Triumph Repair: Triumph carbs.

Question
Hello Mr. Fitzcharles,
I have dual Stromberg 150's on my 68 GT6 and want to swap with 175's from a TR6. Can it be done?
Thanks,
Kelly

Answer
Hi kelly,

I have worked on both but I don't remember if the bolt patterns were the same so first measure that. If they are the same measure the spred between the two carbs on your engine. If that too is is the same then you won't need to do any work on the throttle linkage. The size of the intake manifold bore will be close so a little die grinding will mate the new carbs easily.

If you have the manifold and want to swap the mainfolds again you will need to compare the gaskets to see if they are close to the same as I never tried to make that swap.

However, you do have a more serious problem. That is, Why are you wanting to do this? If you had an engine with a small two brl down draft carb on it and you changed to a dual side draft carbs, then you will see better performance. Or you have a stock engine and you put a cam in and do some intake port work and larger intake valves and raised the compression ratio, then the larger carbs will add to the package.

However if you have a stock engine that is not a racing engine but better then most sedans would have and you already have dual side draft carbs and you just increase the bore size of the dual carbs, you may gain a little high RPM HP but you may loose a little low end torque doing it. (You also need to be sure you have either the adjustable needles or the adjustable jets on the 175's)

When you inlarge the carbs and don't enlarge the intake ports and the intake valves you didn't do anything. You have to think, What is the restriction to air getting into the combustion chamber? If an engine manufacture did his homework the size of the intake valve, the timing of the intake valve, the shape and size of the intake port, the size of the ventori of the carburetors and the restriction of the air filter are matched. By increasing the size of any one or more of those will do little to gain more air into the combustion chamber UNLESS you do all of them. Only if the manufacture didn't do his homework and you found where he undersized something can you only correct one or two items in the line and see any improvement.

I have hopped up many engines in my life and rebuilt many high performance engines and to do any good you need to go back to theory. To make a rough general statement about the power of an engine (normally asprirated gasoline engine). The major contributors to higher horse power are in this order. First is the design of the cam, next is compression ratio, then size and design of the intake system (valve size, port size, carb size and airfilter restriction along with port design and shape)
All of this must be matched to the whole exhaust system. All of this does not even say anything about the massive amounts of work that must be done to the engine. Any of these modifications make it necessary to change the advance curve of the ignition and changes in the maping of the fuel mixture in all the ranges. Changing only one item in the chain and you need a different advance curve and a different fuel micture.

Sucessfully hopping up an engine is a balck art and you must study the theory first. Then decide what is the end result you are looking for. Then do the modifications to achieve that result. Usually the amount of power you want is proportional to $. A NASCAR driver and builder friend once told me that it does not require cubic inches to get power, it takes cubic dollars to get power. ha! A little money will get you a litte power and to get a lot of power will require a lot of money. (and a lot of work).

Let me know what type of power you are looking for and I may be able to at lease aim you in the right direction.

Howard