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The age old question... SU's or FI?


Guest bastaad525

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Guest bang847
Originally posted by SleeperZ:

[QBHowever, my ZT with a factory '87 ECU gets 27mpg on the highway, and puts 230hp to the ground with no driveablilty problems whatsoever. Try that with a carb (blow-thru or draw-thru, carbs on a turbo suck).[/QB]

WOW!!! I wanna go turbo right about now... :eek:
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Originally posted by Lockjaw:

Sleeper we aren't talking about turboing a car is the problem. I would agree a draw thru sucks, a blow thru can be workable, particularily with engines that have never been fuel injected.

 

I think you can do alot with the SU's. If you want to get techinical, a batch fire FI system is a controled fuel leak too, and I bet two SU's offer much better performance that any Z fuel injection with the inherant restriction of the AFM. Run a mass air or speed density and I will not argue, but that door in the AFM sucks.

You are right - I strayed as I have experience with turbo engines only. I also agree about the flapper door - too restrictive. I will take issue about batch fired EFI - just as good as an expensive sequential. When your RPMs rise over 2000-3000, most factory EFIs switch over to batch anyway - you simply haven't the time to inject all that fuel in the shorter time the valve is open. AFAIK, aftermarket fuel controllers are the same way. No fuel leaks with that stuff.
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Guest bastaad525

Okay well... good lord a lot of good responses here! The majority seem to lean towards the EFI... however after much thought I decided to go with some new Ztherapy SU's. The term 'clean slate' is what finally got me to make up my mind. Truth be told, I don't think my ZX's stock EFI was really that clean of a slate to begin with. The problem being that though it ran fine for the stock motor, it did run into some problems after I rebuilt the motor with different head and higher compression. That's when I started having to resort to aftermarket add ons to get my car running decently. And I'm sure there was more work to be done to really get it tuned 'right'. Also I found out that you really can't use the stock 240 fuel tank with the FI system, and that I'd have to hunt down a later model. And I got a good idea of all the other custom work or parts that would need replacing.... So all together, even going with the stock FI, just swapping it in, was gonna cost a heck of a lot more. And... in the end, it would still be a 23 year old system (minus what sensors have been replaced), that may or may not develop yet more problems in the near future. Plus, I agree that the stock AFM IS way too restrictive and I think these SU's will allow the motor to breath much better. Again, if I COULD afford something like a TEK system then I wouldn't even have posted this question. My cash flow is limiting my options, with priority being that I just really needed the car running reliably ASAP so I can get back to work. I'm keeping the intake manifold and injectors though and probably some day in the future when cash allows I will upgrade to an aftermarket EFI unit so that I can really get every last ounce of power AND driveability out of this thing... till then, I'm just hoping the SU's will work out and make for a FUN car!

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Sleeper we aren't talking about turboing a car is the problem. I would agree a draw thru sucks, a blow thru can be workable, particularily with engines that have never been fuel injected.

 

My friend and I are in the process of building a blow thru turbo system for his 69 GTO. It will use a carb, although I guess we could always switch to the projection. Fuel injection for a 455 pontiac engine is not within the budget, it would cost 4 to 5k. Power projections with low boost are in the 600 HP range, and you know that will be fun.

 

I think you can do alot with the SU's. If you want to get techinical, a batch fire FI system is a controled fuel leak too, and I bet two SU's offer much better performance that any Z fuel injection with the inherant restriction of the AFM. Run a mass air or speed density and I will not argue, but that door in the AFM sucks.

 

I found another website about tuning su's on the internet today, but I have it at home not here. It has a dos application on it that tells you how to select a needle based upon where your car is rich or lean with an AFRM. I bet that would be interesting to play around with. I am sure once your set up is dialed in and the proper needle is in place, SU's would rock. They are really very simple.

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