GT6 Triple 150CD Strombergs

[Docman]

I am hoping to get some feedback from GT6 owners that are currently running triple Strombergs. How pleased are you with the conversion, was it worth the expense?

Since I already have a mild cam and header, a triple Stromberg setup seems to be the most logical and cost effective next step to improve my engine's performance. Richard Good and Jeff Palty (here is the US) each have decades of building Triumph 6's, and although their main focus is the larger TR6 engine, they claim that the triple 150CD setup has been very effective with the 2L engines.
Also, 150CD's are shorter and fit under the GT6 bonnet without modification.
I know a popular upgrade to series II E types is to revert back to the triple carb setup of the series I cars - that has to tell you something (I would think)?!?

From Richard Good's site:
The Triple Stromberg System has grown steadily in popularity since I introduced it in 1991. More and more TR6 owners are realizing how well it performs, offering the high performance they want without a sacrifice in fuel economy or street manners. I have had great success using this system on high performance TR6 engines that I have built and have received excellent reports from customers who have installed the kit on their engines as well. I have always worked with the 175CD's but some of my customers have had equal success using SU HS6's. Strombergs and SU's have a sliding air valve creating a variable venturi to maintain high air velocity across the jet regardless of the volume of airflow. At idle when the engine is using very little air the air valve is only open a crack so the air still rushes past the jet to properly mix the fuel. As the throttle is opened and the load on the engine is increased the air valve rises, riding on the airflow to maintain velocity. At full throttle under load the air valves are fully open exposing a wide-open passage for air. This performance simply cannot be matched by a fixed venturi carb. If a fixed venturi is sized large enough to provide adequate flow at high rpm it will not mix the fuel properly at low rpm resulting in poor fuel economy. With triple Strombergs the fuel mileage is generally in the mid 20's and the performance is fantastic with instant acceleration and smooth power throughout the rpm range. Installation is easy with no modifications required to the stock carburetors. This system is a worthwhile improvement to a stock engine and is of even greater benefit to a modified engine.

[smithy]

Ah, the good old carb conversation... here we go!
Generally, Webers are preferred, more adjustable, sound better and also look better (some say). I presume they are more expensive - I seem to remember they were, in the Moss catalogue. And of course fuel injection with electronic ignition's better still. Must be.
Strombergs though - I like 'em!  :)
Even though the Good kit is not a cheap set-up (you don't want the emission carbs, probably) and you'll need a nice new fuel pump too, and decent rolling road tuning to get them to perform at optimum, it's still a cheaper alternative that performs well and looks great.
(Especially if all the dash pot plungers are the same colour - unlike your photo!)

[GT6boy]

Docman: you are right to ask the question.
I've rarely seen quantifiable resulting 'improvements', aside from sales pitch from the fella selling the things.
I've got triple SU's on my 2 litre.
Whilst mine is a successful job- this was a long and expensive process to tune to a usable RR 150hp. It could still benefit from further RR needle and spring/ignition advance adjustment.
Triple constant depression carbs on a Triumph 6 cylinder is a fundamentally flawed installation for low revs due to the firing sequence. You can make them work very well but, the same amount of time and money spent on a twin CD carb would ellicit much better results. That's what i'd do, if I were doing it again.  ;)

[Docman]

I have queried the Sideways forums and there are discussions regarding Triumph 1-5-3-6-2-4 firing orders not being condusive to 3 carb setups, odd cylinder pulse pressurization resulting in reverse induction (fuel stand-off), balance pipe and manifold heat optimization, and on and on.  
Series I E type firing order is the same, as was the SU carbs targeted.  What made them perform well by comparison?
Am I missing something, have Richard Good and Jeff Palty engineered out these issues or should I avoid this conversion like the plague?

And you brought up another point Smithy, I currently have emmision carbs.  I would probably need 3 pre-emmision units.

[GT6boy]

Oh, I should say: I don't have the Richard Goode triple set up, but a British equivalent, flowed to within an inch of its life to match a go-much-faster head on a flow bench by by Gareth Thomas (thanks GT- still grateful for your efforts)  :)

[GT6boy]

Bob- a CD carb is that, a CD carb. If the SU's were shorter, they'd use 'em.

[GT6boy]

Engineered out these issues? If the firing order doesn't suit triple carbs, a decent manifold balance pipe will only improve it to a certain extent.

[Docman]

What made series I E types (same firing order and SU carbs) run so well?

[thescrapman]

I suspect the engine being much larger meant it was less stressed so the perceved issues were less.

Or I could be talking rubbish.. :-)

[GT6boy]

Ditto that.

[James]

The thing is that we know of highly tuned tricked-up 2 litres putting out a lot of power from "just" twin HS6s. (Stromberg 175 equivalent)

There's nothing to say going to triple Webers or triple SUs or triple Strombergs would make more power on a highly tuned setup — but for sure the twins are not the limiting factor until you get to that point.

[James]

thescrapman wrote:

I suspect the engine being much larger meant it was less stressed so the perceved issues were less.

Or I could be talking rubbish.. :-)

A big Jag engine has very mild cams compared to a Triumph— as overlap is the cause of reversion then it's likely not to appear on a Jag engine.

Bruce's cam is fairly wild (I think?)

[GT6boy]

GT6 mk2 25/65 65/25 50 degree overlap Duration 270 lift .261
TT RF83  37/63 74/28 65 degree overlap Duration 280 lift .288

My cam on a 2 CD carb install, whilst not ideally suited to the Triumph given that the profile originates from ford, it was routinely recommended by some folks whose opinions i valued greatly, as they had far more experiance than me.

[James]

Where as a Jag is around 250 degrees I think — at least the "uprated" cams start at 260 degrees and a race cam is 290 (according to Newman) — so a different kettle of fish entirely.

[Docman]

Then there's the predecessor to the 2500 PI that was sold in Australia, the 2000 MD (Managing Director) which ran triple 150CD stroms and was reported to be spitited and very tractable.
http://www.flickr.com/photos/28130065@N02/7174238096/

I wonder what cam it was running?

[Docman]

Lest we not forget the Holden Torana GTR XU1.  The OZ folks seemed to have success with triple 150 CD Stroms.

[GT6boy]

Indeed, there do appear a fair number of triple CD installs on other motors, but I remain concerned that there is paucity of back to back or evidential testing to show quantative results for the Triumph install.
Have you enquired of the suppliers for quantative results? Surely if they have been producing this product for 20+ years, they would have something approaching before/after dyno type testing to validate their claims?
It seems most people fitting after-market performance 'upgrades' only appear to make vague assurences of performce improvements after fitting the product in place of something that may have been worn or life expired and therefore offering questionable performance as compared to whizz-bang brand new carbs with no worn throttle spindles and inappropriate needle/worn piston spring etc. :-/

I don't want to sound negative- I'd love to see some decent evidence to prove all that outlay would be money very well spent  :)

[piman]

Hello all,

the E-Type Jaguar doesn't need it's 3 x 2" S.U.s, it would perform just as well with 2 x 2" units but it looks better with 3. William Lyons although frugal was also very conscious of appearance. The MK 2 3.8 saloon on 2 x 1 3/4" S.U.s wasn't much down on power compared to the E Type.

For me Webers on a road car are not going to give any gain over Stromberg or S.U. units, if tuned for tractability and by all accounts use more fuel?

Alec