Bill Jenkins , Larry Meaux and header wisdom.

[Stan Weiss]

From an article in Car Craft Jan '75. The PDF is to large to post.

Stan

Jenkings_CC_75_Page_4.gif

[PackardV8]

That was a different time and different science; what we know works best today was only dreamed of. Bill Jenkins wouldn't build today what he built then.

When I look back at the 301"s which won Bobby Allison Modified Special titles in 1962 and 1963, and his 327"s which won NASCAR National Modified championships in 1964 and 1965, they were so shadetree as to be laughable today, but good enough to win it all back then.

[Stan Weiss]

OK looking at the article again I guess my cam was not that far off. As Jack said this was a different era. My roller was on a cast core.

Stan

jenkings_CC_75_Cam.gif

Code: Select all

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BBDC__Deg_ATDC_____________Area
_________0.00000___102.52_|_102.38_|_384.90_|__60.23
_________0.00600____93.33_|__85.16_|_358.48_|__60.13
_________0.01000____89.83_|__76.72_|_346.55_|__60.02
_________0.02000____82.05_|__64.88_|_326.93_|__59.77
_________0.04000____72.08_|__52.43_|_304.52_|__59.32
_________0.05000____68.57_|__47.66_|_296.23_|__59.32
_________0.10000____54.18_|__32.30_|_266.48_|__57.88
_________0.15000____43.37_|__21.13_|_244.50_|__56.48
_________0.20000____33.89_|__11.59_|_225.49_|__54.57
_________0.25000____25.03_|___2.78_|_207.81_|__52.12
_________0.30000____16.25_|__-5.78_|_190.47_|__49.09
_________0.35000_____7.30_|_-14.41_|_172.89_|__45.51
_________0.40000____-2.14_|_-23.41_|_154.45_|__41.41
_________0.45000___-12.48_|_-33.21_|_134.31_|__36.84
_________0.50000___-24.32_|_-44.67_|_111.01_|__31.83
_________0.55000___-39.31_|_-58.47_|__82.21_|__23.84
_________0.60000___-65.07_|_-81.63_|__33.30_|__12.12
CAM
_________0.00600___139.67_|_142.02_|_461.69_|__43.70
_________0.01000___125.71_|_125.65_|_431.36_|__43.54
_________0.02000____93.33_|__85.16_|_358.48_|__42.97
_________0.04000____73.72_|__54.34_|_308.06_|__42.12
_________0.05000____68.22_|__47.19_|_295.41_|__41.95
_________0.10000____48.46_|__26.04_|_254.50_|__39.65
_________0.15000____33.71_|__11.41_|_225.12_|__38.22
_________0.20000____20.46_|__-1.67_|_198.80_|__35.57
_________0.25000_____7.11_|_-14.59_|_172.53_|__31.70
_________0.30000____-7.25_|_-28.49_|_144.26_|__27.40
_________0.35000___-24.57_|_-44.92_|_110.50_|__22.10
_________0.40000___-50.10_|_-68.13_|__61.76_|__12.52

[hoffman900]

A friend interviewed Mark Donohue, and he talked about the exhaust testing they did on the AMC's

Calvin's system on the Cobra Automotive vintage Trans Am cars is 1/2" smaller than what they were doing and those engines make 100-150bhp more than they were then...

[nitro2]

NASCAR has their own box and they make great use of what's inside that box, and some valuable things leak out to other applications from time to time, but there are plenty of things outside the NASCAR box that are better than what's in it (i.e. blowers, turbos, methanol, nitrous, nitro, larger displacements, custom this and that, etc. etc. etc.), lots of fun things that are not so fully developed.

[Mummert]

Making an exhaust work well at overlap over a narrow rpm range is easy as pie, so that's not where the discrepancy lies.

NA engines making a LOT of power per cubic inch run into blowdown issues, especially so if the heads didn't flow as well as they do today. When you get to that point, the point of having blowdown issues that can't be further effectively addressed with cam and porting, but only by the exhaust, that's when the exhaust has to change drastically. Most people never actually make the drastic changes because ingrained logic and sim soft programs don't point them in that direction.

2.125 - 2.25 headers are good for the 1000hp territory +/- from a blow down point of view. It doesn't matter wether or not his heads flow as good as ones today, it matters that they flowed enough for what he was doing with his combination of parts.
When it comes to blow down at RPM it a (time area issue). The only reason you would exaggerate the area is if you decreased the time. With 294* @.050 he's not reducing the time.
Old iron sbc engines are very prone to side exit the intake port especially with 2.05" or bigger valves on 4.00" bores, this makes them very prone to scavenging problems.
They made "Turbo" heads in the 70's from GM that pushrod hole spacing widened, and the MSCA was at the short turn for specific racers. These flow 280 or little better on the intake and 215 or so the exhaust well ported from the 70's. His airflow wouldn't have been too far off.

[CGT]

Jenkins engine would be relatively low VE by todays standards. One trend that tends to be pretty consistent. Increasing VE from production power levels tends to involve an increase in sizing of ports and pipes(not as much the case today on some platforms but historically it has been) but after a certain point as VE gets to higher and higher levels, ports and pipes tend to start getting smaller in size.

My take is, that engine just wasn't evolved enough to have smaller headers on it. It wasnt possible for it to be with what was available at that time. Sure would like to own that old engine though

[digger]

That was a different time and different science; what we know works best today was only dreamed of. Bill Jenkins wouldn't build today what he built then.

When I look back at the 301"s which won Bobby Allison Modified Special titles in 1962 and 1963, and his 327"s which won NASCAR National Modified championships in 1964 and 1965, they were so shadetree as to be laughable today, but good enough to win it all back then.

this doesn't explain why pipemax provides a different recommendation as the lower level of development is captured by the program. I'm sure Larry developed it on some of the older school stuff to. People use it to good effect on engines that don't remotely resemble a V8.

[joespanova]

Pipemax doesn't make a distinction between 1975 and 2021, iron or aluminum . If Jenkins engine had a VE around 100% he'd require LESS header than what he used. Even at a baseline 110 he still doesn't get any where NEAR what he used. Using 331 inches and peak power speeds around 9000 plus he MAY get in to a 2 inch pipe / 3.5 collector ( at 331 inches , possibly towards 355 ). The cylinder head requirement to make 700 plus ( what his claim was back then ) you end up in the 310-320ish range. Unlikely he gets past that given what they had to work with . At the desire for simplification , I'm not sure I'm getting exactly WHY ( given everything I'm saying above ) I don't quite grasp these explanations / what is explained here. And I know some of you guys operate way beyond the scope of my experience , so help me out here.
All of this Q n A sort of connects to my new engine combo and just needing new headers period.

[Rick360]

I spoke with Jenkins at Topeka back during the Pro Stock Truck days and I asked him about the 292 heads they used. He said they got up to 340cfm when they were welding them. When I asked about writing a newer book he mentioned he was still getting $500/month from the old one which was close to 20yo at the time.

As far as header differences it may have to do with ...
- cam/valvetrain changes since then
- a trend to smaller exhaust valves since then
- they weren't using long radius bends on their headers back then
- compression ratio lower due to fuel

Rick

[PRH]

Anyone know what the typical ET’s/MPH and race weight was for P/S back when that was current technology?

[Stan Weiss]

In this article he said he shifted @ 9000 RPM.

Also he was not running real high CR.

Stan

Jenkins_CC_CR.gif

[af2]

I spoke with Jenkins at Topeka back during the Pro Stock Truck days and I asked him about the 292 heads they used. He said they got up to 340cfm when they were welding them. When I asked about writing a newer book he mentioned he was still getting $500/month from the old one which was close to 20yo at the time.

As far as header differences it may have to do with ...
- cam/valvetrain changes since then
- a trend to smaller exhaust valves since then
- they weren't using long radius bends on their headers back then
- compression ratio lower due to fuel

Rick

Rick they had some of the best fuel back then.. Even a welded 292 I have seen is south of 300 like all the heads claiming over 320 now a days have a different approach with the shape. Some are good and most are not.

[hoffman900]

I spoke with Jenkins at Topeka back during the Pro Stock Truck days and I asked him about the 292 heads they used. He said they got up to 340cfm when they were welding them. When I asked about writing a newer book he mentioned he was still getting $500/month from the old one which was close to 20yo at the time.

As far as header differences it may have to do with ...
- cam/valvetrain changes since then
- a trend to smaller exhaust valves since then
- they weren't using long radius bends on their headers back then
- compression ratio lower due to fuel

Rick

Rick they had some of the best fuel back then.. Even a welded 292 I have seen is south of 300 like all the heads claiming over 320 now a days have a different approach with the shape. Some are good and most are not.

The boutique racing fuels from VP, Sunoco, Torco, etc are superior to anything they had back then by a lot.

Compression isn’t everything. Grumpy was smart enough to know combustion quality matters as much as outright compression ratio.

[nitro2]

Making an exhaust work well at overlap over a narrow rpm range is easy as pie, so that's not where the discrepancy lies.

NA engines making a LOT of power per cubic inch run into blowdown issues, especially so if the heads didn't flow as well as they do today. When you get to that point, the point of having blowdown issues that can't be further effectively addressed with cam and porting, but only by the exhaust, that's when the exhaust has to change drastically. Most people never actually make the drastic changes because ingrained logic and sim soft programs don't point them in that direction.

2.125 - 2.25 headers are good for the 1000hp territory +/- from a blow down point of view. It doesn't matter wether or not his heads flow as good as ones today, it matters that they flowed enough for what he was doing with his combination of parts.
When it comes to blow down at RPM it a (time area issue). The only reason you would exaggerate the area is if you decreased the time. With 294* @.050 he's not reducing the time.

You think so ......?