Possible 307 Upgrade to 403? Looking for Opinions

[m002922]

Situation: I have an 87 Cutlass Supreme with a 307 with 180k+ miles that has coolant in the oil. At 180k I figure its had a good life. I bought the car as a solid starting point for a project (no rust, good interior, everything works) intending to upgrade to an LS, Megasquirt, etc. etc. Now there just isn't time for that level of build.

I need a relatively simple motor upgrade that will give me some more power. To that end I started reading about upgrading to an Oldsmobile 350 or 403 Olds. I understand this isn't a huge step up from the 307 power wise, but it would be OK for my purposes. What I do not want to do is end up with a ton of unintended consequences / problems like happened here: viewtopic.php?f=13&t=29540#.UfJvB6z9wrU (no offense to 81X11 - I learned a ton from that thread, and everything turned out beautiful). I am trying to minimize the unknown.

Bottom line: If I bought a re-manufactured 403 (which from my research is externally identical to the 307) could I drop it in in place of the 307 and hook up the existing systems (CCC being the big one) and with a reasonable amount of turning (2ndary jets, etc.) get it running well?

DoubleV and some others in the above thread seem to think so. I'm not clear on if my existing 307 manifolds (exhaust and intake) would be useable - I seem to be finding conflicting answers on that (I believe it is intake no, exhaust manifolds yes - but I could be wrong). Additionally, I'm curious if I can use my existing 307 valve covers, timing cover, oil pan, and water pump. I'm assuming those would be fine, but I could be wrong. I have read I would need a new harmonic balancer again, some conflicting opinions on this). It seems most posts dealing with 307 to 350 or 403 are starting with complete motors as opposed to re-manufactured engines, and thus these questions never come up.

Also, my car is 1987 and thus does not have to comply with emissions inspections, but I will keep the stuff that works (i.e. air pump probably gone). I've tried to give complete information on what I'm looking to do. Also, I'm not looking to do this on the super cheap, the time to get it done and source the parts is more important. If there is some simple and not too expensive option that I'm overlooking, I'm all ears.

Thanks to everyone who posts here, I have been on this forum non-stop since getting my car - it has helped me out countless time.

 

[King_V]

What I've read is that it is, in fact a drop-in, and the computer should be able to handle it.

BUT . .your car is a 1987, and therefore you have a roller 307 - the intake and exhaust manifolds are a no-go. They will, in effect, be forcing the 403 to breathe through a coffee-straw.

I BELIEVE that the non-roller 307 intake and exhaust manifolds are reasonable, though I don't know how much more/less they'd flow than the stock 403 pieces.

That's about the extent of my knowledge on it - I'd wait for at least another reply or two before taking what I say as gospel...

 

[m002922]

King_V - thanks - I did some more looking around after this post and you're right about the intake & exhaust - they would have to be replaced (or, as you said, choke the engine). I'm also pretty sure the harmonic balancer would need to go as well - but given the mileage of the transplant, that would probably be the prudent route anyway. I think the rest of the stuff should be OK - but if I decide to go this route I will shortly know for sure.

Its been posted many times before, but for anyone considering something similar, lot of good information on the topic here: http://www.robertpowersmotorsports.com/G-bodyV6-V8.html

I'm going to go back through the original thread I posted at least one more time to make sure I've got everything there - that seems to be the richest source with the biggest discussion on options.

 

[olds307 and 403]

The early 307 stuff will be very close to the 403 stock manifolds. Get the A4 aluminum intake and the cast iron manifolds will do but headers are worth 20 hp or more. Eliminate the awful cross over and go true dual at least.