The 128 drama!

[GARY C]

Gary, I never disagreed about changing the displacement that’s kinda different. F1 cars have a ton of curtain area and cams are about 270@0.040” for 4v not exactly small don’t have CL data It’s the curtain area not the port area. Fill in the ports 25% and the idle will not magically become good.

A 25% reduction of a port flowing 600 cfm on a 200 ci engine is still a big head on a small engine, curtain area plays a part like anything but the port has to be sized accordingly, when I say a "big head" I am thinking of it in terms of everything being sized accordingly, not a 240 cc port with a 1.94 valve although that would suffer in idle quality as well due to lack of velocity at low rpm.

[digger]

Garry the port velocity at idle is always bugger all such that making it a lot smaller has little effect on idle quality as it’s still extremely small

[RevTheory]

Great discussion on hot street/strip, Gen 1 small block Chevys, lol

[peejay]

I don’t think the port size has much to do with idle (other than low lift curtain area ) it’s mostly the overlap and associated curtain area , cylinder size and cross talking which is not the same as looking at LSA saying it will idle poorly . Small duration and 100LSA can idle fine, the same IR will tolerate More overlap

What cam does an F1 engine run that causes it to idel at 7000 rpm?

I always wondered about that... I don't think it is about the cams as much as it is an oil pump that is efficient (minimum power loss) at 16,000-19,000 RPM will not have enough flow to keep the engine alive at low RPM.

[hoffman900]

Great discussion on hot street/strip, Gen 1 small block Chevys, lol

I think 90% of the threads on this site cover those.

[RevTheory]

Great discussion on hot street/strip, Gen 1 small block Chevys, lol

I think 90% of the threads on this site cover those.

That was in reference to DV's 128, Bob. These threads always get blown up with stuff about modern engines with multi-million dollar engineering budgets, VVT and all kinds of stuff that doesn't apply.

[hoffman900]

Great discussion on hot street/strip, Gen 1 small block Chevys, lol

I think 90% of the threads on this site cover those.

That was in reference to DV's 128, Bob. These threads always get blown up with stuff about modern engines with multi-million dollar engineering budgets, VVT and all kinds of stuff that doesn't apply.

What is there to discuss?

It's a forced equation for camshaft LSA on a 10:1, 350ci, street engine, that maximizes torque but may inhibit drive ability. Furthermore, some of this equation runs in conflict to things Harold Brookshire and Mike Jones have shared here. They may not have written books, but they designed camshafts that have produced championships on the professional level.

Is this Speedtalk where we are trying to learn how engines work and make them better or produce cookie cutter engines that you can find in the pages of all those defunct TEN magazines?

David has his own subforum for promotion.

[Stan Weiss]

Bob,
There has been 3 pages of discussion, so i guess other disagree about there being nothing to talk about. You don't like or think the formula works, other don't have the same opinion. David posted up a free formula for people to try. If it works great, if it doesn't all someone has lost is a little of their time. I also think that you missed the fact that not everyone here is at the same knowledge level, or is here looking for the same information that lets say you are.

Stan

[RevTheory]

I'm sure Bob flagged CamKing again to get the thread moved. Oh well, at least he's out of the conversation back here.

[digger]

peejay wrote:
> [quote="GARY C" post_id=842480 time=1578375960 user_id=21117]
> [quote=digger post_id=842469 time=1578368433 user_id=6525]
> I don’t think the port size has much to do with idle (other than low lift
> curtain area ) it’s mostly the overlap and associated curtain area ,
> cylinder size and cross talking which is not the same as looking at LSA
> saying it will idle poorly . Small duration and 100LSA can idle fine, the
> same IR will tolerate More overlap
> [/quote]
> What cam does an F1 engine run that causes it to idel at 7000 rpm?
>
> [/quote]
>
> I always wondered about that... I don't think it is about the cams as much
> as it is an oil pump that is efficient (minimum power loss) at
> 16,000-19,000 RPM will not have enough flow to keep the engine alive at low
> RPM.

If Honda can get a 9:1 speed increase on a street car then even the 20,000rpm older engines should have been only 2500rpm

[David Vizard]

Sent: Wed Jan 08, 2020 5:38 am
From: trmnatr
Recipient: David Vizard

David, can you explain this 128 number or explain a number for a higher rpm 23 degree small block?

I have ran 234/244 hydraulic through 260/268 solid and 248/254 through 283/291 solid rollers

4.030” or 4.060” bore x 3.25 (sometimes 3.26) stroke

Thanks
Butch

Butch PMed me with the above and I thought his questions might be of interest to a few of you out there.

First let me be clear the 128 number for a 23 degree SBC is not about the rpm range. It is about the CR and the rocker ratio/valve acceleration. If you are not following this I have explained it in detail in the other postings on the 128 subject. I am sure some other ST posters can steer you here.
DV

[David Vizard]

Hi Don, Dave and others.
A friend and racer (Dave) from Cranbourne in Australia put me on to this forum and subject.
I told him that I, with friends had attended a seminar where David Vizard spoke in Melbourne in the early 90s. If I recall correctly it was the Anchor and Hope (Lou Molina's) Hotel in Richmond, more on Lou later.

Ian,

I remember that night - A bunch of smart guys with a load of original tech to pass on to me, great food, great company and this get-together went on to the wee hours of the morning. Love to do this again!!!



Here is what I sent to Dave tonight.


Essentially, I think he's trying to work on a streetable overlap for a daily driver and the 23 degree 10.5:1 package are a giveaway to that. He wrote about this in the late 80s.

Ian, sorry if I was unclear on my explanation here. This 128 apples even if the motor is required to turn say 9000 rpm. The 10.5/1 CR is just the baseline CR I used for the majority of the tests. If you followed my outline of how to use the 128 number posted elsewhere you will see that there is a correction for the LCA, after it has been calculated for 10.5/1, for any increase or decrease in CR. So if you were building a 14/1 CR engine for racing you would need to correct the calculated LCA to suit that CR.

As a rough guide your best streetable maximum overlap is no more than 60 degrees. I concur with this, I once replaced a #151 350hp 327 cam with a custom cam that was a Sig Erson 1H but ground on a 105 LCA. It had 72 degrees overlap versus around 60 for the #151.
At full throttle it came on 500rpm lower than the Duntov, even though it had 14 more @.050 on the intake alone. Full throttle launch (no 2 foot braking) it would smoke the tyres in my HQ ute with a 350/2000 converter/T400/2.75 gear and FR70/14s. With the #151 you needed a left foot or a puddle to boil 'em.
In this form, the 3500lb HQ ute felt like a strong low 13 ride with a freeway gear, at least to 6600 in first and second.
But at anything less than 3/4 throttle it was a bad mannered pig. Worse, as a car used in city traffic it'd draw cops like flies to horse shit. After a couple of weeks of that behaviour, I settled on that tiny Cam Dynamics cam with 204 and 214 @.050. Less power and torque than the Sig cam, but more power and torque than the Duntov. As you know, that little cam just flat works in everything. It's LCA is 114. 107 intake and 117 exhaust, so I have always set it up 2 before in a 350 and 5 before in a 400 to suit the shorter rod/stroke ratio.
I never ran 0-30 or 0-60mph on them all, but I reckon the Cam Dynamics unit would eat them all in this range.

Ian, if the engine was a 350, or worse yet, a 302 or 307, the 105 LCA was too tight. Having too tight a LCA causes poor idle and low speed drivability. This is easily exaggerated if the tune up for the ignition advance curves and the carb are not on the money.

You mentioned Sig Erson as the cam source. Sig was a good friend of mine. He actually crewed for me for a couple of my British Touring Car Championship races. I used a number of cams very similar to the one you used. A 10/1 350 requires a 108 LCA, a well set up vacuum advance distributor and a vacuum secondary carb. With pocket ported 186 or similar head castings my engines along these lines regularly dyno'ed out at close to 400 hp on a two plane intake and delivered around 410 plus lbs ft. Such a build made a great truck motor - my Sierra would smoke it's wide BF Goodrich TA's well into second gear.


I think from memory it had about 56 degrees of overlap, I'll check when I unpack some of the stuff I've got packed in case of bushfires. Remember that for every degree you take from the LCA you add 2 degrees to the overlap. Bad on the street.
On the track however, a "tight" LCA will give you shyteloads of midrange if the package has sufficient compression, gearing and airflow. In the distant past, I used to get a lot of cams ground by Motor Improvements near the Greyhound Hotel (opposite St Kilda town hall), when Rocky was the counter salesman. I can't recall who did the grinding, but I got a lot of SBC cams ground on a 105-108 LCA.
The comment was always the same "That would be a hell of a dirt track/ski race cam". Nitrous was getting big then in Melbourne in the early 80s, so I suppose the 112 -114 cams were more popular.

Think about this - what the above indicates is that the LCA is highly influential. Knowing how to match it to the engine spec and application to get the 'most productive' LCA has got to be one of the best solutions to the cam selection blues.

Now, if I was doing an N/A 434 I'd go 104-105, and for Blown/Nitrous/Turbo it would be a 348 or 377 with a 4.125 bore and a 116 LCA

Ian, You are generalizing too much here.Yes you would be good with a 104-105 LCA for a 10.5/1 434 with say 2.05 or 2.08 intake valves.

A positive displacement blower needs to have the LCA suit the boost used. The LCA is not just changing because a blower is installed - there is more to it than that.

For Nitrous the cam events need to reflect the amount of nitrous used and whether or not the application is as a 'power augmentation' or a 'full time' application. I did quite a few nitrous BBC cam tests for Comp Cams back in the mid 80's but I don't think the results were fully implemented.

As for a turbo cam nothing here can be selected until some idea of the pressure ratio across the engine is known. Cams that are simple advertised as a 'turbo' cam are just a rip off unless you happened to be lucky.

DV

[David Vizard]

How do car factory designers choose camshaft timing for engines that don't have variable valve timing? I was under the imagined impression that the idle and/or emission considerations determine the overlap (given the displacement and the heads). Then, the redline rpm and head flow will determine the intake and exhaust duration. Whether the cam is advanced or retarded doesn't matter much because the factory heads usually flow so well for the rpm*displacement. Lobe separation angle ends up being whatever it ends up being, if that's the design procedure.

I often ask myself the same question!!!!!

I think the 'that's good enough' or 'that will do fine' line of thinking often prevails as it is usually the marketing department that tells engineering what the engines power should be to suit a certain market. Insurance rates also can get figured into this.

[ptuomov]

David Vizard wrote:
> [quote=ptuomov post_id=842410 time=1578351090 user_id=9433]
> [b][i][color=#0000FF]How do car factory designers choose camshaft timing
> for engines that don't have variable valve timing? [/color][/i][/b] I was
> under the imagined impression that the idle and/or emission considerations
> determine the overlap (given the displacement and the heads). Then, the
> redline rpm and head flow will determine the intake and exhaust duration.
> Whether the cam is advanced or retarded doesn't matter much because the
> factory heads usually flow so well for the rpm*displacement. Lobe
> separation angle ends up being whatever it ends up being, if that's the
> design procedure.
> [/quote]
>
> [b][i]I often ask myself the same question!!!!!
>
> I think the 'that's good enough' or 'that will do fine' line of thinking
> often prevails as it is usually the marketing department that tells
> engineering what the engines power should be to suit a certain market.
> Insurance rates also can get figured into this. [/i][/b]


Even with the current tax and regulatory regimes?

[David Vizard]

that's a lot of dyno testing; about 23 tests a week for four shops for 4 years. All working on the 128 formula ? You know and I know this may work in some cases but not all. So are you saying this works in every engine in every application, or just some of them.

Steve,

If cam testing with the volume involves here you do not just get an engine off-the-shelf and start testing. 23 tests a week is shockingly slow. With the special cam test SB Chevy's used we got the shut down to start up with a new cam to just on 20 mins. We could change advance retard in less than two mins. Rocker ratio's in less than 5 mins. Ignition timing and carb main jets on the fly and, if required, in the middle of a pull.
Between 3 of us we could do 1 cam an hour on which 4 tests for rocker ratios and at each R/R test up to 5 cam advance/retard settings were tested. Typically we ran through 12 cams a day. 2 or 3 days a week we would run 8.00 pm to 1.00 am shifts.

No these tests were not working on the 128 formula. At this time it did not exist. We were working on isolating trends for particular engine spec changes. IE how did the events change for a given fixed parameter. This could have been the CR the intake valve flow/size, the intake valve acceleration, stroke and so on.

Isolating one parameter and testing events timing across the board with that parameter fixed can - with enough money and patience, reveal an incredible amount about the trends that are revealed when enough data is gathered.

Ref your comment' You know and I know this may work in some cases but not all.

It works every time within the parameters I have outlined. That is for a 23 degree SB Chevy. Other engines would require a base number other than 128. For instance a 20 degree SB Ford with production style ports is 127. A BB Chevy needs a number of 131 to 132 and so on. Every engine has it's number. It is just a case of figuring out what that is for the engine configuration concerned and it is mostly head dependant.