Draw through carb turbo setup

[Serban]

Greetings fellow Z enthusiasts!

I just picked up a very very rough Z (which will go to the scrap yard), but it came with a supposedly built L24 with a draw through carb turbo setup. In my internet search, I found something similar, made by Crown many years ago. What I have is very similar, but the log manifold that connects the two carb manifolds is different, and looks custom made, also, very nice piece despite all the rust.

The guy I bought the car from said the previous owner had about $9k worth of engine work done, I won't know until I pull the engine out and get it checked out. What I found interesting about this whole setup was the use of pipe fittings and valves everywhere, pretty sure this setup was done before AN fittings were available

 

The carb inlet pipe has two nozzles in it that spray right into the carb, not sure if that's for extra fuel? A single SU carb doesn't seem adequate for a turbo setup in my opinion. The fuel line was connected to a T that goes to the custom made balance tube, and on one end was some kind of electric sensor, or switch? It could be that someone just stuck a hose on that fitting over the years to cover it, I don't know for sure. I also have an adapter for using a Weber carb with this turbo.

 

I'd love to hear more from those of you who may have some info on this setup, it's pretty unique. If this is a fully built engine, and still good, I struck gold for sure! At that point I might just ditch the carb setup, and go for a more modern EFI setup. This will eventually make it's way into my 280Z which I recently converted to carbs since I was tired of all the EFI problems.

Here's some pictures of this thing:

 

[Tony D]

Crown-based but heavily modded. Don't know why they would change the crossover tube.

Sadly, I see what they did, it was humping probably 21 psi or slightly above. They were spraying anti detonated in a fairly crude approach , but definitely high volume of anti detonant.

 

Lots of this looks to be home fabricated emulations of commercially available technology of the time. Spearco had great water injection systems available then, and AN fittings predate the Z-car by at least 40~50 years!

[Serban]

Tony, thanks for sharing, what are your thoughts of keeping this turbo setup (obviously with more modern fittings, etc.) vs switching to a proper EFI system. All this is dependent on if the engine is good, and if it was purposely built for turbo of course.

[Tony D]

There is an SU housing that takes two injectors if I'm not mistaken. Running two 1100CC injectors should be close to it... running a dual channel you could run a 550 or 720 in the front on the methanol injection spacer and basically use it for N/A operation at idle and then transition into the 1100 cc units on boost. It would be fairly easy to conceal, and updating to Methanol Injection as opposed to straight water would give some gains as well.

I'm all for updating Crown Kits. You can add modern stuff and keep the period-vintage look. These worked pretty well if you took the time to sort them. The Corvair Turbo they used when Hybridized (right, hybrid turbos are a 'new concept' --- like 1965 huh?) with the early model 63/64 turbine and the later 180HP Compressor section would enhance boost response and allow boosting to 21psi without much effort through the 46mm SU... The downfall on that system was detonation as the jet couldn't flow enough fuel and they invariably ran lean around 17psi. You could tweak out to 21 with wiper fluid (methanol mix with water or straight methanol)... it's why most ran a wastegate as that Corvair Turbo uncorked really boosted until the engine blew from lack of fuel. They just sprayed more in the inlet to keep it all together.

It would make a nice project IMO

[Serban]

21psi seems like a lot of boost and I'm surprised a single SU is adequate enough, even 17psi... This is a neat setup and I would like to run it. I thought about using my 280Z intake manifold and going EFI, but the E31 head does not have the holes to put a 280Z intake manifold on. 

 

Either way, I think a more modern T3 turbo and wastegate would be a better option than the hybrid Corvair turbo. I also found the Crown adapter for a Weber carb. Would that be a better suited carb vs. the single SU?

[Tony D]

Generally they were a 0.250" jet 2" SU from a Jag. They would change the needle so basically after about 3/4 throttle the bottom three or four stations on the needle were completely out of the jet. The Position of the Floating piston determined the vacuum exposed on the jet and determined how much fuel was  sucked through the jet orifice. a 1/4" hole can flow a LOT of fuel if you don't suck the float bowl dry or below a proper float level that keeps fuel right at the bridge to be sucked in easily. This is why guys used Hobbs Pressure  switches  after about 12-15psi to run through like a rochester jet in the line and start dumping more fuel directly into the throat of the carb. Just remember "carbs are easy"! Repeat that Mantra... I will repeat mine: "Click, Drag, Ctrl Arrow Up Up Up.... Click, Drag, Ctrl Arrow Down Down Down"! LOL "Been there, Done  That!" You will be surprised how much HP you can get even from a single SU. On the Corvair 180's you got a low more torque,  boost  earlier, and around 200~220 HP. Uncorking  the exhaust by dropping the Turbo Muffler (yes, that's  where they came from, guys all wanted Corvair Turbo Mufflers on their cars!) and that's when the boost came on hard in the top end.

 

Now, to the "Weber Carb"... it's a MISERABLE compromise. The ONLY way it works is to turn it into a progressive two barrel. Run a 45 DCOE with a split throttle shaft and a progressive linkage that brings the second barrel on in the last 1/4 of throttle play. Jet the first barrel for most of your driving and  for a smooth transition into boost. Jet the second barrel (usually the one facing the front of the car, or towards the engine on a Z) for fuel dumping...HUGE main jet, and nothing in the idle system. Basically it only opens above a given throttle position and is not in play at all at idle, It comes on with a smaller than normal booster venturi to get the fuel flowing as the vacuum drops on the first barrel and it momentarily leans out. It usually transitions smoothly like that,  and pulls like a banshee from there on. Using the Weber as a weber, you end up compromising way too much in terms of fueling as the mains have to be MUCH larger to fuel it under boost than you normally would have as an purely N/A car.

Now, if you put that Weber Manifold on with a DCOE ITB.... NOW we're talking! Then you can run a couple of 720's in there and  I lay money you will have more than  enough fuel under boost. That should support around 250 280hp.... Likely a set of 550's would do you just fine.

As for newer T3's I was the demented bastige  who thought "Hey, if they can take those 280Z EFI's and put them on the Corvair 140's, the ZXT is rated  at 180 HP as well, so why not?"  Putting on a Datsun Turbo with internal wastegate transforms the Corvair Turbo. With turbine technology 20 years  advanced it REALLY makes  for a nice driving car. Similarly doing a proper T3 with internal wastegate will give you your terminal Pounds Per Hour the turbo can flow at max boost. This in turn will let you know what fueling you need to get Max HP, and then you size your jets or injectors  accordingly. 

I feel you should be able to make something that looks VERY 'period correct' with that DCOE body (or the TWM Twin Injector SU Body) that should easily be in the 220 HP range reliably and drive quite nicely. With the addition of Methanol Injection like a hidden Snow arrangement you could probably bump that considerably as it would allow you to run much more advance and  much more boost from the intercooling effects. You could keep the old school MSD 6BTM on there as an example of Old School, but hiding one of the new 1, 2, 3 Ignition  Distributors would allow completely modern programmable MAP - Based 3D Timing map to be used and retain the look of a conventional distributor.

This is totally doable and would make a great stealth conversion. The trick for me would  be  hiding the EFI bits so it looks totally carburetted. I have done one of these before where I simply gutted the SU straight through, and  put two big honking 1100's in front of it (what does an 1100 look like different from a 280cc???) and it looked like one of those mid-80's AIC setups. The big injectors supplied all the fuel for the engine through an EMS tucked up behind the glove box. Ran better than the SU did...especially when cold!

 

And you;re right, generally 10psi is about as far as you can  reasonably go on the SU, but if you didn't Wastegate it your  foot was your wastegate and a 2" SU would boost to 21 psi EASILY. On a Datsun you break pistons and  blow head gaskets. On a VW or Overbored Corvair you split Jugs, or blow the head right off the engine pulling the head studs out of the case. That's a noise you never forget. And that is why "Case Savers" were invented!!!

[HowlerMonkey]

I like that curve in the exhaust manifold to turbo pipe.

[z-ya]

When I orginally got my 240Z, it had the Crown kit on it. Modified in a similar way with ethanol injection. It's a Rajay turbo, which you can probably still get parts for.

 

I could not get more than 5PSI boost without serious detonation on my setup. It was the original L24 with an E88 head and flat tops. If you have flat top pistons, a good swap would be a P90 head, which will lower the CR, and be less prone to detonation. Some sort of intercooling would also help. I had two float bowls on the single SU to get more fuel capacity near the carburetor. The needle was what ever came with the kit.

 

 

I've attached pages from the Crown installation manual. The last photo is of my Z.

 

I long ago replaced this setup with an L28ET, and I have never looked back. I'm now working on a new L28ET engine for the same car.

 

Pete

[Serban]

Very cool z-ya, thank you for sharing those pictures.

 

I can't wait to start digging into this engine, but I've been idle with it now since my other car decided to get a nice rod knock. I've got that engine torn apart at the moment while I wait for parts.. When that's all done, I'll start tearing into the L24!

[Serban]

Hey everyone, it's been a while since I posted on this thread, but I finally got around to pulling the head off. Pistons look fine. This is an E31 block, and E31 head. It's got dished pistons which I'm told is not the stock piston on the E31, and the bore is 83mm. Pistons look clean with no sign of detonation. I haven't measured the valves yet to see if they're oversized. But what is everyone's thought on this?

 

The head looks pretty clean. I guess next step will be to drain the oil and pull the oil pan off and investigate a little more. 

 

I still plan on cleaning this engine up and swapping it in with the Rajay turbo it came with, as long as it checks out. I'll also add an external wastegate. I don't like the idea the idea of not controlling the boost. I'm also not looking to shatter any records, I realize doing an EFI carb body would ultimately be the way to go, but I just want to keep this as it was 30 years ago. I don't want to spray any methanol, if the SU will handle 10-12psi without running lean, I'd be ok with that.

Edited June 15, 2017 by Serban

[Tony D]

E31 head is worth something. Interesting they took the time to put in dished pistons. Very interesting indeed!

If you think you want to keep the SU, you will need to retaper the needle and by all means use a wastegate to hold boost at a given level while getting the mixture right. Problem is you will have to determine needle station height to and use the starter lever to give more fuel then cut the needle for that station  and move on... The way the needle tapers you go from lean to rich which is the absolute wrong way to go when tuning a turbo under boost!

You may not "want" to spray methanol, but I'm telling you 30 years ago you sprayed methanol from a winshield washer tank and a carburettor jet stuck in the aircleaner activated by a hobbs pressure switch on the manifold. As Z-Ya said, you WILL start detonating in short order unless you rezise the jet in the SU or retaper the needle to flow much more fuel once you go on boost!

[Serban]

Tony, your input is very useful, and I appreciate it. I'll see if I can find some time tonight to pull apart the SU carb and see if any of that's been done. If the dished pistons are a surprise, perhaps there are more? I was told 9k went into the engine build, just curious where all that money was spent, if that's an accurate number.

[Serban]

Valves are 42mm and 33mm, looks like they're stock size.

[Samurai7one]

I like the simple approach of using the stock exhaust manifold and just using a flanged u-shaped pipe up to the turbo.

[texis30O]

My old turbo tom set up sprayed water, then I swapped to methanol...... just a jet size change..... Tony how is that set up? lol want to sell it back to me? lol.... with another car..... @Tony D

[Tony D]

that box is really durable...

[Serban]

The L24 is in, and ready to go! I only get to work on the car a couple hours a night, so it took me about 3 nights from start to finish. Initially the L24 had low compression on a few cylinders (between 30-40psi). I put some Marvel Mystery oil in each cylinder, and after about 4 hours I tried again, and got about 150 across the board, seems promising! It starts and runs, and holds idle great! I have yet to drive it, I think there's a huge exhaust leak somewhere. I can't pin point it yet, but when you rev up the engine, exhaust smoke is coming from the manifold to turbo up pipe. So I'll probably have to pull it all apart and see how the welds are, or if there's a crack. But so far so good. Here's a few pictures from the swap!

 

[Serban]

https://youtu.be/IA-Wr9WPeFk

 

Here's a video of it starting up!

[Serban]

I found the source of my exhaust leak...

 

The turbo inlet flange has this channel in it (not really sure what it's for), and the new T4 inlet gasket I bought didn't fully cover it, which in turn made for a nasty exhaust leak. I'm using the one that came off the turbo in the meantime until I find another one.

 

With that being fixed, I took the car for a drive, and it struggled to even make 4psi. I double checked everything then researched the wastegate hose placement. I'm supposed to run the hose to a boost source before the throttle plate. In this case, everything before the throttle plate has no boost. Tial does not recommend connecting it to the manifold, as vacuum could cause problems with the diaphragm, so I tried disconnecting the hose, and running it as it was before, without a wastegate, and got about 7-8psi. A little better. The wideband was around 13:1 afr, but without a wastegate, this turbo just wants to make more boost, and I have a feeling it'll lean out.

 

I may try connecting the wastegate again, and adding a boost controller. It has a 4-5psi spring at the moment.

 

Has anyone that has run this setup been successful with using an external wastegate? 

[HowlerMonkey]

If you use a "grainger valve" it will protect your diaphragm from excessive vacuum and you can adjust the boost.

 

It acts as a one way valve allowing only pressure to reach the diaphragm.

 

You can plumb it to the intake manifold without worry.

 

You just have to make sure you have that tiny hole between the diaphragm and the valve so the wastegate will close again.

 

As with any changes to boost control............take the first drive ready to back off the throttle in case things aren't right.

 

Also.....what kind of timing and curve do you have going on?