Engine question

No you remove the sleeves and clean everything meticulously then using a torque plate and head gasket you machine the sleeves in the block to accept the oversize pistons. I often go 1mm over standard and order pistons accordingly then machine the sleeves once you have the new pistons.

 

Once the pistons do have 1/10th mm of wear, it is recommended to change the pistons and bore the sleeves. Standard piston size is 81mm, fist oversize is 81,5mm second oversize is 82mm (i.e 412 pistons). This is specified in the workshop manual (section B9), best to read it first...

Superformance are offering Wossner pistons of good quality and reasonable price (~$2000), maybe you can source these locally in order to avoid import tax? OEM pistons are not forged, Wossner are forged. They are a few manufacturers as my mechanic is also working on Rovexenius car, and the new pistons are different from the Wossner (also forged and nicely made). So you can chime around for a deal.

 

Any thoughts on going with a higher compression? Also are modern pistons better than the originals?

 

Maybe the high compression cylinders can be used, as this is what carobu did on the hybrid 356GTC4 / 412 engine, but that's probably a lot of work. Higher compression means more pollution, and bear in mind that the cylinder head is fragile so you are probably better off with standard compression.

If you want higher compression, you will also have to change inlet camshaft timing as the valve closure is slightly delayed on the 400i compared to the carb or 412. No point in playing with the cylinders without adjusting camshaft first: the 412 reaches higher compression with 82mm pistons and 4°more of inlet timing. just my 2cts.

Just my personal opinion, but modern pistons do LOOK much better. The machinist said the design was more aggressive on the lower part (skirt? sorry for the bad English). Anyhow he liked this design, but no idea how these perform as my engine is like a box of Lego for now...

 

I have used JE and Cosworth forged pistons in racing Jaguar engines, they run about .005” skirt to bore clearance instead of the.0015” employed by OEM cast pistons, this is fine except for audible piston slap until the engine temperature reaches about 50deg C. Does anyone know how the aftermarket forged pistons for our engines behave in this regard ?


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Higher compression pistons are a no-brainer and require no other modifications. The factory quoted compression ratios are generous on ALL engines from this era. I measure every one before taking them apart and without fail a 9.2:1 engine is really 8.5 -8.75:1 and the 8.8:1 cars are really 8.5 and slightly less.

 

That piston to wall is fine on a race engine or something running power adders but no good on a street car where the piston will never grow to the right size. You want half that for a street application.

 

If these are the pistons with the square valve reliefs Ive seen, throw those as far away from you as you can because the ratios are out to lunch.

 

How can a valve relief be square? Looks like more work for a bad result.

In a sense you are correct though: Superformance was not in a position to provide me the pistons I wanted so the Wossner were sourced by Eurospares. Lee Thomson was quite helpful and had several choices of 1st oversize pistons : 81.15mm bare piston 81.3mm bare piston and 81.5mm complete with rings. The prices ranged from £155 to £190.

So no idea about Superformance quality.

Have you tried the high compression set on the 400i? I would really be extremely cautious about these.
1) Too much compression equals bent valves, and we've got sodium valves...
2) The high compression pistons were meant for the 365 with shorter stroke. Long stroke plus high compression piston means even more compression
3) Cylinder dome thickness is less than 2mm! Rovexenius gave me two of his heads: cracked. I bought one in the UK, cracked again. In other words, these are really fragile and hard to find in perfect conditions.

My machinist said he would not offer guarantee on his work with the high compression cylinders, which was his own way of convincing me not to do it

Anyhow if Temerian really wants to increase compression, he'd better optimize the camshaft first. No point in swapping the cylinder if the camshaft is "sealing" the cylinder so late: the compression phase is not long enough on the 400i. With its specific camshaft timing the 412 has the same compression ratio as the 365, using regular pistons (and longer stroke). So Ferrari tweaked the camshaft instead of fitting one of the many 82mm high compression pistons they had laying around.

 

Compression ratio selection really has nothing to do with what type of valves you run or how long the stroke is. Compression ratios effect torque and all you have to do is look at newer cars running 11:1+ ratios on pump fuel to see that. Ferrari was conservative back then when it came to compression ratios and it could be so they will run on any crappy fuel available at the time, especially over there. Here and now its not a problem and technology is also to thank for that. Carefully selecting a ratio means 10:1 on a 400i, a boxer, testarossa, 308, 328 etc. Tossing the sodium valves is also a no-brainer. I have boxers running around with 10.5:1 pistons in injected cars with performance cams, low restriction exhaust and they work great! Ive built CIS 308's with high compression and cams too. You can go to the boxer section and see the Injected boxer thread about "cams and compression and other goodies" and read feedback from an impartial guest. How about a 308 QV I did that dynoed at 375HP and it runs on 91 octane fuel. Naturally aspirated too. A 400 has the potential to kick butt. It needs compression, cams, porting and some larger valves. That and a loose torque converter in my case so I can launch it properly.

 

Ferrari never had high compression pistons just laying around. Where did you hear that? Nothing had good compression ratios, even a daytona sucked. The injected cams actually increase dynamic compression ratio over the carb'd versions because of the cam timing (seat timing specifically) which is partially to thank for the increased torque and lower 0-60 times. Ive built injected boxer engines with 10:1 pistons and stock cams, Im in the middle of another one right now actually and a 400i is no different, its not special in any way.

On a side note Ive noticed you provide a lot of information in your posts like you know what you're talking about but they're so full of misinformation I don't know where to start. Its why I had to break it up into two responses. You're consistently wrong on so many points I often sit in awe at what you posted. This thread is no different. Reminds me of the you dispensing more of your wisdom telling a 365 owner that a testarossa and boxer share the same chassis and suspension! Im still in disbelief and I hope for their sake nobody believed you!

Please stop giving technical advice.

 

Resurrecting this old thread for the record... I bought a while ago the eurospares oversize pistons, paid for the expensive variants (forged, fully dressed, custom oversize). Long story short these may fit in a 365 block, but my machinist is going to have quite a lot of work before these could work together with the 400i crankshaft. There is close to 4mm of material to be removed.

They are nicely made so I am not going to toss these away as newman said, but if you buy these pistons be ready for some additional labor cost. Should I had known about this I would have probably bought the 365 high compression pistons and shaved the bottom as this is basically what we are about to do!

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Curious as to why does you machinist feels he needs to remove material from where you indicated ?

 

My mechanic asked for the skim and the machinist originally did not want to do it without the engine block, as he thought he could get away with machining only the skirts...

Here is a pic of the crankshaft, as can be seen there are two "counterweights" per cylinders.

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These counterweights do have quite an important diameter and do "hit" the new pistons unless lots of material is removed. At the end of the day they programmed their tool so as to remove 3mm from the portion that is close to the pin and 3.5mm from the skirts. In order to have the same clearance as the original pistons they should have removed probably a bit more. Did not have a camera when they made the modifications, but will post some pics from the bottom of the block once all the pistons are installed: it's still an extremely tight fit.

Under normal circumstances I would have returned the pistons back to Eurospares, but these were ordered on January 2018. So it's a bit late to complain. On top of it the other sellers (superformance) told me their oversize cylinders would not fit the 400, so my guess Is that they are probably selling the same parts.

I've managed to have some professional work 200m away from my mechanic... Another 400 engine is next to mine: it's been a real pleasure so far to see these two piles of shiny parts getting back to life, let's hope no other horror story is going to spoil this!