Im sure its on this site somewhere but I cant find it. and I cant find my manual either.

What is the compression rating for the 305 TBI in 1989.

I went to indiana this weekend for the 500 a friend lives up there, any ways on the way up I fouled a sparkplug and so we decided monday to change them out in his garage, and do a compression check. This is the numbers I got

#1 145
all others were 149-152 PSI

This seams real high for a stock motor, and it should be a stock 305 with 190k miles on it. Oh if it matters it is a 700r-4 tranny.

 

The stock compression ratio is 9.3:1. It is listed in the "new to TBI" sticky at the top as well.

 

thats not real high, actually thats about right.. well... pretty good considering the mileage. I dont know what these things got for psi numbers stock but i can tell you my 305 .030 over with a big cam and low compression (8.8:1, its 10:1 now) did about the same as what yours did and my engine was fresh at the time

 

Thanks for the help, I knew it was somewhere on this site, LOL there is a formula is there not to take the 9.3 to 1 to get what the psi rating is for each cylinder right. If so what is it.

 

there is really no way to get that, the cam plays a major roll in effecting the cranking pressure. You could use a DCR calc, and figure hte dynamic compresion, then find the total volume in they cyl. at the point the intake valve closes, then figure how many PSI would be created at a given compresion, for that amount of air, in the ammout of space left. not persay an easy task.

I wouldn't worry about those numbers, you are consistant across all 8 cyls, that is more than most poeple with that many miles can ask for.

 

Yea im not worried about the numbers, I am trying to figure out if the engine had been swaped/rebuilt since the car was new, to my knowledge and reasearching the history on the car the engine is stock and has never been taken out, I have rebuilt the tranny though. I was kinda expecting to have to rebuild the engine sometime in the next year and from the looks of those numbers unless I have something break I should be good to go for a good while. I use no oil inbetween changes with 10w40, I've had the car for 5 years and have put the last 80k on it.

Maybe by the time the engine goes down I can afford to put in a LS1.

 

Chech this out...
https://www.thirdgen.org/newdesign/tech/techdb.shtml
Some GREAT info about your specific car there. Heck, I thought my car came with the 2.73's just like everone elses but I looked a little closer and saw it was actually 3.08's

Bruce (90RS305)