20valvevermont

hello i recently heard that if you change the 20v engine block with a 10 valve, that it lowers the compression rate and makes the car faster. of course you need some things in the car like the turbo and wastegate and whole fuel system, but would this work? rather than converting to a 20v turbo?
thanks
andrew

Disco Stu

due to the oil lines. Although I am not sure which engines you are refering two. Do you have a N/A 20v and you want to put your head on the block from a 10 valve.

20valvevermont

its a 1990 90 20valve sedan, and i was going to put on the 10v or 10v turbo block

cuatrokoop

first of all, a lower compression ratio (with out a turbo) will decrease your performance (higher the CR, the higher the hp, within limits of octane/fuel types). if you want to put a 20v NA head on a 10vt then you'll still need things from the S2/RS2, if you want to keep your AC. the costly parts of the 20vt are the IM/EM/turbo. you could maybe use the 10vt turbo and EM, but a 20vt IM is a must (10v has intake and exhaust on same side, 20v has them on opposite, turbo and non-turbo alike).

the only way to lower the CR by this method (block swap) is to increase the clearance volume in the cylinder. it may or may not do that, the 7A has about a 51cc clearence volume per cylinder, the 10vt has?? most (all?) of the 7A clearence volume is in the head, not the block. the MC1 or MC2 may or may not have shorter rods, or dished pistons to lower the CR. i have no idea, i've only torn into a 7A (don't own an MC). why not talk to bernie benz about his project. he's grafting several 20vt parts onto a 7A, but is not going internal to do it (ie, no pistons, rods, etc). to drop the effective pressures in the cylinder (to avoid knock/ping), he is having the 7A cams spec'd and reground to have the (guessing) overlap increased, so that the forced air will not only fill the combustion chamber, but some will also exit via the exhaust. btw, the NM and 3B use the same head gasket (both 81mm bores), and the NM uses the 7A's head (with different cams). the biggest difference i can think of with the 10v and 20v is that the 20v should have more oil and water jacket ports in it. personally, i'd just get new pistons (dished) for the 7A, to drop the 10:1 CR to 8.5:1 or 9:1. you'd have to check the MC block out anyway, which means pulling pistons, checking bearings, etc. why not do that to the 7A block. JE pistons are not that expensive (i *think* about $130/piston, plus rings). you can also get your 7A cams reground to S2 spec (or whatever you want) for much cheaper than buying (used) turbo cams. talk to tuners before you do something, and talk to other people on various lists who have worked on both engines, or are building a turbo engine.