Turbo Compression Question

[JamesBaumann]

Ok guys, I have a quick question here. I have a cylinder head that I am currently using in my n/a 2.3. It is ported & polished, has the roller cam & roller followers, and it is shaved .050". Here is my question. If I wanted to build a turbo motor for this car, could I still use this cylinder head even though it is shaved a little? Or will the compression be too high. Lately I have been entertaining the idea of building a turbo motor and if I were to I sure would rather use this head than porting and polishing another one. Let me know how you feel about this guys. Thanks for any help you may be able to give me.

 

[Red_LX]

I would say it would probably be a bit too high for a turbo engine, since the head has been milled. The dished pistons in the turbo engine would drop the CR a little, but probably not enough (stock turbos had about a 8:1 CR, n/a's were 9:1). I don't know if you would be able to open up the combustion chamber to make up for the milling, or not.

 

[JamesBaumann]

If the formula I am using is right, that much milling would add about .7:1 compression. (.007" = .1:1) So therefore I would be at around 8:7:1 compression, which is still lower than an average n/a engine. Anybody figure thats low enough or is that still a little high?

 

[Dr_EluSivE]

i think you would also need to drop in some turbo valves.. I believe that the turbo motors had special valves that resist heat better then the N/A ones do.

Dr.

 

[BELL]

i'm gonna side with Dr. E on that i think the valves are different. ditch the n/a keep the cam for a turbo head...

 

[Turbo_Raccoon]

well yes the turbo motors had different valves but they had the same comprestion ration which was 9:1.

 

[freakintiger]

I thought only the early carbureted ones had the higher compression...

 

[JamesBaumann]

I've never heard of turbo motors having different valves.

 

[Touring23]

*EDIT* What about a "head saver" shim:
http://www.partsamerica.com/product_images/AAP/FEL/8471SP_TOP.jpg
Fel-Pro 8471SP
It's a spacer specifically designed to add volume and thus reduce compression. Alas, I dunno by how much. Maybe someone can post in with that info...?

 

[joebford]

A .050 mill is going to get you close to 1 full point rise in compression ratio.

These engines don't like much over 8.5:1 until you get into detonation issues. They are marginal at the stock ratio of 8:1, especially the t-coupes. That is why they later engines have a fuel switch. If you raise boost pressures, you sure don't want an increase in compression ratio.

You can get a thicker head gasket, and I would go that route as opposed to shims. Too much combustion pressure under boost. Shims don't work well.

I would use the stock head.

The Merkur's are thought to have inconel exhaust valves. Haven't seen proof of that tho. Standard valves work fine. joe

 

[JamesBaumann]

Thanks for the info Joe. I've got the old completely stock head that I took swapped off when I swapped this new one on, so perhaps I should just use that. We'll see, it'll be a whlie yet before I swap in a turbo motor, (if I even do) so I have some time to weigh my options.

 

[bhuff30]

*EDIT* What about a "head saver" shim:
http://www.partsamerica.com/product_images/AAP/FEL/8471SP_TOP.jpg
Fel-Pro 8471SP
It's a spacer specifically designed to add volume and thus reduce compression. Alas, I dunno by how much. Maybe someone can post in with that info...?

A thicker head gasket isn't a good solution. You loose all the quench area which of course increases the tendency for detonation. It is quite common to hear that someone had less detonation with the higher CR than a thick HG and lower CR.

 

[Touring23]

Good point

 

[99blkcobravert]

I have an 88TC motor with a fresh build with all the tricks if you're interested.

 

[JamesBaumann]

How much?

 

[raceguy13]

just run methonal it wont detonate