supercharging a realy high comp RV8

disco-v8 · Post by **disco-v8** » Sat Oct 18, 2008 8:47 am

from my understanding most turbo/supercharged engines run lower compression ratios then a stock engine.... i dont know 100% why but i get the jist of it...

my question is... is it possible to supercharger an already high compression enigine, and i dont mean a stardard 9.35:1 RV8, i mean something like my V8 which runs at 15BAR

im not intresting trying to get 2.5 bar or anything like that out of the blower, something less than 1bar will do just to get a quicker respons from low revs, and hopfuly more power..........

if it is possible to get higher pressure, then that would be great but im not intrested in trying to make a drag car here, just more power from a blower

topcatcustom · Post by **topcatcustom** » Sat Oct 18, 2008 11:17 am

My understanding is that a blower replaces the need for any high compression engine parts as it does the same (or better) job the proper way. I think trying to pressurize a high compression engine will result in really bad pre detonation and maybe just a big bang....

But I am pretty much a complete novice in this area so dont take my word for it!!!

If you want some extra power nitrous is a cheaper way and you only need to use it when you want to! (And you probably wont have to change anything on your engine with a small shot)

JP. · Post by **JP.** » Sat Oct 18, 2008 3:09 pm

Yess its possible.

Alloy engines have differend expansion ratings and heat transfer ratings than their Cast Iron cousins so it's easyer to run higher CR's and boost.
There are even supercharger kits available for 10.5cr Corvette's ( which also run alloy engines).

Higher CR's and more boost requires also a Boost Timing Master or some similar device that retards the ignition advance by the amount of boost.
Water injection is also needed.
Probably need to run Hi Octane Racing Fuel also.

Should I do it..............definedly no

I do not have enough money to run my engine on the edge.

kiwicar · Post by **kiwicar** » Sat Oct 18, 2008 5:43 pm

not quite sure if you are saying you have already supercharged you engine with a 9.35 CR and 15 psi of boost or that you want to run 15psi and what cr you should use, or how much boost you can use with 9.35 but
with standard rover heads and 9.35 I would stick to about 9 to 10 psi max and be ready to add waterinjection if you need it, if you want 15psi boost then go for about 8.75 CR max and again use water if you have to.
If you intercool it then you will be able to without water. If you want 15psi boost and 9.35CR then you will need intercooling and water injection and superunlead. If you have an E85 petrol pump near you then chuck the above out the window and use 9.35cr and 15PSI, infact go 9.75 cr and intercooling and 15PSI if you can get E85.
Mike

disco-v8 · Post by **disco-v8** » Sat Oct 18, 2008 9:42 pm

kiwicar wrote:not quite sure if you are saying you have already supercharged you engine with a 9.35 CR and 15 psi of boost or that you want to run 15psi and what cr you should use, or how much boost you can use with 9.35 but
with standard rover heads and 9.35 I would stick to about 9 to 10 psi max and be ready to add waterinjection if you need it, if you want 15psi boost then go for about 8.75 CR max and again use water if you have to.
If you intercool it then you will be able to without water. If you want 15psi boost and 9.35CR then you will need intercooling and water injection and superunlead. If you have an E85 petrol pump near you then chuck the above out the window and use 9.35cr and 15PSI, infact go 9.75 cr and intercooling and 15PSI if you can get E85.
Mike

ive got to stop typing these things when ive just got up..... what i was trying to say was, ive got an engine which ve modified to get 15BAR as standard with out and charges

but ive always been intrested in putting a small supercharger on it, or even a big one if my engine can handle it

.... but was woundering if its possible with a high CR as mine, as most charged engines have lower CR

make any sense now or you still confused

CastleMGBV8 · Post by **CastleMGBV8** » Sat Oct 18, 2008 11:47 pm

Sorry, what exactly have you modified and what do you mean by 15psi as this does not relate to any realistic compression ratio, or do you mean 175psi which would relate to a high compression (for road use) engine.

Kevin.

kiwicar · Post by **kiwicar** » Sun Oct 19, 2008 6:18 am

More modern installations use higher compressions than used to be used, as I indicated above you can use 9.35:1 CR and with good design and efficient intercooling would get you to about 10 psi of boost. If you want to co higher boost or higher CR with 10psi of boost you would need E85 fuel or very high octane petrol.
Mike

disco-v8 · Post by **disco-v8** » Sun Oct 19, 2008 10:09 am

ive just realised what ive done....... TWICE aswell

15 BAR not 15 PSI..... what a complete tit i am

http://uk.youtube.com/watch?v=h7-bxfn1ld4

CastleMGBV8 · Post by **CastleMGBV8** » Sun Oct 19, 2008 10:32 am

That makes things a little clearer, what is the actual spec of the engine ie pistons, stated compression ratio, head mods, and steel or composite gaskets?

Also are you using a standard cam or if modified what is it.

With that information the blower guys will be able to advise more specifically.

Kevin.

kiwicar · Post by **kiwicar** » Sun Oct 19, 2008 5:12 pm

Cranking pressure of 220psi (15 bar) is pretty high for a normally aspirated engine on normal unleaded petrol, though it is also effected by the exhaust system and cam at peak torque, but without a detailed spec it is not easy to say. Boosting that engine as it is I would think could be a bit iffy.
Mike

Post by **Rossco** » Mon Oct 20, 2008 9:31 am

Am I missing something here.

You have a normally aspirated engine which you say you have modified to get 15psi.

How?

disco-v8 · Post by **disco-v8** » Mon Oct 20, 2008 10:43 am

Rossco wrote:Am I missing something here.

You have a normally aspirated engine which you say you have modified to get 15psi.

How?

is this a micky take over my miss printed PSI instead of BAR

or did you mean to put BAR instead of PSI

chodjinn · Post by **chodjinn** » Mon Oct 20, 2008 10:57 am

I have absolutely no idea what this thread is about. All I can gather is that someone is probably going to have an engine go bang. Supercharging or turboing a high comp motor is not recommended unless you really know what you are doing.

It's generally held that a standard Rover V8 won't take more than 10psi of boost without some form of modification, as a minimum ARP head bolts etc, and that certainly isn't on a high comp motor.

Post by **Rossco** » Mon Oct 20, 2008 1:00 pm

disco-v8 wrote:
Rossco wrote:Am I missing something here.

You have a normally aspirated engine which you say you have modified to get 15psi.

How?

is this a micky take over my miss printed PSI instead of BAR

or did you mean to put BAR instead of PSI

No.

Unless I'm missing something you claim to have a normally aspirated engine that is running at 15psi of boost.

If this is what you are saying then you have found a way to achieve a volumetric efficiency of around 200%. Even a full race engine would struggle to get past 120% and even then it would be at an rpm that the humble Rover would never achieve.

Of course I may not have understood what you said in your first post and if that is the case then I stand to be corrected.

No mickey take or offence meant

chodjinn · Post by **chodjinn** » Mon Oct 20, 2008 1:22 pm

I think he means he has done a compression test, which has produced 15bar, as per the youtube link. I dont really understand what you mean when you say you have modified your engine to produce that though?

Had the heads skimmed? Different pistons? Gaskets? What?