ideal CR for FI?
Discussion
After finding out about my standard/non-standard pistons with the help of Rob and Spend 
What would be the ideal CR for a single turbo on a 450 RV8? I'm not so concerned about monster boost, but more about drivability as if I go that route I don't want huge lag before turbo kicks in if CR too low. Obviously I'd like moderate boost safely so not too high. Thoughts?
What would be the ideal CR for a single turbo on a 450 RV8? I'm not so concerned about monster boost, but more about drivability as if I go that route I don't want huge lag before turbo kicks in if CR too low. Obviously I'd like moderate boost safely so not too high. Thoughts? It depends how much power you want really...
Even 9 will give quite exceptional results as long as the charge temps & ignition are managed properly....
You only want to be getting into 8's if you are wanting extremes of boost, IIRC 8.0 would be OK for 660bhp+ with appropriate (grenadier) components
Even 9 will give quite exceptional results as long as the charge temps & ignition are managed properly....
You only want to be getting into 8's if you are wanting extremes of boost, IIRC 8.0 would be OK for 660bhp+ with appropriate (grenadier) components
macdeb said:
After finding out about my standard/non-standard pistons with the help of Rob and Spend What would be the ideal CR for a single turbo on a 450 RV8? I'm not so concerned about monster boost, but more about drivability as if I go that route I don't want huge lag before turbo kicks in if CR too low. Obviously I'd like moderate boost safely so not too high. Thoughts?
If it's lag you want to avoid and drivability you want why don't you consider supercharging? Happy to show you mine when I re road tax it. It's easy and uncomplicated under my SC bonnet. What would be the ideal CR for a single turbo on a 450 RV8? I'm not so concerned about monster boost, but more about drivability as if I go that route I don't want huge lag before turbo kicks in if CR too low. Obviously I'd like moderate boost safely so not too high. Thoughts? spend said:
It depends how much power you want really...
Even 9 will give quite exceptional results as long as the charge temps & ignition are managed properly....
You only want to be getting into 8's if you are wanting extremes of boost, IIRC 8.0 would be OK for 660bhp+ with appropriate (grenadier) components
Exactly my point, I don't want monster power as a modest 400 or so would suffice with good manners. So my initial thoughts would be high 8's bordering 9.Even 9 will give quite exceptional results as long as the charge temps & ignition are managed properly....
You only want to be getting into 8's if you are wanting extremes of boost, IIRC 8.0 would be OK for 660bhp+ with appropriate (grenadier) components
?????
Mr Supercharged said:
If it's lag you want to avoid and drivability you want why don't you consider supercharging? Happy to show you mine when I re road tax it. It's easy and uncomplicated under my SC bonnet.
Hiya mate, we did meet once and a very nice install you have. However I have weighed up most things and would've gone supercharged but have come down on the side of a turbo, adjustable boost maybe. I will still take you up on the offer on a drive out sometime 
Out of interest, what CR are you running?
macdeb said:
Mr Supercharged said:
If it's lag you want to avoid and drivability you want why don't you consider supercharging? Happy to show you mine when I re road tax it. It's easy and uncomplicated under my SC bonnet.
Hiya mate, we did meet once and a very nice install you have. However I have weighed up most things and would've gone supercharged but have come down on the side of a turbo, adjustable boost maybe. I will still take you up on the offer on a drive out sometime Out of interest, what CR are you running?
Standard 400 spec CR, 9.35:1 or less if the other thread on here is correct. Engine untouched from the factory, apart from replacement worn out cam and followers at 40,000 miles ish. Now has 50 odd thousand and seems to cope with the 7 to 8 psi boost no problem. The Turbo kits seem very reasonably priced and the attraction of controlling boost is a definite advantage but I would ask where the catalytic converter has gone in the conversion otherwise you may have fun at MOT time. I believe the SC power kits have come down in price recently.......Only advice I'd give you would be to consider the FI ground camshaft Real Steel do. I don't have one myself but it makes perfect sense to me. Minimum overlap to avoid pumping compressed air out through the exhaust!
There's far more to it than *just* settling on a, 'ideal' CR - the turbo frame size, compressor map, turbine housing, flange size and type, wastegate, intercooler layout etc etc will all impact on spool characteristics and perceived 'lag'. Where do you want the thing to make its power? It's a movable feast and you can put the urge where you like within reason but, like all compromises, there will be consequences elsewhere to balance the gains... ie a turbo that's all in by 3k rpm will likely not be doing much more than restricting the exhaust at 6.5k. A turbo delivering hard at 6 will likely be idling at 2.5 (perhaps that's not a bad thing, think about it)
As for cams, the short overlap theory might conceivably hold good for superchargers but it's by no means a given for turbos. Remember the turbo sits in the exhaust stream and is increasingly resisting flow as boost levels rise... there's plenty of subscribers to the theory that what works well for you NI will just do more of everything with FI by turbo (ie better in the 'good' areas but worse in the 'bad'). I wouldn't rush to change an otherwise good cam until I'd tried it.
Remind me of this when you see me post up my cam doesn't work!
As for cams, the short overlap theory might conceivably hold good for superchargers but it's by no means a given for turbos. Remember the turbo sits in the exhaust stream and is increasingly resisting flow as boost levels rise... there's plenty of subscribers to the theory that what works well for you NI will just do more of everything with FI by turbo (ie better in the 'good' areas but worse in the 'bad'). I wouldn't rush to change an otherwise good cam until I'd tried it.
Remind me of this when you see me post up my cam doesn't work!
OleVix said:
I think these turbo kits work well with the std comp of 9.35 (400, 450). Low boost but zero lag and very drivable. Modern turbo engines like Mercs SL 63 (5.5 v8 turbo) has 10-1 compression ratio! Its up to the ECU/ ignition and intercooler to keep it safe 
And the engine design too plays a massive part....Im sure a Merc is built to do it. Rover V8's which have been around since the earth started probably not so
db484bhpv8 said:
Where is the extra cc coming from? Is it due to the LR block expecting a tin gasket or a difference in head chamber?
So have you had your bits properly measured then Mac?
Not trying to make any point, just interested.
All measured correctly and backed up by Rob [V8D] on another thread, also by Sardonicus on his rebuild thread. It threw me into confusion as I thought like everyone else that because it has 9.35:1 stamped on the block, that's what it is. But they're not. Gasket, piston height and valve cut outs seem to be the culprits. So have you had your bits properly measured then Mac?
Not trying to make any point, just interested.
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