TR4/4A TR4A Intake Manifold on a TR3A

[karls59tr]

The curved intake of the 4A looks like an improvement over the earlier log type manifold. How come more 3 owners dont use it when they are modifying for performance...or do they? Anyone switched over their manifold to the later one? Karl

 

[billspohn]

One problem is that the intake ports on the early heads are larger and a mis-match for the later heads. You are right in saying that the TR-4A flow is better - but only if matched with the TR-4A head.

 

[Don Elliott]

The carbs from a TR3A mounted on the TR4 intake manifolf leave very little space for the air filters. We had to make up some special filters just before we completed this one for the owner. Then he complained that he felt the small size of the air filters was starving the engine because he wasn't getting the power he felt he should. He never came back to say what he found after I told him to remove the air filters for a test to see if it really was caused by the small air filters.

SU make a shorter carb HS6 (S = shorter) and these fit better on the TR3A with the TR4 intake manifold.

 

[TR3driver]

SU make a shorter carb HS6 (S = shorter) and these fit better on the TR3A with the TR4 intake manifold.

Once you solve the throttle linkage problems, of course.

From what I'm told, the stock 4A manifold doesn't flow as well at high rpm; it's improvement is mostly in the mid-range.

 

[Simon TR4a]

I think the intake runners are longer on the TR4/4a manifold, which is the one in Don's picture, and that is what makes the air filters tight against the inner fender.Longer runners are supposed to be good for mid-range power, and the straighter path compared with the earlier design is good for top-end power.

I may be wrong, but always thought the "S" was for "separate" meaning the float chamber is separate from the body of the carb.

In either event, the manifold is an alloy casting, so could easily be opened out to match larger ports if that is desired.
I would add that the pancake air filters do seem restrictive compared with stock filters, but this is just my impression, no figures to back it up. The inner fender on my TR4a had been "relieved", i.e. bashed with a hammer, by a previous owner to clear the deeper K&N filters, but now is back to standard configuration, and stock air filters.
Simon.

 

[Twosheds]

The present owner of my old TR3 racecar plans to use the TR4A intake manifold with H6 carbs. He is going to (has?) cut the interfering part of the inner fenderwell out and weld it back in upside-down to allow clearance. A much more elegant solution than my idea, which involved the use of a BFH.

I don't know if he is using air filters or the velocity stacks that were on the carbs when I sold it. Seems the stacks would have more clearance than the air filters.