I have a question for you guys...I know i seem to have a lot but here goes.

I am going to need a rebuild soon, my 88 is on its second used motor and its ready to fry any day now. I have an 89 longblock with no trans and the origianl 88 longblock that came in the car with no trans attached to it. My question is: SHould I rebuild the S5 motor and use the S4 accessories and parts to make it run right on stock equipment, or rebuild the S4 and just sit out the time. I only have the one trans and its the 5-speed that went withthe S4, but I do wonder if it will fit up to the S5.

 

IIRC, the tranny's are interchangable.

It's probably easier to just 'stay within your series', but it's not TOO difficult to swap a s5 motor in place of the s4. Since you have all the parts for both motors, you should be able to do it (if you decide to go that route).

Check out: rotaryresurrection.com in the 'Tech' section. Kevin Landers has a basic overview of what the s5 into s4 swap entails.

I would personally just rebuild the s4 and save yourself the headache...

Also, you should open up BOTH motors and use the BEST (interchangable) parts to create your "new" motor.

 

if the s5 engine is in good condition, how about using the s5 shortblock with your s4 attachments? that way you get the lighter higher comp rotors with out having to deal with s5 wiring/ecu stuff. if you do mix and match parts like erikseven suggested, youll have to keep the rotors together becuase they are matched to each other.

 

As I'd told you during our detailed conversation, you can go either way with the shortblock, as long as the externals remain s4, which is a requirement so that all the wiring matches up. The power difference will really be marginal at best, 0.3:1 compression jump is nothing to get excited about. The ports and castings on both engines are identical, and there is no power or modification potential difference in either.

IMO, from having worked on and driven hundreds of these cars, s4 rotors give a nicer feel of bottom end and midrange but fade slightly on top, while s5 rotors give a feel of a strong top end while sacrificing a bit of low end tug.

The main consideration, as I also spoke of, is that a blown s5 engine will cost a bit more to rebuild than a blown s4, because s5 parts are more expensive to replace (rotors and housings) compared to the 3x as common s4 stuff. When you consider that rebuilding the s5 block may cost you $200-300 more than rebuilding the s4 block, yet it will only give you maybe 5hp, it doesnt seem cost effective to me to worry about it. Still, there are those that would lose sleep over it.

All the NA trannies bolt up the same, provided that you use the crossmember that came with that respective seris transmission...the way the crossmember bolts to the trans case does differ between series so you can't mix and match crossmembers to transmissions.

 

Thanks guys. I had a momentary lapse in memory when it came to the transmissions, had remembered reading it somewhere here and i even spent the better part of last night looking again. But I think when I do finally do the rebuild, btw thanks for the clarifications yet again Kevin and I hope to be doing business with you soon(the current running motor is bout to bite the big one), I think ill just use the block and rotors of the 89 and get it done. Im buying another car that runs so ill have it to run around in while i get the kinks worked outta the 88. Thanks everyone who read and tried to help.