i recently bought a '91 RS with a TBI 305 with a 5 speed..... well i think it's a 305 i havent checked to see if the engine has been changed ..... the car has 76k miles on it. my delima is this it seems far too strong for a TBI 305. i have no timing equipment but it runs about 92 or 93 mph in the quarter mile. i also have a '92 RS with a TBI 305 and auto trans, but it seems to be a dog compared to the '91 ..... other oddities ... there is scrap yard paint pen marks on the bottom of the oil pan ... my questions are this ..... is it likely that the TBI was tuned to feed a 350? . how can i tell if the prom is stock or hypertec, jet,..... ect? there is no other sign of modifications .... other than i added a k&n thanks David

 

If you pull the ecm down and uncrew the hatch, the eprom is right below that. If it says ANLU and the ecm number is still an 8746 then you have a Lo5 350. You can also look under the TBI at the injectors. Go to www.diy-efi.org and go to the gm-ecm page. There is a link to colors of the injector tops that will tell you if it's stock 305 or 350 injectors. The TB is the same on all small blocks from the factory, only the 454 got the 2" bore version.
If the ecm is a 7747 and not the stock 8746 then it's also highly likely you have a 350.