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TR2/3/3A 2" SU's on a TR3...Overkill?

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karls59tr

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2" SU's on a TR3...Overkill?

Saw a pair of 2" SU's from a 66 volvo for sale and was wondering if the addition of these to a rebuilt TR3 engine, with a street cam and headers, would add anything to performance or would the car be over carburated? What does over carburation mean exactly anyway?
 
Re: 2" SU's on a TR3...Overkill?

You could, but intake mainifold will have to be enlarged or replaced because there will be a 1/4" lip where the carb meets the manifold that will disrupt the airflow, causing a drop in preformance, IMHO.

But I'm not an expert.

Jim
 
Re: 2" SU's on a TR3...Overkill?

The carbs from a Volvo are angled and the rod which centers the float in the float bowl will not be vertical when you mount them onto a TR so they will not rise as they should. Suppliers of SU carbs will sell you the proper float bowls to correct this problem.
 
Re: 2" SU's on a TR3...Overkill?

karl,
They might work but not really sure.
When you go to larger throats you change the air flow charachteristics. The throat size and intake run create a controlled disturbance created for max air/fuel mixture (the exhaust assists in this thru the breathing process too).
When you have larger throats and all else remains stock you get low turbulance at low rpm creating flat spots. It may produce more power at peak rpm but that is acceptable only for racing purposes.
It depends on opening up your intake and tuning your exhaust (size and run) with the right degreed cam for proper overlap etc.
Just putting a larger carb on doesn't always get the desired results and I would suspect you'd have lost some lower-mid rpm responsiveness.
 
Re: 2" SU's on a TR3...Overkill?

Volvos didn't use the 2" but Jags and Rovers did.

While you could fit them to a TR3, it isn't going to gain you anything, as the engine is well served by the existing carbs.

One conversion that makes some sense is to find a TR4A intake manifold, which has better design on the runners, and use the HS6 carbs, which are less likely to leak. Check inner fender clearance with this combo, though - I have a nagging memory that there may be an issue.
 
Re: 2" SU's on a TR3...Overkill?

Ideally, for clearance, a TR4A inlet manifold needs the shorter, later model HS6 SU carbies, as fitted to the last of the TR4A's.

I have seen E Type Jag 2" HD8 SU"s adapted onto a TR4A inlet manifold by chamfering the two inlet bores out to match.

However there's a fair bit of other work in it, as the Jag HD8's run horizontal, and have to be adapted, as Don said, to run at the upward angle of the TR inlet manifold.

These 2" SU's were fitted to a full race TR2, and I can say that there was only a marginal increase in output on the race motor when dyno'ed, after quite a few changes of needles. So hardly worth fitting to a road motor for extra power, but they do look impressive.

Viv
 
Re: 2" SU's on a TR3...Overkill?

vivdownunder said:
Ideally, for clearance, a TR4A inlet manifold needs the shorter, later model HS6 SU carbies, as fitted to the last of the TR4A's.

Viv
Click to expand...

You can use the "long" SU H6s with the long runner TR4A intake manifold in a TR3 if you do not run air cleaners. On the front carb anyways.

Here is a photograph of my old TR3 racecar. The new owner installed a TR4A intake manifold and retained the original SUs. As you can see, they fit, but only just, and only because he is using the velocity stacks with no air cleaner. I got the stacks from Moss. Probably some aftermarket air cleaner could be used as well.
 

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Re: 2" SU's on a TR3...Overkill?

Bassplayer, if the diameter of the carb is 1/4 inch larger the lip will be 1/8 inch, unless they are mounted eccentrically! Of course, your point is valid....

I think there is nothing to be gained from this exercise but frustration and an engine that runs poorly at low revs.
 
Re: 2" SU's on a TR3...Overkill?

I was thinking 1.5" carb instead of the correct 1.75". Had just been on the MG forum and had a brain fot.

Jim
 
Re: 2" SU's on a TR3...Overkill?

As we are talking about the nicer TR4A intake, I thought I'd throw in a pic of the manifold I made for my MGC. Look familiar (there are 1 1/2 TR4As running around without intake manifolds....)

mgc1.jpg
 
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