interesting cam grinding

[lyonsy]

Was talking to a mate the other day and he has a very tough 250 xflow with around 170rwkw after he installed a new cam in.The interesting part is it has a three grinds on this cam one for no1 + no6 one for no2 + no5 and one for no 3 + no 4.
he would not elaborate what cam it was only it is smaller then the one he had which made 160rwkw.
he said it was best for getting the same amount of fuel into each cylinder to prevent lean burning esp of the no1 and no6 cylinders which when he leaned off to make power where breaking ringlands.With the expertise on here I expect you will probably of been doing it for years but its is new to me and very handy for the new class I am going into as engine's are reasonable stock so any advantage is an advantage.

 

[JackFish]

I like that idea, can you get the exact specs on that cam?

 

[jamyers]

Interesting...never heard of doing that before. Wonder how it'd work on a log head?

 

[rbohm]

8) the idea isnt unique, but rare. i can understand how it would work, but i wouldnt expect things to be as smooth as cams with standardized lobes.

 

[Lazy JW]

There was some discussion about this over at www.speedtalk.com a while back. Lots of opinions, no real consensus. Interesting idea though, and if it works, go for it!
Joe

 

[80broncoman]

Sounds Expen$$ive. a lot of extra work for sure. But it would work after lots of trials.
Only down side is with each new intake and exh plumbing a new grind is required to maximize the results.

Sounds like someone has put in the time to work it all out.

 

[BIGREDRASA]

You might also try using a higher ratio rocker on the outer intake valves. Say 1.6:1 for #s 2-5, and 1.7:1 for #s 1 and 6.

 

[lyonsy]

up untill i herd about this style of cam grinding the only other trick id seen is to grind a cam with a slight twist 2deg max but this was only with a 3L six that was spun out to 10'000rpm to allow for cam shaft twist at high rpm

 

[fb71]

honda did something very similar back in the 60's on a 250cc straight 6 motorcycle engine. Cam was driven from the center, cyl 2 & 5 had a slight advance of the lobes, 1 & 6 a bit more. Lobes had a slightly different grind for each pair (1/6, 2/5, 3/4). The shaft was also hollow and tapered down from the center to each end, to reduce rotating mass. Had no flywheel to speak of, idled at 2k-3k rpm, and would chuck a rod if the throttle was blipped with no load on engine (neutral or clutch in). Which I could have heard one in person...

 

[xctasy]

Wasn't aware of Hondas expliots, but considering their engineering first philosphy, nothing would supprise me.

It was repeated in 1982-1988 with US Crane based aftermarket Vizard VP cams by Piper. They are designed 'scatter' cams for A-series Austin/Morris engines, with variable lobe centres and profiles in some cases. They cost five times a stock cam on just a an 8 lobe A-series 4-cylinder engine, and the results are great if you are racing, but not there for a regular engine.

The benefit is inertial ramming, and creating the same cylinder to cylinder torque figures. Like the early Max Wedge 413 cross ram Intake with variable intake lengths. Same deal with lowering compression on detonation prone cylinders, another proven winner on engines at 11/10ths.

All discussed in the past. Normally, the concept of a blueprinted engine excludes scatter pattern cams, but there are plenty around these days.

 

[XPC66]

Isn't the firing order 153624? I can't come to terms on how a scatter profile would be any benefit? Four pots with bifurgated inner ports yes, but a six?

 

[wallaka]

Well, since the outer cylinders traditionally have less flow, it makes sense to me. Just have progressively more duration by cylinder pairs, 3/4, 2/5, then 1/6.

 

[XPC66]

Well that wasn't the traditional reason for them, but I can appreciate the thought. The trouble is you could be effectively derating the engine in the process, as opposed to being a little more clever with the runners or the number/distribution of carbs.

 

[xctasy]

There are no wrong cams, only wrong engine combinations...

The pre-cross flow I6 in any of its forms is the engine for a scatter cam.

Unfortunately, we have our engine cast in iron, and then spend on the carb, exhast and then the cam to suit. This is especially so with the US 200 and 250, and to a greater extent, the shared intake port A-series and 6 and 9 port GM L6's, where a scramble pattern cams ensure that intake charge is not cross scavanged during over-run or wide open throttle.

The scatter cam works brilliantly, but its ath the top end of the cost pyrimid, well beyond the sane cost of just modifying the intake runners with a 3-carb adaptor or a 2V head. It's value is in a stock controlled engine formula or when a 3 carb and /or 2V head is in use.

The rule for maximum power is not to ever have a "what applies to one applies to all six" rule. The power can be based on super-imposed variances when there are detonation, exhast valve or intake flow rate issues. The work done by Phil Irving and David Vizard in the earlier days of engine design showed that carbs had fuel standoff issues which sometimes varied between cylinders. The pre-cross flow, log head, ME, SP or 2V has unequal runners, and needs scatter cam when performance is the objective. Due to the time of concentration and feet per second the fuel air mix has to cover, there are variances which cannot be over come even by brilliant intake design. Example is that on a Falcon pre-cross flow, the runners from cylinders 3 to 4 are far wider than 1 to 2 and 5 to 6. Evidence is to look no further than the Haynes SU book. Look at the SU needle settings for Reliant Scimiar engine by Andrews, or the AC Acea's or Competiation Zephyr 6 Mark II with its Raymond Mays 2600 I6 Fords. Triumph and Healy L-6's had similar issues. Same with some Jags and Astons....the centre carbs often have different jetting to the outers in some cases, even different spring ratings. And its not just for cold starting. On the Ford, its due to intake runner length issues on those engines, on the Jags and Astons, its some other aspect. They were set up on a dyno, and the operater did EGT readings until he was satisfied that the fuel enrichment was safe overall.

 

[MustangSix]

There was a lot of experimental activity on Big block Chevies in the seventies by Smokey Yunick using double pattern cams. The BBC is a little awkward on the intake layout, so the tracts are different lengths on sets of four. He deliberately ran different patterns so that the engine would run like a pair of slaved V-4's. Very wide torque and HP bands, as I recall.

 

[XPC66]

I would need to see proof that an inline six would see any performance benefit. Trouble would be getting a reading without any other mods.

 

[lyonsy]

well going off my mate who just had his engine freshend up and installed this cam he gained 10rwkw.
class iam going to run 10rwkw is worth the cost.