Since Joe mentioned talking to me I figure it's okay for me to chime in and add a few comments.
Prof. Taylor's similar engine rule states that two engines, identical other than stroke will make about the same peak power at about the same mean piston speed. Prof. Taylor managed the MIT Sloan automotive labs from the thirties to the sixties and wrote the two-volume 800-page tome, The Internal Combustion Engine in Theory and Practice that I consider the engine designer's "bible".
Some of you may not be familiar with this term, but it's an excellent and easy to calculate way to compare any two engines even if they are of substantially different size and configuration like lawnmower engines and large two-stroke turbocharged marine diesel engines that power cargo ships and tankers.
Mean piston speed is simply double the stroke, in feet, times RPM. If your 327 makes peak power at 6000 which is 3250 feet per minute, then Taylor's Rule says increasing the stroke to 3.75" with no other changes will make about the same peak power at about 5200 RPM.
The higher an engine's peak power mean piston speed, the higher the specific output. The current limit is about 5200 FPM, which is typical of NASCAR Sprint Cup engines and F1 engines before they got rev limited and turboed in the last few years, and it's pretty amazing that a large pushrod V8 can peak at the same mean piston speed as a small DOHC 32-valve V8. Maybe pushrods aren't so bad after all! The LS7 is running 4700 FPM at the 7K redline, which is higher than any production engine other than a handful of exotics!
Commercial engines that are designed to operate at or near full output most of the time run at much lower mean piston speeds. Big rig diesels that typically have 6" strokes are usually governed at 1800 RPM. You can do that one in your head - 1800 FPM. The largest marine diesel I know of has a bore of about three feet and a stroke of about seven feet. It can be configured with 5 to 14 inline cylinders and makes about 7000 HP per cylinder at 100 RPM. Typical cruise is about 90 RPM for about 15-16 knots, and the mean piston speed is 1260 FPM. Cruising on the freeway in a 327 runnning at 3000 is only 1625 FPM, and they are no where near maximum available power at that engine speed, so they are relatively loafing.
I don't think Joe mentioned this, but the ...657 block has bearing retention notches for both main bores sizes. The transfer line must have broached both notches before the main bearing bores were machined. You can see them in photo #5, so all that's required is align boring to the larger size, and any competent machine shop should be able to do the job. That's a very nice feature that is unique to the '67 model year. It's even easier to stroke a 350 because you don't have to align bore, but you should still use a "stroker rod" and carefully check for adequate block and cam clearance.
Joe used a roller cam, but my choice along with massaged heads would be the McCagh Special camshaft, maybe retarded a few degrees for an original 300 HP engine and the massaged heads along with the L-46/82 cam for an original L-79.
...great article, Joe, and hats off to you for your excellent research, block clearancing work, and documentation of the project!
I LOVE CHEATER MOTORS!!!
Duke
Prof. Taylor's similar engine rule states that two engines, identical other than stroke will make about the same peak power at about the same mean piston speed. Prof. Taylor managed the MIT Sloan automotive labs from the thirties to the sixties and wrote the two-volume 800-page tome, The Internal Combustion Engine in Theory and Practice that I consider the engine designer's "bible".
Some of you may not be familiar with this term, but it's an excellent and easy to calculate way to compare any two engines even if they are of substantially different size and configuration like lawnmower engines and large two-stroke turbocharged marine diesel engines that power cargo ships and tankers.
Mean piston speed is simply double the stroke, in feet, times RPM. If your 327 makes peak power at 6000 which is 3250 feet per minute, then Taylor's Rule says increasing the stroke to 3.75" with no other changes will make about the same peak power at about 5200 RPM.
The higher an engine's peak power mean piston speed, the higher the specific output. The current limit is about 5200 FPM, which is typical of NASCAR Sprint Cup engines and F1 engines before they got rev limited and turboed in the last few years, and it's pretty amazing that a large pushrod V8 can peak at the same mean piston speed as a small DOHC 32-valve V8. Maybe pushrods aren't so bad after all! The LS7 is running 4700 FPM at the 7K redline, which is higher than any production engine other than a handful of exotics!
Commercial engines that are designed to operate at or near full output most of the time run at much lower mean piston speeds. Big rig diesels that typically have 6" strokes are usually governed at 1800 RPM. You can do that one in your head - 1800 FPM. The largest marine diesel I know of has a bore of about three feet and a stroke of about seven feet. It can be configured with 5 to 14 inline cylinders and makes about 7000 HP per cylinder at 100 RPM. Typical cruise is about 90 RPM for about 15-16 knots, and the mean piston speed is 1260 FPM. Cruising on the freeway in a 327 runnning at 3000 is only 1625 FPM, and they are no where near maximum available power at that engine speed, so they are relatively loafing.
I don't think Joe mentioned this, but the ...657 block has bearing retention notches for both main bores sizes. The transfer line must have broached both notches before the main bearing bores were machined. You can see them in photo #5, so all that's required is align boring to the larger size, and any competent machine shop should be able to do the job. That's a very nice feature that is unique to the '67 model year. It's even easier to stroke a 350 because you don't have to align bore, but you should still use a "stroker rod" and carefully check for adequate block and cam clearance.
Joe used a roller cam, but my choice along with massaged heads would be the McCagh Special camshaft, maybe retarded a few degrees for an original 300 HP engine and the massaged heads along with the L-46/82 cam for an original L-79.
...great article, Joe, and hats off to you for your excellent research, block clearancing work, and documentation of the project!
I LOVE CHEATER MOTORS!!!
Duke
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