Topic: Low Buck 750 Cylinder Head Project

[TurboD]

I have been poking around on here lately asking about and discussing 750 engines and cylinder heads for performance use and racing, I have been a old school DIY guy for many many years.

In my resent travels (yesterday), I picked up another 77 750F parts bike that came with two 750F 410 heads. Its cold out side and the weather here has went south for basically the next three months, so I have decided to start work on one of the heads as a nice project for fun.

The fun and goal is to take a stock head and in a Low Buck fashion (no over size valves, stock intake mounting, no epoxy), and work on it to see the improvements gained. I thought that it might be fun to post work and any improvements along the way if anyone is interested, in some "free intertainment". I will flow test the head before any work is done, during the process and ultimately when I throw the "towel in". Hehe.  Again as long as there is interest.

I will say this is my first SOHC head that I will be modifying and don't claim to be an expert by any means, I have ported many of old big bore Kawasaki and Suzuki heads over the years, along with a number of small and big block chevy heads, Last winter I worked on a couple of sets of a the new LS1 chevy heads. 

Here are some pictures of the base head after disassembly and a little quick cleanup to see just what I dealing with to start off.
 

 

[KayOne]

Subscribed.

[dusterdude]

Me too


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[dragracer]

I'm in!!!

[TurboD]

Thanks for your interest, I am getting the fixures setup to hopefully have some baseline numbers in the next couple days.

[VTCBike750]

Subscribed

[Greg H]

I'll be watching this with interest 

[harald]

Very interesting, I might learn something

[joe p]

It will be very interesting. I have ported a few SOHC head for the street, and one I drag race that ran 11.00's in the 1/4 but that was a long time ago. I have a few heads 1971, 73, 74. I plan on working on one this summer, so this will be right up my alley.

[TurboD]

Thanks again for the interest.  I got a little side tracked today, I decided to start out with and clean up the second head, it has a little less carbon in the ports and is all around a bit cleaner. If I were going to just jump in and start work, it would not matter, but wanting some numbers up front I will take less work.

I still have a couple loose ends before testing, but I am getting closer.

[MRieck]

Looking forward to this.

[johno]

Me 3 Turbo, have fun, nice distraction from winter.

Just a thought, why dont you tackle it two ways over a period of time,

1st standard type hand tools basic drill , 1/4 " rod 8 inch long with slot in end and use strip abrasive,   super cheap and see what numbers you can get , might encourage the enthusiasts to have a go.

2nd use more advanced machining techniques and machines like valve facers and back cut etc.

Anyway I'm along for the ride mate. ciao johno

[cougar]

Hmm ! Subscribed as well ! Always eager to learn backyard tips and tricks  !!   ...cougar...

[BPellerine]

will be a good primer for new guys like me!bill

[nccb]

subscribed

[TurboD]

Ok, I finally got everything in place today to do a little flow testing.

Before I begin. I want to say the numbers that I post are from MY flow bench, when I built this bench it was calibrated using a Super Flow 110. That said my numbers may slightly differ up or down from other benches and or operators. Flow numbers can and will differ from benches and operators, things such as the size of cylinder bore used to test or if a radiused entry was used etc. all have an effect on the end results. When I test, I always try to setup and test to give results that are consistent and repeatable.

The bench that I currently have at home is setup to do intake (vacuum) only, so for now I will focus mainly in the intakes (flow number wise).

Stock 1977 750F "410" head
Head #1  Intake #2 Cyl.
Flow numbers @10 inches

Lift             Flow CFM
.100              24.7
.200              46.1
.300              52.1
.400              54.3
.500              55.1

This gives a starting point and baseline so that we can see just what kind of improvements can be expected using a Low Buck approach.

[TurboD]

With the festivites pretty much over for the day, I had the chance to work on the head a little. Going on Johno's request, I performed what I would consider a simple "stage 1" or "bowl cleanup" type of job. This would be simliar to something that a person at home could do easily using some basic tools.

I took care to mainly just remove any high spots and blend the port making it smooth, I did not enlarge or reshape the port. Again, I wanted to show what might be done by someone new to porting work.

Now Johno suggested using a drill with a flapper type sander. I would recommend shopping around and picking up a carbide or two, they can be found online or most auto swap meets for about $15 each. Also I would suggest a mandrel for holding the "sanding drums" or "grit rolls". When looking for a carbide cutter I perfer the small and medium oval shaped ones for motorcycle ports, the forth and fifth ones down from the top.

[TurboD]

Sorry for multiple posts, I dont know how to put pictures in between the paragraphs.

Here are some before and after pictures along with the flow numbers. When looking at the numbers, the low lift number did not change much as I would expect. Remember I did not enlarge or reshape the port, I simply blended and smoothed it out. the .300 and .400 numbers showed some improvment. By taking the flow numbers and doing a little calulation, the increase in flow would work out to right at 2 horse power, times this by 4 and now you would have a head that is capable of supporting 8 more HP. Not a bad little boost for the 30 minutes invested.

                    Before                 After
Lift             Flow CFM         Flow CFM
.100              24.7                 24.7
.200              46.1                 46.2
.300              52.1                 56.6
.400              54.3                 57.7
.500              55.1                 57.9

[EnginebyAdam]

You know I will be watching this very closely and taking notes Your plan for this head is very close to what I want to do with the F3 head I am looking at. Should be fun

[kghost]

Cool Project!

[Ace]

I don't have a flow bench, but I also have just cleaned up the ports in a head. Your pics are handy.  Good luck and the keep the posts coming.

[Tim2005]

Really interesting to see this, especially with the numbers. One thing I'd be interested to know- how do the other cylinders' "before" figures compare to the one you are working with- did Honda get all 4 equal?

[Tintop]

Really interesting to see this, especially with the numbers. One thing I'd be interested to know- how do the other cylinders' "before" figures compare to the one you are working with- did Honda get all 4 equal?

Good question, interested to see how this works out.

[johno]

Turbo, I suggested the 1/4 rod with slot and course tape because those long shanked carbides you have are $100. each in my part of the world , so if you buy 3 of those then a some course , mdium then fine tape it would work out around $400. before you start , be easier and more performance then to get a pro like Mike to do a basic port and valve job.
I have a good selection of cutters but it amazes me If you use really coarse strip on a rod how much and how quick you can  smooth the port and blend the guide area  very quickly , even to the point of leaving it with course finish to hold a boundary layer of air and maybe help atomise the fuel.

When ever I used to do minor repairs , like a valve job or change seals etc for a customer I used to allow myself 1 hour to tidy up ports like that, the customers always commented on the difference in performance when they got the bike back, cheap, quick and feel the difference , tossed it on the bill and everyone was happy.

[Bill/BentON Racing]

Great job and pics. Thanks and keep ' em coming! Very good! Appreciate your sharing, Bill