View Full Version : TR6 TR6 side draft TBI

Paul Slice
05-24-2006, 07:05 AM
Hello all,

has anyone here had any experience with this Fuel injection kit https://sidedrafttbi.com (https://sidedrafttbi.com.) Looks like a very cool mod, yet retains the stock look of the twin carbs.

Any comments and suggestions welcome,


05-24-2006, 09:55 AM
This is interesting and looks promising. I like the part about the GM ignition module.
I could not get the web site up until I deleted the index part. https://sidedrafttbi.com/

05-24-2006, 11:07 AM
That's pretty cool. I guess the the GM injectors fit under the dashpots?

It's not a bad idea (gutting a carb and using it as a throttle body), but I'm not thrilled about having the injectors on the atmosphere side of the throttle plate (as opposed to the the engine vaccuum side). A lot of racers do it that way - but racers wear nomex to work and many have on-board fire supression systems in their cars. I don't think GM has done it that way for quite a while. And they were downdraft systems, mostly V6s and V8s, where gravity would take the fuel to the engine eventually.

The custom EFI setup looks neat but I would also consider the MegaSquirt set up which also uses standard GM sensors.

Just my 2 cents. /ubbthreads/images/graemlins/square.gif

05-24-2006, 11:40 AM
I had considered doing that to my race car (MG) engine which runs a couple of DCOE Webers - use the carbs as throttle bodies and locate a fuel rail with injector under the intake manifold. I like playing with that sort of thing.

Only thing stopped me was that the vintage racers might not figure that was kosher and the gain would probably be more in tunability than power.

You could do the same thing with a TR-6 using a Weber manifold and throttle bodies from TWM and gain considerable power on a TR-6.

05-24-2006, 01:49 PM
What problems would you expect in a side draft installation? I think it would be at least as safe as the original carburetors. Carbs deliver the fuel on the Atm side of the throttle plate, and have a float bowl full of fuel.

05-24-2006, 09:29 PM

The custom EFI setup looks neat but I would also consider the MegaSquirt set up which also uses standard GM sensors.

[/ QUOTE ]

As someone who had a CustomEFIs-type injection system (I bought my fuel map from him for my 79 CJ7 with a 304 but assembled the pieces myself) and is now doing MegaSquirt I would STRONGLY suggest using MegaSquirt for the ECU instead of the GM system. The GM setup that CustomEFIs sells uses an EEPROM to store the maps which requires UV lights to erase the chip and an expensive programmer to reprogram, plus software that is a pain in the butt to use and has been reverse-engineered to tune. MegaSqurt on the other hand can be tuned on the fly from a laptop in the car and has all sorts of good programs to help analyze and adjust the maps. No reason you couldn't use his TBs with a MegaSquirt but he charges $125 per carb plus $99 for the TPS adapter, for $350. Before I got my PI manifolds I had arranged with a local machine shop to fit my injector bungs for port injection in the carb manifold. I think it was ~$200 for the machining, $63 for an 8-pack of injector pockets, and I got a pair of throttle-bodies off of a Nissan 300ZX that almost bolted straight on the carb manifold for free from a friend and had a built-in TPS. So, ~$100 cheaper than that setup and a lot cleaner IMHO. Just another route to think of....

Or you could adapt a PI manifold....


Or build a custom manifold like alana.

05-24-2006, 09:48 PM
Bear in mind that the PI manifold I had went for $800 on Ebay, and a custom one was quite a bit more than that to have made. The only other place I know of selling something off the shelf is TWM and they are mucho dinero (like $4k).

Pattens setup is not nearly so much $, and CustomEfis will have maps for stock already setup from the test mule. It's also pretty simple to put it back to stock if you ever want to.

Is MegaSquirt better? Yes if you are a tech and enjoy fiddling, or want to do it all yourself. If you just want it to run, this gives you a relatively simple route.

If you are looking at FI, then you probably know everything else you need to do already. If otoh you want a (basic) primer for the other bits you need for tbi, the Moss manual for their MG setup is pretty nice in this respect.

Is it worth it? Yes, probably, if you want driveability. If you are after more power then this isn't the way to go (at least not on its own - think cam or supercharger as well).

mnsho only ymmv of course.

05-24-2006, 10:00 PM
Carbs don't "deliver" fuel on the atm side of the throttle plate like FI "delivers" fuel. Carbs depend on the venturi principle creating a vacuum to atomize fuel. No air flow, no vacuum, no fuel flow. Or at least no atomization.

The FI will deliver atomized fuel, under pressure, whether or not the engine is running, whether or not there is any air flow at all. Indeed, some EFI will deliver a quick shot of fuel upon activation before cranking even begins or the throttle plate moves from idle. I'd rather have that fuel/air mix on the other side of the throttle plate.

If the injector fails/clogs open I'd rather have the fuel contained on the other side of throttle plate.

But that's just me - racers will put injectors waaaayyy at the tippy top of a velocity stack - you can get more power that way. The TWM website just basicly says "We don't do that on street vehicles."

Liquid fuel is flammable and kinda dangerous. But it can drip on a hot exhaust manifold and not ignite. But atomized fuel/air mixture is mind-bogglingly CRAZY dangerous explosive. (Hey - WHEAT dust will explode when atomized in a fuel/air mix.)

I have no problem with side draft FI. But I would simply drill/heliarc injector bungs on the stock (or other)manifold and keep the atomized fuel mixture on the inside of the engine where it belongs. Just like Triumph did it.

That's how I see it. /ubbthreads/images/graemlins/thumbsup.gif

05-25-2006, 09:16 AM
Replace the word " "delivers" " with introduces or supplies. Maybe that will help you understand my statement.
My '92 Somoma uses a throttle body injection system. The injectors are on the atm side of the throttle plate. No problems after 14 years and 155K miles. No leaks, no backfire, ever.
I think you are confusing port fuel injection with throttle body injection. TBI is a compromise, a cross between the traditional carburetor and injection. Computer controlled injectors replace the needle and seat in throttle body. Externally a TBI looks a lot like a carb. Your discussion revolves around port injection (allow me to extend the meaning of port to include the intake runners) The side draft TBI units Paul mentions in his post are not port injection. These TBI units introduce fuel into the airstream at the center of the "carb" body, in basically the same location as the stock delivery point, except from the top. It's hard to imagine a situation where atomized fuel will be sprayed onto the exhaust manifold. It's no more dangerous than a carb with a stuck float valve.
The Triumph PI system was not a throttle body system.
Wheat dust is not "Atomized". It is still the same dust. A pile of wheat dust may ignite if you put a flame to it. A cloud of wheat dust can ignite quickly and violently if the ratio of dust to air is sufficient to support combustion.

05-25-2006, 09:55 AM
Rusticus actually pointed out his concern and the exception of the GM throttle bodies in an earlier post. The TBI units on the V6's and V8's having gravity to help direct the fuel where it needs to go. His concern is in the side draft nature and gavity not helping direct the fuel into the intake manifold. Though your point about it being no worse than a stuck float needle is valid.


Simon TR4a
05-25-2006, 10:29 AM
I suppose a V engine design is slightly safer from any type of fuel mishap as the intake system, whatever it may be, in in the valley between the heads, and the hot bits are on the outside, so a dripping line or whatever is a little further from the exhaust system.
Also, the plugs and wires may be further away, too.
I guess this is another reason to maintain these components well on our little cars.

05-25-2006, 03:21 PM
Hey dude, if you like your TBI on your Sonoma and you want to put something similar on your TR, more power to ya'... literally.

I know what GM TBI is and I know how carbs work, and they are different. Injecting fuel under pressure is inherently different from atomizing it via a vacuum and a jet with a carb. It's the "fuel under pressure bit" that calls for the extra caution. And yes, I realize that the pressures involved with GM TBI are lower than the typical injection setup, but they're still triple or quadruple the pressure of a carb system.

I'm glad your TBI on your Sonoma has been safe and trouble-free, but me, I wouldn't bet my family's, myself, or my car's safety that some "homebrew" TBI system, (well, homebrew compared to the GM effort, anyway) would be as safe and reliable. I would try to engineer a little extra safty margin - by putting the injectors on the other side of the throttle, where I think they belong.

I know that's no longer TBI in the General Motors sense.

So, to sum up, I think side draft TBI (as implemented in the OP) is a bad idea. GM style TBI is no longer used by GM or any other major manufacturer. (Maybe Holley still sells that Pro-jection?)

The TWM SU style throttle bodies (and Triumph PI throttle bodies) have the injectors located on the throttle body, but on the other side of the plates. So I think that could rightly be called "throttle body injection" as well. Toe-may-toe, toe-mah-toe.

If you don't think that atomized fuel is more dangerous than liquid fuel - well, I just disagree.

Cheers all. I'm headin' home for a /ubbthreads/images/graemlins/thirsty.gif

05-25-2006, 06:16 PM
You missed my point.
I'm saying that modern injection uses a throttle body (or multiple throttle bodies), with individual injectors downstream of the throttle plate, in the runner, or port as I am calling it. Most have an injector for each cylinder. The injectors are not in the throttle body.
Throttle Body Injection has the injectors in the throttle body. Sort of an electronic needle and seat.
TBI is not port injection.
I never said pressurized fuel is not dangerous. I said I don't see a situation where a throttle body injector is going to spray fuel onto the exhaust manifold.
I will add something to clarify my statement about the Triumph PI system. It is not a TBI system. It was a true port injection system, albiet a mechanical one.
The GM TBI was one step in their evolution of electronic controls for fuel delivery. Like the carburetor it's reached it's limits and was replaced. The same evolution happened with mechanical injection.
In my initial post I asked a simple question and commented with my ideas on the system. You decided to lecture me on the principles of the carburetor?
Like Paul I am intrigued by the adaptation of injectors into the Stromberg bodies. Weber side drafts also deliver the fuel on the atm side of the throttle plate, but they are too pricey and complicated for my taste. The TBI setup is pretty simple, somewhat modern and hopefully reliable.
Based on your initial post I thought you may have some first hand experience with side draft throttle body injection.
Sorry for the confusion.

05-25-2006, 07:12 PM
If the injector fails/clogs open I'd rather have the fuel contained on the other side of throttle plate

[/ QUOTE ]

I've been rereading this thread - and I have to ask. How on earth would something clog open? Especially a fuel injector.

You are far more likely to spring a leak at a union, which granted could spray fuel all over, or have the throttle plate jam open (which can equally well happen in carbs or tbs).

If installed properly, I don't see this as any more dangerous than the regular fuel supply. Then again I'm using AN fittings and braided hose or hard line right through in mine rather than rubber and clamps.

My tank:emissions canister hose was plastic and it was melted under the engine. I reckon that's just as big a fire hazard. Plenty of vapor there...

05-25-2006, 09:36 PM
"I've been rereading this thread - and I have to ask. How on earth would something clog open? Especially a fuel injector."

Easy. Piece of rust or other detrius in the fuel jams the injector partially open. This is one reason why FI systems have rather elaborate filter systems. Somtimes injectors leak - they wear out - the electronics can short - it's just an electric valve - is it that hard to imagine that it might fail?

Like I said, do it to your car, if you want to. I just don't consider it good practice and I feel I'm in good company. (TWM, Triumph, Bosch, and every current OEM in the world.) /ubbthreads/images/graemlins/square.gif

05-26-2006, 08:37 AM

You're more likely to be struck by lightning.

PS: It's Detritus

05-26-2006, 11:17 AM
They don't use carbs either on new cars. Best you throw yours away right now. Total fire hazard.

I saw gasoline flood the engine bay once with a set of faulty carbs (actually on a TR6 as it happens). If the exhaust had been hot rather than the guy cranking it, you get the idea...

As to the detrius (sic) blocking the injector partially open, you are more likely to have the engine fall out of the car as you drive down the road imo.

05-26-2006, 01:26 PM
Thanks for the spelling lesson gentlemen. Now that I know you're watching out for me, I will be sure to include at least one spelling error per post to keep you properly entertained. Thouroughly chastised, I will retreat to my shadowy lair, er, garage. The shame - I can't bear it. /ubbthreads/images/graemlins/cryin.gif


08-16-2006, 02:08 AM
Hello - Let me introduce myself as the creator if the sidedraft tbi that has been discussed here. I understand this is not the place to hawk my wares but there is some misinformation that ought to be corrected. I have no ax to grind and I'm not advertising here as I can barely keep up and still enjoy my TR6 as it is. So:

1) Tightened emission standards are why GM stopped using TBI. It is an absolutely dependable system that has logged billions of trouble free miles. It can be repaired by nearly any local garage (even on a TR6).

2)Fuel pressure is 12psi

3)Fuel is sprayed onto the throttle plate behind the bridge in the floor of the carb. In case of the extremely unlikely "stuck" injector fuel would run into the intake and stall the engine. Much less likely to happen than a stuck carb float.

4)The programmer is expensive. It's $125.

5) $350 for my parts is expensive compared to $263 and a friend giving free parts. You got me there.

Sorry about the retort but just wanted set the record straight. Feel free to contact me directly if you wish to discuss the set up.

Rick Patton

08-17-2006, 06:51 AM
I'm at 320k on the GM TB set up on a '94 Suburban. Bought the boat new and The TB has never been been a problem.