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Hi Everyone,

A few friends an I are talking about building three, mostly identical, BECs. The engine of choice is the Triumph three cylinder 955/1050 engines that have been available for a little over 10 years in the US. That with miata donors for the rest of the parts and some economies of scale should make this a fairly doable project for the three of us.

We do have some questions that have been coming up in our discussions. Has anyone used this engine before? We are worried about steering clearance since the engine has to be offset to the left hand (from drivers position) side of the car. I'm sure this question has been covered in our BECs so I may find some answers while searching. We were also considering using e30s as donors due to the easy of finding a numerically lower rearend (325e and 325es), but we are worried about the quality of cars found and the fact that they are a fair bit older than miatas.

Thats all for now.

Also, picking up one maybe two Triumph 955i STs this weekend!

Picked up the first donor bike!

2000 Triumph ST 955i. Good bike with a fair amount of parts to sell that came with it. CHEAP!!

Looking forward to these builds! I love the speed triple

I sold my 99 Sprint ST last spring, the miata had pretty much replaced it for my use (fair weather commuting). Should be a good BEC engine, decent grunt, lower revs, not a powerhouse compared to the Jap liter bikes though.

Singleslammer if you are not a member on the British "Locost Builder" site you should be. They are the experts on BEC cars. Russ

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You meet the nicest people in a Locost Se7en.

Looks in good shape. Clean title? I plan on doing something sort of similar.

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-Keith

I love Triumph triples. I've got an 07 Speed Triple, and I never plan on selling it.

I too looked into building a BEC with the 1050 or 955, but the biggest issue I ran into was gearing. The primary reduction of the 1050 (maybe the 955 too, it's been awhile) is geared very high compared to other common BEC engines like the R1, Hayabusa, or GSXR. Again, you'll have to double check the numbers for the 955, but I don't think you'll be able to practically use the Miata differential. With the 3.9 final drive of the Miata, you'll end up with a very low top speed, which will translate into a very high cruising rpm on the highway. I remember looking into it and deciding I needed a differential final drive somewhere in the neighborhood of 2.3, which is a little hard to come by.

Don't take my word for it, do your own homework. It's been a long time since I did the math, and I can't guarantee that 1) my math was correct, and 2) my memory is correct.

Does Rosebud, Mo. still have the motorcycle salvage place??? There is one in Ottawa, Ks. which is not too far from me. Russ

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You meet the nicest people in a Locost Se7en.

Hey there,
I'm Paul, the engineer on this project. I own a Triumph '06 Sprint ST 1050. And my friend and cobuilder Dan has an 06 Speed Triple. My buddy Jordan just bought the orange Sprint you see above.

Yes, thanks for the heads up. I've been running the numbers on the gearing. All the big triumph triples do have a 1.75:1 primary reduction, but I think we may find it usable with a 3.0:1 diff.

More to come.....

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-Paul
Columbia, MO

I played around with the gear ratios spread sheet I had. If you use a Miata Diff (3.99 final drive) with a 195/50/15 tire and the 955 engine (assuming it has the same primary reduction as the 1050), you'll have a car with a max speed of about 92 mph. If you use a 3.27 diff, the max speed will be 113 mph.

Compare this to the R1, where the Miata diff yields a max speed of 112, and the 3.27 diff yields a max speed of 135.

Again, it depends what your end purpose is, but I think a car with a max speed of 92 might be taxing to drive even on the track. Just food for thought!

You can look at some Ford diff. The 7.5 diffs have some pretty low ratios stock and different gears for them are reasonable.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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Hey All,

I'm Paul, the Mechanical Engineer / Designer behind this Trio of LoCost builds with the Triumph 955 or 1050 Engine.

I'm not a desk-bound engineer, I started my career as a machinist and fabricator. In fact, I never finished my Eng. degree but I play one on TV.

I'll be modeling the parts, frame, and whole car in Autodesk Inventor 2012 (& 2013 beta).
I can FEA the assembly and parts for some verification of durability and the right amount of lightness added (yippie!)

1st step, Complete gearing calcs to achieve decent cruising RPM. (So we can choose a final drive solution)
(*Its looking like 3.0 to 2.7 right now, weighing our real world options of E30 325 BMW vs Ford 7.5 IRS.)
2nd step Build a model of the 955 motor, then start in on Modeling some Miata parts.

Our idea here is to minimize the garage floor hammering and hacking, by having a hard plan in a 3D model and prints. Then harness the efficiency of building 3 or more cars off one plan and splitting the assembly/Fab stages amongst us to save set up and "where's that tool" wasted time. (I've played with a FFR Cobra kit, and was disgusted by the lack of planning, a manual that was wrong half the time, and ill fitting parts...)

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-Paul
Columbia, MO

Thanks for the comments guys. We figured out after very little research that the miata gear is a no go. We are thinking either the ford rearend or possibly a BMW e30 325e IRS (complete) as they have a 2.79 ratio. That with a relatively tall tire will get us fairly close to the stock triumph gearing. We considered a chain drive but decided that the only way to do that is with a middy and then we get into a whole new set of problems.

I phoned a friend and said; "I need a quantity 3 '85 BMW E30 325 rearends. Would those be in your back yard?"
Friend; "Yeah, they are."


Gotta go get one for a weigh-in and look see.
BMW E30 325
*2.79:1 is in '84-'85 325 Only *1415mm rear track. *Car was 2770 curb weight.

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-Paul
Columbia, MO

Holy duplication Batman!