The V8 Owners Forum -

hi there just a quick question im building a twin turbo rover v8 3.5 and im going to buy a very tasty act carbon fiber plenum .this is lower than the original . i was told buy the guy who makes them that i will need to cut the trumpets down or take them out compleatly as they will foul the top cover that i understand BUT he says that as its a TURBO engine they dont need any trumpets is the true? would this give me any beter performance ? i dont mind blending in where they came out from as this would be easy. any advise would be of great help
thanks

No you dont need them but you will have to radius the tops of the holes that are left. Sounds easy but it isnt as you will be left with big holes where you go through the casting. Much easier to cut down the trumpets I think. Course your also changing the tuned induction length which could be good or bad but thats up to you.

A turbo engine is a NA engine running at a higher ambient pressure. So anything that gains (or loses) power in NA trim will gain or lose power in boosted trim.

Pulling out the trumpets altogether is not a good thing.

what turbos will you be using?

Which of the ACT plenums are you going for?

i bought a old janspeed kit that was runing on twin su but have deided to go injection so the turbos came from there. im making my own stainless manifolds just having the flanges lazer cut .the act plenum im buying is the westfield type that comes in at the front or the back of the engine depending on what way you bolt it on. this should make mounting the intercooler easyer, im also fiting a stand alone ecu with no air flow meter .ive also got steel timing gear, steel rockers ,arp stud kit for the mains the big ends and the heads .also got the crank out of a late 3.9 and the front cover off a serpentine engine with the better oil pump. but now for the bit when you all cringe. standard new pistons well your all pobably saying why did you not go beter pistons well

1 forged are very expensive
2 i had these pistons already sitting about anyway so if it goes bang i wont lose anything much
3 i would like to see if its built well and set up properly you can run tubos reliabley on standard pistons

I think 6-7 psi is the max you can run on standard pistons.

Why not use the later 4.0 bottom end? You could do what i'm doing and get the mains turned down to fit the earlier block that way you end up with a much stronger piston, better rod and better crank. They're the same in strength as the 4.6 pistons which one member on here used to build a 500hp twin turbo rover v8 in his Granada.

Also the reason why i'm using them as i'm hoping they can take the full 150bhp of gas my nitrous kit can deliver.

Gav those pistons should be okay for upto 9-10psi, especially with an intercooler and ECU to control the timing/retard ignition etc. Yeah the later ones are better (solid skirt), and can take upto 15psi, but think on that the original Janspeed kits ran no intercooler, no water injection and no timing control and ran a circa 7psi out of the box. The Le Mans TR8s running the same kit with a dry sump pushed out 600bhp . . .

I have exactly the same Janspeed set up on my new motor, and I'm using a standard 3.9 (balanced) bottom end, albeit with top hat liners. Should have gone for O-rings really, but ah well. Reason I didn't go for forged pistons is exactly the same, bloody cost!

I'm planning on fitting a simple water injection kit later down the line, mainly for safety. I'm going to use megasquirt (also binned the carbs 'cause they're bobbins!) so can get the WI control built in.

Its the solid skirt jobbies i have woohoo!

I wonder if i can break the 450 raging stallion mark with the next motor!

I don't think you can compare the load on an engine/piston from forced induction with nitrous; physics are different. Mind you, look at Tony (v8kid) he's running a 150bhp shot of the go-go-gas no worries. Think mgbv8 is as well.

nothing wrong with 3.9 pistons Gav, mine are fine,
its not the case just building an engine and dumping 150bhp gas into as Gavs going to find out,
I can see this ending in tears...
you going straight to 150 bhp then Gav???
if so where you getting the jets from? as highpower would only sell me mine after i had done A LOT of testing and had done at least 5 runs on the current jets....

think this should carry on in the nitrous section if you reply...

Carbon plenum with forced induction might be a bit of a gamble? I've known people to split them on a backfire just with an ordinary NA engine and I imagine the problem will be more severe with a turbo - I know some of the backfires with my supercharger have been quite eye-watering.

ive found this on another forum this is running twin turbos and nitrus
nice setup http://www.pistonheads.com/gassing/topi ... 344409&h=0

I have no idea how thick the act stuff is made but CF is stronger than steel when properly done so there is no reason why it cant easy out perform a cast alloy plenum. Course I think they should be told what your doing so they can allow for it as they might well make them thin as generally they are under vacuum.

My ACT carbon one is quite thin, I didn't have any trouble with it but I've heard of other people who've had them split after a backfire, and I would have thought that any backfires that occur with forced induction are likely to be more severe - as I said, mine produces some really spectacular bangs.

So its that a "no" dont run without trumpets?