A 5" x 1" V4 would have a major negative going for it in both F1 (where is wouldn't be legal, but forget that) and production type engines:

At 78.54 cubic inches it would be giving up about 104 cubes in the 3.0L format and about 68 cubes in the 2.4L format. Don't you always say go for the max cubes allowed in the class? Of course if you stroked that engine to 3 inches with the same bore you'd triple the displacement to about 236 cubes which probably would make (a lot) more power than the 78 cube engine.

Most folks reading this board don't have a tough time agreeing that 3 times the displacement will make more power.

Given a displacement limit, what bore/stroke ratio would you choose for a max performing engine? 5:1, 2.3:1, 1.67:1, 1.3:1 or ??? Why?

 

I would choose a bore that works in the block I have and then add enough stroke to use it in an rpm range that makes sense.

If I could do my own block it would be a big stroke small block probably like 4.185 bore and 4.250 stroke with 375 cfm heads that turns around 7000 peak.

Bore/stroke ratio has no real effect on anything unless you hold cubic inches constant.

Bore sets how big your intake valves can be and how many you can have and stroke pretty much determines where in rpm you will make that power at.

 

So you'd choose .985 bore/stroke ratio for a 468 cube engine because "Bore/stroke ratio has no real effect on anything unless you hold cubic inches constant?" That's not how most folks build 468s unless maybe detonation on poor 91 octane is a problem. Interesting out-of-the-box concept.

I'd choose a 4.500 x 3.678 large block for the same cubes with a 1.22 B/S ratio. I think B/S ratio has a real effect. Note that my choice gives about 8100 rpm at the same PS as your 7000.

"Different strokes for different folks." as they say. Thanks for your input.

 

The stroke has an effect on where you make power but the bore / stroke doesn't reallyl Oldstroker unless you are talking about the same inches.

A 2X2 will turn double the rpm of a 4x4 even though they are both square.

 

Oldsstroker,

I also said where I want my powerband (max 7000) at but for unlimted rpm I would go smaller stroke and larger bore. I would need much more info to know what actual dimensions I would use. At 468 I might even go higher in bore and lower instroke than you did especially if it was a 4 valve engine since I could use more rpm at that time but I might even go to a V 10 or 12.

I did not take "max performing" to be boundless because otherwise I wouldn't even stay wih 8 cylinders. Extremely large bores have poor thermo and burn characteristics and lower efficiencies when operated at extreme rpm. It's also really hard to make good pistons that are stiff and seal and last long at huge bore sizes.

 

You are a moving target!

How about this one: A 2006 EMC rules engine that needs to be a "max performer" in the 2500-6500 range at 300-330 rpm/second. Scoring is average torque PLUS average hp in that range.

V8, pushrod 2 valve head, 434.0 cubes max, small or large block, 10.5:1 SCR max, one 4-bbl on a cast manifold, 91 octane pump gas. Those are the basics.

What bore and stroke would you use and why?

 

I would do a 4.300 stroke by 4.000 inch bore to make the smallest chamber possible. I could still run the airfow I needed which at 434 inches and 6500 rpm can easily be achieved on a 4.000 bore with commercial heads. I am still thinking of what I could do with what is really out there. i wouldn't put that in stone though but I have done some very detonation free stuff myself but at 10.5 to one it would be less important now.

 

Interesting. I'd run oversquare with about 80% of your PS. Both of us would require special cranks. It will be interesting to see which way the EMC contestants go.

 

they seem to go a little under square. or like in John Case's bbf engine he found the bore the heads flowed the best at then had a crank made to reace the maximum ci.

 

OH and one more question now. how bad are the negitave effects on an engine when the chamber diameter is larger than the bore. how bad does the lip caused by the chamber hurt the engine. example I have a set of track 1's that the chamber is 4.185 from side to side. what if I put those on a 4.03 bore block. If I had a dyno or $ I would just test it, but I hope one of yall can help.

ps sorry for the side track.

 

It's not good especially if the gasket hangs in there too and can turn into a glow plug. Believe it or not a lot of head porters do that too and it's good in general.

 

If the bore is shrouding the intake at the LEDGE at the top of the block it's not good. Ya need to cut the bore back at this point to relieve the shrouding.

 

I'm not sure that was the design approach.

The static compression limit in the 2006 EMC rules may have shifted the focus from anti-detonation. We'll see.

 

It's not good especially if the gasket hangs in there too and can turn into a glow plug. Believe it or not a lot of head porters do that too and it's not good in general.



DAMN! That's what I meant to say!