700hp 300ci pushrod V8 race engines how do they do it?
700hp 300ci pushrod V8 race engines how do they do it?
(OP)
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.





RE: 700hp 300ci pushrod V8 race engines how do they do it?
What fuel are they required/allowed to run? "Pump fuel" is somewhat nebulous. Amazing things you can find coming out of the pump, some places.
A NASCAR tech had an interesting viewpoint with regards to making more power. I can't find the quote (or the speaker) but in a nutshell, he said that they were supplying enough fuel to make over 2000hp but various losses meant that only 850-900 actually make it to the flywheel, so a large focus in their effort is reducing those losses. A 1% gain in efficiency is enormous.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
Mike Halloran
Pembroke Pines, FL, USA
RE: 700hp 300ci pushrod V8 race engines how do they do it?
I believe the drag race engines making that power 40 years ago had very narrow power bands, no limitations on CR or maximum rpm or fuel and had engine life measured in minutes not days so not exactly a relevant comparison.
I expect there is a lot of development around maximising flame speed so later ignition timing can still obtain peak cylinder pressure at around 12 deg ATDC
I believe there has been a trend toward bigger inlet valves at the expense of exhaust. Last I heard it was 2.08 and 1.65. That required moving the valves toward the exhaust side of the chamber. I don't know how much further it has moved in that direction since, but I guess maybe 2.1 or 2.125 ish with 1.55 ish to give exhaust flow around 60% of inlet flow rather than 65%. There used to be a trend to just get about 65% of the inlet flow you oped for on the exhaust, then get as much as yo could with the inlet and forget exhaust. I expect they now try to get more out of a smaller exhaust valve so they can use an even bigger inlet valve.
I believe or suppose they have tended toward smaller chambers with smaller area but deeper dishes in the pistons to give the required CR with maximum squish and the most compact chamber possible to keep the bulk of the charge as close as possible to the plug with a minimum of flame path obstruction in the chamber.
I also expect they pay a lot of attention to bore finish and maybe some teams eve use a Nikosil treatment of the iron bores. I know a company in Melbourne was intending to gear up to do that on iron V8 blocks. I also expect they use very narrow low tension rings.
I would expect despite the 7500 rpm limit they still use light weight titanium valves so they can run lighter springs or ore aggressive acceleration rates on the cams.
I also suspect they work on ways to trick the rev limit.
Regards
Pat
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RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
300 cubic inch = 5 litre displacement, so we are talking 700 hp from 5 litres = 140 hp per litre.
At 7500 rpm, this would require almost 100 lb.ft of torque per litre of displacement.
A "normal" naturally-aspirated two valve per cylinder engine running on gasoline is usually in the 60 - 65 lb.ft of torque per litre of displacement (I know it's an odd set of units, but it is what it is), a good one is in the 70 - 80 lb.ft range (1000cc sport motorcycle engines are around 80, and those are DOHC 4-valve, but fully emissions-legal and noise-legal), and very well tuned racing engines may be around 90 lb.ft per litre, but this takes exceptionally good intake pulse tuning and ramming effect, and it's bound to be in that range only in a narrow RPM band.
100 lb.ft of torque per litre under the conditions given, sounds outside the plausible range to me, unless fuel chemistry is in play, since fuels other than gasoline will act differently. Ethanol makes more power than gasoline. Toluene, likewise.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
Smaller might refer to certain areas only and volume, but maybe not the areas found to be the most restrictive.
Notching the block aside as that is a very very old trick, if they reduce exhaust valve size and/or move the exhaust valve toward the bore, they have more space for the inlet valve.
I know they reduced the inlet manifold size when they reduced engine size some years ago but I no longer have the throttle plate sizes that where popular.
Regards
Pat
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RE: 700hp 300ci pushrod V8 race engines how do they do it?
Modern engine blocks are far less flexible than the junk that was around then, which helps reliability. I don't know what engines would be used, though. The current Ford and GM V8s that I am familiar with do not meet those rules, although it's well possible for a "production based" race series to have its own specific components.
Alcohol/toluene as fuel? With a compression limit? I wonder what kind of coolant/oil temps they try to get away with. The last time I paid attention to this type of engine, they were running coolant around 115-120C by design.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
Until you see a dyno run on a trustworthy dyno then 700 hp is just a conversation starter.
Cheers
Greg Locock
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RE: 700hp 300ci pushrod V8 race engines how do they do it?
http://www.youtube.com/watch?v=V0OMCB3qg_w
RE: 700hp 300ci pushrod V8 race engines how do they do it?
I always take advertised or promoted power figures with a grain of salt, especially when coming from bench racers. That being said V8 Supercars make a lot of power considering the restraints put on them. I don't follow their rules and the changes all that closely except where parts or materials might also be of use to me, like good E85 becoming available commonly enough for me to run my toy on it.
I think they use old technology aftermarket blocks like NASCAR. ie GM Bowtie or World Products Little M blocks and equilivent in 4 bolt Windsor blocks for Ford
Last I heard, the blocks have basic dimensions of the late part of last century offerings, but are cast much heavier out of tougher iron.
The heads are pure aftermarket aluminium with substantially different layout re port and valve positions. The Chevies do away with the side by side inlet and exhaust pairs and reduce charge robbing on the inlets and the exhaust layout no longer creates the gasket blowing hot spot between the two centre cylinders.
Regards
Pat
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RE: 700hp 300ci pushrod V8 race engines how do they do it?
Understanding airflow, parts selection, engine assembly, combustion, fuel prep and valve timing are just a few things to consider.
The only things that make 'secrets' are just because one person hasn't found the same thing or similar on his/her mill, yet. If everyone had a flowbench, dyno etc, I think there would be more highly knowledgable gearheads due to their extensive researching.
For example of oval vs rect. ports. They can flow the same CFM but have a different level of velocity throughout the CSA.
Application is paramount when building any engine.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
I will have to disagree on this. The more efficient you can deliever your fuel and air, atomize your fuel and homogenize your mixture within the chamber. You can make good amount of power without drowning your engine in fuel. Larry Widmer had an article in the 80s titled "Swirl power" with Circle Track magazine.
http://www.theoldone.com/articles/
RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
Also Larry has been known to make explanations somewhat lacking in accuracy at times. The one that springs to mind is "a roots blower does not compress the air, it kind of folds it into the manifold".
Regards
Pat
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RE: 700hp 300ci pushrod V8 race engines how do they do it?
As for Larry's explanations, whatever they may be, swirl power, I used as an example of why mixture motion is needed. We can have two chamber sizes and still produce good HP & TQ numbers through a complete burn.
The better we atomize and vaporize our fuel the LOWER our fuel consumption is in turn more power present from every drop of fuel employed into our airflow stream or chamber itself also equalling lower BSFC. Anyone can build an engine that uses a lot of fuel and hopefully ingest adequate air as well to burn. Perhaps I just thought his statement was too much of a 'blanket' IMO.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
If you think top A fuel, blowers and turbo chargers etc., and of course you can't dump fuel in and hope to burn it without proper atomization and a correct ratio of oxidizer.
Most all that are regulars here know those basics you mention.
In most highpower applications it is desired to make the mixture fat, for detonation suppression. This disscusion was about a racing engine, not a high milage economy engine.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
Anyone have experience on this aspect?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
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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RE: 700hp 300ci pushrod V8 race engines how do they do it?
Pat, why would this N/A class want a deep dished piston in the cylinder rather than a flat crown?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
Regards
Pat
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RE: 700hp 300ci pushrod V8 race engines how do they do it?
I am sure there must be a lower valve angle and possibly a canted arrangement within the head design.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
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.
RE: 700hp 300ci pushrod V8 race engines how do they do it?
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.
htt
Regards
Pat
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RE: 700hp 300ci pushrod V8 race engines how do they do it?
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?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
RE: 700hp 300ci pushrod V8 race engines how do they do it?
So... I apologize for "hijacking" the thread...