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Discussion Starter · #1 ·
My 72 240z came with an old Rotomaster turbo and a big Holley 2bbl on the L28 swap, with nearly a dang foot of 3" rubber hose to get the air/fuel through the turbo compressor to the intake. I don't see much talk from folks using a carb besides the SU. Is this too old? Should I be puttin' FI on it? Anybody out there using anything like this? My guess is that this was a popular L28 + turbo kit and carb mod. maybe in the late 70's?

Kurt
 

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Hi Kurt----------------IMHO, you would be way ahead to consider going to one of the available engine management systems. SDS, Haltech, Electramotive and Jim Wolf Technologies are some---there are others.

The setup you have now is pretty much outdated and won't give the performance that the later systems yield. Turbo engines are easy to extract lots of power from, but the risks can be high unless you run an adequate system. There has to be a balance between all components before you really raise the hp figures, or your engine will wind up in pieces.

Again IMHO, I believe the FI systems to be far superior to a blow-thru setup using carburetion. While the carb has been called a "controlled fuel leak", the FI is a carefully metered fuel supply and as such can be fine-tuned to accomodate any condition that fuel demands may require. It's just simpler to extract the power from FI in turbo applications.

Of course, any of these management systems are on the pricey side. But for maximum performance, they can't be beaten. If budget problems are a consideration, you also might consider installing a turbo setup from an '81 to '83 ZXT. Although not a red-hot setup in stock form, the ZXT system can be tweaked for additional hp, especially after the addition of an adequate intercooler.

Hope this gives you something to ponder. Let us know how you sort things out.

Roadman
Gulfport, MS
 

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Believe it or not, I disagree!

That system is VERY capable of putting out GOBS of power!
That Holley isn't a 500CFM model is it? That setup with proper timing control will net you 13's in the quarter mile easily. Andy Flagg had a setup similar running on a Turbo Block that ran low 12's using a 650 Holley. Richard's Z & ZX service down in LA had a 240 in the low 11"s back in the mid-late 80's with a similar setup. No intercooler, no intercooler plumbing. Just a four barrel, and a turbo sucking through it!
Thing is, the turbo really REALLY helps with the atomization of the fuel particles, GREATLY helping fuel dispersion and distribution in the inlet manifold. Comparable to EFI any day of the week.Smokey Yunik called the turbo an "Homogenizer" being how it literally pulverized the gas particles and intermixed them with the air. The turbo is also very much like a CV Carb in the sense that it linearly draws in increasing velocity.
Granted, it IS dated technology. There are better systems on the market to do the same thing, but you can spank a LOT of EFI cars with MUCH more expensive systems on that setup. Drivability can be difficult sometimes, which is why most people used vacuum-actuated secondaries on the four barrels. This allowed you to really trim how the boost "came on" by letting velocity in the front two barrels get fairly high. This made for a nice driving car, and the turbo coming on like gangbusters once underway.
The big two-bbl may or may not work as well, you should get decent power out of it. Just get some rigid tubing, and replace that legnth of hose! You're all set!
Check the timing and see if there is provision for retard under boost. If not get the MSD turbo timing master, and you're set to run in the 13's with about 17# of boost...
 

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Discussion Starter · #4 ·
Re: Believe it or not, I disagree!

Yeah, it's a 500 cfm Holley 2300. I've got an MSD 5 and looks like the 240 points dist. The carb is mounted on some sort of funky airbox with coolant lines to and from it. An early model intercooler? And it is rigid tubing, didn't know what to call it. I can make 7lbs of boost without trying hard, but need to go through the suspension before I push it at all. . There is no wastegate in the exhaust or blow off on the turbo. Question: Is it only capable of making a fixed amount of boost, or will a turbo keep building as long as you keep stuffing more air through it?

-Kurt
 

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Oh baby...

Sounds like an old Crown Knock-off unit.
The boost is really controlled by the restriction on the inlet, and the plugging of the exhaust. Crown units used a Corvair Turbo, and they would make 17# no problem!
There is no intercooler, and you CAN'T use one on this system! The fuel particles will fall out of suspension. Thing is, on this system, you don't need it. The fuel acts like intercooling, keeping the discharge of the turbo relatively cool.
The lines you have on the carb bottom is for manifold preheat. If you are keeping with 7# boost, that's fine, and really helps drivability. But if you replace that setup with a holley fourbarrel (the four barrel casting was still available from turbo city in orange as of last year) then you may want to consider prividing for a water shutoff under boost to allow maximum inlet cooling. Under boost, you want cold air into the turbo, not the warmer stuff that gives you good drivability in cold weather.
Get the turbo timing master module, before trying to go higher in the boost, just for safety's sake.
That system can run all around all day long with 17# of boost, you just need a few small things to get there.
Uncorking the exhaust will give you more boost---what is it currently?
Uncorking the inlet (carb sizing) will also do that, too, but you need to do the exhaust first...
If you want to come up in steps, you can always fab on a deltagate of something to control the boost.
Problem with the old systems is getting jetting correct, cause the longer the foot is in it, the more boost it makes...
 

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Discussion Starter · #6 ·
Re: Oh baby...

I've got a double-pipe J-tube exhaust inlet to the turbo, and what looks like a 3 inch S tube out the back of the turbo which tapers down to 2 1/2" and then out via turbo muffler. Pretty quiet, nice growl at idle. Looked at the MSD boost timing control - good idea...I have noticed some pinging at full throttle and high rpm's. What could I use to cut the coolant flow to the preheater under boost, that sounds like a good idea too.

-Kurt
 
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