compression effect on boost

Obviously an engine with a lower compression can hold more boost but approximetly how much does the compression change? For example say you have one engine with a 9:1 and another engine with 10:1, how much would the 1 ratio difference affect the amount of boost it can take on stock internals?

it makes a huge difference to how much boost you can run. but you must understand something. lowering the compression then boosting is done to make sure your car doesnt ping and knock with this cheap 92 octane gas and sissy engine management systems we have. technically you can run high boost on high compression but it would require race gas and an insane engine management system to do so.

also, if you boost 10 psi on an engine with 9:1 compression and you get an extra 50hp, then youre hp per psi of boost level would be 5hp per 1 psi. but if you boost 10 psi on an engine with 10:1 compression the hp boost could be 75hp instead of 50. so at higher compression, each psi nets more power then at lower compression. but as i sais it all depends on the engine management and fuel you have to use.

Thanks for the info, it's very helpful. I've got a few more questions if you or anyone else can answer. I'm comparing turboing a b18b and a b16a. The b18b has a 9.2:1 ratio and the b16a has a 10.2:1. Using 93 octane and with stock internals how much boost do you think each engine can handle reliably?

well for one thing, civic rods are weaker then integra rods. but thats really not a limiting factor. the fuel system will lean out before your internals give out. the most important thing is to upgrade your engine management and then your internals. either one of those engines could be boosted to 8 psi safely but again above that you will get knock and all the bad stuff of turbocharging.

Wouldn't detonation occur as different boost levels for each engine due to the compression difference? I don't know the exact numbers but I'll estimate that a b18b would need an octane rating of 89 to withstand detonation while a b16a would need probably 91. This being considered, when using 93 octane fuel a b18b would have 4 more octane then needed that could be used for putting boost while a b16a would only have 2 more octane. Since the b18b has more octane left over it can hold more boost before detonation occurs than the b16a. So just guessing I'd think that maybe the b16a using 93 could hold up to 8 psi and the b18b could hold 10 but I'm no turbo expert, I just understand the fundamentals behind it. So do you think my estimates are correct? Sorry if this is a little confusing with these numbers everywhere.

your theory may sound correct if you dont know enough about turbochargers and it is a good theory. but it is incorrect. the fact that the b16 is SUPPOSED to be run on higher octane (not everyone uses 91 on their b16's) does not mean it cant handle as much boost as the b18b. there is no such thing as left over octane. it just doesnt work like that. now there is a slight connection between what you said and what actually is true. on stock internals the b18b can handle more boost. that is because the compression isnt as high as in the b16. but either engine turbocharged must use the highest octane available. but again as i said before, its not always how much boost youre running that determines your output. the 8 psi on the b16 will make more power then a b18b with 10 psi. because the starting compression is higher and the vtec does increase power in turboed applications. get it?

I think I understand what you're saying. Thanks for all the info, you really help me understand the science behind this better. Heh, I know there is no such thing as leftover octane, I just couldn't think of a better way to word what I was thinking. When I wrote it I'm was thinking how ridiculous it sounds but I think you understand what I meant. So the b18 can hold more boost than the b16 but the b16 stock higher compression wil make it produce more power even though it has less boost. Basically what I still don't know are the limits of 93 octane fuel, exactly how much boost can it handle before detonation?

there is no set limit that i know of. it really depends on how well you monitor your engine and your enegine management system. ive seen plenty of people running over 30psi of boost on 93 octane. but they had stand alone engine management which could be very expensive. 93 octane can go a long way if used properly.

Wow 30 psi? I got a lot to learn, I figured you'd need to use alcohol to run boost like that. Thanks for the help, I'm gonna post a new thread to see if anyone knows about 93 octanes limits.