably want a 3" pipe if you really expect to get 500+ BHP, but how you fit it under the car with silencer cans I don't know. If It becones an issue, you can split a 2.5" pipe down the middle and make an ovel pipe of the same area as a 3" but it is alot of welding, is this going to have to be road leagle??
Best regards
Mike

Hi Mike, thanks for the reply. Yes the car will be street legal, the 500ish power is give or take, 4.6 rover about 250ish then 250 to 275 of gas. I was thinking of 2 different systems, 1st , sbf manifolds 1 5/8 primes to 2 1/2" outlet and making side pipes with muff driver silencers. (but not sure of noise level ?? ). 2nd sbf 1 3/4" primes 3" outlet to 3" Y-piece to a single silencer at the rear. Both manifolds need to be cut about abit to fit, but im open to suggestions. Advice is much needed. Or does anyone know where i could get some manifolds already for the rover the size i need,to save me making them ?? rich