Does high compression(big bore) + boost = bad news?

[himarker]

I think i have heard this before, but doesnt boost on a big bore mean trouble? IE: I have a UBR 900, is it possible to run turbo kit for a 800 ves on it? Dont ya need low compression to use boost?

himarker

 

[maxwellzx]

big bores and boost work very well for example the cat 1200

but high compression and boost typically dont work well from what i know anyways.

most people lower compression with a base gasket or head shim.

theres a turbo kit for a 800ves in marketplace right now

 

[Scott]

Not high enough octane to run high compression even if you are running straight race gas. I've heard of guys coming up with 125 octane...don't know if that's enough. LOL

 

[06MXZXRenegade800]

Bore size is not that important, its the compression and elevation and the ammount of boost you want to run.

if your running 14:1 domes/sea level/15psi and expect to run Avgas, you can expect to walk home....

But, if you were to drop the compression to say 10:1 or you moved up to 10,000ft elevation you will be fine other than it being a bit of a dog befroe the turbo lights.

 

[aus091]

if it helps im aware of 146 octane race fuel a guy i know ran it in his stock car so he could run higher compression heads i think it was sunoco that made it but i might be wrong it might have been leaded stuff that he bought from another company

 

[Spaarky]

I wont explain myself very well, but I will give it a shot.

The compression on the big bore can be changed, not a big deal. Its the porting. Someone else can explain this much better. Most big bore motors the ports are opened vertically. The way the turbo pushes the air through the motor and port timing, it doesnt work well.

If some one was to port a turbo motor it would more likely be horizontally. Stock porting is optimal, with a little touch up maybe. There is a few people testing porting on these motors. I would suspect the big bore cat motors are being built specifically for turbos.

 

[06MXZXRenegade800]

Cant say much for the porting on the bigbores, but i had my jugs ported when i went to twin crankshops a few years back. Mind you they arent hogged out near as much as some of the bigbores probably are, it runs like a champ.

I do have to agree though, in theory, a 'lazily' ported engine would be best for forced induction to reduce the ammount of intake charge being blown out the exhaust....

 

[snowx22]

boost is a lot like adding compression and a engine that is ported vertically needs more compression to make it run good. moral of the story is if you are going to boost a big bore, make sure you know what the port timing is and your just going to have to find that delicate balance between compression, boost and how much octane you need. It might take a couple sets of pistons to figure it out too, thats the worst part. It can be done, but might be expensive like all big horsepower is.