TR6 TR6 engine "improvements" - specifically carbs

OK, so I decided that since it's started smoking, and it's getting worse, I'll have the engine rebuilt when the weather gets colder. I don't have the space to do it myself (car or engine in garage not both), so I'm going to have to farm out the work. I got a couple of quotes, which were a nasty shock both in terms of cost and turnaround time, but I'm just about over that now.

I figured since I'm paying through the nose I might as well go the whole hog, and get it warmed over at the same time. Up the compression to 9.5:1, a slightly hotter cam, the rest of the usual suspects.

I want a faster street car - basically UK spec or better but carb'd - not a grenade. If there was a viable bolt on supercharger I'd leave the compression alone and go that way, but so far I haven't found one. I'm off the V8 route, although the way things are going it would probably end up cheaper.

This windy preamble brings me on to the real question - what to do with the carburettors? . Now I'm happy to admit that I'm crap with carbs, so any help is obviously appreciated.

I've read about so many choices now that my head is spinning. Twin ZS, Twin Webers (40 and 45), Twin SU HS6, Triple ZS, Triple SU HS6, Triple Weber 40's. Of course each has it's proponents and detractors.

Now given that I'm looking for advice, not to start a war, can anyone give me a hint as to what I should be looking for. Remember I'm a complete muppet when it comes to setting the things up - I want set and forget insofar as possible. Cost is less of an issue when compared to reliability (especially given the cost of the rebuild - just don't tell my wife), I don't have access to a fully equipped workshop, so it needs to be bolt on, and lastly I want (and I quote) more power...

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Thanks in advance.

I had a friend that improved his TR3 with Webers. He found problems with wall washing due to excessive gas flow thru. Constant adjustment problems. Too much juice on a partially rebuilt engine.
If your doing a full rebuild, this can no doubt be overcome

I am currently running my TR250 with a "warm" cam and triple ZS's. This is a very nice setup, with the manifold available from "Good Parts" <https://www.goodparts.com/parts_strom.html>. This setup has the advantage of being cheap (only need to buy an additional ZS) and looking somewhat original. It certianly delivers enough "omph" too, and I have not had any problem tuning the ZS's . Having said that though, if money and originality were not a concern, I would go for the side-draft webbers.

Other improvements you may want to consider durung the rebuild include an external oil feed for the head, the "improved" crank thrust washers, and a steel front block saddle <https://imaconstruction.com/sealingblock.htm>. Not performance parts, but all improvements that wil1 increase longevity of the motor.

Rob.

I'm in the midst of a rebuild and am switching from twin ZS carbs to twin SU's. I have not run these SU's as yet but their fundamental construction appears superior to the ZS. Fewer adjustments, solid piston dampers unlike the ZS rubber gasket which is prone to tears. I've spoken with a number of TR owners whom have made this switch and their remarks are positive. Once I get tired of the twin setup I'll likely tryout Goodparts triple manifold and add one more carb. If you really want to get radical I've seen setups using motorcycle carbs, one for each cylinder....wow!

you can go to prirace.com and find the Mikuni and Keihin multi-carb set ups for various triumphs. Will blow your mind but I personally wonder how well they work overall since I have yet to see someone on these boards with this type of set up.
Achtung

If I had the money and your car, I would go with triple SUs, install the wideband sensor dealie on a 6-3-1 header and hire out a good dyno man.

The latest "Classic Motorsport" has a feature article on improving the TR6 - using Richard Good's modified car vs. a total stock restored car for comparison. The triple carbs and his G3 cam look good to me too.

Why not go the whole nine yards and toss the old engine out and replace it with a V8? Use an aluminum head Ford 302 and you get twice the displacement, three times the power, and it waeighs about 35 pounds less.

See https://www.britishv8.org

Dan,

I've seen your site - awesome btw - and I was seriously thinking about doing something similar. Two problems though, the first is I can't mig for toffee. The second is that I don't even have the space to do an engine rebuild, let alone a conversion of this size. That's why I'm going to be paying someone to do the work for me.

This means that I'd be left having to find someone to do the welding and plumbing. I figure I'd be looking at the thick end of 20k even with a stock 302 crate engine, a t5 and the narrowed ford rear (no way would I put used parts in after all that trouble). That's assuming I could find someone I'd trust (ie with experience) to do the work.

The 10k ish I was thinking of for a rebuild and some go fast goodies is much nearer the mark.

Now if anyone wants to chime in and correct my pricing (or suggest places in the NE with experience) then I'm all ears

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Hi,

You forgot downdraft Webers on your list.

Just kidding. Downdraft Webers are more an economy/reliability conversion. It sounds as if you are seeking a more performance-oriented setup.

I agree that a V8 conversion would be lots of fun and interesting, but the TR6 motor is a good one and has lots of potential too.

Why have you ruled out an EFI conversion? EFI would boost power better than any carb setup, and modern EFI systems would likely be the most reliable/trouble-free of all the performance options. However, cost would be an issue.

The Lucas PI system used on European-spec TR6s is an early and more primitive form of fuel injection. All originality issues aside, a modern system might be a better choice, although initially expensive.

On the other hand, triple Webers ain't cheap either. And, I *would* recommend triples, so that each cylinder has it's own carb, in effect. That allows for the most precise tuning potential. Unfortunately a triple setup means you need 6 each of most jets and venturi, but you might get save something if the set you buy has the right size main venutri, for example, which cost $25+ apiece if you have to change them (ouch!).

With careful shopping and patience you might be able to get a reasonably good deal on a used set of DCOEs (sometimes pulled off a car by someone who gave up on getting them properly set up for their car). The downside is that a used set might have weird jetting when you get them, and need more dollars invested to get the initial setup and/or need rebuilding.

40 DCOE will generally be less expensive to buy and more easily set up, compared to 45s or some of the no-longer-manufactured sizes such as 42s. The latter are harder to get parts for. 45s just cost more, but would be the right size for a 2.5L engine set up with two carbs, if seeking high rpm performance.

Even bought at the right price, though, it costs to have Webers dialed in. This really *should* be done for each individual engine and situation. The general jetting guidelines used even for brand new sets are just to get the setup in the ballpark, the carbs really need to be fine-tuned to get the best out of them. Dyno tuning and/or exhaust gas analyzers are probably the best way to dial them in, especially if the shop doing it will swap jets/venturi with you rather than selling you all new ones!

Webers' biggest advantage over SUs or ZS is their acceleration pumps. Thess will give a nice shot of fuel to the motor just when you want it. Neither SU or ZS have acceleration pumps.

Another advantage of Webers is that they have minimal moving parts to wear. Fuel and air metering is done by fixed jets and venturi. So, a setup doesn't change once it's established. The downside to this is that air density does change if you drive to a higher or lower altitude, or even when ambient air temps and humidity varies. Most racers using Webers have a box full of jets to really fine to their car to local conditions each race day! A bit of overkill for street cars, though.

Webers seem intimidating at first, but once you figure them out they really aren't such a big deal. They are extremely flexible in terms of different size venturis that can be used, allowing a car to be tuned to different performance levels. I've had dual 40DCOE on my TR4 since the late 1970s and really like them. 45DCOE are more commonly used with the 4-cylinder, for peak rpm performance. However, I use smaller venturi to preserve lower rpm performance, for street use and possibly some autocrossing.

If you decide on the Weber route, if at all possible I'd suggest trying to get a manifold that is "one-piece", rather than the "separate-manifold-per-carb" arrangement. A one-piece manifold makes carb-to-carb linkage more accurate and balance is more easily maintained.

Another important consideration with Weber DCOE is that there is no provision for vacuum take-off at the manifold or carbs. This means your car's distributor must be modified or replaced to operate with only mechanical advance. Also, crankcase ventilation needs to be reworked in some way, and that might effect emission controls on your car. I'm currently exploring possible crankcase evacuation systems to use on my TR4, probably with an electric vacuum pump.

SUs and ZS are fine setups, too. I don't knock them. Of the two, SUs are probably more easily serviced and maintained, due to wide availability of parts. Both these carbs are more self-adjusting than Webers, but probably can't be as precisely set up. By "self-adjusting", I mean that, by design, SU/ZS adapt to changes air density due to altitude, temperature, humidity, etc., within a reasonable range.

Problem is there really isn't such a thing as a "bolt-on" setup, no matter what anyone tells you. *Any* conversion is going to need fine-tuning.

The closest thing to "bolt-on" is probably a modern EFI setup with some sort of computer management, purchased from a TR specialist, who is working from specific build info for your car. The vendor will most likely need to know the cam being used, any oversize pistons or valves, compression ratio, any gas flowing work that might have been done to the head, even what exhaust manifold and system you have installed. Then they would need to know how you generally intend to use the car. Armed with that info, they can do the initial setup of an EFI system for your car, and an onboard computer would take care of the fine-tuning after it's installed. This sort of system would also self-tune for a reasonable range of air density variations.

Drawbacks to an EFI system, besides initial cost, include necessary improvements to the fuel system to handle the higher pressures involved, including fuel pump, filtration, fuel lines, etc.

You might shop around in your local area for tuners who can help with any installation and setup, then let their experience and recommendations guide your choices.

Since you are about to rebuild the engine, I'd also suggest floating a question here to get advice from folks who know the 6-cylinder, can suggest improvements that might be made and will give you a heads up about things to watch out for.

You have lots to choose from! Good luck!

Alan Myers
San Jose, Calif.
'62 TR4 CT17602L

The reason I didn't list EFI was the paucity of information on conversions that people have done, completed and that work. I discounted the lucas system from day 1 as too much trouble and too few parts available here.

The closest I can see to a plug in conversion was this one - https://topshamautoparts.com/tr6/tbi.htm - and while it's interesting, and the chap who did the work looks to have done a real nice job, it seems still a bit experimental for my taste.

I want to drive the car. I spend all day looking at a computer, so eprom flashing torque curves on a weekend is not my idea of a good time.

As to the webers - they are on my list. Initial setup is fine - I know my limits, and welding and carbs are it, so I'll pay to have it done. The thing is that I don't want to pay every other week...

Your suggestion about floating a "what should I do" question is a good one. I'll do it closer to the time it's going to the shop.

Still drooling over a v8 though...

Actually, the Richard Good triple Stromberg setup is a straight bolt-on. I had Gary Martin build my Strombergs for me with the extended shaft (concours condition, by the way), at Richard's suggestion. The linkage took a bit of fiddling, about an hour, and the baby cranked first shot, zero adjustment (Gary set them at a average adjustment for me). I have never regretted the setup. Now, many people out there will sell you the triple Weber DCOE carbs but the usually ask that you lose their phone number after the sale.

Bill

So two happy goodparts customers so far. That's nice since I just ordered a bunch of suspension stuff from him...

The prirace setup mentioned in a previous post *looks* cool. I wonder if anyone actually fitted it. Price is about the same as a set of triple webers so not totally outrageous (in that context). I also wonder how much attention they need.

Does anyone actually have triple webers installed? And are they happy with them?

I second the quality of Richard Good's parts. My car has a bunch of his stuff on it... (Triple carbs, GP2 Cam, roller-rockers, adjustable trailing arm brackets, springs, Nylatron bushings, and Nissan LSD diff). Put simply, his stuff kicks butt.

My engine with 10:1 CR, the carbs, cam, lightened flywheel, headers and sport exhaust is a beast. The carbs required some very minor adjustments at first, but zero maintenance since then. It'll outrun my 175hp SVT Focus to 60, after that the tall gearing in the SVT takes over.

I think you'll be hard pressed to equal the reliability and performance of the triple su/zs kit. The webers are great for all out performance, but I don't think they're as streetable as the su/zs setups.

Thanks for the info. Unless I get a magic V8 bullet, so far it looks like Mr. Good will be getting some more of my hard earned...