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MG Midget and Sprite General - Bonneville 970 Midget project

Greg Blagus lives in Plymouth, MI. He specializes in making custom cranks, company name Ro-Dy Crankshafts (do a google search on that name and tons of sites come up, of folks who've used his stuff, mostly racing and custom, auto and motorcycle, plus the Big 3 use him for small volume, really custom stuff too, at times).

He made a billet crank for a '71 Midget with an unusual engine, owned by Chris Conrad (in Wisconsin).

A friend of mine is good friends with Greg, and he sent me this awesome video of it running on a rolling road dyno. Note that the shifting is being done at 9000RPM (this particular engine set up produces no power below 4500RPM, its goal is maximum speed at Bonneville). The sound of this engine at speed is really something (be sure to have your volume turned way up to get the fullest enjoyment). The music starts about 50 sec into the video.

http://s361.photobucket.com/albums/oo58/milwaukeemidget/Dynoday/?action=view¤t=MidgetonDyno.mp4

here's another run:
http://s361.photobucket.com/albums/oo58/milwaukeemidget/Dynoday/?action=view¤t=DSCN4472.mp4


I got in touch with Chris and asked his permission to post this here for everyone's listening pleasure, and here's what he told me about this engine:

"The basis for the engine is the 970 Cooper S spec, which has the larger 2.780 bores of the 1275, and a 2.439 stroke. The problem of course, is that the Mini crank and the inline Spridget crank do not have the same flywheel flange, so even if I could have found a 970 Mini crank, and there were fewer than 1000 of them ever made, it would not have worked. As it happens, BMC made a few short stroke 970 cranks for the inline engine, and I mean very few - probably fewer than 30 - and these were intended for Formula 3/Formula Junior drivers running works cars. One recently came up on E-Bay - it needed complete re machining, and went for almost $950.00.

The crank I had Greg build is a billet piece, and it easily weighs about 1/3 less than the stock 1275. The whole assembly is balanced to within a gram, and it is the smoothest inline 4 cylinder engine I've ever owned.

Now that said, the camshaft is an APT scatter pattern unit, and it's intended for engines 1275 and larger, so the car has virtually no acceleration below 4500 rpm. But it's intended for Bonneville, and it's intended to wind tight and wind high.

The plan is to race at the World of Speed event at Bonneville in September."



For the full story, here is a link to the Land Racing forum where Chris recorded his build of this unique car (make yourself comfortable, it is 58 pages long, and covers more than 3 years):

http://www.landracing.com/forum/index.php/topic,4087.0.html

BTW, the wheels are covered with Moon discs, so they look kind of like they are standing still, in the first video.


here is a link I just found with some photos of Greg's work (scroll half way down):

http://amccars.net/cgi/yabb2/YaBB.pl?num=1293734066

in this case, an AMC V8 crank, from a 360 lb piece of bar stock down to a 59 lb finished crank, that is a lot of metal chips to make a crankshaft!
enjoy,
Norm
Norm Kerr

Intresting thread norm.

I have one of the 1000 crankshaft and had it worked over big time, but that said even at 9000 rpm i doulbt it would hold togather long
id be curious how he was able to stablize the block from flexing...

in fact how did he manage to rob all the power below 4500 rpm...Wouldnt that be more of an effect of the transmission and gearing


There are a couple of billit crank shafts producers...they do make them nice...esp with carrilo rods...YAAAA OUCH!!

Thanks for sharing im looking forward to his boonville run

prop

Prop

Hi, Prop -

I'm Chris - let me see if I can address your thoughts.

The reason I've got nothing below 4500 RPM is that I'm using a cam with 310 duration, and a large valve Longman GT head on an engine of 1 liter capacity. The car doesn't come up on the cam until ~4500 or so, but idle and off-the-mark performance is not critical for land speed racing. Producing peak power at the right RPM is.

While inconclusive, my initial dyno runs indicated a peak of 61 hp at the rear wheels between 7500 and 7750, which is pretty close to where I need to be making peak power with a 4:22 differential and 22"diameter tires. The record in the class for this engine size is 121.779 mph. The power curve is right, but I've got to get the overall power up. By being able to rev to 9000 RPM, I can over-rev the engine in 3rd, and fall back onto the power band for the final push through the lights.

As far as keeping the bottom end together is concerned, it's all about keeping the reciprocating assembly as light as possible. I've got the numbers somewhere on my build diary, but I can state that the combination of the pistons and the connecting rods I chose (Saenz rods, J&E Pistons) weigh less than stock 1275 rods alone. The block is a thick flanged 1275 with a strapped center main bearing cap, and relieved casting and machining marks. The flywheel is a Fidanza extruded aluminum piece, and the entire crank/flywheel/clutch assembly was balanced. If you put your hand on the engine at any speed, you'd likely be shocked as to how little vibration you can detect - it's incredibly smooth.

But key to it all is the stiffness of the crank. The inside of the arc made by the rod journals is actually within the outside diameter of the main journals, the radiuses are very generous, and it's turned from EN40B. Given the short stroke, the light weight of the components, the 2.45 rod-to-stroke ratio, which minimizes side loading of the pistons in the bores, and the fact that I chose to use standard width bearings, rather than going with narrower crank and rod bearings, I really don’t think I’m going to encounter a lot of flex or vibration. Here’s a link to a picture of Greg’s work at Ro-Dy

http://i361.photobucket.com/albums/oo58/milwaukeemidget/970%20Spec/DSCN4289.jpg

As far as durability, I can't say yet. But let's look at the application. If this were a regular club racer, one would be on and off the throttle for hours over a season. You're stressing the thrust bearings in both directions as you accelerate and decelerate, up shifting and down shifting, possibly missing a shift in the heat of battle and floating out your valves, and you run the risk of momentary oil starvation on hard turns.

At Bonneville, you coax it up to speed and then run it flat out for about a minute and a half in 4th – about 7800 RPM, I hope. I’m only touching 9000 at the top of 1st, 2nd and 3rd. Yeah, it's hard on an engine, but I would argue less taxing on the bottom end and reciprocating assembly than road racing.

Now with all of that said, I don't know for sure how it’s going to hold up - I'll know better next September, but I feel pretty confident about durability. It’s all a grand experiment.
Parts, hearts or a record - something is going to get broken.
C.A. Conrad

Prop
You do not have one of the 1000 short stroke formula junior cranks.
You have one of the en40 1275 cranks iirc.
Rare but not that rare

Chris
Cool project!!
Fun to see a car usualy setup for racing go for top speed only.
Have not read you other thread yet so might ask a silly question.
Why not go the 1380 long diff route?
Less rpm needed so les critical on volumetric effeciency.
Or do rules dictate a certain engine volume?
Onno K

Hi Chris,
unfortunately, the photo bucket link doesn't seem to work.
After deleting the end of the string, I was able to see your album, but after searching through the 9 pages wasn't able to find one of the crank.


Norm
Norm Kerr

Norm,

If you copy and paste the link into your browser it works fine, nice looking crank. The embedded space %20 screws up the link.
David Billington

You have to copy and paste the Photobucket link.

That said, WOW. I'd really get the willies standing that close to an engine doing WOT on the dyno. Seen too many vids of them exploding, thanks to YouTube. :-)

But that crank is a work of art, and Chris, I wish you all the best on your record attempt! Fantastic work.

-:G:-
Gryf Ketcherside

Cool. Keep us posted on the progress and outcome please.
Alex G Matla

Nice crank but have you seen this...
http://www.swiftune.com/Product/972/swiftune-dc5-crankshaft%2c-conrod-and-piston-set.aspx
to bad it is not for an inline engine
Onno K

Hi, Onno -

The classes for Bonneville dictate engine displacement. I'm running in the I/GT class.

"GT" is for two seat production cars with no aero modifications or supercharging permitted. "I" indicates engines between 754 and 1015 cc's with stock port configuration. A 1380 would run in the "H" class, where the record is 145.760 mph.

There is simply no way to push a car as aerodynamically challenged as a Midget to that kind of speed with a 5-port head. Additionally, I'm not sure I'd want to drive a car with this short of wheelbase at that kind of speed.

I went the 970 direction to get the bigger valves of a 1275 without having to notch a 948 block.

I've seen the swift tune crank, and on a larger displacement engine with heavier rods and pistons, it would probably be an excellent choice.

Gryf, I do have a ballistic blanket around the clutch and flywheel assembly.

I'm not sure why this forum won't give me a link when I post for pictures, but I'm on photobucket as milwaukeemidget, and all of my photos are free to access. Feel free to grab one, if you like, but if you use it elsewhere, I'd appreciate an acknowledgement.

Tanks for everyone's interest. It's a fun project.
C.A. Conrad

As I've successfully used an 8200rpm limit on a 1380 with a standard (balanced)EN16T crank for a few seasons without problem - The crank did break eventually after about 70 races...

a reliable 9000rpm on a steel short stroke 970 S spec engine should be easily attainable - I would be aiming for closer to 10000rpm on that spec - that is what the FJ racers would have had to use to keep up with the Ford MAE engines...

JB

James B

And they did.
Have heard tales of ridiculous out puts and usable rpm ranges over 10000rpm!
And have seen a 970 mini on zandvoort go to 9500rpm sounded great as well.

The trick seems to be lose as little power as possible.
Might a straightcut gearbox be worth the investment?
Or do rules prohibit those aswell?

Again love the project hold the octagon high!
Onno K

Onno -

The rules permit me any transmission I want to use. I'm sticking with the ribcase for the time being.

A trick a lot of the racers use is to go with automatic transmission fluid and plumb a cooler into the transmission case, which seems to be typically good for another 2 to 3 hp on the chassis dyno. Durability is important, but you're shutting it down in less than 3 minutes.

As to how high it actually needs to rev, I only need it to be on the power band when I shift from 3 to 4, where the revs drop about 2400 rpm. So from 9000 to 6600, and keep coaxing it along to about 7800.

I've been told it's not quite as easy as that, but that's the theory behind it.

Yes, holding the octagon high. BMC has a long history on the salt flats. I can't think of a single factory backed racing effort that has held more records at Bonneville than Austin Healey and MG.

I am following in the footsteps of giants.
C.A. Conrad

The straight cut gear set goes in the ribcase without mods and is not that expensive.
Should limit the drive train loss
Check www.magicmidget.co.uk
Onno K

This thread was discussed between 02/12/2011 and 04/12/2011

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