best RV8 for supercharging?
Discussion
can anyone offer any tips? im looking to swap the engine in my capri for a 3.5/3.9 Rover but they come in so many different flavours im a bit stuck! specifically it seems the compression ratio varies wildly across the range and this is significant as sooner or later id like to supercharge the engine and am scratching my head a little trying to make my mind up as to what ratio may be best. is it irrelevant for the time being? presumably if i go for a reasonably low CR that will give bigger scope for forced induction? is there a source of engines, ie, SD1,p6 etc that are known to be 'better'?
Also on the same topic, would it be necessary to swap the camshaft for a turbo item to minimise blow through when i eventually get my super?
any hints and tips gratefully recieved!
Also on the same topic, would it be necessary to swap the camshaft for a turbo item to minimise blow through when i eventually get my super?
any hints and tips gratefully recieved!
I don't know.
Boosted is probably your man for this.
I don't know all the detailed changes that have occurred over the years, but I do know that there are some significant featurees in the 4.6 which make it particularly suitable for forced induction: it has bigger bearings, a cross bolted (stiffer) bottom end, stronger pistons.
As far as I have been able to pick up, you can use low pressure supercharging (< 5 psi) on pretty well any stock engine spec, the additional mechanical loads are negligeable. The 4.6 seems to be pretty robust up to around 6-7 psi, to go far beyond this I think you may need to invest in some forged pistons.
To be honest I'm not sure quite what the rules are for CR, I think to be completely conservative you would drop the compression ratio as you raise the boost so that the total compression ratio remains the same, but I get the impression that it isn't necessary to be quite this conservative, for example I've been running 10:1 and 6 psi for the last few thousand miles without any obvious damage. I am dropping the CR now because I think it will be safer (less vulnerable to detonation), but this may just be me worrying over nothing.
Edited to add: unless you have cats (not likely!) or plan to run very high boost levels I would stick with a conventional mild cam. I recently changed to a super stumpy s/c special and it seems to have killed the top end without making that much difference elsewhere.
>> Edited by GreenV8S on Sunday 26th June 12:36
Boosted is probably your man for this.
I don't know all the detailed changes that have occurred over the years, but I do know that there are some significant featurees in the 4.6 which make it particularly suitable for forced induction: it has bigger bearings, a cross bolted (stiffer) bottom end, stronger pistons.
As far as I have been able to pick up, you can use low pressure supercharging (< 5 psi) on pretty well any stock engine spec, the additional mechanical loads are negligeable. The 4.6 seems to be pretty robust up to around 6-7 psi, to go far beyond this I think you may need to invest in some forged pistons.
To be honest I'm not sure quite what the rules are for CR, I think to be completely conservative you would drop the compression ratio as you raise the boost so that the total compression ratio remains the same, but I get the impression that it isn't necessary to be quite this conservative, for example I've been running 10:1 and 6 psi for the last few thousand miles without any obvious damage. I am dropping the CR now because I think it will be safer (less vulnerable to detonation), but this may just be me worrying over nothing.
Edited to add: unless you have cats (not likely!) or plan to run very high boost levels I would stick with a conventional mild cam. I recently changed to a super stumpy s/c special and it seems to have killed the top end without making that much difference elsewhere.
>> Edited by GreenV8S on Sunday 26th June 12:36
I used a totally stock 4.6 LC short motor for well over a year with 15psi turbocharged, revving to 6kmax. I sued 4.6 composite gaskets and ported SD1 heads 36cc chambers, which should have given me around 7.5:1.
I probably wouldnt go quite so low next time if I ever used an RV8 again, but it still worked good for me.
Std cam will work well when blown, but a mild upgrade is also good.
Dont even consider anything wild, or with long duration.
Having said that I did once use a RS Typhoon+Rhoads lifters in an old TT 3.9, and it was superb. I just got greedy with 18+psi and well, the obvious happened lol
Ive tried various cams from that, including a couple of custom grinds, albeit all in the 4.6, and was never that happy with any of them. So much for relying on cam grinders suggestions.
Id buy the biggest engine you can to use...simply put.
>> Edited by stevieturbo on Sunday 26th June 13:34
I probably wouldnt go quite so low next time if I ever used an RV8 again, but it still worked good for me.
Std cam will work well when blown, but a mild upgrade is also good.
Dont even consider anything wild, or with long duration.
Having said that I did once use a RS Typhoon+Rhoads lifters in an old TT 3.9, and it was superb. I just got greedy with 18+psi and well, the obvious happened lol
Ive tried various cams from that, including a couple of custom grinds, albeit all in the 4.6, and was never that happy with any of them. So much for relying on cam grinders suggestions.
Id buy the biggest engine you can to use...simply put.
>> Edited by stevieturbo on Sunday 26th June 13:34
cheers for the replies guys - looks like ive got still more homework to do considering my engine choice! my current dilemma is whether or not to go with my existing type n box (which i know wont last) or to go with a T5 unit that should handle the torque. trouble is of course that the T5s arent cheap but the bellhousings arent interchangeable. do i do the job properly first time round or change it when i use forced induction? 
should be phenomenal when its done though - a real sleeper! ach - whats a 26 year old need with a savings account anyway
>> Edited by paolow on Sunday 26th June 23:18
should be phenomenal when its done though - a real sleeper! ach - whats a 26 year old need with a savings account anyway
>> Edited by paolow on Sunday 26th June 23:18
I used to use the standard Rover box on my old 3.9TT.
Before I built a decent engine, the box's lasted up surprisingly well.
Once I had a good one, I was breaking them one a week. After a month I got fed up shanging them, and went for Toyota Supra Turbo R-154 5sp box.
You wont break one of them easily.
I only managed to break a tooth once, on 3rd gear, after well over a year of useage.
It will easily handle 400+ all day, every day.
Before I built a decent engine, the box's lasted up surprisingly well.
Once I had a good one, I was breaking them one a week. After a month I got fed up shanging them, and went for Toyota Supra Turbo R-154 5sp box.
You wont break one of them easily.
I only managed to break a tooth once, on 3rd gear, after well over a year of useage.
It will easily handle 400+ all day, every day.
you could always go for a Ford small block (302cid or 5.0ltr)! these things are very tunable and very strong. also i think the prices are coming down over here as more and more people are using them. with a set of throttle boddies on there and 300+bhp on a very mild engine is very possiable.
then again, you could fit low comp pistons and a Weinad 142 blower on there! roll on 500bhp!
Chris.
PS. supra box is a good idea. very strong!
then again, you could fit low comp pistons and a Weinad 142 blower on there! roll on 500bhp!
Chris.
PS. supra box is a good idea. very strong!
Thanks for all the continued help everyone, this is a trickier decision to make than i thought! i think though it may be helped along by the car itself which, sadly is far from concours. this in mind i might use this as a 'practice v8' and take a cheaper route forgetting the super for the time being.
it would probably be best to continue waiting for a 2.8i to turn up locally so i can use THAT for the mk2 conversion once ive made ( and learned from) all my mistakes etc on the first one.
the big issue for me now is the gearbox and i seem to have 4 choices.
existing type n/9
new T5
existing rover
new supra
the trouble is i know full well that im more than capable of killing the existing box if i rag it with that engine, but its a LOT easier to go that way than fitting the rover box. a T5 would be a good compromise but theyre a bit pricey. supra boxes are insanely strong but again a bit hard on the pocket. maybe next time
having said that the 2.8i is rated at 160 bhp and the rover 3.5 is the same. i know obviously the torque fiqures are very different, but is there any chance i can get my box to last - even if it was for just 10- 15k? it really is SO much easier this way and those boxes are ten a penny!
thanks for your thoughts
it would probably be best to continue waiting for a 2.8i to turn up locally so i can use THAT for the mk2 conversion once ive made ( and learned from) all my mistakes etc on the first one
. the big issue for me now is the gearbox and i seem to have 4 choices.
existing type n/9
new T5
existing rover
new supra
the trouble is i know full well that im more than capable of killing the existing box if i rag it with that engine, but its a LOT easier to go that way than fitting the rover box. a T5 would be a good compromise but theyre a bit pricey. supra boxes are insanely strong but again a bit hard on the pocket. maybe next time
having said that the 2.8i is rated at 160 bhp and the rover 3.5 is the same. i know obviously the torque fiqures are very different, but is there any chance i can get my box to last - even if it was for just 10- 15k? it really is SO much easier this way and those boxes are ten a penny!
thanks for your thoughts
Relatviely speaking, Supra boxes can be incredibly cheap to buy.
Bellhousing etc cots a bit more though.
But using the Supra box, will also give you a propshaft about twice the size of any Ford or Rover item.
Whn I first got it, it looked huge in comparison to the old Ford/Rover combo.
The Supra one now liike tiny compared to my current shaft !!!
Bellhousing etc cots a bit more though.
But using the Supra box, will also give you a propshaft about twice the size of any Ford or Rover item.
Whn I first got it, it looked huge in comparison to the old Ford/Rover combo.
The Supra one now liike tiny compared to my current shaft !!!
How about a real budget approach? A couple of decompression plates, longer pushrods and a home spun head? I'm not convinced that forged pistons are better (you may get more favourable shapes/dishes). As well as a decent rebuild?
I reckon that a lot of people are barking up the wrong tree with supercharged engines and for some reason are buggering about with billet rods/cranks/etc, I can't see that it's necessary. A well known mini converter is getting 170ft/lb out of a 1330 mini engine by the moroccan method. I can't see why it couldn't work.
I have chosen a cam with a fast road inlet (shortish) and a high lift and about +15deg on the exhaust to get the exhaust up to the job.
Shit, I've just realised I've left the jeep outside with the roof off in the thunderstorm!
I reckon that a lot of people are barking up the wrong tree with supercharged engines and for some reason are buggering about with billet rods/cranks/etc, I can't see that it's necessary. A well known mini converter is getting 170ft/lb out of a 1330 mini engine by the moroccan method. I can't see why it couldn't work.
I have chosen a cam with a fast road inlet (shortish) and a high lift and about +15deg on the exhaust to get the exhaust up to the job.
Shit, I've just realised I've left the jeep outside with the roof off in the thunderstorm!
love machine said:
How about a real budget approach? A couple of decompression plates, longer pushrods and a home spun head?
Don't forget to make your intake manifold wider as your heads will be further apart.
I don't like decompression plates. Sure they may work but it's a quick fix. If on a budget then leave the compression stock and boost the engine as it is.
Boosted.
Boosted LS1 said:
How about a real budget approach? A couple of decompression plates, longer pushrods and a home spun head?
Don't forget to make your intake manifold wider as your heads will be further apart.
I don't like decompression plates. Sure they may work but it's a quick fix. If on a budget then leave the compression stock and boost the engine as it is.
Boosted.
I agree, it is too simple and cheap to be good. If you match the chambers to piston "ledges" with the plate, the squish stays the same. If you leave the voids as bore width, you're asking for more trouble. I can't remember what RV8 Chambers are like but I think there is little material to remove....... I'll have a look at a head next time I see one. My logic is that race heads have big valves/ports and people don't want them if they have been overskimmed, cue my plate and cheap head! A popular approach is to mill the chambers out circular and to the depth of the valve, keeping the squish the same. You can get some monster chambers this way.
On a budget, it would be possible to get ba Mazda Millenia screw blower (about £150), bung that on with an intercooler, blowing through a couple of SU's with 8:1 you should be able to get about 12PSI residual in there. That should work a treat. I'd avoid a rootes blower on principle. (unless you've got a cheap one). I suppose you could use 2 Eaton M45's. They would easily cope with 1/2 an RV8, £100 a piece on ebay (brand new).
I'm sure that forged pistons, fancy heads, etc, etc are a total waste of money and better spent on a decent gearbox/diff/halfshafts.
Being a skint mofo, I like the "what works" approach, the sky is still the limit on a budget, you just have to use your noodle and still have a strong engine.
That's just my opinion though.
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