View Full Version : SU and Stromberg Carbs on Modified Motor

11-17-2006, 08:32 PM
Just curious, I'm rebuilding the engine in my TR3 (part of the resto), and am going to do some performance mods. I'll increase the compression ratio, install 87mm pistons, put in a mild cam and a set of headers. I'm only looking for maybe another 20HP or so. I'm going to retain the SU carbs, as I feel they should be able to handle these modest increases.

What I'd really like to know, is how much horsepower can a set of (2, 1-3/4") SU's or Strombergs handle on both the four cylinder TRactor motor and the six cylinder TR6 motor?? At what point would more carberetion be neccessary?? /ubbthreads/images/graemlins/confused.gif


11-18-2006, 10:25 AM
I have the 89's but no mod cam/or headers and the motor/ carbs run very strong. I think you'll have no problem. What compression ratio are you looking at? Have you considered an MSD6 unit for the ignition system. I've found these to be superior to the pertronix units in spark duration. I run one with the points and they never pit, no need to worry about dwell just replace them at 10k miles as the spring gets weak. That would compliment your set up.

Simon TR4a
11-18-2006, 10:47 AM
Hi Art, for your purposes there is no need to worry about the carbs, they will flow plenty of air to support that kind of power output.
My TR4a has dynoed 100bhp at the wheels, (I think a stock engine should be in the 75-80 range at the wheels) with the stock carbs.
Although I do not know at what point the carbs become restrictive I can tell you the vintage racing guys are getting 130 rwhp on SUs, which may be 160 to 180 bhp at the clutch.

11-18-2006, 01:08 PM
Group 44 racing campaigned the TR6 in D Production quite successfully with ZS's. Of course, they had a genious by the name of Brian Fuerstenau massage them.
SCCA racers have always used the original carbs on their cars. So there is no problem with making them work. Radical changes though cost radical $. But what you are talking will probably be an adjustment, at worst, new needles.

11-18-2006, 02:17 PM
1 3/4 SU's are good on both 4cyl TR and MGB motors up into the 190+hp (at the flywheel) range.

11-19-2006, 07:29 PM
The secret is to get a carb to flow enough air for the CI and RPM of the engine...and the SU's should be up to the task.