36hp tuning thoughts

Ok two blog posts in one night.

This one is more as a place to jot down some more 36hp tuning ideas. Some of these are older and others new or at least new to me.

Cranks. I want to make a billet crank. It sounds easy when you say it fast.

The reasons for this are as follows. Stock 36hp cranks crack. Stock 356 cranks crack (nfi if all types do but I belive it is very common.) you can get aftermarket 36hp cranks but a) they are decient money even before you have them crack tested and shipped. plus i'd want to get it counterweighted, nitrided and shot peened, more $. what you are left with at the end of this is a rather expensive 50 yo crank with limited grinds left on it and made using 50 yo metalurgy knowledge. PLUS I have been tossing around the idea of increasing the journal sizes. At the very least the centre main but possibly the crank throws and maybe even 1 and 3 main as well. Why? I hear you ask. My reason was to increase the overlap on the throws. I have drawn it up but have yet to bother calculating the increase in overlapping area, needless to say it is a lot... somewere roughly around double the area if you step from 50mm main and rod journals on a 69mm stroke crank to 55mm on the same stroke. My thoughts on the centre main were backed up when I read this post on the samba: http://www.thesamba.com/vw/forum/viewtopic.php?t=428447 imparticular the letter copied there.

maybe my reasoning is a little different from that in the letter but that is why i'm not an expert (and have so much to learn)

This makes me like my other thoughts on lightening the pistons/pins etc but does put into question my thoughts on running 55 rod journals. Yes I was thinking or using 40hp rods. The rethink is due to the increased weight of the rod and journal itself. Having said that I haven't even tried mocking up a 40hp rod on a stock 64mm crank to see if it will fit.

Ok my reasons against just fitting a 365sc or 912 crank are that again it uses old metalurgy they still weren't designed for the hp I want and I want to use a different shape counterweight. The last one may sound petty but I have seen how effective the shape weight I want is.

That leaves the SCAT 356 crank... but at $2500us or there abouts... no thanks. Sure, the metalurgy will be top notch but again the counterweights, plus to be honest I only really want to go to a 69mm stroke not 74mm. You may think thats silly (which it probably is) but well that's what I want. Another reason is though i'm not set on 55mm rod journals the scat crank doesn't have them. I was also hoping to find a bearing that was a suitable width but maybe even up to 60mm journal. I'm sure the oiling would need to be modded to cope but I never thought that this would be easy. (to be honest i'm sure I have no idea what I would be/am getting myself in for trying to design a crank)

I sat down and worked out an order of opperations to machine up the crank, no idea if it would have worked as I haven't used a lathe since the late 80's but I liked the ideas anyway. It was an interesting exercise in thinking things through.

That is only one area of the 36hp I have been looking at. Over the months/years I have thought about my ultimate version of most parts in a 36hp motor. Parts that have gone past just thinking about stage are the rockers. I've been through 3 different designs and eventually went bact to the first. I still need to do a stress analisys to see if it would work. I also considered running different rocker designs on the intake and exhaust. From my rough working concepts the exhaust rocker would need to be stronger as at the end of the combustion stroke it is initially opening into a pressurised chamber. At no stage does the intake valve have to do so. A lighter rocker on the intake valve would nicely offset the heavier valve, hopefully this would mean that if you got the balances right all of the valves would bounce at the same rpm on a given spring pressure. If running the same weight rockers (in my head at least) you could run lighter springs on the exhaust valve due to the lighter, smaller valve. Again NOTE: this is my own missinformed type of logic. If it actually happens this way in the real world only time would tell.

i guess i only got to two areas i have been thinking about. stil a lot more to put down.

i won't tell you my ultimate goal hp from a n/a 36 based motor on pump gas as you would probably laugh. to my knowledge no one has gotten close yet but i firmly belive that it is do-able and to that end i'm trying to think of every possible way to get there. even a fracton of a hp is useful. hell every fraction of a hp from every available source would be needed to get to my ultimate goal hp as i'm not thinking small. do-able but not simple.