Upgrading 80 SC w/ 88 3.2 P&C's

[motiv8ed]

Car has PMO's, SSI's, and stock SC cams...I'm looking for a nice bump in power. Will stock 88 3.2 P&C's provide a noticeable improvement? Any compatibility issues to be concerned with? Any recommendations on a cam for this application?

[Flat6pac]

The wrist pins are different sizes. You can open the rods to the 23mm pin size but the 9,5 pistons will drop to lower compression with the short stroke.
Bruce

[motiv8ed]

So for a quick upgrade the cylinders can be used but with a different piston combination? Perhaps a JE selection.

[KTL]

Bruce is correct. Someone chose to do just that on my previous engine- bored pin bushings to 23mm & used Carrera pistons. What happens is the pin location in the Carrera piston is further up in the piston. So it effectively shortens your rod & piston combo when using SC rods. It worked w/out any sort of catastrophe but certainly was not optimum by any means with way too much deck height.

Originally Posted by motiv8ed

So for a quick upgrade the cylinders can be used but with a different piston combination? Perhaps a JE selection.

Yep you could put a set of JE 9.5 pistons in there no problem. Just have to make sure the Carrera cyls you are getting are Nikasil/Mahle. JE won't work with KS alusil cylinders unless you have them Nikasil plated.

Also you have to ensure your piston-cyl clearance is right. So that means either, a) have your JE pistons made to the desired dia. to match the meas'd bore of your cyls, or b) use "off the shelf" JE pistons and have your cyls honed to fit the pistons.

So bottom line is, the '88 3.2 bits don't get you a 3.2. 3.0L SC and 3.2 Carrera have the same diameter pistons and cylinders (95mm). The 3.0L is created by it's 70.4mm stroke crank, 127.8mm c-c rod length and 34mm pin height/compression distance in the piston. The 3.2L Carrera is created by its 74.4mm stroke crank, 127mm c-c rod length and 32.8mm pin height.

My opinion is the JE 9.5 pistons will suit you well because they will be shaped to accommodate the carbs compared to the swirl-dome shape of the CIS pistons. Plus the JE have valve reliefs in them which afford you the opportunity to use more aggressive cams- more overlap and duration. S or Mod S cams are a nice cam for a 3.0L street engine.

[Henry Schmidt]

In order to use the 3.2 Carrera pistons on the 3.0 crank and rod combo all you need to due is offset bore the rod for the larger 23mm wrist pin. The end result is actually a better engine configuration. By offset boring the rod you increase the rod length.
The Rod length to stroke ration in the 3.0 is shorter than what might be consider optimum so any increase is beneficial.
If memory serves me, the offset is .030" or .040" ?

[KTL]

To maintain same 198 mm cylinder deck (including 1 mm deck height) with SC rods offset bored, SC crank and Carrera comp. ht. pistons you need a 129.0 mm rod. So you have to effectively lengthen the rod by 1.2 mm with the offset bore?

Question I have, do you use a new 23 mm ID bushing with larger OD to accomplish this? Because if you offset the bore by 1.2 mm, even though you're increasing the bore size a bit, you have some left over hole from the 22 mm bore that is not "covered" by the new 23 mm bore. Or am I mistaken that we're not actually going to lengthen the rod to 129 mm?

Pictured here is simply a 22 mm bore (area inside red herringbone pattern bushing) covered by a 23 mm hole (white hatch area inside white herringbone) offset by 1.2 mm. See how the remnants of 22 mm bushinghole still remain? I just made an assumption that both bushings are 1mm thick

[Henry Schmidt]

It does require a custom solid bushing. We've done this for many engines over the years. Generally for 3.3 turbo pistons and a 3.0 crank.
Most of the 3.2 conversions we did used euro 3.2 Carrera pistons with .060" deck requiring less offset to bring us back to a reasonable compression ratio. 10.3- .5 -.020' deck = about 9.3:1

[KTL]

Thanks for confirming my suspicion about the need for a special small end bushing. Makes sense to add a little bit of deck height to drop the comp ratio, but not too much that you lose your squish at the periphery. My wacky 3.2SS was probably way off on comp ratio (using 9.8 Mahle motorsport Carrera pistons) with a deck ht of ~0.095" (approx. 2.4mm) and the squish zone around the periphery was pretty fat.

[Henry Schmidt]

Originally Posted by KTL

Thanks for confirming my suspicion about the need for a special small end bushing. Makes sense to add a little bit of deck height to drop the comp ratio, but not too much that you lose your squish at the periphery. My wacky 3.2SS was probably way off on comp ratio (using 9.8 Mahle motorsport Carrera pistons) with a deck ht of ~0.095" (approx. 2.4mm) and the squish zone around the periphery was pretty fat.

A .095" deck will result in a compression difference of about 1.4 points.
If you started with 10:1 @ .040" your new compression would be close to 8.6:1. yikes!

[KTL]

Originally Posted by Henry Schmidt

yikes!

That was my feeling exactly when I found the 23mm pins, checked my C-C length and compression distance in the pistons. Not happy....

So I decided to replace with suitable SC style 10.5 comp 98mm JE pistons, rebush the Pauter rods to make it "right." Then the oiling system failed (operator error in there somewhere...) grenaded all the bearings and ruined those nice parts and many others... So i'm doing it all over again.

[Henry Schmidt]

Originally Posted by KTL

That was my feeling exactly when I found the 23mm pins, checked my C-C length and compression distance in the pistons. Not happy....

So I decided to replace with suitable SC style 10.5 comp 98mm JE pistons, rebush the Pauter rods to make it "right." Then the oiling system failed (operator error in there somewhere...) grenaded all the bearings and ruined those nice parts and many others... So i'm doing it all over again.

Don't feel like the Loan Ranger: I put a reconditioned oil tank on a short stroke twin plug MFI engine I build for a very nice RSR replica and it turns out they blasted the tank and didn't clean it before they painted it. Needless to say, everything on the inside was wasted.
Better luck on the next build.

[KTL]

Well i'm in good company then? JUST kidding of course. Thanks for the good luck wish this go-around.

The kick in the head was ruining those nice Pauters & pistons. Two rods were smoked and the pistons all scored. Cams I was able to get repaired, got some used cam housings and a crank. Only one head died for the cause on account of the rod trying to depart the crank & head was oh so slightly doinked by the piston around the perimeter. Good thing the heads were chamfered for the 98mm piston/cyl or I suspect would have been much worse.

Next time (let's hope no next time) it's instant shut down when things sound notsogood, despite having oil pressure (fluctuating madly) on the mechanical gauge. Limping back to the paddock wasn't the main cause of the carnage but it certainly didn't help!

[0396]

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