4 valve head swap?

Injected wrote:

Evads dyno sheet came up at 82HP... If Dave did get to 90 he would have mentioned it.

I know he's running .360" lift cams with a cleanup port match job with 10.5:1 compression.

Even if he went with some huge cams and a full on ported head that motor would be hard pressed to crack 90 without going to a bigger bore with more compression... you need that big bore to get there without power adders.

This is not player hatin... I just know from experience.

Air cooled naturally aspirated (NON TURBO) 650 based motors - I have never seen a dyno sheet at 90HP for a street motor, except mine... which at that point was a 831cc 13.5:1 big valve, full on drag motor barely able to make it a few blocks without melting my legs off!

Most the 810 based street motors (under 11:1) I have heard of make about 80 HP unless they are running radical cams (+.410") plus the head work to make them breath better (+75CFM)... you also need carbs in the 33mm range (non BS34s !!!)

I am just letting you know because I have built 3-4 big bore non turbo 650 motors - carb or FI... does not matter.

You can't get to the 100HP range working with a small air cooled motor without power adders - a turbo 750 or going to a swapped 900 motor with a 1075 kit, as far as the 2V stuff goes - were talking street going motors here... naturally aspirated you need big CCs unless it is an all out race motor.

You also need to know that HP ratings from manufactures are very subjective and dyno numbers are sometimes also subjective (some more real than others)

Your on the right track with the 4V water cooled idea... that's why they got away from the air cooled stuff in the first place.

Good luck on your conversion - it would be interesting to see what you come up with.

A little late to the party, but what about this bike?
Tuning for Zephyr 750

To quote Steell from a few years ago when discussing this bike( Re:100 hp KZ650 ):
steell wrote:

That's 93 PS, or 91.7 hp (according to an online converter), and that's at the rear wheel, so somewhere near 113 hp at the crank.

He says something about 2nd gear wheelies, wish my German was better.

Google translation

Looks like the 83-85 GPz750 head combustion chamber as I posted earlier, and it has not been cut for more compression.

A 55% increase in power is nothing to sneeze at!

Injected is there any chance you could post some pictures of your bike?

I'm assembling one of my spare 1980 twins for my Lady, and clearing out all my 750 four stuff. My brother has the Turbo and the spare Turbo motor, but everything else needs to go. I'm pretty certain that over 125 hp at the crank is possible, assembled by a professional builder/tuner, and the parts are there to do it.

It's all listed in the classifieds now

hardr0ck68 wrote:

Injected is there any chance you could post some pictures of your bike?

Hope he don't mind if I post the one from cyclemadness

And this thread www.cyclemadness.com/cmforum/index.php?topic=645.0 has a link to the magazine article about the bike.

I'm impressed!

Pic deleted because there are better ones on the next page, so no sense wasting Woody's bandwidth.

Yeah, that's OK... I posted a bunch of pic's in there because it seems to be easier for me...

I rode that bike on the street for a while with a MTC 13:5:1 831cc kit and a big valve head with GSXR 33mm flatslides - power wheelie in 3rd gear at 100MPH... that's when I knew I had a monster on my hands.

I am currently reusing those old pistons on a street motor I am building, but this one will be much milder... probably shooting for around 75HP instead of 90. Cylinder block and head are stock looking and the only non standard thing on the bike is the VM26 carbs - it will have stock air box and 4 into 2 exhaust. Head flows 72CFM with a Andrews 20 cam... which is matched to the carbs max airflow. Compression has been lowered to about 10.5:1

Can I post A few of that bike?

:laugh:

:laugh:

:huh:

It gets around! I just like it better, my way.

Here's an old picture:

That's a bit much on the pic's... I don't want to high-jack this thread and make it about my bike - then you throw in Noard's bike? (which is a turbo motor!)

I think we should keep the perspective of the 4V head swap experiment and not shift it onto drag bikes or race motors.

If anybody needs to see pic's of my stuff they should go here:

www.cyclemadness.com/cmforum/index.php?topic=507.0

www.cyclemadness.com/cmforum/index.php?topic=550.0