Race Engine Forum UK

I have a question for all familiar with the Lampredi Twin Cam 1,6 Turbo.

A friend of mine bought an engine that was high mileage but belived to be good and he now dissassembled it and is prepairing to rebuild it propperly. I have only today had a look at the engine parts and my jaw dropped!

The engine that has had one prior rebuld and has done something like 200.000-250.000km. And the interesting thing is that the engine when it was rebult was bored out to 84,8mm and a set of NA (1,6 or 2.0 not sure) pistons were used. I will make some pictures durnig this week.

My question is how is it possible that the engine has done around 150.000km with NA pistons in a Turbo engine. I allways belived that the difference in compression ratio was achived with the diffent piston. My mistake maybe. Is there a difference in the rod lenghts? Any ideas how this even functioned? I really don't see how an engine with a compression ratio of 9,7 and 1 bar of boost could survive for so long?

Want pictures of combustion chamber and pistons!

G

Sorry it took so long. But here are the pictures.

I'm not sure you are right about the CR, see my calculations below.

May be atmo pistons but with flat top and run flush with block deck it would not be as high as you assume, if I got my maths right that is!

I've assumed 0.4mm oversize but a bigger rebore size would only make a fractional difference by the way..


G

If i am not mistaking the block, head, crank, and gasket are all the same on NA and Turbo engine. The only difference I belive are the pistons and I have now checked eper and it seems that the conrods have different part numbers. So if the pistons in fact have the same height the difference in bowl is not that great.

Do you perhaps have any data on the lenghts of the NA and Turbo conrods?

The Engine was rebored to 84,8mm but as you said that doesn't really influence the compression much.

Can your expert eye see any detonation issues?

No difference in rod length atmo vs turbo or anything else that would affect CR.

Hard to see if det has taken place with resultant pitting because it's all covered in carbon and oil but the distorted gasket fire ring region at chamber 4 suggests something has gone wrong..

Detonation often also shows as damage to edge of the crown of the piston and the upper ring lands - pitting and crack/fracture, can't see from here. In severe cases it can shatter the top and second rings.

Is it actually a Delta 1600 ie turbo head? It should have sodium-cooled ex valves and bronze ex guides & low lift ex cam.

G

Will inspect piston rings more carefully!

Not sure about the head NA or Turbo. Will se when it will be taken apart.

So in OE applications the only difference in compression was achived with use of lower/bowled pistons?

Sorry I don't remember the style of the OE pistons used in either engine I have seen so few of them. Could well be the turbo had flat top like these and the atmo domed, dunno.

Of course you can also have a variation in compression height of the pistons - that has a big influence on CR.

G

I have checked and acording to a few sources the rod lenghts are the same on NA and Turbo application!

So the only thing that creates the difference is the piston. And the OE HF turbo pistons have a similar design as the 8v integrale (but with a smaller hole).

I have also had a chance to take a better look at the pitond rings and the head and they all look OK.

For now my only theory is that the entire build was done so badly that the blow-by on cylinders (which look like they have been honed with a brick) was preventing detonation any maybe the turbocharger was a bit off and was providing only 0,5 bar so maybe that prevented a catastrophic failure.

Guy, the "distorted gasket ring region" on cylinder 4, are you referring to the "bulge" in the thin area where cylinder 3 and 4 meet, in the middle bit between them?

yes, that distorted bit might be indicative of detonation..

G

I can't see the post I left here yesterday.

In short I would like to know if this head is usable or not. It has been rebuild, refaced, valve seats cut, new guides, helicoiled plug threads.... And only after all the work has been done I noticed the cracks on the bulge in front of the exhaust valve guide. The intake side shows no cracks.

Do you think this crack will propagate?

If it wasn't there before, then perhaps the valve guide has been pressed in too tight.

Some posts were lost in the server change, sorry.

Crack - Those heads are way thick there I would not worry about it. Guides were too tight, yes.

G

samo wrote:I can't see the post I left here yesterday.

In short I would like to know if this head is usable or not. It has been rebuild, refaced, valve seats cut, new guides, helicoiled plug threads.... And only after all the work has been done I noticed the cracks on the bulge in front of the exhaust valve guide. The intake side shows no cracks.

Do you think this crack will propagate?

wow - a pic of my car :)