Engine and Transmission Tech

tips, technology, tools and techniques related to vehicle driveline components

Go to Thread: PreviousNext
Go to: Forum ListMessage ListNew TopicLog In


Moderator
Curtis Jacobson
Portland Oregon
(4533 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Destroking a BOP 215
Posted by: Moderator
Date: June 23, 2022 01:45AM

Reducing stroke is a time-honored way to meet racing class restrictions whilst achieving superior volumetric efficiency.

Most famously, Jack Brabham won the 1966 Grand Prix World Championship with Buick and/or Olds 215s destroked and otherwise modified by Repco to 2.5 liters.

There's quite a lot of anecdotal evidence that destroking Buick and Olds 215s was common practice in multiple forms of racing during the 1960s. I've just done a quick Google search, and found mention of destroked 215s for SCCA sports car classes (probably to 3.0L), for Midget open-wheel dirt track cars (to 2.5L), and also for hydroplanes. But I'm curious to find more specific information.

- Can you guys help me document any specific examples of destroked 215s from that era? (By whom? To what displacement? For what racing series and class? Was the exercise successful? Etc.)

- What are your thoughts about the technical issues? (How much can you realistically reduce a factory 215 crank's stroke via offset grinding? Would it be practical to "weld" the crank for even less? What other tricks or techniques might facilitate success results?)


mgb260
Jim Nichols
Sequim,WA
(2270 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Destroking a BOP 215
Posted by: mgb260
Date: June 23, 2022 02:18AM

Curtis, I think the 62 Mickey Thompson Indy motors were destroked. The Brabham 3 liter Olds v8 was also destroked. Looked everywhere for bore and stroke specs?

[www.macsmotorcitygarage.com]



Edited 3 time(s). Last edit at 06/23/2022 02:40AM by mgb260.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6261 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Destroking a BOP 215
Posted by: BlownMGB-V8
Date: June 23, 2022 08:37AM

If there was a forged crank available it was probably quite practical to weld up and destroke the crank to whatever you wanted. At 2.8" it was a short stroke crank to begin with.

Jim


mgb260
Jim Nichols
Sequim,WA
(2270 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Destroking a BOP 215
Posted by: mgb260
Date: June 23, 2022 12:37PM

Curtis, If you offset grind to a smaller journal these rods would work. Have to figure compression height for pistons.

[www.ebay.com]


Dan Jones
Dan Jones
St. Louis, Missouri
(278 posts)

Registered:
07/21/2008 03:32PM

Main British Car:
1980 Triumph TR8 3.5L Rover V8

Re: Destroking a BOP 215
Posted by: Dan Jones
Date: June 26, 2022 06:46PM

> also for hydroplanes

De-stroked (and sleeved for smaller bore) Buick 215s were used in the the 2.5L A-class hydroplanes:

[www.vintagehydroplanes.com]
[www.vintagehydroplanes.com]

Buick 215s were much more popular in the 225 cubic inch N-class:

[www.vintagehydroplanes.com]

Stroked Buick 215s were also run in the larger displacement E and F classes.

> whilst achieving superior volumetric efficiency

Don't get hung up on VE. It's a mathematical equation and largely irrelevant. The only reason racers de-stroke is to meet class rules, often to get a more advantageous weight break.

> I think the 62 Mickey Thompson Indy motors were destroked

That's incorrect. Mickey Thompson's Buick Indy car engines displaced 256 cubic inches (3.625" bore by 3.1" stroke). The May 1970 issue of Hot Rod magazine ("Inside Buick's Back Room") states a re-worked factory iron crankshaft was used in the 1962 entry as there wasn't time to develop and manufacture a steel forging:

[wildaboutcarsonline.com]

Lance Reventlow's Scarab sports racer was also stroked (3.56" bore by 3.0" stroke) for 239 cubic inches. The Brabham-Repco BT-19 engine was a 3.0L (183 cubic inches) with 88.9 mm (3.5") bore and 60.3 mm (2.374") stroke.

Dan Jones


MGBV8
Carl Floyd
Kingsport, TN
(4320 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: Destroking a BOP 215
Posted by: MGBV8
Date: June 27, 2022 09:11AM

Great info, Dan. I was not aware of the hydroplane use.


Sorry, only registered users may post in this forum.