S90 engine build best specs?

[northernbigbird]

Hello all

So I've been slowly reading up about the differences between s75, s90 and SC engines and want to get the full low down on them. I want to build a solid engine that will give plenty of trouble free mileage but also one that can take a bit of hammer, although I won't be going racing with it so no revs over 6k. I have a 95% complete s75 engine but don't think many parts will be right for this build.

I'm gathering bits together to build an engine but want to know what the most cost effective/durable solution is for a good engine. I have a s90 case and want to build it up around that. Is it best to go for a SC (or stoddard/scat) crank counter weighted. Barrels and Pistons I will likely get new larger to take it up to 1750cc(or what ever the exact cc is). And heads, I have a set of s75 but will want a set of s90 or SC/912 heads. Carbs will be straight shaft 40's? I read there's a difference between s90/sc by a casting on top of the carb somewhere maybe a breather? What else is recommended, it seems that most s90 parts will have been well used and cracks on the crank/heads will be my biggest problem.

I'm relatively new to the 356 world so any information will be greatly received!
Thanks

[Simon Harding]

Hi there!
My S90 is running an S75 engine fitted with S90 Carbs.
It goes like stink and is dead reliable!
You are correct about the carb tops, they're a different type of alloy to the main carb body and the breather pipes on a 912 Solex are short and fat, whereas the S90 ones are longer and thinner.
It's actually quite obvious, even more so when side by side!!!
Keep us updated on your build, personally I would (I am?) try to buy a 912 engine as they're a little beefier than anything before, perhaps not in HP as say a 356SC but certainly in respect of the heavier construction!!!

[Phil Planck]

Big Bird(owl, eagle?)
I would stay away from S90 crank, flywheel and heads, as all are unique and bearings virtally impossible to find if crank is ground.
Phil Planck

[northernbigbird]

Great thanks guys
Ha good question which bird!? I used to have a colleague who called me big bird as my hair was pretty large! yes my username was brought about when all the normal ones were gone on other sites!

That's what I thought about s90 cranks. What is the best combo to go for in terms of crank/flywheel/heads with an s90 block?

Thanks
Mark

[Phil Planck]

Mark
I have a 63 S90 coupe, and went with 912 crank and heads when I rebuilt the engine. Used AA p/c set(cast iron cylinders).
Phil

[JTR70]

I thought the hot set up for pushrod 356/912 engines were super 90 heads with the exhaust valves enlarged? Super 90 runs a larger intake valve than 912 no?

[Craig Richter]

S90 heads aren't so bad. Fun when you keep the revs up a bit. Maybe late heads are better for various features, but if you got S90's, I'd run 'em. The other guys are right about using a good counter-weighted crank, and don't get carried away with the cam. You're well on your way to choosing the right parts for a good street motor.

[Phil Planck]

Thanks for chiming in Craig. My S90 had 912 heads on it when I bought it. I thought I had read a comment by Vic Skimants regarding the downside of the bigger valves, but could not find it using the R search feature.
Phil

[bbspdstr]

My $.02:

The most important pieces of an engine are those of "reciprocating mass." Spend your money wisely, prioritize the new parts accordingly.

Insurance for longevity is now proven to be with SCAT cranks. Any old crank, unless it's true history is known, is a crap shoot.

Later original rods are great if the oil holes in the small end are in the correct location.....in fact, all this is in Craig's book about "Making old Porsches Fly."

There was some wry wisdom in something Vic Skirmants told me many years ago; "Harry Pellow built some of the longest-lasting but slowest 356 engines ever." At least it was something like that...Harry built engines to be strong, sacrificing power....but just enough power to be fun.

The largest 'legal' valves for 356 racing were the 40mm S-90 intakes and the 912 exhausts (or so I remember...for the facts, see Craig's book and/or the one by the late Duane Spencer.) That is over-sized for most street apps, just as too much cam can be limiting as much as "fun."

Stay away from the Version 1 Solexes or be ready to update the innards. Again, it's in "the books." Split-shaft 912 Solexes get a bad rap and are usually a little more affordable but can work well if understood.

1720cc is the "big bore" P&C and yes, A&A is fine for the money. A little more torque is good with 86mm bore.

Power is compression (heads and valves and their timing, cam) and 'breathing.' (Key to power is getting the air/gas mix in smoothly and fast, get it to explode just right at the right time and get it out as fast as possible to do it again, 1-4-3-2.) It's all in the balance of the ingredients. It is very difficult to better what Porsche engineers designed over 50 years ago, so often "blueprinting" an engine makes the most sense, as when new, any model 356 was "fun" to drive!

-Bruce (deferring to the real engine experts)

[Craig Richter]

That was about as good a rendition as any of the "real engine builders" come up with...