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Discussion Starter · #1 ·
Guy,
I have the Grom head just about ready for the flow bench, All I'm waitng on are the 4 Honda hold down studs. They are due in by Thursday. I'll do a complete baseline test, just the way the parts were manufactured by Honda. Then I'll start modifiying the ports, to see how they respond to changes. At first glance, I think the port work will be fairly straight forward. The whole process will take about a month.
Brian S
 

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Yeeeeeee this is whats up! Awesome.

Do you have an entire bike for dyno testing afterwards or only flowbench testing?
 

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I'm very interested in how much porting can be done to the stock head. I was thinking for my mod path on my Grom I would head to a slightly bigger bore for a total displacement of 150cc and then some minor head porting with a more aggressive cam should just about do it in terms of power mods. No need to get crazy like some of the companies are offering.
 

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Discussion Starter · #7 ·
Grom Head Porting

The first rule of porting a head is: bigger is almost never better.
Flow direction and correct port dimensions through out the port shape are way more important.
I have run the math on almost every valve dia. / eng. displacement combination.
Air Flow Requirements:
A stock Grom head is good for a max bore of 125cc @ 9000
A stock Grom head is good for a max bore of 136cc @ 8500 - largest bore in a stock cylinder
A stock Grom head is good for a max bore of 150cc @ 8000
Now will the 150 kit make more grunt at 6000 to 7000, you bet!
As you go up in displacement, the intake & exhaust valve & ports get smaller, or at least as far as the engine knows, they go sonic, and block up
175cc kit - needs porting, manifolds, valves, cams & springs, & no OEM air box $$$
Average Grom Piston Speeds:
7000 - 2649 ft per min
8000 - 3027 ft per min
9000 - 3406 ft per min
Indy Car engine - 3800 / 4000 ft per min
Keep it below 9000
Brian
 

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Noting that you said 136cc at 8500 explains why Kitaco is releasing a 133cc kit

Good info, thanks for taking the time to do this
 

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I don't have a tach, but my ATC90 is punched out to 138 and has everything done to it. That thing revs to the moon. I definitely understand not revving it too hard, but I will probably do it anyways.
 

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Piston speed of a CBR1000RR at peak RPM (13,000) is 4,706ft/min. Will a forged connecting rod and forged piston not be enough to keep the lil Grom motor together at high RPM?
 

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Discussion Starter · #12 ·
Piston Loading/RPM

Guys,
Please don't equate what you can do with a current model Japanese superbike & the Grom. Superbike parts have a lot of FEA work in them, along with a ton of high RPM testing. The Grom has nice parts in it, but.
The average superbike engine is loping along at 1/2 RPM most of the time. The Grom is at 6,000 at 45 mph, all the time, with little parts, IE, 13mm piston pins.
Brian S
 

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Is there any way to strengthen it with beefy forged parts? I'm just wondering because as far as I know the Yuminashi guys were running like 11,000 rpm on their 180cc bike. Then again, from what I hear, the longevity of their product is questionable.

I'm not trying to argue or disprove your case. All of my posts are for the purpose of my education only. Thanks.
 

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Discussion Starter · #15 ·
Different Idea's

Guys,
I learned many many years ago that good insight & knowledge can come from anywhere. There is no such thing as a bad or dumb question? The only question that is dumb, is the one that is not asked! One of the things that I like about this forum is that everyone is polite, and that there is a genuine interest in gaining knew knowledge by everyone on the site. I only hope that I can help a little. Between all of us, we should have this new bike covered.
Brian Sheridan
 

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Keep up the good work, I learned long time ago that when I had my 66VW 1300cc engine the first thing I did was line bore the stock engine and flux it for any case cracks etc. I than had the crank and all the new pistons balanced and had 1600cc cylinder and heads put in, and the fly wheel and clutch system was also upgraded. The heads and valves and ports where flowed and polished. A S90 Porsche cam duration was used and the electrical was converted to 12v from 6v. The carbs where dual cadrons, and a external oil filter was added. With all that mods it was easy to out run most 327 chevys. Only down side I did not upgrade the braking system and was a hope and pray to slow down and stop at high speed.

Yep best thing is to flow and port and polish and run your engine on a dyno before and after the mods to see what new results or if any results came about.

Keep up the Good work and thanks for the posting.
 

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Any idea of how much HP can safely come out it thes motors for every day use. Thanks for all the info on bore size , head work and exhaust.
Are you still working on an ECM for the bike. So many good things to come.

Thanks
 

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Discussion Starter · #19 ·
Baseline flow test completed

Guys,
I have tried to attach the Adobe air flow graph from the Superflow Honda Grom cylinder head flow test that I did today, for about 1 hour. I can't get it into Photo Bucket. So I'll just list the numbers. This is the baseline air flow test that sets the bar for any future tests or work.
Stock valves, seats, ports, chamber, stock everything:
All valve openings in mm, & corrected CFM:
lift -Intake-Exhaust
.5 - 7.6 - 3.4
1.0 - 13.5 - 7.3
1.5 - 18.5 - 12.3
2.0 - 24.2 - 17.7
2.5 - 29.1 - 22.0
3.0 - 33.9 - 26.2
3.5 - 38.9 - 28.2
4.0 - 43.2 - 29.0
4.5 - 46.6 - 30.9
5.0 - 49.1 - 32.1
5.5 - 50.3 - 33.1
6.0 - 50.7 - 34.0
6.5 - 51.1 - 34.6
7.0 - 52.2 - 35.2
Brian - 2nd post to explain the numbers
 

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Discussion Starter · #20 ·
What do the flow numbers mean???

OK,
* First it sets the base level for any future testing.
* It gives me a set of flow numbers to calculate from for advanced work
* The most important data is from 30% lift to 80% lift
* Max lift is only a very quick moment in time, 30% to 80% has crank/piston movement, or dwell
* The exhaust port is weaker than it should be about 68% to 70% of the intake, where it should be about 82% to 88% of the intake flow
* The throttle body flows 86 cfm, way more than the ports, no restriction
* This was the head only, so when I add manifolds, rubber intake tubes, air cleaners, mufflers, cats, the number WILL go down
* Increase the displacement to 170cc, + 36%, the flow needs to go up by at least 36% as well, max flow = 51.1 cfm X 1.36 = 69.5 cfm
More to come
Brian S
 
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