Is it worth replacing the inlet manifold and trumpets...

[M@H]

..on my standard 400 for some 45mm ones..?

Now just to start this off, I am not one of the "usual suspects" on here who goes shopping for "power bits" on ebay and then wonders about what to do with them afterwards. That aside I have had some things come into my possession that I can either get rid of or fit to my car if it seems worth it. They are:

ACT enlarged inlet manifold (45mm)
45mm Plenum Base (well whole plenum chamber actually) with shortened flared Ally trumpets

Now I don't want to embark on some massive engine upgrade here but if it is considered that I might get some useful gains from fitting these then I might as well do it rather than not as its not a difficult job. I assume though that there could be a range of limiting factors in the rest of the engine that in real terms make it a fairly pointless excersise - your thoughts please all.

Cheers,
Matt

[Pupp]

Depending on how the manifold has been reworked, you may have an issue with the inlet ports on your heads... wouldn't be helpful to have a step or ridged 'restriction' facing flow just there

Valve sizing is likely to become the limiting factor

[M@H]

Good points - I am not about to embark on some massive head modification programme so the original valve sizes would remain (unless I found some reworked/larger std heads)

I do actaully have another manifold that is bored out to 45mm at the top trumpet side and could be smoothed internally to taper down to the original head port...

Edited by M@H on Wednesday 18th May 12:56

[Andy chimaera]

hi there, i had an induction kit, carbon fiber trumpets, smooth bore hose, air flow meter, stealth cam, hydrolic lifters eprom chipped, mapped and rolling roaded to get 253bhp, it was running 220 standard (mine is a 400 too by the way) and that cost just under 2 grand i think, i was thinking of getting the ACT inlet kits and they said them selves you wont get any benifits from these with the 400, they said it will make throttle response better, but no real power gains, so fair play for being honest they could have sold me one any way, he reconed the cars need to be pumping out closer to 300 horses to get any power benifits from the twin plenum, ive learned that unless you improve the beathing right through, any 1 or 2 small mods prob wont make much different (IMO)

[900T-R]

To optimise a std 400 you'd want the 38 mm superflare trumpets; going to a 45 mm ported intake manifold and trumpets won't give you any more power and possibly/probably lose you some low/midrange torque and driveability (lower gas speeds - risk of fuel 'dropping out' of the mixture before it reaches the combustion chambers).

With a plenum insulating gasket and induction hose kit you've pretty much got it all covered until/unless you're going for a complete engine rebuild/upgrade (at which point one should look long and hard at the SC kit - at least if there's no reason to open up your engine anyway).

[M@H]

Thanks for the replies chaps - I am not overly suprised in your findings. I already have the smooth bore induction kit and the car runs very well as it is so I guess I shall be putting some stuff on Ebay - I think I have 2 complete plenums at 38 and 45mm and a couple of manifolds.

Without going over stony ground what is the current thinking on trumpet length ?

Thanks,
Matt