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.

 

[izzmus]

Drag engines were in this vicinity ~40 years ago, with fewer restrictions but also 40 fewer years of refinement and the attendant technology updates along the way.

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.

 

[MikeHalloran]

I assume there is no requirement that the engines idle at an rpm that would be appropriate for a street engine. That may be a clue.

Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I believe they run a special race and controlled E85 which is I think 85% ethanol and 15% toluene. It would certainly benefit from substantially higher compression, like 13:1. Are you sure they retained the 10.5 rule when they moved from 95 ( I think from memory) octane controlled pump fuel.

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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[e21jps]

Its true thay have recently (couple of years ago) moved to e85 fuel but before that they were required to run 98oct PULP i think the power didnt change much at the time. The rev limit is the killer! As far as tricking it goes thats impossible they run a controll MoTec ecu and every race is logged so the scrutineers can check such things. Valves are big so much to relieve the bores a little, roller follower and Ti. valves are the norm but all thats mothing new or uncommon these days, ive been told durations are about 270@050 but again nothing you wouldnt expect, Im more curious about the intake ports there must be some interesting and innovative designs there. Again going from what ive heard they are a lot smaller than one would immagine but the million dollar question is how small?

 

[BrianPetersen]

Back of notepad plausibility check

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.

 

[patprimmer]

No one is going to tell you their port sizes.

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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[izzmus]

Pat, that's exactly what I'm talking about. First you make the power, then you figure how to make the power more usable and durable, and with tighter constraints.

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.

 

[GregLocock]

Um, aren't you taking the rather hysterical first post a little too seriously? Work out the VE. If it is greater than 120%, then give the numbers the boot.

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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[e21jps]

My point exactly.... if you do the sums it doesnt add up, I believe the hp claims are not too inflated one of the teams ran a 1/4 mile promo run last year and for a 1400Kg (3000lb) car that has 500lb rear & 1100lb front springs, rock hard circuit tyres and a 2.5 first gear they still did 10.8 @ 135mph... that doesnt happen on anything less than the sort of power they claim to have

http://www.youtube.com/watch?v=V0OMCB3qg_w

 

[patprimmer]

Greg

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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[FahlinRacing]

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.

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.

 

[dicer]

The main things that are done as mentioned above are, trying to get as much fuel and oxidizer as possible into the combusiton space, and extract as much energy possible from it. More fuel/air and more speed means more power. Its just that simple.

 

[Toddr8541]

Does anyone have any more details on the blocks and heads and rules for these cars. I know the fine details will be left out for obvious reasons but maybe some generalities. For example do what range of stroke or bore do they use.

 

[FahlinRacing]

...trying to get as much fuel and oxidizer as possible into the combusiton space, and extract as much energy possible from it. More fuel/air and more speed means more power. Its just that simple

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/

 

[BrianPetersen]

^ That statement is not in disagreement. Those factors are part of "extract as much energy as possible from it". A good fast-burn combustion chamber is part of what's needed to do that. Good site, by the way.

 

[patprimmer]

Like Brian says.

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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[FahlinRacing]

Yes, we put as much fuel in our charge *within reason* to extract the most energy possible. But, we do not dump fuel into our engine a hope we burn it regardless of chamber size. Efficient combustion relies on a air/fuel ratio to produce good power without hurting the engine due to wall wash as one example.

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.

 

[dicer]

My more fuel and air statement was a simplification.
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.

 

[FahlinRacing]

When forced induction introduced, its been said that removing the quench area(s) is needed in order to operate the engine when boost pressures are present to make the power they do.

Anyone have experience on this aspect?