We are currently racing one tr4 (SVRA & VSCDA) and a second is being
prepared. Jack Drews, the more analytical of this pair of vintage
racers, is running his/our parts through several flow bench iterations.
He has a question that he would like me to put on the internet. Any and
all observations and recommendations would be appreciated.
A couple comments in advance:
I have run the much maligned stromberg carbs the past 3 seasons with
great success and NO maintenance...(testimonial: 2:59s at Road America
with VERY modest engine prep). We also found out that my unmodified
stromberg flows better than a slightly modified s.u. I guess i bring
this up because so many people were put off by my use of the strombergs.
Second comment: the flow bench expert says that the tr4a head requires
very little attention to achieve good flow characteristics. first in
line of changes to the head after modest porting would be larger exhaust
valves. (btw I run a tr666 iskendarian cam and Jack plans to use
something more radical...closer to a g-3 cam)
Third comment: the flow bench expert sees very little difference in the
cfm on the long branch vs. the log type intake manifolds, although i
assume that the torque characteristics change somewhat. (we are both
using the "long branch" manifolds) i guess i expected the long branch to
flow significantly better.
Now for Jack's question pasted in:
"Joe, here's the question on which I'd enjoy getting Internet response:
I'm preparing a Triumph TR4 for racing. I have a question regarding
carburetor and intake manifold preparation. This engine has two
carburetors feeding four intake tubes / four intake ports. I'd like to
know if I should modify the carburetor for higher flow and risk poorer
low rpm performance and tuning difficulties.
The facts are these: Component flow, measured individually on the flow
bench at 10 in. water vacuum, are: head 110 cfm, manifold 154 cfm, and
carb148 cfm. Total system bolted together gives 95 cfm. If I modify
the air passage in the carburetor I can increase carb flow to 171 cfm
but the total system flow just increases to 101 cfm. Further mods may
result in further increase in carb flow.
My question is, will I see a power increase that is larger than the
apparent flow increase from the carburetor modifications, since on the
flow bench I'm just able to measure one port at a time?"
Perhaps there is someone out there with some experience and data that
can be shared to our mutual benefit. My own objectives have been to
develop a well balanced car in all respects without traveling very far
beyond the confines of my own garage (it's a checkbook thing, so sending
our engines out to Comptune is not an easy alternative) Also, the KISS
concept has kept me on the track with very little work in the pits.
enuff rambling, eh?
Thank you,
ALEXANDER RACING & UNCLE JACKS RACING
rw20232@deere.com
cedar falls, iowa
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