Turbo upgrade on RV8
Discussion
Getting back on track then, is there an optimum CR for a turbo install? I believe Neil had 'plates' that sandwiched between the heads and the block to increase combustion chamber volume. So, if this is possible is there an additional power and torque increase to be had by lowering the standard CR when turbocharging? I'm running 10.5:1 so when the SC goes on this winter we're only going to be able to run about 4psi of boost to avoid the dreaded detonation issues 
Chilli.
ETA, just thinking about these 'plates', they would (obviously) move the heads further away from the block, I'm just wondering if this would cause issues with inlet (and possibly exhaust) manifold alignment
Chilli.
ETA, just thinking about these 'plates', they would (obviously) move the heads further away from the block, I'm just wondering if this would cause issues with inlet (and possibly exhaust) manifold alignment
Edited by Chilliman on Thursday 11th October 07:51
Ah, serious issues!
I believe lower compression for optimum performance but any engine can be super or turbocharged, it is as you say, a matter of lowering the boost.
My engine is running about 12.1 comp and I would like to know is this engine could be turboed at a low boost.
Experts, the floor is yours.......................
I believe lower compression for optimum performance but any engine can be super or turbocharged, it is as you say, a matter of lowering the boost.
My engine is running about 12.1 comp and I would like to know is this engine could be turboed at a low boost.
Experts, the floor is yours.......................
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.
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.
phazed said:
Ah, serious issues!
I believe lower compression for optimum performance but any engine can be super or turbocharged, it is as you say, a matter of lowering the boost.
My engine is running about 12.1 comp and I would like to know is this engine could be turboed at a low boost.
Experts, the floor is yours.......................
Two small questions ..What did you do to your engine to make the CR 12.1 and how is the boost adjusted ?I believe lower compression for optimum performance but any engine can be super or turbocharged, it is as you say, a matter of lowering the boost.
My engine is running about 12.1 comp and I would like to know is this engine could be turboed at a low boost.
Experts, the floor is yours.......................
Been reading some of Peter Burgess stuff , he explains the best way to drop CR is not plates or pistons but to actualy do it by head work .
phazed said:
Ah, serious issues!
I believe lower compression for optimum performance but any engine can be super or turbocharged, it is as you say, a matter of lowering the boost.
My engine is running about 12.1 comp and I would like to know is this engine could be turboed at a low boost.
Experts, the floor is yours.......................
That's what my first engine had, and it lasted 4 days before putting a hole in a piston I believe lower compression for optimum performance but any engine can be super or turbocharged, it is as you say, a matter of lowering the boost.
My engine is running about 12.1 comp and I would like to know is this engine could be turboed at a low boost.
Experts, the floor is yours.......................
I didn't know the cr was that high until JE tried to fix them (somewhere around 11.5-12:1). He had to swap them out for a set of lower comp heads off his shelf in the end which was a shame as they were matched and ported as great expense.
Having the heads ringed may have prevented it blowing a compression ring but not for long, and MA had to retard the ignition back to around 20-22 Deg. to stop detination. It did feel very responsive...for 4 days
Edited by Bluebottle on Thursday 11th October 09:40
This thread has been fascinating, and has convinced me not to mess with my 4.0 Chim, but to enjoy it for what it is......unless I go for a complete new LS package.
Your comments only lead me to believe that upgrading only part of the package just leads to endless heartache when it either doesn't work properly, or it causes something else to break.
Your comments only lead me to believe that upgrading only part of the package just leads to endless heartache when it either doesn't work properly, or it causes something else to break.
I would go lower CR than standard to be honest esp with the quality of our fuels!
I would run 9.5cr max but only on some forged pistons...I think 4psi will not be enough for you chilli..i ran mine at 6psi to start with and it just didnt have that kick...wound it to 10psi and jesus the difference was night and day. Yours is higher CR so maybe you will be happy but that leaves you no room to tweek it up further down the line.
I went 8.5CR for some safety and it ran sweet. Some people think removing a full point will make it a dog outta boost. Will a 4.6 be doggy ...not in my experience.
Nothing wrong with de-compression plates as long as there held in with decent ARP studs as you obv would with a turbo build I hope...
Why restrict yourself with higher cr's when adding boost your approaching serious pressures and higher temps.
And when you get bored running 10psi you can hike it up to 15psi knowing it will hold together nicely.
People do favour higher compression on more modern engines with turbos and clever ecu's but at the end of the day mines a rover v8 old design so older low compression ways were applied and work great
My new Chevy engine I will run approx 9.0 - 9.5 because I can, forged crank, rods, pistons
I would run 9.5cr max but only on some forged pistons...I think 4psi will not be enough for you chilli..i ran mine at 6psi to start with and it just didnt have that kick...wound it to 10psi and jesus the difference was night and day. Yours is higher CR so maybe you will be happy but that leaves you no room to tweek it up further down the line.
I went 8.5CR for some safety and it ran sweet. Some people think removing a full point will make it a dog outta boost. Will a 4.6 be doggy ...not in my experience.
Nothing wrong with de-compression plates as long as there held in with decent ARP studs as you obv would with a turbo build I hope...
Why restrict yourself with higher cr's when adding boost your approaching serious pressures and higher temps.
And when you get bored running 10psi you can hike it up to 15psi knowing it will hold together nicely.
People do favour higher compression on more modern engines with turbos and clever ecu's but at the end of the day mines a rover v8 old design so older low compression ways were applied and work great
My new Chevy engine I will run approx 9.0 - 9.5 because I can, forged crank, rods, pistons
phazed said:
Daz, I have 4.0 pistons in my 4.6 + the block has been decked.
whats the difference between 4,4.6 and 5 ltr pistons is it just skirt length ( I know they are all 94mm) is the deck height the same.also whats the differences in the rods?
I've got a spare used set of 5ltr pistons and rods ( rods need the big ends re sizing) is there any advantage of using with different capacity crank & rods..
Graham said:
phazed said:
Daz, I have 4.0 pistons in my 4.6 + the block has been decked.
whats the difference between 4,4.6 and 5 ltr pistons is it just skirt length ( I know they are all 94mm) is the deck height the same.also whats the differences in the rods?
I've got a spare used set of 5ltr pistons and rods ( rods need the big ends re sizing) is there any advantage of using with different capacity crank & rods..
4.0 " higher CR but not flycut for bigger cams, (but that can be machined) strong.
5.0 " shorter skirts, raised gudgeon pin position, fly cut and very weak, (by comparison)!
Graham said:
whats the difference between 4,4.6 and 5 ltr pistons is it just skirt length ( I know they are all 94mm) is the deck height the same.
also whats the differences in the rods?
I've got a spare used set of 5ltr pistons and rods ( rods need the big ends re sizing) is there any advantage of using with different capacity crank & rods..
3.9, 4.2 & 5.0 pistons are VERY different, comp height, rod lengths + main, big & little end sizes.also whats the differences in the rods?
I've got a spare used set of 5ltr pistons and rods ( rods need the big ends re sizing) is there any advantage of using with different capacity crank & rods..
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.
so does the raised pin height on the 5 ltr pistons give a lower top height, and lower compression.
i.e. if you used 5 ltr pistons on 4.6 crank and rods ( why) it would give you lower compression.
and if you used 4.6 pistons with 5 ltr rods and crank, which i assume you cant as the skirts would foul you would get higher comp ?
i.e. if you used 5 ltr pistons on 4.6 crank and rods ( why) it would give you lower compression.
and if you used 4.6 pistons with 5 ltr rods and crank, which i assume you cant as the skirts would foul you would get higher comp ?
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