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Old 02-28-2007, 12:24 AM   #1
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But why would you stroke an engine and maintain a low compression ratio? Don't you stroke an engine to increase the compression ratio? I'm not kidding, I really want to know why.
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Old 02-28-2007, 12:38 AM   #2
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stroking is just adding more displacement, stroking alone will increase compression ratio but there's ways to keep it down. even with the lower compression ratio the longer stroke will make more torque. more torque helps spool turbos faster
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Old 02-28-2007, 12:47 AM   #3
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It's a way to increase displacement. You can only increase the circumference (over bore) of the cylinder to a point. Shave off too much, the block can loose strength, and possibly deform under load.
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Old 02-28-2007, 12:51 AM   #4
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OK, I went back to school.

http://en.wikipedia.org/wiki/Engine_displacement

So the compression ratio would be adjusted with the shape of the top of the piston in relation to the top of the cylinder to keep it low when stroking to increase displacement.

Seems to make sense. Guess an old dog can learn; sometimes
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Old 02-28-2007, 09:12 AM   #5
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Okay, next question, why are you asking about stroking an engine? Is there something that you're not telling us you sly dog?
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Old 02-28-2007, 10:00 AM   #6
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No, I was sitting with a friend the other day wondering why you would want to stroke a turbo engine. In the old days (like the Jurassic period) we would have an engine bored to increase displacement and stroked or the head shaved to increase compression.

It was foreign to me why you would want to increase compression on a turbo engine, not thinking about just doing it for displacement when you couldn't bore it any further or not wanting to add heavier(read larger diameter) pistons.

Remember, my days of engine technology come from big iron blocks.
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Old 02-28-2007, 12:29 PM   #7
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well isnt there a place in our hearts for a high compression low boost setup
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Old 02-28-2007, 12:50 PM   #8
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as long as you could still use pump gas i wouldn't mind one
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Old 02-28-2007, 12:58 PM   #9
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i stroke my engine every day :gay:
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Old 02-28-2007, 01:39 PM   #10
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Quote:
Originally Posted by Oscar View Post
i stroke my engine every day :gay:
you sir, need a white jacket and a padded room.
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Old 02-28-2007, 01:41 PM   #11
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Don't forget all the fun math involved with piston speeds and ideal stroke ratios....
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Old 02-28-2007, 03:25 PM   #12
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Quote:
Originally Posted by Splitime View Post
Don't forget all the fun math involved with piston speeds and ideal stroke ratios....
and flame front speed when you start boring....
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Old 02-28-2007, 03:28 PM   #13
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Quote:
Originally Posted by Arkmage View Post
and flame front speed when you start boring....
Then piston design and head chamber design come into play alot too.

Isn't it fun?
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Old 02-28-2007, 03:46 PM   #14
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The reason for lower compression ratio is turbo's prefer lower comp. You can run higher boost.

Where as on a NA motor higher comp. is better for more HP
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Old 02-28-2007, 04:24 PM   #15
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Quote:
Originally Posted by gwilo View Post
The reason for lower compression ratio is turbo's prefer lower comp. You can run higher boost.

Where as on a NA motor higher comp. is better for more HP
Turbo's prefer as much compression as you can get. But the knock threshold and such becomes more dangerous with higher compression.

People run low compression because it makes tuning the car that much easier.

It's just easier to up the boost some... to make up for the loss of power with lower compression.
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Old 03-01-2007, 07:41 PM   #16
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stroking an engine does not mean the compression will be higher.
You can add more cc by enlarging the bore, but thats not stroking.
Stroking is to machine a custom crankshaft with custom shorter rods so that the cilinder goes deeper into the block. The cylinder will maintain the normal top level.(fm stroker kit)
You are increasing stroke, not bore.
I now some people that work there oem crankshaft so the new rod bearring will be smaller. You need to shave the crank towards the outside.
You try to get more stroke so youll need smaller rodbearrings and shorter rods.
3mm shave equals 6mm displacement. That makes a 1840cc miata an 1904 cc

(as you see english is not my main language)
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Old 03-01-2007, 08:27 PM   #17
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Quote:
Originally Posted by Splitime View Post
Turbo's prefer as much compression as you can get. But the knock threshold and such becomes more dangerous with higher compression.

People run low compression because it makes tuning the car that much easier.

It's just easier to up the boost some... to make up for the loss of power with lower compression.
That exactly what I said but you said it much better.
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Old 03-01-2007, 09:20 PM   #18
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stroking alone will increase compression(more swept volume into the the same size combustion chamber), as mentioned before there are measures you can take to tailor you compression as needed

Quote:
Originally Posted by greddymx5 View Post
stroking an engine does not mean the compression will be higher.
You can add more cc by enlarging the bore, but thats not stroking.
Stroking is to machine a custom crankshaft with custom shorter rods so that the cilinder goes deeper into the block. The cylinder will maintain the normal top level.(fm stroker kit)
You are increasing stroke, not bore.
I now some people that work there oem crankshaft so the new rod bearring will be smaller. You need to shave the crank towards the outside.
You try to get more stroke so youll need smaller rodbearrings and shorter rods.
3mm shave equals 6mm displacement. That makes a 1840cc miata an 1904 cc

(as you see english is not my main language)
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Old 03-04-2007, 08:44 PM   #19
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Stroking an engine is not something you can easely do.
True, if you compres more air youll have more compression...
Of course you can do anything to keep the compression lower (domed
pistons) Moving the lower pistonrings under the (where the rod meets the piston) dowel pins???????? (dont know the name)

Exotic stuf....
Now find someone who makes a custem stroker for cheap that can handle up to 30psi (3 bar map sensor)
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