I was reading in Chevy High Performance they were talking about how hyper-square motors are very efficient and used in F1, IRl and so on. I had no clue what that means, CZ28's Finest want to chime in on this subject?

 

I'm just the moderator, not a "CZ28 Finest", but I read the same article....

Darin Morgan explains it pretty clearly in the sidebar you read in the magazine.... "hyper-oversquare" means the cylinder bore is twice the size of the stroke. He also explains why its good.... lower piston velocities, less windage, smaller crank counterweights, decreased rod angularity, shorter deck heights, and a cleaner induction package. The shorter deck height puts the valve train closer to the deck - less mass, more RPM with less valve train resonance and flex. Works great on a Formula 1 engine that can be revved to 18,000rpm.... but its not a practical approach for a "street" engine.

And remember... with a 4+" bore limitation on a SBC, you'd be talking about a 2" stroke, and now you have limited displacement to about 200 cubic inches. That's why Darin can't use it on his 500ci Pro Stock engines ("If I could that in a Pro Stock motor, I'd do it overnight")..... you'd need a block big enough to handle a 5.4" bore.

 

Current 2.4L V8 F1 engines can be 2.46:1 Bore/Stroke ratio with a 98 mm bore. At 20000 rpm that's a mean piston speed about 5200 ft/min. A 3.60 stroke Pro Stock @ 10,000 has a mean piston speed of about 6000 ft/min. According to Jason Line, the inertia loads resulting from that rpm and stroke and minimum piston, etc. weights are the limiting factor for max rpm.

 

thats why I relaly like the little 302ci chevys..

4" bore with a 3" stroke makes for a lot of rpm...I would turn 7,700 with the stock dontov 3030 cam.....fun stuff

 

Now make that a 4.185" bore and you are getting someplace!

FWIW GM does have a short deck SBC race block. 8.2" deck height, large bore capable as well. It's good for those guys who want to run Trans Am or Comp Eliminator motors that are low 300 cubes. You can then run something like a 4.185 x 2.80 setup, that's about as crazy as you get really.

Bret

 

I personally like the Olds 403 motor with it's 4.351x3.385 dimensions. I first got introduced to them when I had my 79 T/A. Making a lot of power with them takes a lot of work though with the oiling system and main web shortcomings. I like the fact you can run Olds BB heads with it

 

This is just for curiosity's sake, but does the article mention anything about what point a motor crosses over from "undersquare" territory into "hypersquare" territory?

 

It's prolly when the bore > 2x stroke, but it's more than likely subjective... like when does a 'fast car' reach 'really fast car' status.

 

Hey Bret,

Do you have any idea what those blocks cost? I hesitate to ask, my checking account may die of shock.

Sounds like the perfect platform for a low cube SB2.2.

Jeremy

 

Conventially. "undersquare" means bore is smaller than stroke or Bore/Stroke <1. (B/S is usually spoken of as 'bore-to-stroke ratio')

"Square" meand Bore = Stroke or B/S =1

"Oversquare" means Bore is larger than stroke or B/S >1

In the case mentioned, "Hyper-square" means B/S => 2

Typical B/S ratios:

NASCAR Cup 1.28:1

Pro Stock 1.31:1

Olds 403 1.285

350 SBC 1.176:1

302 SBC 1.33:1

4.8L LR4 1.156:1

5.3L LM7 1.04:1

5.7L LS1 1.076:1

6.0L LQ9 1.10:1

7L LS7 1.03:1

F1 2.46:1

 

I seen that a 3.8L V8 was running like 12,000$. The size of the pistons and such are subjective to it.. depends on the block that is used. I mean lok at the 5.7L V12 motors... pretty high reving, and they have displacement...

 

Surely you jest. Respect +1

 

LOL! Thanks, but it's a BIG reservation with heap-many smart fellas "Injuneering" things. Those Pro Stock engine builders leave me in awe.

 

I thought f1 was limited to 93mm bore or about 3.6"?

 

96-98mm bore, 98mm is the max