[boodlefoof]

Originally Posted by Stan Weiss

This is the piston acceleration of a 4.12" bore, 4.3" stroke, 6.8" rod against a 4.15" bore, 4.21" stroke, 6.625" rod.

Stan

Stan,

Any chance you could run a comparison of these against the piston acceleration of a longer R:S ratio? I'm curious just how big the difference is. The two engines you've mapped there have a 1.57 and 1.58 to one ratio. How different would the curve of a stock 400 with 1.77:1 ratio look?

[Stan Weiss]

I am not sure what you would like to see. The first graph is a 400 ci Red Line and a 455 ci Green Line at 6500 RPM. The second graph is the same thing but the 400 ci is also shown at 7000 RPM Blue Line.

Stan

[GOAT WHORE]

I've read where Smokey said run the longest rod possible and have also read other big name builders that say the only thing they consider when it comes to rod length is that it connects the piston to the crank.
I am just under the impression that it does not matter much in most if these builds.

[gtofreek]

I look at head port size as a consideration also. If the engine is fairly small, and the head ports fairly big[Rec port BBC on a 396, or 4 BBL Ford 351 Cleveland for example], then a shorter rod, can help set up port velocity when it yanks the piston down off TDC faster. If the ports are small[Pontiac for a good example] then a longer rod just makes life on parts easier.

[boodlefoof]

Thanks Stan. I was just looking to see how significantly the piston acceleration at the ends of the stroke slows down with the longer rod ratio.

Goat Whore - you're probably right that it doesn't make a huge difference for most engines, but I'm not letting a little thing like practicality get in the way of a good academic discussion of engine physics!

[ta man]

Originally Posted by Will

Well, that's still pretty streetable and I bet it wouldn't slow down all that much with a 3.23. Still very impressive!

Basic .030 over 455 build here with the 290cfm heads and Old Faithful 3.08 gearing and 3200 Continental Convertor..11.40 at 3900 lbs...very docile street car!

[Firebob]

Been thinking about this for the last couple of days and then while reading the thread on the PowerTrax rear end it occurred to me that I can build a 525+\600lb motor and drop it in the car and most likely be happy for all of about 5 minutes until the rear end exploded, or the clutch flew apart or some other expensive collateral damage happens. Then my little $3K that I put into the motor turns out costing me three times as much. It certainly wouldn't be the first time something like that happened. Not sure where I would gain in that scenario. Gonna have to rethink spending the baby's milk money on a new heart for the car. It's so easy to get carried away when you got visions of tire smoke and time slips running through the back of your mind.

[68azbird]

Geez bob
Why such a Debby downer

[GOAT WHORE]

Just don't run sticky tires!

[AdamIsAdam]

Originally Posted by GOAT WHORE

Just don't run sticky tires!

X2
LOL

[Interceptor]

Just read this. My 400 just went south and it's time to upgrade. Have access to a 455 and a 400 to build, leaning towards camming up a 71 455 with my #13 heads.

Why are the 1970 400 and 455 so closely rated for hp, with the 400 usually being faster in magazine road tests of the day?

[TheGrudge]

I’ve always wondered about that one. Traction is the only reason I can think of. 500 ft lbs 3.31 rear TH400 had to be a pretty snappy performer in its day regardless of the way it was marketed. 70 455 GP supposedly ran 14.19 to 70 455 GTO 15.0??? Doesn’t add up.

[dmac]

Originally Posted by GOAT WHORE

Just don't run sticky tires!

If they aren't sticky, they are spinning, and tires are expensive too!!!!!!!