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Post by alex on Apr 28, 2018 17:13:03 GMT -5
As there are no OEM, NOS or used cranks available I have to have mine rewelded. The hardest part was finding a shop to reweld and grind the crank to spec. Since the head was good, I don't want to spend the extra money to machine it down. I figured I may as well stroke the shaft to raise compression. I saw there is a 2.43mm gap, i figure 2mm upon pullung apart engine. Any one have an opinion as far as how much to add? I'm thinking around 1.5mm, seems like madmatt says there is more room.
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Post by madmatt on Apr 29, 2018 4:11:33 GMT -5
Giggly giggly good fun! Ok, away from all my notes etc... but I do recall my next plan was to deck the block around 1.5mm so that's 3 mm I would have lost. So for arguments sake you could do 3 mm and likely get away with it from a clearance issue... But I'm not sure how close the upper rings would be to the cylinder chamfer. Bear in mind this though... I'm currently around 10.5:1 comp with no issues on pump gas... Somewhere in my mind I recall calculating that the next 1.5 mm of the block would send me well over 11.5:1 into 12:1 territory. This would be the issue with going crazy on the stroker. As when I took off head depth, I also removed quench pad, and therefore the comp did not go up as fast! If you did 3 mm... with the added down stroke you might just go off the scales on comp and blow it up It would take some math.
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Post by chooch on May 14, 2018 15:41:28 GMT -5
What does it do for the engine capacity? The increase may not a cost effective solution compared to lowering the compression for a turbo?
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Post by madmatt on May 16, 2018 21:02:23 GMT -5
Just a skim will decrease the capacity... but the overall bump in torque is usually worth it. Really needs a cam to make it sing.
Of course it won't outperform a turbo... but the sound of NA power is just oooh soo sweet.
And cheap... cam, skim, done.
Now stroker crank is getting into turbo money, but if you have to spray weld the crank to get it useable... it's a fixed cost. And stroker crank will keep or increase theoretical capacity, depending on the numbers.
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Post by alex on May 19, 2018 14:00:52 GMT -5
Top ring 3mm down from piston crown. 6mm down from deck height (according to the cylinder wear/discoloration) on my block. I measured the piston volume cc at about 5ml. I will measure CC's of combustion chamber once all the parts are cleaned up.
I found a perfect crank in Spokane WA, last one they had. No rods or pistons, but alas, I know for sure i will not be the last one searching for a crank. It will good for the site to have these measurements.
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Post by alex on Jun 13, 2018 2:33:39 GMT -5
SUBARU JUSTY 1.2L 9 VALVE Combustion chamber average volume as witnessed by plexoglass, vaseline and a child's tylenol syringe is 45ml, AKA 45CC, max measure was 46.25ml. 9 to 1 seems like bullshit to me (1988 carb 4x4 1.2L). NO WONDER you were able to shave over a millimeter off. headgasket looks to be 1mm thick too. piston measured at a pube hair over 5cc.
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Post by jasin on Jun 14, 2018 1:00:05 GMT -5
I confirm your measurments resaults, I had similar, but from my point of view accuracy of such measurments is quite low anyway, assuming that piston velume is 5ccm, head gasket thickness is 1.5mm - to achive CR=9.1 chamber volume should be 37,77ccm
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Post by madmatt on Jun 17, 2018 22:25:54 GMT -5
yes.. dug up some numbers...
I have no stock head cc numbers, however after a very light skim I had
CC of piston stroke = 396.8 cc
CC of combustion chamber = 48.5 head = 37 head gasket (80mm/1.4mm)=7 cc piston dome and block =4.5 445.3/48.5 = 9.18
I went back and had 1.3 mm taken off (for an estimated 1.5 total from stock)
this led to a head cc of 31cc
Which lead to 439.3/42.5 = 10.33
My next step if I do anything is to knock the block down... or make a thing head gasket... and go for 11:1.
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