74' Turbo Offy specs?

[aurfalien]

Hi.

I'm curious if the community knows the turbo size for the 74' McLaren which uses the turbo Offy.

I can't seem to find particular specs regarding the turbo size.  It  looks big so perhaps 4" - 6" or so?

[Ace-Garageguy]

Try search terms like "1974 McLaren 16C", and "159 cu.in. Offy turbo 1974", or combinations and derivatives.

Somewhere, there's an article that will call out what the brand and basic number of the turbo is, and from there, you can search the specs for that particular unit.

At least, that's how I'd approach it.  

[aurfalien]

Hi and thank you sir.

This Offenhauser fellow (I feel like saying Professor Offenhauser) was a fascinating gentlemen.

I would have enjoyed sweeping up his shop to absorb his knowledge and experience.

[Art Anderson]

On 6/9/2018 at 7:50 PM, aurfalien said:

Hi and thank you sir.

This Offenhauser fellow (I feel like saying Professor Offenhauser) was a fascinating gentlemen.

I would have enjoyed sweeping up his shop to absorb his knowledge and experience.

Brian, from my Indy Car modeling days (and 1974 was right in the middle of that),  the Turbo in the AMT Mclaren kits is pretty danged close, if not spot-on, to scale.  Of course, for 1974, the Mclaren M16D Indy Car had a 10" extension collar between the engine and the transaxle, which provided clearance for that "underslung" turbocharger, which does make a difference--an easy part to make and install.

 

Art

[aurfalien]

Hi Art and many many thanks for this info.

[Art Anderson]

18 hours ago, Art Anderson said:

Brian, from my Indy Car modeling days (and 1974 was right in the middle of that),  the Turbo in the AMT Mclaren kits is pretty danged close, if not spot-on, to scale.  Of course, for 1974, the Mclaren M16D Indy Car had a 10" extension collar between the engine and the transaxle, which provided clearance for that "underslung" turbocharger, which does make a difference--an easy part to make and install.

 

Art

I said Underslung, but that was the way turbochargers had been set up on Offies from 1968 forward.  On the 1974 M-16c Mclarens, in order to lower the center of gravity a fair bit (those turborchargers are actually quite heavy), they decided to mount the turbo "overslung", that is, with the hot exhaust gas inlet being above the body of the turbocharger, which placed the unit directly in between the rear of the cam towers and the framing for the rear suspension, so that 10" extension "collar" was designed, and machined in forged aluminum to give the needed space.  To trim as much weight as possible,   a fair amount of metal was milled away on the outside, between the bolts holding it to both the Offy flywheel housing,  and the suspension bulkhead (remember, with McLaren, as with the Eagle Model 6, the engine and transaxle served as a part of the chassis, bearing the weight, torque reaction,  and the stresses of corning speeds at the Indianapolis Motor Speedway, where lap speeds were approaching the 200-miles per hour milestone.    Those Turbo-Offy engines were overall a charcoal grey metallic in color, with the cam covers being the same color (still raw cast iron & cast aluminum, with the finned crankcase side cover plates, and the water jacket covers being raw cast aluminum.  On the tub, for 1974 and onward, USAC mandated just 60-gallon fuel capacity, and eliminated the right side fuel tank altogether, requiring that space to be filled with an energy-absorbing material, and on the actual car, just one fuel filler plug, and that appears on the left side of what on the model kit, is molded as if it were merely a head-rest (in reality, that was the so-called "seat tank", to which an electric fuel pump pushed the ethanol fuel from the left side fuel tank.  What AMT made, and look like fuel filler plugs that they engineered to be glued to the outside of the left side of the tub, In reality, slightly recessed aluminum plates, black anodized, which were the access points for inserting the puncture-proof rubber fuel "bladder" into the box-section monocoque chassis sides (left from 1974 onward,  on both sides on the McLaren M-16's from their introduction in 1972  through the disastrous 500 mile race of 1973.

A review of the numerous photo's of this car, and it's 1975 successor,  can guide you to the correct shape and length of the nose cone, and also the much narrower rear wing  (AMT did this one as a cheaply done follow-on to their 1973 McLarens (the ones in Penske Sunoco colors), which is pretty far off.  This is a very good walk-around video of the actual car, which is now part of the Indianapolis Motor Speedway Hall of Fame Museum collection   

 

Art

Edited June 20, 2018 by Art Anderson

[aurfalien]

Hi,

What a lovely video, thanks for posting.