I have a 1995 ESI, which comes with a 420a engine. And if i wanted to put a turbo on it. its better to do an engine rebuild first as i have been told. and as it says on top of the forum page. but now comes the newbie problem for me. when it means to do an engine rebuild. do i rebuild the head or the bottom?

 

rebuild the bottom end and get the head ported and polished. most likely, you would have more problems with the stock bottom end than you would with the stock top end.

 

Rebuild the whole thing. Why, if you have it all apart to rebuild the bottom and make it bulletproof, would you not bother doing the top at the same time? And get the head, intake, and exhaust manifolds ALL port and polished. If you're going to do it then do it right the first time instead of having to spend more $ and redo it later.

 

well if your getting a "rebuild" the port and polished thing is jsut an extra. The rebuild will be more on the bottom end. But for the head i would replace all the seals and gaskets at least.

 

after all those things? will i be able to boost more than 5-7 psi?

 

stock the motor can take 8 psi, after a rebuild with good parts the motor will go up to 30 or so depending on what hardware you use (apr studs, mls hg). IF you just want basic power I would say rebuild the bottom end only, if your going to be running over 15psi or your going to want to get the most possible hp out of your car with out going over 15 psi I would build the head which would include a 4 angel valve job, a poilsh, 0014 crane turbo grond cams, pt cruser rockers and springs, and ss valves if you feel the nesecity.

The only reason a rebuild is reccomened is becase the motor in your car is most likley over 100k and stock the motor can hold 10 psi but after 100k mils and all of the abuse... it can still hold it its just going to fail very quicky.

 

ok i guess i will do an engine rebuild before i put in a turbo. but now i have another question that comes to my mind. on the piston part. theres few of them, which one should i pick? choice of 8.6, 10.5 or 12.5 compression?

 

Again it all depends how much boost you plan on running and how much power you want to make... I can't remember if the turbo likes the lower compression or higher.... I think a 9.5 ratio is fairly common isn't it?

 

turbo <3 low compression.

A turbo's job is to add compression to the cylanders to make hp. The motor can only hadel so much compression, so their is a compression limit. Hypethically speaking, lest say the limit is 250psi per cyl. and you have high compression pistons that make the compression 235psi. You can only run 15 psi before the head gasket will blow. Where if you have low compression pistons that make 220psi per cyl. you can run 30 psi before the hg blows.

each lb of boost effects the cyl. pressure differently(the higher psi you go the more it effects it, example 1psi=4hp, 2psi-6hp, 3psi=8hp... these arent real numbers.)

Whats it all mean? short answer run low compression pistons (8:6:1 if you can find them, if not the stock 8:8:1 will work but dont go over that).

Long answer, it depends on what kind of hp you want to make at 5psi high compression pistons are going to make more hp where at 15psi low compression pistions are going to make more hp. So its really a matter of what you want. I personally havent seen anyone run over 15 psi on pistons that have a higher compression of 8:8:1. I would recomend low compression becuase it needs less fuel at lower psi setting, it will give you much less problems down the road, and if you ever wanted to cam the motor doing so with would be easier in the respect that the cams also add more air... making more compression. Plus if you had high compression and ever wanted to get more psi then 15 you would have to do another rebuild.

 

Ive seen a RS with a t25 ghetto rigged all to hell with a setup under $500 and it lasted for a good half a year. Thats with EVERYTHING ELSE STOCK except the turbo/manifold/lines/exhaust. I'm talkin it had to be running lean and all sorts of crap. and this was at 10psi daily. The kid was an idiot.

Honestly rebuild the bottom end, maybe change the pistons to something with a little bit lower compression or perhaps use a thicker head gasket to get a lower compression. The head should be fine stock. BTW do the 8.6:1, the lower the compression the higher the boost you can run. Its a trade off, do you want to be compression happy or boost happy? I prefer boost NOS can always take care of the lower compression.

Personally in my talon I was running 9:1 JE pistons at 25psi and it ate it up, but I was also using DSMLink and my tune was perfect So yea stick in the 8's for compression. The guy above me explained it quite nice