NASCAR 302 or 351? Things that make me go hmmmm...

[Unit 5302]

Hmmmm...

I occationally wonder, could a 302 whip the 351 on the high speed ovals? NASCAR forces builders to use a restrictor plate correct? That restrictor plate limits the amount of cfm that can flow into the intake manifold, and therefore, into the engine.

The 351 obviously gets a bunch of power taken away from it's maximum potential, look at the rpm they run on high speed ovals versus other tracks.

My question about is, wouldn't a 302 be able to achive just as much power as a 351 when limited to a certain amount of cfm flow?

The way I see it the 302 has this going for it

• Greater efficiency
• Less restriction of max performance
• Higher rpm capability
• Quicker response

The 351 would retain
[list][*]More displacement[*]Lower rpm reliability[*]and Known potential[list]

I don't think anybody will dispute a 302 is a more efficient motor than a 351, but when is the tradeoff really reached under high powered applications? A greater amount of drag due to longer stroke versus the added drag from from higher rpms. The greater reciprocating mass from larger rods versus greater piston velocity. Could a 302 spinning at say 9000rpm with the restrictor outpower at 351 at 7800rpm?

My personal opinion, I'd like to think the 302 could whip the 351 with a restictor plate, simply because I hate the 351, and I love the 302. Don't ask why, I couldn't explain it if I tried I don't think.

[matt cook]

I think that I have heard that the guys have some leeway on what bore and stroke to run, as long as it comes out to 358, so i think that they tune them to the track a little in this way also. could be wrong. but kinda the same train of thought...

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1982 Mustang GT

[Unit 5302]

From my understanding the engines can be up to 360cid. The Ford 351W is actually 352ci. They named it 351 to avoid confusion with the 352 Y block of earlier years.

The 351 is then bored .030 coming out to 356cid.

[Rev]

What you are saying would be true if CID varied any, or if the restricter wasn't always the same. They all run pretty much the same displacement and the resticter plates are mandated as to diameter of the restricter itself. They don't vary. That makes a pretty even playing field even though I personally don't like to see the engines throttled. They say it's in the interest of saftey, but many think that's debit rather than an asset.

Rev

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

[69fastback]

What about a dohc 5.4? Ford got the cobra R up to 170. It makes me wonder what it could do in a NASCAR like at daytona or talladega.

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69 428 cobra jet: tons of mods.
97 f-150 5.4 xlt mark III
BUCKLE UP. SUCK IT IN.
Objects in the mirror are about to disappear...
QUICKLY!!!!!!

[PGkelly]

Nascar engines are limited to 327 ci. and they are all pushrod, 2-valve V8's. but they run at 9000 rpm

[mustangII460]

A 4 cyl could hold its own when carb plates are used. I cannot remember which series it was but they ran 4 cylinders and were faster at Daytona than NASCAR.

Do not confuse 351w with the motors they run now. It is a variant of a 351C. They went to a Clevland when the displacement changed years ago. Cant beat those big heads.

[Unit 5302]

Well, the 5.4 cannot legally be used in NASCAR due to it having overhead cams.

Engines must be production units (Ford must have a waiver) be no more than 360ci in displacement, be carbuerated, and be of overhead valve type.

Under those rules the 302 could run in NASCAR, but the 5.4 couldn't. If it did run it'd clean house quite frankly.

Seeing as though the restrictor plates are all the same size, they can only flow so much cfm. The total hp they make with the restrictors is around 600, without, 800 if I'm correct. Now, that is 75% power if 800 is the maximum potential of the motor. The 302 is 87% of the displacement of the 351, so if the 351 can make 800, the 302 would have no problems making 600 and being competitive with the restrictor.

You would have to determine whether or not the 351 could create a significant vacuumm effect and pull more air through the restrictor than what it's technically rated for. That would be kind of a reverse ram air. If it can, which would be more effective, the longer slower pull of a 351's greater stroke, or the shorter faster pull of the 302? In my experiance with fluid suction devices, a long slow pull is more effective. If that is the case with these restrictor plates, then the 302 would be at a disadvantage. That is of course assuming the vaccumm created in the intake can actually pull in enough air reliably so as to not throw itself out of balance with the other components. IE: the heads and cam are built to flow 1000cfm and the restrictor is built to flow 900cfm, the 351's vacuumm effect allows for 1000cfm to flow through reliably. Otherwise, the engine wouldn't be optimally matched, right?

Can somebody help me out with the restrictor plate question? If the restrictor plates are flow tested for a certain cfm, can an engine flow more than the max by creating a negative pressure vacuumm in the intake manifold? Would such a vacuumm be reliable, or would it starve cylinders and become detramental? I would assume its no different than having a small carb on a motor, say 369cfm 2bbl. With that 2bbl and everything else being setup for maximum performance could a 351 pull more cfm through the carb than a 302, reliably?

I guess the questions I have are
[list=1][*]Is the friction of the longer 351's stroke less than the friction of the 16% greater engine speed of the 302?[*]Does the greater weight of the 351's moving parts outperform the additional weight from spinning the 302 16% faster?[*]Can the 351 flow more through a regulated cfm restrictor than a 302, assuming both are tuned to flow the maximum cfm possible through the restrictor?[*]Would a 351 spinning at 7800rpm be more fuel efficient than a 302 spinning at 9000rpm?[*]Would the extra inertia inherent to the 351's greater rotating mass overcome the 302's ability to spin faster allowing for a more stable top speed?[/list=a]

Why hasn't the 302 been run at a NASCAR restrictor event to find out?

My thoughts
[list=1][*]No, the 302 is more efficient.[*]No, the 302 has less rotational mass.[*]No, the vacuumm has to balance allowing maximum flow to be roughly the same, especially considering the closeness of the different motors currently run when the motors have different strokes.[*]No, the 302 is more efficient inherently, therefore even with the additional rpm required, it would still be more fuel efficient.[*]Yes, the 351 with the same amount of hp and torque, at the same rpm levels will outperform the 302 in a flat out top speed run on a banked oval track due to greater inertia associated with it's reciprocating mass.[/list=a]

Perhaps the 302 is not run do to needing an additional waiver for a now non-production engine, or perhaps the old idea of "There's no replacement for displacement" rings true to many of the engine builders in NASCAR, or possibly the engine builders have been studying and designing the 351W for so long, they don't consider viable alternatives do to the research and design costs.

BTW, this is the kind of stuff I think about all day long. Jeez... I need some quality summertime with my car. We're supposed to get up to 12" more of that white **** .

[Unit 5302]

PGkelly The Dodge is running the 360 right now, Ford is running the 351, and Chevy is running the 350. Is Pontiac still in the mix? If they are, they are also running a 350. None of the motors being used is under 350cid, sorry but the 327cid maximum is totally false. Also they most certainly do not run 9000rpm's on the high speed oval's. The restrictor plates limit them to about 7800rpm for max power, or at least they did last year. Anyway, this if comparing the two engines on a high speed oval, not an event which doesn't require restrictors, the 351 would beat the 302 in that event due to the increased, wait, no it might not, the 302 has spun up to 11,500rpms at F1 series level, the 351 would never hit greater than 9500rpm at a NASCAR event, which would allow the 302 to have a maximum potential greater than the 351? In fact, I'd say the 302 may outperform the 351 in all races. Hmmmm...

mustangII460 So they are still running canted valves? Interesting, I thought they were running straight up Windsor motors. I don't think the Dodge or the Chevy has canted valves, which would seem to be a huge advantage to Ford in races that do not require the restrictor plates. That seems strange, even so, the Boss 302 had the same, actually better heads than the 351C's so it would wash out to still being 351 vs 302.

[This message has been edited by Unit 5302 (edited 02-24-2001).]

[Mach 1]

Man, you have way to much time on your hands....lol.

Unit 5302: Pontiac is still in the mix - sort of. The Grand Prix body has a Chevy engine in it. On a side note, the switch of some of the more notable Pontiac teams to Dodge this year makes me wonder about the future of the Grand Prix in NASCAR. Really interesting thread you've started here...

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Greg
91 LX Convertible

I think the 327 cid was a minimum displacement engine and the max is 358 ci. I think the minimum is higher though, because some of the Ford teams went to smaller motors (331, in the 80's) and started kicking brand x's a$$ (when restrictor plates were used), so Chevy started crying and made a minimum displacement rule.

The reason it works is because the Ford has the Cleveland style heads with healthy ports, canted valves, and the like. The Chevy uses wedge style heads with smaller rectanguler ports (I believe). The Ford is choked more and suffers more from the restrictor plates. The Chevy benefits from more velocity from the restrictor plates.

I believe Bill Elliot was one of the first to try this, because his brother built his engines, and decided to see if this would work.

[This message has been edited by 88GT5.013.02 (edited 02-27-2001).]

[Unit 5302]

So there is a minimum size restriction. That would now make sense to me, cause my Math is telling me the 302 would likely be faster than the 351 under a restictor. Still, I think Dodge is running a 360 are they not? I think the most you can evenly bore a 351 and get it to come out in displacement is .040, which makes a 358cid or something. I'm pretty sure Dodge is running their 5.8L.

I don't really follow NASCAR much anymore, I think it's kind of a joke. Still, the idea of a 302 cleaning up 351's sparked an interest.

Thanks for the info 88GT5.013.02!

[jonnyk]

What about a 347 stroker? Retains the lightweight advantage of the 302, and adds the extra stroke for more torque coming off the corners and *potentially* more horsepower. Less frictional losses than a 351W also due to smaller journal sizes. That would be an interesting combo to throw in there as well.

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1991 LX Hatch 5.0L

[matt cook]

I think that the engines have the smaller Cleveland journal size anyway.

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1982 Mustang GT