700hp 300ci pushrod V8 race engines how do they do it?

[e21jps]

There is a class of circuit racing here in aus that uses a conventional gm or ford derived v8 They have a few engine limits like 18 degree parralel valves 10:1 comp 7500rpm and pump fuel along with component weight limits for crank, pistons and rods to eliminate exotic materials like Ti. I think valve train is open but the rev limit takes care of that. Yet they mak in excess of 700hp.

Of course getting a look at some heads is difficult because all the teams start with a blank casting and cnc everything from the chambers to ports and even spark plug holes and keep there designs quite secret. Intake is ITB injection.

How do the experts here think they do it because given the limitations they make far more power than they should and bare in mind these are circuit race engines with lots of flexability too not drag race engines. I know this can only lead to a lot of speculation unless someone working in the industry is willing to share but im really interested to see how people think they achieve this with regards to cam and head.

Most interested to hear thoughts on port and valve sizes and cross section area/velocity specifications etc.

 

[Lou Scannon]

Well, among other things, large quench area and relatively low compression ratio create conflicting requirements for chamber geometry.

 

[patprimmer]

If we stop hijacking this thread with bullshit and get back to the being relevant to the OP, that was about a quite high octane fuel AND NA, relatively low compression by class rules.

It is also a class where there is plenty of room for deep dish pistons if required and plenty of budget to pay for them.

Regards
Pat
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[FahlinRacing]

Forgive me as the question was farther off topic than I first thought since we were speaking on combustion.

Pat, why would this N/A class want a deep dished piston in the cylinder rather than a flat crown?

 

[patprimmer]

By having a small chamber, a plug as close to centre as possible and a small beep dish in the centre, you keep the shortest possible flame travel path. From a flame travel point of view, a spherical chamber with the plug at the centre is ideal although obviously also impossible.



Regards
Pat
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[FahlinRacing]

So more or less we are just containing the burn directly over the piston in this case. Are the heads located in the center as well then?

I am sure there must be a lower valve angle and possibly a canted arrangement within the head design.

 

[Lou Scannon]

FahlinRacing, more information needed. Can you perhaps explain in terms of force vectors on the piston/valves/chamber?

 

[BrianPetersen]

Fahlin, what do you mean by "heads located in the center"?

4-valve pentroof cylinder heads have the spark plug dead center. Two-valve engines of the type discussed in the original post cannot have the spark plug dead center if you want valves that are as big as possible, which you do. There is a balance between valve arrangement and combustion chamber shape and spark plug location that has to be struck.

 

[patprimmer]

FahlinRacing

That most certainly is not what I said. Did you not see the part about shortest possible flame travel.

In the class rules, pistons are free. Cylinder heads are restricted to some extent.

http://www.v8supercars.com.au/technical/tabid/1269/default.aspx

Regards
Pat
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[FahlinRacing]

Sorry Brian, thinking one thing and typing another. I mean't to say chamber in the head. Pentroof is of course placed directly over the piston as the wedge style chambered heads are offset.

Pat, I didn't miss anything. What I was thinking was with a small chamber and a dished piston, however large it may be. The majority of our burn would be positioned within this crown area. Although not all the combustion would be contained to the space. Maybe my assumption is off. I didn't know the pistons were subject to no-limit to a certain design or if they utilize a squish & quench band around the cylinder or in specified areas.

Thanks for the link. I see the valves must be left in the original position for whatever approved head is used, but can be enlarged if needed. They can have a free for all on chamber mods. I never really looked this indepth for this type of racing, its pretty wild.

Hemi, I will have to say no I can not.

I have not seen any photos of these heads btw. Are the ports raised at all?

 

[izzmus]

One of the things Larry Widmer has constantly pointed out is the piston top is the bottom of the chamber and shouldn't be ignored. With that in mind, a flat top piston makes about as much sense as a flat combustion chamber.

 

[pontiacjack]

Actually, there are MANY ways to skin a cat in this crazy infernal-combustion arena. My little 500cc Moto Guzzi pushrod twin DOES have a flat "chamber"- the so called Heron head design. Yet it's quite powerful (49 HP peak), with a very broad torque curve. This is a totally stock grocery-getter machine making about 1.63 HP/c.i.- I can easily envision a "race" version of it meeting/exceeding the 2.33 HP/c.i. that this thread is concerned with.

 

[pontiacjack]

Oops- the original post mentions an 18 degree inline valve rule, which eliminates any consideration of a zero-degree Heron head.

So... I apologize for "hijacking" the thread...