more compression = how much gain?
 

my only real competition around here is currently from a dude that i work with. he drives a 90 integra with no interior and a few simple things done to the engine. anyway... he's working out the issues of acquiring a built b18b block (12.5 comp, ready for a vtec head). anyway. assuming nothing but the raised compression, what kind of gains should i tell him to expect?
yes, we both realize that he's going to need more than just the block, it's his winter project. we're hoping for 300bhp all-motor (maybe using some n2o) by the time all is said and done. i'll try to take some pics of the new parts, car, etc. but it won't be for quite a while.
any input would be appreciated.

You'll never get 300 bhp all motor out of a b18b. The most I've ever seen out of an "amateur" (as in not pro drag) is 240 to the wheels. Set a reasonable goal- 215 is actually very respectable.

Just 12.5 compression ~ 10-15 whp, tops.

If you want 300 whp, boost it- 'nuff said. If you want 200+ whp, be prepared to spend at least $5000 inside the motor alone, in addition to bolt ons and the initial price of the complete motor, and steer clear of a B18A/B. Get a B18C (or an H22!).

that helps a lot. actually, the plans are to take out the stock engine and build it up with lower compression, beef up the head, and have it all balanced so that it can rev near 9k or higher safely with a big turbo (at some point, a new tranny will be necessary, obviously)
i suggested keeping the ls block because i've seen a couple sub-13sec hondas that have the ls block and a b18c(and c5) head.
240 to the wheels on or off the bottle?

No nitrous.

BTW- That was $5000 for 200whp all motor.You can 250 whp for $3000 with a turbo.

High revs are not necessary for turbo. Bulk up the engine, yes, but prep it for high boost, not for high revs. Get new rods and pistons, bore out the cylinders, and kick some ass.

i forgot to mention, the other option(s) for turbo would be either boring the cylinders, or getting a longer stroking crank. the whole reason for revving so high would be for the massive turbo to get and stay fully spooled (with 1.8l having so little exhaust pressure), hence the consideration of boring/stroking.
we were discussing an increase in displacement a little while back, and i think tim (owner) had said that he saw a stroker kit that was a little under $1k that would increase his engine to 2 or 2.1 :mad: why do dsm stroker kits have to be so expensive?

Do NOT stroke the motor and attempt to rev it. Actually, just don't stroke it at all. Stroking the engine makes for a shorter rod ratio, which will drastically reduce the motor's ability to rev. Stroking is the worst idea to hit Hondas since Daytons.

As for your turbo staying spooled, it's the least of your worries. If you're gonna run a turbo that big, it won't be spooled until the top of second gear anyways, and its own rotational inertia will be enough to keep it going. The ability to rev the engine will not reduce the amount of turbo lag you experience. If you're that worried about it, go with something smaller. A t3/t4 will give you more than enough (up to about 1.5 bar) for just about any "amateur" setup.

i appreciate the opinions, we'll have to see where this goes and what happens. i think the money is going out tomorrow for the block, so i think all the necessities for the all-motor engine will be together (not assembled though) by the end of january.