SU Spacers / Blocks

[JSM]

I searched for SU spacers and only came up with three threads. Maybe I'm calling them the wrong thing.

 

What advantages / disadavanteges are there running thin or thick spacers between the SU carbs and the intake.

 

I bought an N36 intake awhile back that came with thin 1/4" or so ones. The other intakes E48 & E88 all have the thicker 3/4" or so ones.

 

I know the carbs were differnet for the years of the intake, was the size just due to carb size?

 

Thanks!

[1 fast z]

Insulators.

[Zmanco]

I believe their primary function is to insulate the carbs from heat transfer from the intake manifold. I'd guess the thicker ones insulate better.

 

When I still had SUs I sometimes I'd get fuel percolation in the floats. I switched to the thicker insulators but that didn't solve it, so I don't know how much better they really are.

[JSM]

Insulators.

 

SU Insulators gave me three more threads....

http://forums.hybridz.org/search.php?searchid=1412403

[JSM]

Anyone else?????

[BRAAP]

Hmm. Good question. Though I have no actual experience to back up my opinion, my guess would be the thicker spacer would offer the least compromise for the following reasons.

 

 

1) Less heat transfer to the carbs via conduction from the intake manifolds. As mentioned above, this does not help in heat “radiation” from the exhaust manifold though.

 

2) That much more distance for the air fuel to be atomized, though carbs by nature have extremely good fuel atomization characterizes, this benefit would possibly more for consistent distribution of the fuel to the cylinders, i.e. less separation during WOT conditions.

 

3) One possible down side would be the larger “plenum” area that the thicker spacers present. This would result in the fuel falling out of suspension during light load condition such as cruising down the freeway because of the slow velocities in that “wet” plenum space.

 

 

If I am barking up the wrong tree here, please don’t hesitate to correct my theories.

 

Paul

[JSM]

Thanks Paul!

[Tony D]

I thought I mentioned that some of the Auto-X guys will run the N36 intake with a pair of Thick Insulators --- two Thick Insulators per carburettor, four total for more midrange torque. (Use EGR studs to connect the carbs to the manifolds...they need to be around 75mm long; and use a linkage from the pedal to the bellcrank through the firewall as the downlink from the crossbar to the carbs as you will have to readjust the length to prevent overcentering the linkage and locking the throttles at WOT or 1/2 throttle, cut 5-7mm off the end and then use the threaded portion to make the proper length.) I ran this setup for quite a while, before retiring the car...I still have the complete setup waiting for another car. You could use ONE more spacer in there, but you won't be able to fit the stock aircleaner...at least and still remove it for filter changes. With two on there, you can juuuuust get the filter cover and filter out and off for routine maintenance like checking synch and etc...

 

The N36 intakes had a separate water line to the carbs, and one for the manifold that was thermostatically controlled, so thinner gaskets made sense. The Earlier Manifolds were plain SU's without thermostatic manifold preheating, so they insulated the carbs with thicker spacers.

[JSM]

Great info! Thanks Tony.

 

Would space allow for 1 thick and 1 thin or is there little bennift in doing this?

[Tony D]

I'd go with BRAAP on this one, and maximize the plenum volume. I wouldn't bother with a thick and thin combination, just put the most in there that your setup allows, and then retune. The thin spacer will not likely have much of an effect one way or the other, while the two thicks will work nicely and is a proven commodity. I suppose someone with a thick block of phenolic can make up their own!