SU carburator on jeep

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Re: SU carburator on jeep

Post by Michael Browne » Tue Feb 06, 2018 7:35 pm

bantamj wrote:
Tue Feb 06, 2018 11:43 am
Mike, The engine was equiped with a fuel injection, not a carb.
The injectors were close to the inlet port of the engine.
Nice setup but... as you have discovered the siamesed ports have a small problem, 1-2= 540 deg and 2-1= 180 deg spacing resulting in one lean cylinder and one rich one, a recipe for backfiring
I would have tried that manifold with a carb (SU carb) , but a buddy of mine talked me out of it as he said the manifold will freeze.
He said that such a long manifold needs temperature as fuel will condensate along the line.
This can happen on must cars without manifold heating. MGB use SU carbs and it is not uncommon to freeze the intakes with a long full throttle blast on a cool 3 degC day, damm things just ice up. :lol:
I made that manifold to create an air enertia...you know...the air moving at high speed that comes to an abrupt stop when the valve close and compress.
The length between valve and inlet is important and change engine caracteristic's.

I have not yet studied the SU carb, but I have been told that it is a nice carb for such mod's.
SU carbs a favorite of mine for use on "hotted up" cars, easy to tune, cheap to buy, flexible and amazing performance if set up right. Engine does need to be in good condition as they rely solely on vacuum and velocity to work correctly
An injection would be better as that system does not need a ventury to suck fuel through the jet.
You could try a single inject (centre port injection) with that manifold but need to address the icing up.
A ventury restrict the air flow.
At least, that's what I have been told...am not an engine tuner at all.
You could try a short tube type manifold on each port and fit a SU carb to each ( MGB use 1 3/8") with a small balance tube between the tubes. there should be room in the jeep for that. :wink:


Best Regards,
Luc
Cheers
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Re: SU carburator on jeep

Post by tamnalan » Wed Feb 07, 2018 7:46 am

I have a cj-3a that I will use for similar purposes, though I want to focus mostly on trail performance. I want to install a 2.0 Ford Ecoboost motor. The Go Devil runs out of power for highway use at altitude. The 2.0 seems perfect for jeeps - it's a small gasoline engine that acts like a diesel. Excellent torque at low RPM.
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Re: SU carburator on jeep

Post by Wolfman » Wed Feb 07, 2018 7:56 am

:idea: The fog is beginning to clear !
I wondered what was attached to the bottom of the short manifolds that are fastened to the intake ports. Fuel injectors.
So, you are using constant flow injection with a metering valve on the throttle body and not timed port injection ?
When and if you decide to pursue the SU carb. again, I would be installing the carb or carbs. as close to the intake port as possible.
My only contact with the SU type carb. was on motorcycles and don't recall seeing any with long intake tubes.
Synchronization of multiple carbs. is a real pain.
On the motorcycles, the multiple carbs are mounted side by side with a common rotating shaft with arms on the shaft to each carb. Much more stable than a cable to each carb.
I'm rambling.
A WO is a great option.
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Re: SU carburator on jeep

Post by Wolfman » Wed Feb 07, 2018 8:05 am

A small gas engine that acts like a diesel. Glad you said it has good low end torque.
My first thought was it rattled a lot. :lol:
You going to make an adapter plate to connect the Ford to a T-90 or go with a different drive train ?
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Re: SU carburator on jeep

Post by tamnalan » Wed Feb 07, 2018 8:20 am

I'm not sure. Probably a T90-C, but I would like to synchronize first gear too so maybe something else.
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Re: SU carburator on jeep

Post by Fabrizio » Wed Feb 07, 2018 9:19 am

Wolfman wrote:
Wed Feb 07, 2018 7:56 am
:idea: The fog is beginning to clear !
I wondered what was attached to the bottom of the short manifolds that are fastened to the intake ports. Fuel injectors.
So, you are using constant flow injection with a metering valve on the throttle body and not timed port injection ?
When and if you decide to pursue the SU carb. again, I would be installing the carb or carbs. as close to the intake port as possible.
My only contact with the SU type carb. was on motorcycles and don't recall seeing any with long intake tubes.
Synchronization of multiple carbs. is a real pain.
On the motorcycles, the multiple carbs are mounted side by side with a common rotating shaft with arms on the shaft to each carb. Much more stable than a cable to each carb.
I'm rambling.
A WO is a great option.

Regarding intake "lenght", not too short!
The lenght of the air column inside has an incidence, as air has a mass: shorter= lighter = best response and less "lag"; but too short cuts the inertia of the air/fuel mass and can lead to poor cylinder filling at low rpms, when air speed is low.
The thumb rule is long manifold=torque, short manifold=high peak power and high rpm.

For a Jeep, I'd stick to the oem lenght, or just a bit shorter.

The recent Ferraris have variable-lenght intakes ;)

This also applies to whatever is before the carb, like intake "trumpets", be it outside or into a plenum/air box


Same rule for the carbs; bigger carb gives more air volume at high rpms, but give poor vacuum at low rpms, resulting in poor combustion and power; while a small carb will grow vacuum and start working conveniently at much lower rpms
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Re: SU carburator on jeep

Post by Michael Browne » Sun Feb 11, 2018 6:01 pm

bantamj wrote:
Wed Feb 07, 2018 11:39 am
Fabrizio, Your words are what I have been told.
If I would go for the double carburator short to the engine the icing issue would be solved.

Don't go too short and on the MGB the carb is what freezes not the manifold... 1.8 litre MGB had about a 100 mm long tube on the dual manifold with a small balance tube between them. That is enough to get the carb away from the exhaust for mounting.
Tuning is really easy if you use the MGB linkage setup and a good ear. Individual cable like on a multi motorcycle can be a little problematic


And the tube from carb's to air box can be made at best performance length without freezing as there is no fuel involved.
The SU carb is a constant vacuum carb, it is a good substitute for the double port carb with one smaller butterfly valve for idle and a second one with big butterfly valve for high RPM.

Mike, This was a timed port injection and that was where the trouble started.
But I can't explain anything about it as I don't have a clue myself.
The guy who did the attempt said it can be done but I didn't want to throw too much money against it.
He must've been the eternal optimist, you are still battling the unequal engine degrees between cylinders. Maybe get hold of a WilyWily head and fit diesel injectors directly into the head

So now I have the old trusty distributor on it and maybe one day a SU carb...or two :|

Allan, I have played with the idea to swap engines, but Belgian rules are different than in the US.
Here you can't do it legally.

All the best,
Luc
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Re: SU carburator on jeep

Post by pkozak1 » Tue Feb 13, 2018 10:25 am

I'm just trowing this out there, but the only side draft carb I would contemplate using would be a S&S Super "G" with a Thunder Jet installed designed for a large bore 1800cc and up motorcycle. It is a side draft with tune-able Air Bleed, primary and secondary jets, very easy. Since you are a fabricator, you will be able to fab up your side draft manifold for it. This post is very interesting.

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Re: SU carburator on jeep

Post by jeepfinger » Fri Feb 16, 2018 12:31 pm

Luc,

My GPW came with a SU carb installed when I bought her 35 years ago. As far as I can remember, it ran fine, but I had never driven a Jeep before, so I guess that I had nothing to compere it to. Sorry, but I can't remember what type it was, I have a photo but you can't see much :( I wanted to return the GPW back to standard, so installed a Carter.

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Re: SU carburator on jeep

Post by jeepfinger » Sun Feb 18, 2018 2:17 pm

bantamj wrote:
Sun Feb 18, 2018 9:45 am
The question is if there is any gain in efficiency with another carb..
Ah, Luc that is one hell of a question.
bantamj wrote:
Sun Feb 18, 2018 9:45 am
enjoy the sun!!
Thanks,

Dave
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Re: SU carburator on jeep

Post by Marty, SoCal » Thu Mar 15, 2018 1:07 pm

A carb with an economizer circuit should improve fuel economy over the stock Carter. IIRC, the later Carter YF ala the M38 has a vacuum operated economizer/metering rod circuit which leans the mixture under lighter loads.

With multipoint injection, the Willys flathead with the Siamese intake port might be able to be fueled in each port with dual single hole injectors aimed at each valve individually. Cylinders 2 and 1 then 3 and 4 fire right next to each other in the firing order.

A possibility would be to reverse the intake and exhaust positions by changing the cam, meaning the intakes are the old exhausts, the Siamese intakes are now the exhaust ports! Probably would require a billet camshaft, though.
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Re: SU carburator on jeep

Post by Fabrizio » Fri Mar 16, 2018 1:32 am

That’s an interesting idea!

Replica fiat 600 Abarths or just tuned up fiat 600s are often swapped with an autobianchi A112 Abarth engine; that needs a custom camshaft to reverse the rotation of the engine.

In the case of the Jeep engine; a big problem I see is that you would have asymetrical intake ports, 1 and 4 straight; 2 and 3 being a Y port; so different sections, different flow; ending in different cylinder filling and probably impossible to set engine!
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Re: SU carburator on jeep

Post by Marty, SoCal » Fri Mar 16, 2018 6:29 am

http://cleverlever99.blogspot.com/

Image

Reversing the intake and exhaust used to be done on the old "Nailhead" Buick engines for better port flow and also on Ford flathead V8's to make them run cooler.

https://www.bangshift.com/forum/forum/b ... ake-engine

Fabrizio, the big block Chevy has differing intake port lengths and shapes in the cylinder head. One could even them out with adjustment of the length of the intake manifold runners.
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Re: SU carburator on jeep

Post by Wolfman » Sat Mar 17, 2018 7:46 am

I checked out Marty's links.
Interesting stuff.
Some show and some had real applications.
But on an L-134 ???
Why ???
Other than to just say you did it.
All the ports are side by side. On the same side.
What is the advantage.
I had a good friend that had the hemi head conversion for the a flat head Ford V-8. Casting blanks. Actual heads and a couple of the converted engines. The engine held it's class record at the Bonneville Salt Flats for a long time. Very interesting set up.
Maybe a hemi head jeep engine. The XH-134 ! 8)
:idea:
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Re: SU carburator on jeep

Post by Wolfman » Sun Mar 18, 2018 7:21 am

Don't know why, Luc.
Once the original design is changed, we are off into the Twilight Zone.
The Hemi head design is one of the best out there and used a lot by several engine manufactures.
Volumetric efficiency is tremendously improved with the Hemi head over the L Head design.
The Ford flat head V-8 I referred to was a push rod engine. Combustion chambers were reshaped so the L head valve ports were blocked off. The guides removed and the lifters changed to accept push rods. Not going into the total details but very impressive mod. Like I said, there were several of these engines built and they were record holders for their class at Bonneville. And this was back in the 50's.
The same thing could be accomplished on an L-134.
Computer controlled ignition and timed port fuel injection. Get rid of the distributor. Intake on the driver's side and with no distributor, plenty of room on the passenger side for exhaust. Would have to get around front drive shaft.
The blanks to mold the Hemi heads for the Ford were Mahoganey. They were beautiful to look at by themselves. Once they were made, it was just a matter of casting the blank heads and machining them. Made that sound easy !!
Of course. Like you said. A lot of people would look at this as sacrelige.
Might not be much of a market.
But, if you had the time and money, I think it would be an interesting mod. and a real show stopper.
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