Author Topic: Porting a 350F head.. UPDATE (Read 3728 times)

mattcb350f · « **on:** September 08, 2007, 08:25:42 PM »

I was just eye ballin' my little CB350F's head as it lay on the bench and noticed that there is quite a lot of room to do a little cleaning out of the ports. Would a porting job on this engine provide a noticable HP increase? should I bother at all....
I'd appreciate any advise, Matt.

mkramer1121 · « **Reply #1 on:** September 08, 2007, 09:47:42 PM »

According to my Clymer's, the only one of the small 4's that should not be modded/etc. is the 350. You should upgrade to a bigger bike. But the book is from the early 80's when there were much more readily available.

From my limited research, porting always helps, as the stock heads don't allow the CB's to properly breath.

mattcb350f · « **Reply #2 on:** September 09, 2007, 07:07:56 PM »

Upgrade to a bigger bike he says..

sounds like 350F envy.

Seriously, anyone ported out a 350F and found anymore power?

kghost · « **Reply #3 on:** September 09, 2007, 07:21:52 PM »

I love my 350 ...could use a little more umph tho...

Course doesn't matter how big...ya always want more umph.

I'd be curious what your results were if ya did it.

Come on be a trend setter.

mattcb350f · « **Reply #4 on:** September 09, 2007, 07:32:38 PM »

Ya, shortly after posting about it I knew I would probably get in there and mess around with it anyway.

Gota tinker with something while I'm waiting on parts.

In theroy it can't hinder performance,
I was just wondering if anyone else here has done it.
I guess we'll find out in the spring when I get er' humming again!

mkramer1121 · « **Reply #5 on:** September 09, 2007, 07:36:28 PM »

I really should scan the old clymer manual pages...Talks about how to upgrade the small fours (CB350-CB550). Like i said, it was the book saying you should upgrade, not me. I'd do it, it can't hurt anything.

bill440cars · « **Reply #6 on:** September 09, 2007, 07:40:23 PM »

Like Mike says, go for it.

You've decided to anyway right?

Not sure about anyone doing a 350F but Jim (Aptech77) has got a 400F that's quite a handful, from what I gather and what I've heard.

I know, a400F is a bit more anyway but, wouldn't hurt to hear from those owners, would it? BTW, I've got one of each, that I hope to go through one of these days and revive them to a higher (even if not much higher) level of performance myself. So, I'll be listening also.

Later on, Bill

Sam Green Racing · « **Reply #7 on:** September 09, 2007, 07:50:32 PM »

I wonder if Mike the head master Reick can shed any light on this one.

Sam.

mkramer1121 · « **Reply #8 on:** September 09, 2007, 08:06:13 PM »

I was just glancing at my ancient Clymer's performance section and it said a hopped up 400F could accellerate with the KZ900's/1000's and pull away from them in the twisties...I'm working on scanning the pages in right now so hopefully I can post it at sometime.

mattcb350f · « **Reply #9 on:** September 09, 2007, 08:26:41 PM »

Accelerate with a KZ900

Those folks at Clymer sure are optimistic!
I keep a look out for the scans, thanks mkramer1121

mkramer1121 · « **Reply #10 on:** September 09, 2007, 08:45:30 PM »

You have to remember, the 400 had 6 gears, not the standard 5. And an overbored 400 to 466 is lightening quick. At only 350lbs, with the right rider you have a chance...

Now, bored to 490CC like Kaz did.....

Dougy Dougy Dune Buggy · « **Reply #11 on:** September 10, 2007, 06:55:05 PM »

Hey Fellas & MKramer to be specific
Hijacked this thread a bit, but my old 400 Four
ran away from my Brothers KZ650 BAD, and he had lots of Yoshimura parts, mine was built by a Honda Mechanic who raced Superbikes back in the day and he said after he buit it-DO NOT BABY this motor, well i had it up to 120 in 5th before a CHP caught me, another story for another day, but the 400 would pull the front end up at least a foot in 3rd gear....so i'm in agreement with MKramer..i see nothing wrong with "cleaning up a bit" or matching ports
Later
DWYJ

mkramer1121 · « **Reply #12 on:** September 10, 2007, 07:15:09 PM »

Really, that's APTech talking through me, I've heard enough from him the last few times we've been out about Kaz and beefed up 400's....

All in good fun.

333 · « **Reply #13 on:** September 10, 2007, 07:23:37 PM »

My '72 CB450 would keep up with (what would later become my) a K4 750 until I had to shift out of first. Does that count for anything?

My 2 cents? Do it!!!

Dougy Dougy Dune Buggy · « **Reply #14 on:** September 10, 2007, 07:30:52 PM »

yeah....i've got a 1972 CB500 Four with MANY engine upgrades
and the previous owner said he "matched" the ports to the intake and exhaust(cleaned up) and said he wouldn't take any more material
than neccessary so as not to reduce vacuum severely..like the old
boss 302 that had too big of ports and could not "flow" as well as a 2 barrel windsor motor! Keep us posted with pix if ya can Matt!
Doug

mattcb350f · « **Reply #15 on:** September 10, 2007, 07:38:33 PM »

I talked to a friend of mine that's going to do the machining work for me, he builds high end car engines in Toronto.. Lamborghini, Ferrari, Porsche etc. Convenient eh!
He says we can work some magic into this engine when we get at it.
He agrees with porting and has a few more ideas too.
I want to keep the rest of the bike stock though so I won't be able to shed some weight which would really make er' sing. Anyway,
Thanks for the interest in the thread guys, I'll keep ya posted.
Matt.

schneider419 · « **Reply #16 on:** September 11, 2007, 05:43:14 PM »

here's what I've done so far. i got a head assy. off of ebay for $25.00 or so. so far I've re- cut the floor of the intake port some where it turns to drop into the cylinder, made it a smoother bend and not so much of a sharp turn. i cut the intake guide closer to the top of the port to open the area up a little. i did remove some of the rough castings in the intake port. i don't want to get the port too big because i don't want to lose too much velocity of the intake charge. i may mill the head to flat or .010'' to .015''. I'll more than likely do about the same to the exhaust port too, but i won't do this until this winter. as of right now I've put a 40 tooth gear on the back instead of the 38 tooth, it hurt gas mileage some but woke the bike up on take off. this is my first try at 4 stroke motors. more to come later i hope.
schneider419

mattcb350f · « **Reply #17 on:** September 11, 2007, 05:51:47 PM »

Thanks schneider419, Thats sort of what I have in mind to do. I too think there is more to be gained from porting the exhaust side, especialy the area behind the valve guide. I was also thinking about shaving it down a little but I haven't looked at that yet.

derekd · « **Reply #18 on:** September 11, 2007, 06:28:07 PM »

Are you familiar with team Hanson Honda they might be a good reference source.They have a great build on there site,a 350f race bike thats outstanding. Have fun and keep the updates coming.

Jonesy · « **Reply #19 on:** September 11, 2007, 06:47:56 PM »

Quote from: DWYJ on September 10, 2007, 07:30:52 PM

yeah....i've got a 1972 CB500 Four with MANY engine upgrades
and the previous owner said he "matched" the ports to the intake and exhaust(cleaned up) and said he wouldn't take any more material
than neccessary so as not to reduce vacuum severely..like the old
boss 302 that had too big of ports and could not "flow" as well as a 2 barrel windsor motor! Keep us posted with pix if ya can Matt!
Doug

I did that stuff to my wife's 550 last winter. All stock except the ported head. Really livened up the top end... It's pretty hard to open the ports up so big that you'd lose much vacuum.

http://www.sohc4.us/forums/index.php?topic=17374.0

MRieck · « **Reply #20 on:** September 11, 2007, 07:19:03 PM »

Quote from: Jonesy on September 11, 2007, 06:47:56 PM

Quote from: DWYJ on September 10, 2007, 07:30:52 PM
yeah....i've got a 1972 CB500 Four with MANY engine upgrades
and the previous owner said he "matched" the ports to the intake and exhaust(cleaned up) and said he wouldn't take any more material
than neccessary so as not to reduce vacuum severely..like the old
boss 302 that had too big of ports and could not "flow" as well as a 2 barrel windsor motor! Keep us posted with pix if ya can Matt!
Doug

I did that stuff to my wife's 550 last winter. All stock except the ported head. Really livened up the top end... It's pretty hard to open the ports up so big that you'd lose much vacuum.

http://www.sohc4.us/forums/index.php?topic=17374.0

If vacuum was so important any brand floor cleaner would have a .250 inlet. Velocity would be pretty good. When you consider what is pushed secondary to revision, poor seal, etc, etc

Dougy Dougy Dune Buggy · « **Reply #21 on:** September 11, 2007, 08:06:47 PM »

That came out wrong huh? I meant "matching" the ports would not affect flow charachteristics
like taking too much material from a ports shape might..wrong analogy using the Windsor motor
reference. I stand corrected MRieck, and i believe your pix of your headwork were some of the most sano i've seen to date, were those 500/550 heads??
Later,
DWYJ

mattcb350f · « **Reply #22 on:** March 05, 2008, 08:15:47 PM »

No turning back now

Got most of the rough stuff done... Need some smaller cones to finish it off:

Matt.

fishman_Phil · « **Reply #23 on:** March 05, 2008, 09:02:18 PM »

Do some porting work. Make the engine breath better. Someone mentioned the 400F 6-speed gearbox, fit that as well. I have an engine here that has one fitted that a previous owner was going to use in a cafe racer.
The only reason why it will not be fitted to the bike I am currently working on, is that she is to be restored to original. Maybe later a 2nd 350F that I have might like to have this engine and 400F box fitted to her.

News:

Author Topic: Porting a 350F head.. UPDATE (Read 3728 times)

derekd