Workup to 900F Cam Swap

[crestview750f]

Setting-up a discussion that will occur in near the future with 900F cams install in my 1982 CB750F SS.  Here's where we started after getting the carbs cleaned and a Dynojet kit.  Jetting was 68/130 (DJ jet, 140 Keihin equivalent), slide drilled out 3/16 holes, clip third from the top.  The lowest rich data point on the dyno was 10; I certainly bagged that one...cough...cough...cough...44hp....



After studying the AFR, and returning to stock jetting, we gained 12hp and were able to read something above 10 on the AFR.  On the Milton dyno, the owner (experienced tuner and racer) has found 13.2 - 13.5 renders max horsepower.  Given that is rich, compared to 14.7 stoc, I'd be happy with a tad rich and still making power.  Currently, stock CB750F with: Yoshi-style 4-1 pipe, stock jetting (68/102 jets, 53E jet needles), paper filter, stock air box...56hp.
Here's the current jetting results:



The CV diagram that shows how the parts work and when:

[TOOLS1]

I have only used the SOMP Dyno and plug readings to do jetting changes. Looking forward to seeing how each change actually affects the curves. Do you have any estimates for parasitic loss?
TOOLS

[crestview750f]

Tools1,
I did some reading regarding parasitic loss that could be considered corrections; my question is the factory's claim of 76 hp: at the crank or at the rear wheel?  Makes a difference since the dyno is the "rear wheel."

One correction is friction loss; depending on the engine, it could be as much as 15%.  That would render a formula of (56/0.85)-56=9.8.  Add the 9.8 to 56 and we get about 66hp; near the 76hp claim by the factory.

Here's the link to a good read .  Not wanting to add correction factors unnecessarily, and perhaps skew the data/hp results, I'll just stay with using the same dyno, same soft/hardware, and the same dyno operator.  The results will be the results; whatever hp I gain, others can determine if the swap is worth the investment and make an informed decision.

Another factor the dyno operator mentioned was "different tire, different results."  Kenda 761 factor may be worth some mental brain power.  ;)

[motogrady]

I kinda remember reading most factory dyno tests are at the crank.

Was reading up on the different models and thought they stated the F models produce a few more hp.
How they get it I dunno, I've looked, but everybody seems to think the K, C and F engines are identical
from the factory.

[TOOLS1]

The 75-76 SOHC F had a different cam, and jetting then the K, and the 77-78 SOHC F had a totally different head. The DOHC engines are all the same.
TOOLS

[crestview750f]

Appointment to install cams this Friday; should pick up Saturday and shakedown the following week before putting on the dynamometer. Given cam chain tension will be reset, and valve clearances will be properly set, I'm not really sure if we can determine what hp/tq increase the 900 cams render. Nevertheless, looking forward to getting it on the dyno afterwards!

[crestview750f]

Reading up on rear wheel hp conversion to crank hp, an effort to determine if 900 cams are worth the swap. Last dyno was 56 hp; divided by .88  (driveline drag loss 12%) renders 63 at the crank. Other converters reflect 78 hp.   Will just see what happens with the butt dyno and, later, the Dynojet.

[TOOLS1]

Interesting, that puts it right around where Honda rated it. I wonder if they rated it with, or without the alternator?
TOOLS

[crestview750f]

Delay in the cam swap; cover bolt snapped off and will need to have it extracted/helicoiled if necessary. Stay tuned for details.

Do you engine builders put milk of magnesia on bolt threads to avoid dissimilar metal corrosion? We used it on bolts in the hot section of T-58 helicopter engines years ago. I have been thinking about steel bolts threading into aluminum heads.

[crestview750f]

Cam swap complete! Mechanic dropped a sprocket bolt down the cam chain hole and had to dismantle the engine to retrieve it. Couple of weeks to ride it around, shake it down, then off to  dyno for tuning. Hoping to have the 900 cam swap dyno sheet for review in a couple of weeks.  Until then, ride safe, always!

[TOOLS1]

I'll bet there were a lot of 4-letter words spoken.
TOOLS

[crestview750f]

Seat of the pants dyno says  the power curve is gradual; 3rd gear pulls from 1/4 to WOT is amazing. Couple of more weeks and we dyno; will post results for all to see.

[shinyribs]

crestview750f wrote

Do you engine builders put milk of magnesia on bolt threads to avoid dissimilar metal corrosion? We used it on bolts in the hot section of T-58 helicopter engines years ago. I have been thinking about steel bolts threading into aluminum heads.

I've heard this mentioned before. I think of it like this:

1- I don't want no aluminum bolts
2- I definitely don't want a steel head
3- That 30 year old bolt I pulled out looks good, if it makes it another 30 years it'll be outlasting me.


For the most part, the whole dissimilar metals thing is take only an issue where electricity ( primarily high voltage) is flowing through the joint. Not really an issue in an engine.

[crestview750f]

Finally!!
During cam swap, the cam chain tension was set and valve clearances were also set; cams were installed using factory markings (no degreeing of the cams). Bottom line, up front:  the bike properly jetted in stock form, dyno'ed 57 hp; with 900F cams and running rich, 59 hp.  I can gain a few hp by changing the main jet from 102 and install 98.  On this dyno sheet, the dark blue line is stock cams; thin red line is 900 cams

To bring you up-to-speed, had to rejet before the cam swap due to AFR at or below 10.  Power went from  44 hp to 57 hp with the rejet alone.  But, I changed coils after the cam swap and before this last dyno run.  The 140403 coils, Accel, caused EMI (could not get RPM readings) so the dyno run was to get max hp and AFR.

I'd venture to guess, 3-5 hp lurks with the jetting change.  With that in mind, is a 14% gain in hp at the rear wheels worth it?  May not be worth it to everyone but it's still a helluva lotta fun!