Turbo upgrade on RV8
Discussion
spend said:
3.9, 4.2 & 5.0 pistons are VERY different, comp height, rod lengths + main, big & little end sizes.
4.0 & 4.6 pistons have the same comp height, so can be interchanged as long as the rods which suit the crank are retained (they are different lengths). The piston bowl capacities are different, so you can increase the CR of a 4.6 by swapping in 4.0 pistons or decrease the CR of a 4.0 using 4.6 pistons. If I was you I'd get a 4.0 engine and use the 4.6 pistons and run a little more boost (its also all relatively cheap to buy / fix if you do break that style engine)
The boost levels you wish to run affect how much work you need to do to lower the static CR. You can get greatly enhanced outputs using low boost, but when you want very high levels for big power things get much more complicated ~ this seems to be confusing many here that simply want a single 'recipe' and are confused by the different things / approaches that they have read. I would never consider decompression plates as they really mess up the combustion chamber design - always seems to me like they are promoting firing down the ring gaps instead of in the middle of the piston? never mind the extra problems of sealing.
Squish is very useful on a turbo engine to. 4.0 & 4.6 pistons have the same comp height, so can be interchanged as long as the rods which suit the crank are retained (they are different lengths). The piston bowl capacities are different, so you can increase the CR of a 4.6 by swapping in 4.0 pistons or decrease the CR of a 4.0 using 4.6 pistons. If I was you I'd get a 4.0 engine and use the 4.6 pistons and run a little more boost (its also all relatively cheap to buy / fix if you do break that style engine)
The boost levels you wish to run affect how much work you need to do to lower the static CR. You can get greatly enhanced outputs using low boost, but when you want very high levels for big power things get much more complicated ~ this seems to be confusing many here that simply want a single 'recipe' and are confused by the different things / approaches that they have read. I would never consider decompression plates as they really mess up the combustion chamber design - always seems to me like they are promoting firing down the ring gaps instead of in the middle of the piston? never mind the extra problems of sealing.
I've never seen 5.0 pistons suitable for the 4.0/4.6 engine (large big+little end rods).
4.0 is the same as 4.6 in respect of block, crank, journal sizes (big & little ends) do not confuse it with the 3.9 series (which many of the TVR 400's are). Arguably the 4.0 crank is stronger than the 4.6 as they are dimensionally the same just with less offset & leverage on the throws. If you can get 600bhp from a 2litre turbo I don't think the 4.0 vs 4.6 vs 4.8 vs 5.0 vs 5.3/4... arguments are really that significant. Getting the best combo that suits the turbo and your pocket would seem the most important criterion IMO.
4.0 is the same as 4.6 in respect of block, crank, journal sizes (big & little ends) do not confuse it with the 3.9 series (which many of the TVR 400's are). Arguably the 4.0 crank is stronger than the 4.6 as they are dimensionally the same just with less offset & leverage on the throws. If you can get 600bhp from a 2litre turbo I don't think the 4.0 vs 4.6 vs 4.8 vs 5.0 vs 5.3/4... arguments are really that significant. Getting the best combo that suits the turbo and your pocket would seem the most important criterion IMO.
Just out of idle interest has anyone here actually confirmed their claimed 12:1 CR by properly buretting the chamber etc? Custard needed?
Secondly, all this talk of 'ideal' CRs and not a mention of the influence on this of cam characteristics? Cue the usual 'you need a mild cam with forced induction...' mantra
Secondly, all this talk of 'ideal' CRs and not a mention of the influence on this of cam characteristics? Cue the usual 'you need a mild cam with forced induction...' mantra
maybe not the characteristic you want for a light, short-wheelbase car 900T-R said:
Lower compression - more outright power potential but worse response/power in the non-boosted part of the rpm/load map, making the overall relationship between throttle and power more non-linear. You takes your choice...
Personally if I were to turbocharge a car with the properties of a Griffmaera for road use, I'd keep the static CR as high as possible.
Spot on! Use as much CR as possible map throttle verses Speed verses Boost compensation Map, 21ST century ecu makes life so much easier Personally if I were to turbocharge a car with the properties of a Griffmaera for road use, I'd keep the static CR as high as possible.
Dom
phazed said:
As I see it you are restricted to a standard cam with the Gems (unless work is done in the timing chest as Gems have a pick up on the cam).
Nope, you can specify any cam for GEMS... I had John Eales build a 4.6 w/GEMS w/ 10:1 CR and a 218 cam - on intermediate valves it made 270 bhp on a std alloy plenum and 282 on an ACT carbon twin throttle plenumV v expensive though
as this was a brand new engine complete with all ancillaries, wiring loom etc. It all adds up to 
levels900T-R said:
phazed said:
As I see it you are restricted to a standard cam with the Gems (unless work is done in the timing chest as Gems have a pick up on the cam).
Nope, you can specify any cam for GEMS... I had John Eales build a 4.6 w/GEMS w/ 10:1 CR and a 218 cam - on intermediate valves it made 270 bhp on a std alloy plenum and 282 on an ACT carbon twin throttle plenumV v expensive though
as this was a brand new engine complete with all ancillaries, wiring loom etc. It all adds up to levelsDom
Tvr Power said:
900T-R said:
Lower compression - more outright power potential but worse response/power in the non-boosted part of the rpm/load map, making the overall relationship between throttle and power more non-linear. You takes your choice...
Personally if I were to turbocharge a car with the properties of a Griffmaera for road use, I'd keep the static CR as high as possible.
Spot on! Use as much CR as possible map throttle verses Speed verses Boost compensation Map, 21ST century ecu makes life so much easier Personally if I were to turbocharge a car with the properties of a Griffmaera for road use, I'd keep the static CR as high as possible.
Dom
900T-R said:
Nope, you can specify any cam for GEMS... I had John Eales build a 4.6 w/GEMS w/ 10:1 CR and a 218 cam - on intermediate valves it made 270 bhp on a std alloy plenum and 282 on an ACT carbon twin throttle plenum
V v expensive though as this was a brand new engine complete with all ancillaries, wiring loom etc. It all adds up to levels
indeed last time i had John spec up an engine for me it came to 14k but as you say that was tun key dynoed and mapped V v expensive though
as this was a brand new engine complete with all ancillaries, wiring loom etc. It all adds up to levelsdry sumped,
dta ecu
complete loom
mapped
5.1
x-over tb inlet
flywheel & clutch
upgraded valve train..
etc..
my current engine budget for the chim is less than a 10th of that though lol
Tvr Power said:
candidate for a turbo kit sir
Dom
Seeing as this went into a TR8 (Federal spec so about as lusty as a Polo Bluemotion in original condition), methinks this will be scary enough when the car's back on the road... Dom
But you never know, they might come back for more at some point
900T-R said:
Tvr Power said:
candidate for a turbo kit sir
Dom
Seeing as this went into a TR8 (Federal spec so about as lusty as a Polo Bluemotion in original condition), methinks this will be scary enough when the car's back on the road... Dom
But you never know, they might come back for more at some point
Dom
Tvr Power said:
900T-R said:
Tvr Power said:
candidate for a turbo kit sir
Dom
Seeing as this went into a TR8 (Federal spec so about as lusty as a Polo Bluemotion in original condition), methinks this will be scary enough when the car's back on the road... Dom
But you never know, they might come back for more at some point
Right, apologies if this question has already been asked, but in simple terms of power and torque increases, what do you get from a turbo that you don't get from a SC? I know how they both work and the losses etc with the crank driven SC versus exhaust gas driven turbo - what is there other than that? That's leaving aside cost and neatness under the bonnet...
And, er, can anyone answer my question above about levels of boost versus CR etc?
Cheers chaps,
Chilli
Dom
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