TOPIC:

After doing a lot of talking, here are the first steps in my Vintage racer build.

It's going to compete in the open class in the Italian Vintage championship. It's going to be up against big 1100 Zed's and Sozooks but as we dont have many horsepower tracks in the calendar, hopefully the quicker, more modern handking handling will make a difference.

Let's start with some frame bracing then?

bottom top tubes are now braced to the top one and also felt like adding to side supports to the steering head that was sticking out so much

another shot showing smal triangulation under new tubes

planning to use the two bottom holes in the cases (they will bolt to those two new ears) as well as going for rigid mounts instead of the rubber ones

above the rear cross tube i welded four ears. gonna bolt to them a1/8" ally plate to make that area more rigid, that plate will serve also as the carrier for the total loss ignition battery

last, never like the idea of the left engine spacer being bent by the chain tension, ite welded to the frame now + a msall bracket transfer loads to the rear cross tube.

all in all, about 1 pound of gusseting added, but have removed about 3 with all the those brackets and spacially THAT side stand bracket!

bosses for the race stand bobbins welded to the s'arm...

last, whiel at the welder's, filled up the side chamfers in the combustion chmaber, effectively "bathtubing" the chambers. this will let me to control better the squish areas as well as making them wider. as a bonus, chamber volume is smaller so yiu can get away with a less bumpy piston. head has been surfaced already, have to reprofile the inner side now.

KZ750 or 83-85 GPz750 head?

gpz 83

turboguzzi wrote:

last, whiel at the welder's, filled up the side chamfers in the combustion chmaber, effectively "bathtubing" the chambers. this will let me to control better the squish areas as well as making them wider. as a bonus, chamber volume is smaller so yiu can get away with a less bumpy piston. head has been surfaced already, have to reprofile the inner side now.

Also a great way to screw up pressure recovery in the cylinder.

I know what you're trying to accomplish but there's a down side to every up side & sometimes the hoped for improvement cancels out other important characteristics. JMO

Not trying to be a dink to you, it's obvious you're not a hack. Just something for an intelligent guy like yourself to consider...

Larry C

x

hi larry

not sure i understand what you mean by pressure recovery. can you explain?

I had pretty good results with a similar operation on my 500/4 racer, built a 0.2" wide, 0.03" thick squish area and was able to run 13:1 CR, 28-30 degs advance without any detonation. see pic

Would be interested to hear your recommendation regarding max CR for a road racing 810. We are allowed to use only pump super premium 98 octane + some additive, so all in all about 100 octane.

injected, not a bad idea, lets see if i find the place to do it.

Sure, if i had the means to scan the CC and then CNC each piston accordingly it could be great, but well above my means now. with this approach all i have to do is turn the pistons on a lathe for a flat external ring and then deck them to the desired squish.

TG

x

We have one. Use it mainly to check thread profiles, keeper angels, etc

ok injected, see now what you mean by a 10X, we actually have one of these at my work place. will give it a try.

before the welding i did a plasticine cast and sliced it to get the radius of the spherical chamber. traced from that a small carton template, so sounds like we are on the same page after all.


grazie mille

TG

turboguzzi wrote:

before the welding i did a plasticine cast and sliced it to get the radius of the spherical chamber. traced from that a small carton template, so sounds like we are on the same page after all.

Yes... that was a good idea.

Here is that tool I made up... picture is a little fuzzy because it was -2C this morning taken before my coffie!

I am based in milano, where are you? by the way you spell coffie it sounds like netherlands

nice tool, would be great to see how your chambers look like now.

Larry, did a bit of homework and sounds like pressure recovery is what i call the diffuser effect when the gases enter the chamber past the valve. So yes, i am aware of a possible downside, in any case. Still want to keep a good squish band, with the current welding i should get something like 28% squished area. really worked for me in the past.

What i might do, time permitting, is play with plasticine and thread streamers in a spare head to see if there's any point in chamfering only the area near the inlet valve for a bit of a diffuser effect.

TG

I am missing the point on the tool (pun intended!) where is the cutting edge? What are you trying to cut? I believe you are cutting a deeper (or new) squish band, but how do you cut it without the tool beating up the cumbustion chamber dome?

x

Awesome... Injected you are a cool cat! It has been a long while since I actually learned something on this forum.

In shop class we spent all our tume rebuilding lawn mower engines... i only used the mill and lathe for maybe 2 class periods in my 4 years. Damn shame the shop teacher was a perfectionist and machinest by trade and basically he hated to see the sloppy work we would turn out. Great guy, not so great teacher.

So when would recomend doing something like this? What compression ratio would require it? Could this be at all benificial for a street machine? It sounds like there is a risk of messing with the heads flow (diffuser effect?) so it this something best left to the professionals?

::EDIT:: Sorry for the hijack and thank you (injected and turboguzzi) for the info!