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Discussion Starter #1
for a street motor:

things that would be the same, compression ratio, quench, cam.

things that would be different, combustion chamber size, 53 vs 63 and flat top pistons -14 cc vs dish -4 pistons specifically for TW heads?

I thought i read somewhere that smaller chambers are more efficient but I don't know the effect of a small chamber and dish piston.

just learning...

the new TW 170 11r's come in a 53 cc, i can use them on my 68 289 and bring compression up and also use them in the future (40-50K miles) when i do the 331 bottom end. When going to a 331 I would have to use -14 dished forged pistons to have 10:1 CR and the correct dynamic. (with the level of cam i want to run for vacuum)
 
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You want quench. That being said, some of the most powerful engines made struggle to get good quench. Some designs are just easier to do so. IMO, you don't want a dished piston. I never use them. So chose your combustion chamber size so you can run a flat top.
 

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+1 PetesPonies, I always thought dish pistons were for interference motors anyway. I know a lot of engine builders use them for other purposes but you really don't gain anything that can't be made up elsewhere and in some cases for less $$.
 

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Using 58cc heads increasing your stroke from 2.87" (289) with 9.0:1 compression to a 3.25" stroke (331) you'd be going up to 10:1 compression from the change in stroke alone. Compression would increase more with bore too.

:cheers:
 

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Discussion Starter #6 (Edited)
Using 58cc heads increasing your stroke from 2.87" (289) with 9.0:1 compression to a 3.25" stroke (331) you'd be going up to 10:1 compression from the change in stroke alone. Compression would increase more with bore too.

:cheers:
thanks, I've run the AFR 58CC calculations before, on the 331 i want to run TW 11R's. the TW come in 66 or 56...on the 190's and 53 on the 170 11R's.

the TW can also be used on bottom end that is only 7-8K old with about .512 lift. I cannot use the AFR 185's due to 2.02 valves and PTV issues.

just looking for options to put a top end on this engine that will carry over to 331 down the road. The TW options work...minus the dished piston (forged D shape) that would be required in the 331 due to compression with smaller CC heads.
 

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Well, I guess I will find out on mine. I'm running 50 cc chamber heads with Probe dished pistons on the 331 I'm trying to get together.

It calculates out to right at 10:1(9.9xx something actually) static compression. The dish is interesting. I imagine Probe carved up a few chunks of aluminum working on that configuration. 0 deck height.
 

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Using 58cc heads increasing your stroke from 2.87" (289) with 9.0:1 compression to a 3.25" stroke (331) you'd be going up to 10:1 compression from the change in stroke alone. Compression would increase more with bore too.

:cheers:
Static compression is dependent on the cylinder bore, block deck height, stroke, piston dome/dish volume, connecting rod length, combustion chamber size, piston/wall clearance above the top ring, head gasket thickness and bore size and piston compression height.

Just saying that compression will increase using a "58cc head" is a little bit of a misnomer. There is nothing to be gained in trying to compare the change to CR made by changing a SINGLE component when the build will result in multiple changes.

Also, in the OP where it says "Things that would be the same" in large vs. small combustion chambers, compression ratio and quench would ALSO be different.

When talking about efficiency, generally speaking smaller combustion chambers are more efficient......as far as the process of ignition of the air/fuel mixture is concerned, but there are other factors that will affect efficiency such as combustion chamber shape, valve angle and shrouding, spark plug angle and position, piston top shape, connecting rod length and offset, piston pin position, etc.
 

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Just saying that compression will increase using a "58cc head" is a little bit of a misnomer. There is nothing to be gained in trying to compare the change to CR made by changing a SINGLE component when the build will result in multiple changes.
No one in this thread is saying compression "will increase using a 58cc head". Looking at single major changes in a pure example like stroke (OP is going from 289 to 331 in future) is useful to see what effect it will have on compression, with same size cylinder head combustion chamber (in my example 58cc). Get it?

:cheers:
 

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Discussion Starter #10
Also, in the OP where it says "Things that would be the same" in large vs. small combustion chambers, compression ratio and quench would ALSO be different.

agree, however before I made that statement i ran the compression calc's with different CC heads, pistons, all blocks zero decked and the large TW milled down 3CC's. All were ran with zero deck with .039 compressed gasket. In other words I picked the 331 rotating assembly with pistons set up for TW in either -4cc or -14cc (D shaped) and calculated with 53cc TW heads and 63 (66's milled down)


when i was running all the calculations it hit me to ask the question of small vs large (53 vs 63cc) chambers.
 

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Discussion Starter #11
Well, I guess I will find out on mine. I'm running 50 cc chamber heads with Probe dished pistons on the 331 I'm trying to get together.

It calculates out to right at 10:1(9.9xx something actually) static compression. The dish is interesting. I imagine Probe carved up a few chunks of aluminum working on that configuration. 0 deck height.
yep those are the ones i was looking at
 

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No one in this thread is saying compression "will increase using a 58cc head". Looking at single major changes in a pure example like stroke (OP is going from 289 to 331 in future) is useful to see what effect it will have on compression, with same size cylinder head combustion chamber (in my example 58cc). Get it?

:cheers:
Get "what"? While you certainly CAN recalculate CR based on a change in stroke, you realistically CAN'T do so without changing either the rod length, piston compression height, or both. Get it?:yoho:
 

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for a street motor:

things that would be different, combustion chamber size, 53 vs 63

Just thought I'd pass on something I learned from Chris Straub of Straub Technologies- they design custom cams. Someone may find this interesting.

Since driving on 87 octane with detonation is an engine killer and if you are concerned about getting stuck someplace in the middle of nowhere and not being able to get premium gas, then go with a larger combustion chamber. We were discussing what chamber volume to use on AFR heads (58 or 72cc) and he suggested 72cc so I could use regular gas in a pinch.
 

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Get "what"? While you certainly CAN recalculate CR based on a change in stroke, you realistically CAN'T do so without changing either the rod length, piston compression height, or both. Get it?:yoho:
:loco:

Don't forget changing crankshaft unless you're building a poor mans stroker bud!
 

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for a street motor:

things that would be different, combustion chamber size, 53 vs 63

Just thought I'd pass on something I learned from Chris Straub of Straub Technologies- they design custom cams. Someone may find this interesting.

Since driving on 87 octane with detonation is an engine killer and if you are concerned about getting stuck someplace in the middle of nowhere and not being able to get premium gas, then go with a larger combustion chamber. We were discussing what chamber volume to use on AFR heads (58 or 72cc) and he suggested 72cc so I could use regular gas in a pinch.
You'd think he'd know better. You'd compromise an engine build solely on the off chance that you couldn't get the desired octane? That's just dumb. I'd suggest he.... and anyone who doesn't understand detonation, read this article.

http://www.contactmagazine.com/Issue54/EngineBasics.html
 

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Right! With a change to the crankshaft....as well as opening up the small end of the rods and running Chevy pistons... A 14 year-old post in the days when strokers were "mix and match" builds.

Also, Tracy Blackford WAS a frequent poster on VMF way back then (kkpony) who I followed quite closely... I believe he blew up that motor. :yoho:
 

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crankshaft

Fast, the 331 budget build is still a good option if you're willing to stay under about 450 hp. Yes, after spending quite some time racing, TrBLKFR did blow that engine up. He the built another 331 using stronger pieces, but BOTH of them utilized an aftermarket crank.


What I want to know is why is our OP looking at building an engine with such low compression ? E85 sells for less than regular, sometimes alot less, and has 104 R+M / 2 of 104. Setting up for E85 is not really that hard. Interested ? LSG
 
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