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Author Topic: What kind of performance can I expect with this combo???  (Read 371 times)

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Online smacd11

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What kind of performance can I expect with this combo???
« on: February 05, 2019, 05:19:19 pm »
I have been gathering up some parts for one of my builds.  As I am new to the SOHC 750, I am looking for advice from you seasoned veterans!.  So far This is what I have...

836cc forged MTC 10.5:1 pistons
Norris H750D camshaft
392 Cylinder head, so far stock. I will probably do a little port work as per Hondamans book.

I don't plan on racing the bike, just building something fun to ride. I have attached a pic of the cam card for reference.

Thanks guys.

Offline HondaMan

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Re: What kind of performance can I expect with this combo???
« Reply #1 on: February 05, 2019, 06:57:24 pm »
First things first: you will need strong valve guides with very tight clearances to control the valves with that much lift. I'd suggest Kibblewhite's guides in bronze, and use intake clearance 0.0008" - 0.0012" for intakes, and NO MORE than 0.0020" exhaust (0.0016-0.0018" would be better). This will keep them straight and will survive the steep lift angles of that cam.

Next: plan on a protracted break-in, or you will suffer short engine life with forged pistons, bet on it. The reason is simple: the cylinder material has a rate of expansion equal to the cast pistons, but faster-moving than the forged types. This makes the cylinders cool much faster than the pistons when the engine is shut off when warm, and if it is started too soon after the shutdown, it can actually stick the pistons for a while until the heat drains from those hot pistons and lets them shrink to where oil can do its job again on the piston skirts. If the engine is forced to start under these conditions, it scratches the piston skirts, shaving grit from them and damaging the rings with it. This is what can cause the short life.

To try to reduce this effect, plan on breaking it in over a 1500-mile period, letting if fully cool down (for shorter periods as it wears in a bit) before each restart. Those who do this can extract 40K miles or more from the forged-piston engines, instead of the all-too-common 10k mile life when this practice isn't understood.

The forged pistons usually come with an instruction sheet that calls for large clearances, like 0.0020"- 0.0024", between the pistons and cylinders. This is also part of the problem, but it is done to try to preclude the "hot seize" scenario outlined above. Unfortunately, this much clearance is also anathema to this engine design: the best-running versions use tinier-than-OEM specs, like 0.0006" (like in my own 750) and the roadracing engines of the past always used less than 0.0010" in any piston size, up to 811cc. This tiny clearance will not work with forged pistons, so you're stuck with something larger: I have used 0.0016" - 0.0018" clearances on Wiseco's forged pistons (the ones with the 4 wristpin oiling holes) by also micro-grooving the skirts, or simply dimpling the skirts (many moons ago) with a ball-tipped bit, dozens and dozens of tiny dimples on the lower portions of those skirts, to try to retain enough oil in the larger clearance zones to help cool the pistons a little more. It worked, but I don't do it anymore for lack of tooling.
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Online 754

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Re: What kind of performance can I expect with this combo???
« Reply #2 on: February 05, 2019, 08:43:24 pm »
 Many forged pistons are used for racing,
 That usually means install fresh bore job Friday, race Saturday or Sunday, no time for break in,  no place for seized pistons..
 So there is that..
 And piston alloys changed,  today's forged pistons, can be run tighter.. different alloys.l
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Online smacd11

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Re: What kind of performance can I expect with this combo???
« Reply #3 on: February 06, 2019, 03:25:25 pm »
Thanks for the replies guys.  I am a bit confused regarding the amount of valve lift.  Maybe I am reading this card wrong.  I read that the intake lift is 0.014" more than stock and exhaust is .004" more than stock K4 cam.  Most of the aftermarket cams appear to have more than this amount of lift.  The biggest change I see on this cam is much more duration.

Online gschuld

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Re: What kind of performance can I expect with this combo???
« Reply #4 on: February 06, 2019, 04:25:27 pm »
FWIW, here is a bit of info from an original 1970s MTC catalog.

George

Online smacd11

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Re: What kind of performance can I expect with this combo???
« Reply #5 on: February 06, 2019, 04:32:42 pm »
Thanks for that info, I guess I have 10:1, not 10.5:1 like I thought. I also have 3 of 4 action 4's 836 pistons. Looking for a 4th to complete the set of anyone has a spare.

Online gschuld

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Re: What kind of performance can I expect with this combo???
« Reply #6 on: February 06, 2019, 05:51:19 pm »
From the Action Fours catalog.

Sorry no loose Action Fours pistons...

George

Online MRieck

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Re: What kind of performance can I expect with this combo???
« Reply #7 on: February 07, 2019, 06:22:11 am »
A lot of exhaust timing in that cam.
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Online smacd11

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Re: What kind of performance can I expect with this combo???
« Reply #8 on: February 07, 2019, 12:11:05 pm »
So when I look at the specs for the stock cam, I think I was confused with the .315 lift being cam lobe lift, rather it is valve lift, correct?  Seems that everyone advertises cams differently.  The only stock cam I have is inside the engine at the moment so I had nothing to compare to.  Are the rocker arms a 1.2:1 ration on these engines?

I really appreciate all the help so far guys, I have lots of thinking to do on the path I will take with this engine now having a better understanding of what I have got.

Cheers,
Shawn

Offline bwaller

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Re: What kind of performance can I expect with this combo???
« Reply #9 on: February 07, 2019, 04:30:19 pm »
1.1:1 rocker ratio

Offline TurboD

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Re: What kind of performance can I expect with this combo???
« Reply #10 on: February 08, 2019, 02:40:34 pm »
I would look for a cam with less duration, That cam will take the fun right out of your "fun to ride" bike.

Online smacd11

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Re: What kind of performance can I expect with this combo???
« Reply #11 on: February 08, 2019, 02:47:01 pm »
Kind of what I'm thinking.

Offline turboguzzi

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Re: What kind of performance can I expect with this combo???
« Reply #12 on: February 08, 2019, 03:04:34 pm »
+1, specially without serious porting. this cam will cam to live at the revs where the stock sports start to choke flow.

Offline HondaMan

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Re: What kind of performance can I expect with this combo???
« Reply #13 on: February 08, 2019, 06:52:54 pm »
A lot of exhaust timing in that cam.

Roger that!
Could it be for keeping the sparkplugs a little cleaner for the street rider? Dunno on this one...
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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Link to website: www.SOHC4shop.com

Offline PeWe

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Re: What kind of performance can I expect with this combo???
« Reply #14 on: February 09, 2019, 12:26:50 am »
Cam card specify 45 degrees overlap or have I misunderstood it?
Many hot cams have more....
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