max boost and hp for 91-94 octane/street gas/buildup?

[Modern Motorsports Ltd]

got a call from a friend tonight.....he'd like to know what a 'smart' buildup of an L28T motor would be, what can he achieve on pump gas of above octane range for boost levels and hp output? what rpm range would this produce in? and any URL's or reccomended builds? he's leaning toward an SU drawthru setup as he'd like to stay away from a lot of wiring but I mentioned aftermarket EFI setups aren't always a big 'mess'....he's not on web so I'll just pass it all on to him..

 

thanks (he'd looked into that Jim Wolf Supercharger unit last year to find out they aren't selling it anymore, not sure if they sold any as I've yet to hear of anybody with one on many boards/lists?)

[Drax240z]

Talk him out of it Ross! A drawthrough setup is really terrible. Tell him to track down "maximum boost" by Corky Bell. (Wilkison's Automobilia on Ontario street will special order it if its not in stock)

 

There are a whole mess of problems associated with a draw through system, a few less with a blow through system, and a lot less with a efi system. Drawbacks of a draw through system include: No intercooling, it will ice up at ambiant temps less than 50F, and fuel will often puddle in the turbo inlet, and other low points. This leads to a bad idle and low speed response. You can counteract that puddling by heating the fuel after it goes through the turbo... but that has the exact opposite effect as an intercooler --> not recommended.

 

Check out the thread in this forum "3.1 280zx" for some turbo buildup ideas and costs. Any more questions fire them at me.

 

------------------

"Gimme Fuel,

Gimme Fire,

Gimme that which I desire"

-Metallica

 

Drax240z

1972 240z - L28TURBO transplant on the way!

http://members.xoom.com/r_lewis/datsun.html

 

[This message has been edited by Drax240z (edited November 02, 2000).]

[clint78z]

I wouldn't try doing a turbo carb setup, especially when an efi setup is already done . In most engines I woudln't say EFI is nessary, but a turbo motor EFI is sort of a requirement . You need to be very precise control over fuel and timing .

[Andrew Bayley]

Ross,

Waaaay back in 1995 a friend and I built up a draw-through L28T engine for my friends 240Z. For the amount of money we had into that project, (or for that matter, DIDN'T have) the car ran amazingly well. The first thing we decided was which method of fuel induction we would use... EFI, suck-thru, or blow-thru. The EFI route was just too expensive at that time and we were having a difficult time figuring out how to properly "boost" reference the carburetor in a blow-thru application. The logical, and final, solution was to use a suck-thru design.

 

In building the setup, we were procured a L28T head, exhaust manifold and turbo for $40 (all in great shape). The turbo head was bolted to the 280ZX na block. This gave us a slightly high compression ratio of 8.5:1 Next, we welded a common plenum joining the two separate SU intake manifolds. This wasn't the prettiest thing on the engine, but it worked. Next, we welded a pipe to the bottom of the intake plenum directly below the compressor outlet.

 

Now, this is where things got tricky. We took a two inch mandrel bent exhaust piece and welded a square funnel-like deal where a Holley four barrel sat. It was a very awkward looking setup. Most people's first comment were, "Your carb's in the wrong spot!" Anyway, we capped the project off by going with a full 3 inch exhaust.

 

As for how it drove... well that could be debated for a long time. Once the car warmed up, it ran "good". However, it was a royal b-i-t-c-h to keep running when cold. Warmup usually consisted of at least a good 15 minutes. Under warmed conditions, the car would pull very hard. We only had 10 psi of boost, we were afraid to go much higher. Regardless, it was MUCH quicker than before. Throttle response leaved a lot to be desired though. It took a good bit of finessing to drive that setup to it's full potential. It would often bog, or sometimes even backfire thru the carb when getting on it below 3000 rpm's. Also, we wanted to run the larger T3-T4 hybrid turbo but could not. I guess the T3 uses a compression type seal between the compressor and main cartridge. This allows the compressor to hold vacuum without sucking in a bunch of oil from the main cartridge. The T4 compressor did not have this seal, so we could not use it in a suck-thru design.

 

A few years we both agree to convert the setup to a blow thru design using a 4 barrel manifold for the L-series motor. However, my co-part was losing interest in the project quickly and I started playing with the V8Z a lot more. This setup is still sitting in my friends back yard rotting away. It hurts me to see it there, but I can't imagine too many other people understanding much about what we did. Heck, most days it amazed myself that it even worked!

 

Again, the car ran strong. The motor was in a 71 240Z with the weaker 280ZX na 5-speed and a 3.7 open R200. On a warm summer evening, he ran a 13.6 @ 100.1 down the 1/4. Also, I know of two autocrosses in Michigan (and one in Minnesota) where this car set fastest time of day. So, it wasn't slow by any means, it just wasn't the easiest car to drive. However, we did manage to take this car all the way from norther Michigan to the Gulf of Mexico in one weekend and we also made it to the 1997 Z car convention in York, PA. I think the final nail in the coffin for the old draw thru design was when my friend and I swapped cars while coming home from the convention. He immediately fell in love with the throttle response and the on-demand torque. I could tell by the way he was driving it

 

Sorry for the long winded response,

I've got a few too many stories to tell. I hope I didn't deviate from the main topic too much

 

-Andy

[clint78z]

The carb plubling and other headaches such as vapour lock ... The EFI is also temp compensated a big thing on a turbo car .

 

If he just wants turbo then on 92 he can probably get 210hp at 10psi, if he goes starion intercooler 14psi, personally I would spend extra $100 on an NPR . Then you could be 240hp at 15psi, with a bigger pump and 36lb SVO injectors .

 

I think why people are reluctant to give pressures and HP on a certain gas is it varies so much . A poor tuned car can detonate at 10psi and kill you car . Proper tuning is the key, and knowing your limits .

[John Scott]

Turbos, having nearly the same adibiatic efficiency as cetrifugal superchargers, will have comprable boost limits. Some real basic rules of thumb for boost are as follows. This assumes tuning is already set to optimum condition, no intercoolers, running on premium. 10:1 max 5psi, roots style only 2psi, 9:1 9psi, roots 5psi, 8:1 about 12 psi, roots 8psi. As you can see roots are way less effecient. The exception to my knowledge is the new Whipple design which approaches centrifugal/turbo #s. Aluminum heads allow a little more. Another important consideration will be cam design. Stick to a dedicated blower/turbo profile with a wide sep. angle. A performance grind often leads to excessive cylinder pressures. Sometimes just a cam swap can make the same engine ping with no other changes. FORGED pistons. Worth every penny.

JS