4 Stroke Head Porting

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Headcoats
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4 Stroke Head Porting

#1 Post by Headcoats » Sun Dec 04, 2016 6:19 am

Anyone dabbled in the art of gasflowing a 4 valve cylinder head :smt024

Matching the inlet manifold to the head,removing the bits of rough casting and unshrouding the inlet valves ???

Seen some raise the inlet floor too for velocity but what is a good bit of general knowledge :smt007
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evan_calgary
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Re: 4 Stroke Head Porting

#2 Post by evan_calgary » Tue Dec 06, 2016 2:00 pm

Flow bench is only way to properly do it...otherwise you are just grinding metal beyond cleaning up slag.

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Re: 4 Stroke Head Porting

#3 Post by JonW » Tue Dec 06, 2016 8:34 pm

Matching the intake is sensible and cleaning up is hardly ever bad, tho some turbulence can be useful, beyond that you need a pro really. Id ask on a Triumph forum and talk to the pros first as I assume thats what this is for?
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Re: 4 Stroke Head Porting

#4 Post by justind97 » Wed Dec 07, 2016 10:14 am

There's a guy on the Sohc4 forum, MRieck (Boston), who does spectacular work. I have a cb550 head done by Mike. Hands down some of the best work in the US. Prices are pretty fair as well.

He typically does CB750s & 550s, but he has done CBR600s as well and I'm sure many more.

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Re: 4 Stroke Head Porting

#5 Post by Headcoats » Wed Dec 07, 2016 10:27 am

I did go on the Triumph Forum but that thing is so huge you just get swallowed up as the forum traffic is manic :smt012

I did ask the question and was just told to get a 904cc big bore kit and I said I'm not doing that !

It does say to keep inlet tract with a semi rough surface to keep the "swirl" up for the incoming mixture but can make the exhaust side super smooth to help the escaping gases

Oh and I need £700 for some fancy carbs :smt005

Anyway all the top end is stripped and removed valves from the head etc so is ready for some fettling :smt021
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Re: 4 Stroke Head Porting

#6 Post by T.RexRacing » Wed Feb 15, 2017 8:36 pm

I spent a few thousand hours with a SuperFlow 600 screamin' in my ears. Got any specific questions?

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Re: 4 Stroke Head Porting

#7 Post by Headcoats » Sat Mar 11, 2017 6:08 pm

Wow that's a work of art :smt025
Few weeks down the line now and just had the inlets tidied up

I do have a new question though !

Has anyone had experience with Keihin CR 35 carbs ?

Just got some second hand ones for the Triumph

They are actually 1mm smaller than the stock CVK 36 carbs but supposed to flow 30% more as they are a smoothbore carb
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Re: 4 Stroke Head Porting

#8 Post by T.RexRacing » Sat Mar 11, 2017 9:24 pm

Oh that's the exhaust. Here's the intake with manifold port match. :smt003

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I've installed a couple sets of the CR carbs on new model Triumphs. Sweet carbs and came jetted well. Just minor tweaking to dial in. Cables even worked out of the box.
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Re: 4 Stroke Head Porting

#9 Post by Headcoats » Sun Mar 12, 2017 6:32 pm

Fitted them today and it was a tight fit, but wasn't too bad

Got it started and running but then it rained so didn't get to give it a test run :smt010

They reckon with these carbs that because they have no accelerator pumps, they hesitate if you grab the throttle too soon
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Re: 4 Stroke Head Porting

#10 Post by JonW » Sun Mar 12, 2017 8:10 pm

Thats always an issue with large cc and a small number of cylinders, the throttle on the large carbs lets in huge amounts of air in a big gulp and its like there is not enough fuel, so the pumper carbs are perfect for them as they give them the fuel you need to whack open the throttle from idle, otherwise the bike can die. Are you sure its not a backwards step to run carbs with no pumps? I ask as Ive fitted them to big single bikes without them for years and enjoyed the improvement.
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Re: 4 Stroke Head Porting

#11 Post by Headcoats » Mon Mar 13, 2017 12:16 pm

I was aware of this and was told to get the FCR flat slides and not the CR Smooth bore carbs but the FCR are a total X rated amount of money but they reckon if you feed the throttle in at low revs instead of whacking it open too soon, the CR's work well and you get a good rush once they are pumping

Hope to do a few tweaks then get it down the dyno with a bag of jets !

Still haven't had chance to get out as I'm the main carer for my 2 3/4 year old !!
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Re: 4 Stroke Head Porting

#12 Post by JonW » Mon Mar 13, 2017 7:18 pm

The FCR is a superb carb, not cheap but Ive run them on big KTM and been delighted. I'd have saved the money personally as they go hard higher up the range like the CRs do and the pump is well worth having as fethering the throttle to pull away from lights gets old fast imho. FWIW I run a TM36 Mikuni on my XT500, had you looked at the TM40s at all? another good carb tho the FCR will always been my fave of this type cos its so proven.
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Re: 4 Stroke Head Porting

#13 Post by T.RexRacing » Tue Mar 14, 2017 12:38 pm

There's only two things better than the FCR. EFI and The Lectron.
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Re: 4 Stroke Head Porting

#14 Post by Headcoats » Tue Mar 14, 2017 5:29 pm

Well managed to get out on it today !

The CR 35 Carbs were a great improvement over the old CVK carbs and pretty pleased

One issue though is they have a little hook spring to help the carbs slam shut, but it's just too heavy

I took the spring off and went for a run and the throttle felt much better but the revs were hanging
It has a push/pull throttle and I guess that little spring is needed

Need to find a spring that is light on the hand but strong enough to help the throttle shut
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Re: 4 Stroke Head Porting

#15 Post by Headcoats » Wed Mar 15, 2017 11:15 am

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