Why do so few people go for an 86 mm crank?

Friday, 24-Mar-2000 14:01:29

208.225.199.161 writes:

Why do so few people go for an 86 mm stroke such as a 2213 with 90.5 bore? How hard is clearancing the tin, and engine compartment? I figure that to get 7:1 CR with 5.5 rods the engine would be about 0.5" wider. My thought is if I am going to all the time and expense to build a motor, a few more details are no problem.

Randy

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My motor is more then a 1/2" wide on each side,(i use to run .512 shim under my cimas) and there was a littel clerancing done just under the seal area, from the top you cant see it.

Go for it.

Muffler Mike

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84mm was considered the unofficial limit with cima barrels. Berg used to have longer 90.5s but those are long gone. Now there are longer 94 mm cylinders so you can build the big motor of your dreams. With regular length cima 90.5,92,94s the longer stroke cranks pull the piston too far out of the bottom of the cylinder. This can cause the motor to unexpectedly explode . The higher you rev the motor ,the higher the compression and the shorter the rod ratio the worse the problem gets. An 84 crank with a 5.4 stock length VW rod spinning 7500 Rpm would be as far as I would push a street motor. Also your deck hieght can effect this also. The more deck you run the farther the piston drops out the bottom. I ran an 84mm with 5.5 rods and 94 cylinders and 8 to 1 compression.

I pulled the motor down after 5000 miles and noticed a pronounced wear line at the bottom of the pistons from scuffing the cylinder. I reassembled the motor with a negative deck of .050 thousands (piston out the top of the cyl.)and plunge cut the heads .100 thou. to give myself .050 deck. The result was that the piston now sat much higher in the cylinder. That same motor now has lasted for years on the street and has been abused with sustained high rpms and has not had a problem. You don`t need to go to this extreme to get your piston higher now becuse they make copper shims that in effect make your cylinders .060 longer and if you want you can buy the longer 94s and run a 90 mm crank with no problems. Good luck,

Mark H

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people would rather run 94's and smaller cranks so they et the displacment. bottom line, big pistons are cheaper then big cranks.

Friday, 24-Mar-2000 20:15:16

205.188.199.140 writes:

i personaly like the 90.5's. thats why i run the 86x 90.5 thick cylinders rule. and big cranks having lots of stroke have much more torque.

when i had my old motor combo of 86x90.5, 7.2:1 compression with ported 40x 35.5 stock heads 48 idas and engle 120 cam with 1 5/8"header and turbo muffler dynoed out at the wheels to 138 horsepower @5800 rpm and 139 foot pounds of torque @4300 rpm. now this was at the wheels not at the flywheel. that was then but now the motor has a bigger head and cam combo. -aaron

bergboy

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Are there longevity problems with an 86 mm if I can't get thick wall 90.5's?

Friday, 24-Mar-2000 21:20:24

208.225.199.170 writes:

The Berg engine kits specify the stroker 90.5's with the thick wall (GB014). How available are these? Are there longevity problems if a regular stroker 90.5 is used(GB012)?

Gene said in the Rod Angle article that he had a motor with 5.352" rods and an 86 mm crank that would pull 9000rpms in 4th gear and the rod ratio had no ill effects on longevity. He also said that 86 mm cranks can use 5.352" to 5.500". The Berg engine kit specifies a 5.500" rod. Are there other factors involved with selecting the rod length besides wanting torque in a 7:1 street engine? I think a short rod 2213 would be awesome. One advantage to using the shorter rod would be that a thinner cylinder spacer could be used. I figure that for a 5.5" rod I would have to use a Cu gasket and a .270 in spacer to get close to 7:1 CR.

Randy

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There is not a problem..

Saturday, 25-Mar-2000 11:15:10

12.73.120.187 writes:

... the thicks are readily available, and is what everybody has now. The big difference other than the size of the holes you have to cut to install the cylinders are the pistons. The early thins had thicker crowns which allowed deeper valve pockets. The pistons that Berg had were also a little longer in the skirt which helped on the longer strokes. Most everybody elses pistons were cut shorter in the skirt so less work was required to make it all fit which can cause scuffing on loooong strokes. Hope this helps.

TaTa

Tom H.

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longevity? no problem. i wouldnt say its the size thats the factor. its the quality.

Friday, 24-Mar-2000 22:41:04

205.188.195.33 writes:

bergboy

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Re: Why do so few people go for an 86 mm crank?

Saturday, 25-Mar-2000 10:53:42

63.27.111.64 writes:

I am running a 86X90.5 motor and I am here to tell you....Its A LOT OF F*#^ING WORK!

It is completely worth it though. The case needs a ton of clearancing, cam, cylinders, pistons all need clearancing. I have .484 shims under the barrels that had to be made. Even the pushrod tubes are special. Basically everything for this motor is custom made or machined.

I wanted a more square motor so I could take advantage of the torque on the bottom end until my turbo would build boost. It worked. I cannot feel any "turbo lag" or flat spots, and this thing just pulls from 2000rmp's on up.

Oh yeah, all of these special parts and machining cost ALOT OF MONEY too! It took me five years to build my motor. I lost track of the total price tag.

Hope this helps.

Marty