hey all, i gots me a b&m 142 mini blower for a great price from a friend, a price so good i couldnt pass the offer up. the issue im having with it is that i not sure what the static cr of my motor is and im afriad to run the stock 5-7 lb pulley.
a little background info, i got the the car like 2 years ago with the motor already in it. i was given contact information for a dave gagnon racing enterpises in connecticut who built the motor. dave was pretty helpful when i spoke to him, but he no longer has the built sheet for the motor. he did, however, remember my car and remember building the motor. he said it was definately a .040 over 350 with flat tops and a stock deck.
the casting number of the heads show them as a world sportsman 2, with a 200cc runner 2.02 int 1.60 exh and a 64 cc combustion chamber. the cr right now is relatively high for a pump gas street motor, you can kind of just "hear" it, if that makes sense to anyone. knowing the 64cc chamber and flat top pistons, i am making a educated guess that the cr is somewhere in the realm of 9.5:1 to 10:1. is that a good guess?
now im doing most of my boost calculations based of the motor being 10:1, i figure i would use the highes possible cr to be safe. it would seem the way im set up now i really cant run any more than 4 lbs of boost to be in the totally safe zone.
now the thing is, i have a handle on a set of the same exact heads i have now, except with a 72cc combustion chamber. if i put those heads on my motor, how much of a cr ratio drop can i expect? would it be nesseccary or beneficial to me to run a shim headgasket in addtion to the larger chamber? or maybe should i scrap the idea of the 72cc heads and just go with a shim gasket on the heads im running now? also, keep in mind this whole 10:1 figure is just speculation, i could be running closer to 9, so ideally i want to be able to drop the cr just enough where i can run 5-7 lbs of boost but also not be in danger of dropping too low and hurting performance.
also, if it has any bearing on the situation, after i got everything all figured out im gonna be calling a cam company(undecided thus far) and get a different "blower" cam. ive read the cam can affect cr by bleeding off at lower rpm, but i dont think i can use a cam to lower overall compression?!? i dunno, im doing as much homework as i can here but theres still a few things i dont get. i need some boost guru to help me out here. thank you!
a little background info, i got the the car like 2 years ago with the motor already in it. i was given contact information for a dave gagnon racing enterpises in connecticut who built the motor. dave was pretty helpful when i spoke to him, but he no longer has the built sheet for the motor. he did, however, remember my car and remember building the motor. he said it was definately a .040 over 350 with flat tops and a stock deck.
the casting number of the heads show them as a world sportsman 2, with a 200cc runner 2.02 int 1.60 exh and a 64 cc combustion chamber. the cr right now is relatively high for a pump gas street motor, you can kind of just "hear" it, if that makes sense to anyone. knowing the 64cc chamber and flat top pistons, i am making a educated guess that the cr is somewhere in the realm of 9.5:1 to 10:1. is that a good guess?
now im doing most of my boost calculations based of the motor being 10:1, i figure i would use the highes possible cr to be safe. it would seem the way im set up now i really cant run any more than 4 lbs of boost to be in the totally safe zone.
now the thing is, i have a handle on a set of the same exact heads i have now, except with a 72cc combustion chamber. if i put those heads on my motor, how much of a cr ratio drop can i expect? would it be nesseccary or beneficial to me to run a shim headgasket in addtion to the larger chamber? or maybe should i scrap the idea of the 72cc heads and just go with a shim gasket on the heads im running now? also, keep in mind this whole 10:1 figure is just speculation, i could be running closer to 9, so ideally i want to be able to drop the cr just enough where i can run 5-7 lbs of boost but also not be in danger of dropping too low and hurting performance.
also, if it has any bearing on the situation, after i got everything all figured out im gonna be calling a cam company(undecided thus far) and get a different "blower" cam. ive read the cam can affect cr by bleeding off at lower rpm, but i dont think i can use a cam to lower overall compression?!? i dunno, im doing as much homework as i can here but theres still a few things i dont get. i need some boost guru to help me out here. thank you!
