Okay I have always heard smaller A.R on the exhaust faster spool?? I know this to be true but I also heard you loose top end??? On the S15 conversion I have a T/3.48exhaust and T/4 .68 compressor, I am at full boost 2700 RPM and it pulls straight on to redline no power loss that I can feel Just wondering If I should rethink the .68 hotside thats going on the Z?? Thanks in advance

 

Read The Book "Maximum Boost"

 

I have.. but like I said it doesnt seem to be true... I am wondering if anyone else has had this expierience..

 

s/c, depends on how high "top end" is. Top end for the L isn't very high so that probably wouldn't be a problem. Also, with a smaller A/R on the turbine side you can run a higher A/R on the compressor side to compensate. Too high though and you'll end up with too much lag due to lack of pressure. Get it right however and you'll get good spool from the turbine and good topend from the compressor. The L is alot bigger engine with 2 more cylinders than the SR(Or I gues you got the KA), but anyways, it'll be able to spool the turbine faster so you can run a higher AR on the exhaust side. If you're running low boost levels then none of this really matters and you should go with the smallest AR on either side that will keep up with the engine without struggling. What sort of boost are you looking to make and how much RPM are you going to be using? Cause in order to lose topend the compressor would have to be putting out its maximum CFM (based on a given turbine speed) before you got throught the powerband. A T4 compressor housing with a .68 wheel should be able to breathe pretty high into the powerband even with a smaller turbine restricting it. Now try putting that same setup on Chevy 454 in a drag motor thats pulling 8k+ and you're probablly going to see that effect of quick spool while losing top end. Basically, you can't compare what would work on the S13 to what'll work in the Z. Two different motors with two different powerbands.

And besides, original gut instinct is usually right. SO go with what you were planning.

 

After skimming through some of my old Sport Compact Car magazines, and their "Suck, Squish, Bang, Blow" articles on turbo sizing and flow charts, I'mma have to go with what J said.

.68 sounds great for what you're using. Let us know how quick that hairdryer straightens your strands.

 

What he said... ^^^^^

The turbo needs to be sized for your specific application to make it work best in your car. Some general guidelines can be derived by the overall size of the engine, but you need to account for a lot of factors in order to get it 'perfect' for your application.

I have a friend with a 383 twin turbo carb'd 260z and he went through about 8 different turbo combinations until he found the one that works best on his 9 sec. car.

Of course, our 'daily drivers' probably aren't going to need this amount of tinkering to find a setup that works 'good enough', but you do need to define your specific application before you can even do that.

Are you looking to make 25psi? 8psi? As you can imagine, these are very different setups. Is your redline at 8000 or 6500 rpm? Do you want boost for the drag strip E/T or for passing tractor trailers on the interstate? How much head work do you have? Intake manifold stock, modified or custom? How much exhaust back pressure do you have?

Sorry, I could go on and on and on and on...

 

Cause the .68 turbo I am planning on using is off of my friends {Z} race car that dynoed at 417WHP on a stock motor at 18PSI.. I will be running 18PSI off the bat, but after the engine is broken in I am cranking it to 20-22PSI .. in hopes to hit my goal of 450WHP .. And before the other suggetions start I have a FMIC, External wastegate, Forged 3.0L pistons, N/A cam, Snieder Valve springs, one peice valve, P&P head and intake manifold, elec. water pump, aluminum radiator, and will be running SDS standalone with Coil Packs.. {That was in case you never read previous posts or seen previous pics of my setup}

 

Well considering the turbo came off the same engine type and size with, and I'm assuming here, a pretty similar setup, then you should know already if it's going to work for you. Did he have any complaints about it? And no I don't mean something like he couldn't make 600HP with it. Did he have any driveablility issues on the bottom end. Would it push through YOUR desired powerband?

Oh, and yeah s/c, we know and we've read Oh and we've seen a whole bunch of pics too. Pics are a good thing I'd have to say all in all you're pretty damn good at keeping us updated. And you better keep it up too. I want to see that beast in action when it's finished. Better get yourself a digital video camera

 

Yeah it came of a L28.. I did more internal than him.. He just polished his head and I copied his spring, he ran it to 7k with no probs on a Dizzy and made good power I am trying to get the DYNO sheet up.. why is IMG code turned off when posting?? Bleach can u tell me how or fix that??

<<Click on my name and view public folder.. My signature is his old DYNO..