"Big Bore" head pipes and mufflers

I am interested in the exhaust system sold by http://www.commandospecialties.com/
and I was wondering if anyone on here is able or willing to comment on their experience with those exhaust parts, the 1.5 inch head pipes and the big bore pea shooters that are sold with them.

If so, how is the fit of the head pipes? Do they result in any improvement in power? if so, or if not, the effect on mid range vs top end?

I could not get an answer from them as to the specs of the mufflers. Are they louvered core or perforated core?

Thanks

They're not a manufacturer, and I doubt they have an exclusive, so perhaps you can find information on google?

I have a set of their non-big bore pipes - manufactured by Wassell but purchased through Commando Specialties - and have been pleased with them. In general, I think CS's prices are a bit on the high side, but fair, and quality tends to be pretty good.

I have the CS 1.5" headpipes and Megaton shorty reverse cones with 1.5" inlets but they are in my "pile-o-Commando" that WILL be a bike one day so I can not speak as to fit. As far as I was able to determine you will not gain any performance from the bigger pipes but IN MY OPINION I think the bigger headpipes look better on the bike.

Unclviny

Commando exhaust ports are already too big. Do you really think bigger pipes will help?

Fullauto said:

Commando exhaust ports are already too big. Do you really think bigger pipes will help?

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Please enlighten us...

Yeh, I'm interested in the answer to that one too.

Yes apparently the factory ports are a bit big for best all around performance. There is a hot rod modification that narrows the exht ports into a flat floor D shape. Peel was only able to best 600's and keep up with 900's in opens when she had the 28 mm port head on and lost power all around with the early Woverhaven CHO Combat head which is known to have over sized hogged out ports, till they got more refined in the production. My factory Combats didn't really come on cam till about 6800. I found 1.5" singles kinda draggy until made into 2-1. Then still doggy disappointing till the muffler made open inside with end plate baffle plate with 1 3/4" vent.
This combo added SpunK from off idle to top out. It takes some breathing mods to get much advantage over 1 3/8" headers. Bathtub squish mods do not seem to help Norton hemi's. In a dyno contest at a rally DynoDave made more power ~49 rwhp than other fancy Combats. He had the 28 mm head on, just like Peel deal.

Postby Fullauto » Mon Aug 17, 2009 4:30 pm
I'm not much of a salesman Z, but I'll give it a go. The heads are standard configuration except for the material and heat treating (6061-T6) and the port configuration. Jim Comstock designed the ports and at this early stage I can say, definitively, that they work with a strong midrange. The valve seats on both 750 and 850 heads are suitable for unleaded (of course). Unfortunately, due to poor packaging, the three heads sent to CNW were damaged in transit and have been returned to Harrop Engineering for scrapping. We now have custom boxes in which the heads are individually packed so this will not be an issue for the rest of the batch.
If you look at the ports, the exhaust ports are much smaller than standard with a flat bottomed "D" shape. The inlets have a shape I would describe as "Cobra's head" shaped

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http://www.mez.co.uk/mezporting/page6.html

Ther are a nice set. I love mine. Good hardware package.
Be prepared to jet a little most likely to enrichen. Try to set up with the most breathable airfilter system to match the "exhale" improvment. Different sound but oh so awesome.
Kinda like a old Ford GT 40 or Chaparral of maybe a Farrari with headers.

Ok intriguing feedback on the effect and sound of properly narrowed exht ports.
In supercharged applications the blower overcomes about any deficiencies in the intake side so they get the most pay back from exht side improvements. Longer-higher valve opening, streamlined port into tuned header and 'muffler'. Generally our size-kind engines like 1/8" bigger OD in near stock tune and maybe 1/8" more ID if maxed out 920 road racer. A TC Dragon Slayer on fuel WOT red lined could use an extra 1/4" over the above for 1 3/4", like any good ole chevy V8 hot rod.

Michael Starkey of British Toys in NC, casted inside of Peel's early March/'72 Woverhaven ported CHO head, to report someone had hogged ports open beyond the plain cast some good percent over prior Norton heads he'd done.
It had Deer's 7mm K/W valve-spring-lifter kit installed. I was sorely dissapointed at loss of sportsbike spanking power the pure factory 28 mm standard low CR head gave. I'd just put it on for break in interval to be shocked when time came to try WOT to 7000 and half way to 8000 at times. Michael almost fitted bronze rocker spacers instead of factory spring wiggle type.

So my thinking is Woverhaven 750 Combat head will act similar to 28 mm head, when its on top 920cc, 10.5 CR and boost + water spray kicks in. Milling for the big pistons made the squish rim expand to 1/4-3/8" width, maybe even enough Singh Groove would have their claimed anti-detonation effect.


Marks are failed attempt to place Harley size compression releases. Standing bet $100 no one else can fit releases either.

Peel's 1st exhaust system, 1 1/2" two>one > long Dunstall hollow megaphone with resonator end chamber caped by butt plate with ~2" flaired venturi exit.
Gutted mega+end cap should weigh ~6 lb. Headers/nuts/O2 bung weigh ~7 lb.
13-14 lb total. Factory duals weigh ~20 lb total. More d/ 2nd mounting plates.

There are epoxies that can stand the blast and temps there [~1400'F EGT if lucky- 1375 more common], any failure just blows out onto road way, so sorely tempted to try this. Insights to do on invited.

opps. Michael Starkey Did give close attention to centering rocker arms over valve stems when he milled custom bronze spacers to replace spring type. No almost.

xbacksideslider said:

Do they result in any improvement in power? if so, or if not, the effect on mid range vs top end?

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I seem to remember that Matt Rambow from Colorado Norton Works said in a post on this forum that CNW tried larger bore slip-on headers and recorded a decrease in performance. This would tally with Fullauto's comments on the exhaust ports being on the large side.

That 'D' shaped exhaust port is very interesting. If I ever get a windfall, I will buy one of Fullauto's cylinder heads. To go with Jim Schmidt's rods and pistons, Steve Maney's crank, and on and on ....

Hobot — you talk about using epoxy to fill in ports. I'm sure you will have heard of one engine tuner in the States who claims that using epoxy on the port floor in Yamaha R6s and the like results in better performance (for racing at least). I'd be interesting in hearing more about this. Funny because when we were young lads we thought that larger ports, larger carbs, etc., were the way to go!

Dave

daveh said:

Funny because when we were young lads we thought that larger ports, larger carbs, etc., were the way to go!

Dave

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Typically the stock configurations on many vehicles were restrictive and bigger was better.

Yep, bigger was better ...and most people who put on a big carb slowed the car down! Same thing will happen to a Commando by putting on 1.5" dia pipes.

Besides speeding the out flow the flat face-lip acts as anti-reversion device.
I'd best farm my head out to Michael Starkey who has done epoxy exht porting on other and pointed me to epoxies up to the task. I'd not heard of the Yammha builder but good to hear of now. I I had a pulsile flow bench could mock up in clay or just grind down epoxy till best effect. Other wise a photo of the Mez head placed on graph paper and measures transferred to head porting. Someone beat me to it please.

hobot said:

Besides speeding the out flow the flat face-lip acts as anti-reversion device

Click to expand...

Anti-reversion device? Do you mean something that stops gases returning to the exhaust port, like a step or wedge that some people welded into their header pipes?

Mototune USA is the guy I mentioned. He hypes up his products a lot, but interesting nonetheless: http://www.mototuneusa.com/

Swoosh — yes, good point, but you might agree that there were many other elements that restricted the performance of older engines, apart from port size. By the way, I watched your video of your Commando idling on another thread. I noticed it wasn't jumping about on tickover. In which case, I'm envious!

Daveh, yes but not by an anti-revision cone, just the blunt face the sonic compression waves bounces back off of before pushing waste gas back into chamber.
I'd seen the site prior but you flashing it back up made me subscribe this time to dig deeper seeing as how epoxy and hand grinding tool is right up my machining alley.


Makes me wonder about using air compression wave fronts rather than pure ram air pressure to boost intake detectably.

Of course there can be too much velocity, as flow in narrows approaches supersonic it can't increase much further w/o greater pressure to force it.
Super sonic turbulence in ventral does not slow down the flow, just sorta caps much increase. But ports don't flow steady and if flow can be made to spike up to super sonic then its got most inertia going to keep flowing well as piston rises and port flow goes back below super sonic for the majority of the time.
Searched for good site but the one you posted is still the best and even demo's epoxy method here.
http://www.mototuneusa.com/super_sonic_nozzle.htm

So what brands of epoxy has the HOBOT found.??

Not a great photo but here is the comparo. Stock on the left.



And the rough casting.



My motor is very noticably stronger from idle up than when the standard head was fitted. Remember it's not all about size, but velocity of the flow as well.

If I may chime in here for a moment - early this year I was supplied by CNW with a FullAuto head for my racer (thanks Ken & Matt!). When discussing with Jim Comstock about what to do to get it right for the track, he suggested we go with standard sized valves and not to touch the ports (exhaust included). I admit I was skeptical - I'd been running a Mick Hemmings Big Valve head up to that point, and going with smaller stuff seemed counter-intuitive to me. Comstock reassured me after claying my ports and trying a few different things he couldn't get it to flow any better. Proof would be in the pudding.

Well, I went WAY up on power, my top end never suffered with the smaller valves and ports, and midrange is fantastic.

I don't know the black magic behind it all - that's for Ken and Jim to elaborate on. But I am a strong believer, and the pudding has definitely been proofed!

This is fascinating...and a pretty good advert for Fullauto heads. So does it also follow that the smaller valves are easier on springs, etc than the larger? What kind of weight difference are we talking about? Of course at 7k rpms even a few grams would seem a lot.

(Taking notes for the Waldo project)

Russ