magnum stuff

So hopefully you say gabe’s awesome polini guide, and I thought I’d show you mine. I’ll be honest, the quality of my work is subpar. The exhaust port is nice, but the intake embarassing. Regardless, it runs really well, and its done stupid speeds, and It’s going to only get dumber.

In the cylinder (exhaust raised a lot, widened a lot, intake opened completely) The little scuffs, one at the rear of the port and the other 2 in front were me not good at using a dremmel.

The intake, again opened up all the way, and I filled it a bit with JB because the malossi 4-petal has a lot of wasted space in there

Transfers opened up just a bit. The most important part is opening up the upper transfers. Plenty of meat on the cylinder, so its un-tapped potential. Also, remember you MUST open up the outer portion of the exhaust port to to actually match the flange of your exhaust. Polini’s are tiny, just a bit bigger than stock, but much smaller than 99% of expansion pipes (except proma circuit, they are a perfect match).

Paz originally built my ZA for some other fella in SF. He didn’t go super deep with the upper transfers, but everything is nicely done. A roller rod was pressed in at the same time. The crank has 2k+ miles on it, so super solid!

Thats my ugly polini. I’d like to get another one in the near future as I worry this one may be slowly heading out. It was seized before I bought it, and there is now a fair amount of discoloration on the nicasil around the exhust port. All the cross-hatching is gone. Compression is OK, but not as good as it could be. That, plus I’d like to re-port another with a lot more care.

So in semi-related news, I’m going to make this thing rip harder than it ever has. Either selettra or HPI ignition (selettra is a few OZs lighter, but I think HPI has a little better curve), and my flatslide mikuni.

I want to race something come april, and even though this probably won’t be competitive, with the right gearing (N8P forever!) it should have really good pull. I don’t want to scrape up my LTD seat or tank, so I’m going to be using a freespirit pan and my spare C5 tank. That plus my disk brake EBRs. My goal is to have it running and semi-tuned by tomorrow. I’ll keep posting. Whistler from the 20th to 27th!


9 Comments so far
Leave a comment

wowzas that is a wide exhaust. i’m curious what a measurement of it is. better pics of the top transfers! good work duders, is it cool if i use some of these pics on my post?

Comment by gabeb

Didn’t I sell you that gently seized Polini? Blast on!

Comment by Responsible Jon

yep, this is that polini.

Comment by zack

oh yea, feel free to use any pics. I’ll get some measurements today.

Comment by zack

Great to see the ZA is still holding up strong. Yea I don’t port customer motor builds all the way.

Comment by Paz

[…] 1 magnum stuff « mopeds […]

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did you ever make those measurements on your exhaust port?

Comment by sethk

no not yet. I’ve been away from the cylinder for some time, but I’ll make a port map next time i have a chance

Comment by zack

devin was just to explaining to me this weekend the difference b/t porting the top transfers vs the bottom transfers. very interesting stuff. i’ll probably end up taking some meat off the top transfers (which is what effects top end if i remember correctly) to squeeze some more rpm’s out of it.

did you widen your transfers at all? seems like if i hogged them out at all i’d be getting into adding to my cases territory.

Comment by gabeb

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