Turbo 76 midget, need advice!

[mightymg]

Well Im doing a custom fuel injection on my 76 midget right now, And Im thinking once im done Im gonna do a Turbo set up running only about 3-4 lbs of boost is all. I figure a little bit might give it some good Zip. I would modify my old exhaust to accept the new turbo, then id run it all through a stock intercooler off of a mid 90s eclipse, the turbo would be off of that too. What do you guys think, Im thinking it might be a fun project.ANY THOUGHTS??

 

[Trevor Jessie]

I think there was a Dodge Charger with a turbo as well. There is a supercharging forum on the MGBBS and Morris has done the FI.

 

[Matthew E. Herd]

Heck yeah! Only thing is, '76 (and maybe '75 as well, I'm unsure) has High Comp. pistons, 9:1 CR, so you'd be limited to a fairly low boost level. Perhaps 3-4 would be the most you could stand safely. With the low compression pistons, '77 on, you could easily do 10+ lbs, if I were to guess.

 

[Morris]

I'd like to hear more about your custom FI set up. And I am also very interested in your turbo setup. I am most interested in how you are going to get it all to fit.

 

[Bugeye58]

A turboed 1500. Now <u>there's</u> a grenade with the pin pulled. /ubbthreads/images/graemlins/grin.gif
Jeff

 

[Morris]

I wonder...

I think a 1500 is just a BL 1300 with a longer stroke, right? And the 1300 hundred is generally considered to be the sturdier of the two configurations, right? So, would it be possible to retrofit the 1500 with the 1300 rods and crank. It seems that a fuel injected turbo set up would more than make up for any power lost by the missing 200cc. And the shorter stroke would allow your engine to rev faster and higher without tearing itself up.

Of course, it's late and I have been at an Aikido seminar all day and I just drove an hour and a half in the rain and my brain is fried and I could be totally wrong about everything I just said.

 

[Matthew E. Herd]

Morris,

It has more to do with the harmonics as a result of the shorter stroke than the actual strength of the crankshaft. I believe the 1500 one is actually heavier (and therefore stronger). It's a matter of the enormous loads added by adding stroke. You'll notice the 14k RPM cycle engines have grossly undersquare bore to stroke ratios (the bore is much greater than the stroke). Conversely, the 1275 and the 1500 have undersquare bore/stroke ratios, about 1.12:1? for the 1275 if I recall correctly, and 1.17:1 for the 1500. These're just numbers i pulled out of my head, but once upon a time I calculated it. (It's a very simple calculation, just gotta check the books).

Either engine would probably do fine, but you'd probably be better off with a torquier engine to turbo, as the off-boost torque/power would be better, as well as the fact that the longer stroke yields greater volume at a lower RPM, leading to faster spool-up versus the 1300. Also, ultimate boost numbers would probably be the same, so you'll end up with more power from a 1500 due to the larger displacement.

As an aside, I believe that a TR5/6 engine (2.5L) is actually just a 1500 engine with a .060" overbore and two extra cylinders tacked on. Therefore, if they do well with turbo's, the 1500 probably would too. Although the longer crank has two more bearings on it, I doubt that makes a big difference in stiffening the crankshaft. In addition, longer cranks develop harmonics at lower RPM, so this would be a negative factor, versus the 1500. The additional center main bearings may help to cancel out the negative presented by the longer crank, but I don't know about that.

 

[Morris]

That's mostly over my head, but I am not talking about the BMC 1275 A-series engine when I refer to the 1300, but the earlier Spitfire engine, which was, I think, roughly 1300cc in displacement. The real weakness with the 1500 is in it's bearings and balance. Or, at least, that's what I understand from what I have read on the forum. I had read in another thread that at least one BCF member believes the 1500's longer stroke is the source of this weakness.

Thus, I think Jeff's statement about the handgrenade refers to the fact that faster rev time due to boosting will dismantle the 1500 from the bearings out.

 

[swift6]

FWIW, the lineage of the Triumph big six (TR5/6 & 2500TC/PI) can be traced to a 1600cc 6-cyl Standard Saloon engine from the late fifties. It was then bored to the 2000cc size and used in the Vitesse, 2000 Saloon and the GT6. Then it was stroked(stroke increased) to the 2500cc size for the TR5/6 & 2500TC/PI. The 2.5 litre engine does develop nasty harmonics at somewhere around 6200 and 8200 rpm. /ubbthreads/images/graemlins/square.gif

I read an article from TriumphTune about making the 1500cc a viable performance motor for Spitfires and Midgets. It said that it could be done but you couldn't expect it to live long if revved past 6k rpm for extended periods and should be used as a low rpm torque engine, higher torque being the result of the longer stroke, instead of a high rpm horspower engine with high rpm being the easier result of short stroke engines.

The same can be said about the 2litre and 2.5litre six cylinders. Though there are race 2.5litres that are capable of high 7k to 8k rpm when they use stronger crankshafts and eight flywheel attachment bolts.

The other similarities between the four and six cylinders are due to cost constraints to reduce production costs. Generating items that could be used in either engine.

At least that is what I have gathered through the different Triumph histories that I have read and the individual engines that I have examined.

/ubbthreads/images/graemlins/cheers.gif

 

[Morris]

Great info!

Can you point me to the 1500 performance article you mentioned?

 

[Morris]

Oh yeah! MightyMG, get rid of your stock fan clutch before attempting any kind of turbofication. I have heard fun stories about fans being lodged in radiators...

 

[swift6]

The TriumphTune article was n the back of the Catalog that I picked up in the mid-90's. It also said that the fundamental problem of the 1500 is the oiling system and that for performance longevity an oil coller is mandatory. It also said that it can trace its roots back to a Standard sedan as well. PM me and I could possibly mail a copy or fax it to you. I have no facility currently to post the article. It is a short two pager.

/ubbthreads/images/graemlins/cheers.gif

 

[Matthew E. Herd]

Interesting information. I'd wager the two engines originate in the same vehicle because of the fact that there are so many similarities. It's one thing to have the same method of manufacturing the valve cover, but the bosses on the block are almost identical. This indicates more than a passing similarity. Besides, it makes logical sense to use all the same parts (or ones with the same base) in designing components for simplicity reasons. If you know the dimensions on one engine, you know them all ...

At any rate, I maintain that they're close cousins, although I don't know things like bore spacing, etc. It sounds like the 2.5L TR 6 cylinders behave similarly to the 1.5L/1.3L 4 cylinders, especially when it comes to harmonics. I believe a proper vibration damper would benefit a 1500 enormously, reducing the vibrations throughout the range, especially at the harmonics. This would make the crankshaft and bearings live longer at higher RPM. While the damper wouldn't change the actual loads being seen, it would reduce torsion and vibration, reducing the wear and fatigue of the parts involved.

 

[Morris]

Matthew,

What is a proper vibration damper and how would one go about acquiring/manufacturing one?

Swift6, you have a PM.

 

[swift6]

I just re-checked the article and it did state that the 1500 4cylinder can trace its roots back through the 1300 all the way to the Standard Eight Saloon. Same car the six developed from.

The article also mentions that the mains are actually not a weak spot on the 1500 because they are larger than the 1300 (1296cc) and that the 1500 cranks flex less than people think they do. They also point out that improving the breathing (less restrictive air cleaners, header and free flow exhaust) and adding richer needles (AAQ) to compensate for the increased airflow netted a 15hp increase at the wheels over the stock 71hp. Very significant increase. The rest of the power improvers get more expensive for less dramatic jumps in power. Such as head work, camshafts, alternative carbs etc... They also point out that whether the engine is in a Spitfire or a Midget is also important. The Cramped engine bay makes the oil cooling problem more significant and the lower final drive ratio in the midget means higher rpm at speed.

/ubbthreads/images/graemlins/cheers.gif

 

[Matthew E. Herd]

Morris, I'm still working on fitting one ... I'll get around to that project sooner or later, but I've got a lot of projects to do ... always something new!

It's amazing to hear that a header and filter, plus re-jetting the stock carb gains 15 hp! Someday I'll have to do some dyno work (when I find a dyno and more time and money!).

 

[Morris]

Do you know about these two dyno surrogates?

https://www.tweecer.com/StreetDyno/orders.html

https://www.charm.net/~mchaney/homedyno/dynokit.htm

 

[Matthew E. Herd]

Meh ... it's a good tool, but never as accurate as a real chassis dynamometer (assuming the tables haven't been fiddled with to make the numbers look better).

 

[mightymg]

Well as far as the Fuel injection goes, its almost done, Im fitting it to my BGT, then its going on the midget. What i did was I got all the injection stuff off a 95 cavalier Computer distributor Throttle body injection, then I BUilt an adapter plate to bolt the TB Injection to the Weber manifold, then I hooked up the fuel lines, ran a return line to the tank. the distributer is a custom made unit, a mg bottom, GM top fitted to it, and WHALLAH! we have a great distibuter, NExt I need to run the wires once thats done , were gonna data log through the OBD1 Port, and re burn our own chip for max performance. ONce its done, I think im gonna put together a kit for you guys if its something you all may be interested in. Later LAne.