I am starting my v6 to v8 engine swap and want to get it done right (not cheap!!). I read the post on it but would still like some suggestions. I got the donor car yesterday, it's an 85 z28 with a 4bbl 305 t-5. That will be going into my 83 firebird in place of the 2bbl 2.8L t-5. Now I will be replacing the motor mounts, should I just get the stock rubber or is the polyurothe worth the extra money. Next I want to upgrade the suspension but not sure about what to get as far as springs and struts. The exhaust definetly needs to be replaced with headers (ceramic coated), y-pipe, and cat back, any suggestions. Now the carb is stock on the v8 but not sure if I should get a better one that isn't controlled by a computer. I don't want to keep the computer if I don't have too but I think if I get rid of it then I would need a new distributer cause I think the timeing is controlled by the computer. My plan for now is to get this v8 swap done then later I will get a 383 built up and just throw that in as it will be easier with the car already converted for a v8. Also are parts interchangable between a 305 and 383. I also noticed that when the new engine warms up the oil pressure drops to just above the red line, should I change the oil pump while the engine is out.? It could possibly be just the gauge. If you have any other suggestions it will be greatly appreciated. Thanks for all your help.

 

The general concensus is that polys are worth it.

Since you've got a manual transmission, I'll go against my "typical" recommendation and say that a carb change is worth it - under one condition: You use a double pumper style Holley or Demon. Any other choice, and I'll say stick with the CC carb and ignition.

A 383 will typically be externally balanced, so you'll need a different damper and flywheel than you've got now. Unless you spend the coin on an internally balanced 383 crank, in which case it will probably be a one-piece rear main seal (although not necessarily), in which case you'd need a different flywheel, anyway (unless you get an internally balanced 2-piece rear main seal crank). Other than that, everything will swap over from the 305 to the 383, including the soon-to-be-grenaded T5.

If you get low oil pressure, it could be the gage, a worn out oil pump, or worn out bearings. Best to determine the gage part before you pull the engine. The other two will wait until after the engine is out.

 

okay I hooked up a mechanical gauge to it and after it warmed up it was ideling at about 750 rpm with 27 psi of oil pressure and at 4000rpm it only went up to 41 psi. I guess this is good but not too sure about the higher rpm's being so low. Is that going to be ok? I also ordered the eibach pro kit springs, KYB GR-2 struts, prothane motor mounts, and a hooker supercompetition cat back system. Still need headers (thinking hooker 2055's but $715!!! is it worth it?), carb thinking holley 4150 but not sure how much cfm I should get cause this engine will only be in until I save up for my 383 guessing 650-750cfm, any help? Thanks.

 

That's normal factory oil pressure.

 

Thanks. I was hoping that would be good. I also have another question for you. I was talking to my brother and he told me if I went with the double pumper carb that the engine would run on gallons per mile not miles per gallon. Is this true? How much would a double pumper cut down on mpg. Maybe you thought I was thinking about turning it into a race car but I am not. I want it as a daily driver with some power even after I get the 383. I just love driving my car too much to take it off the street. Thanks for all you help five7kid.

 

It's all in the tuning. Get it dialed in, and MPG will be just fine.

As long as you keep your foot out of it...