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68barracuda
 Post subject: CR Question
PostPosted: Tue Feb 19, 2008 1:15 am 
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Hi Guys

OK 68 225 slant six 8.8 CR never been bored skimmed etc.

What is the volume off the combustion chamber?

Reason being - want to get a second head to have modified - ported etc - want to know what the chamber volume must be for 9.8 CR and 10.0 CR

Any help will be appreciated

BTW on a 264 seat to seat 215 @0.050 .440 lift intake centerline 106, ex 114

Cam what is the recommended CR? - we do get 95 over here

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Sam Powell
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PostPosted: Tue Feb 19, 2008 4:36 am 
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Send a PM to Dart270. He has build several high compression 225's.

Sam

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sandy in BC
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PostPosted: Tue Feb 19, 2008 6:30 am 
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Without actually measuring your piston to deck height and chamber volume you might just as well piss in a gopher hole and guess,,,,,or even just guess,

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DusterIdiot
 Post subject: The mighty kreskin
PostPosted: Tue Feb 19, 2008 7:01 am 
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Because of variations in the manufacture fo your mill, you'll have to pull the head off and bring a piston up to TDC to measure your deck height then fill a combustion chamber or two to even get close to what you're asking (and you have to settle on your head gasket... shim, composite, O-ring? for the proper calc...)

-D.idiot
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Joshie225
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PostPosted: Tue Feb 19, 2008 9:25 am 
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Yep, just like DI and Sandy said you have to measure. For example my 1973 Vintage 225 had the pistons .177" down in the hole. Using a calculator at www.kb-silvolite.com I found that if I take .100" off the top of the block and use a .040" thick 3.50" bore head gasket that I need 50cc combustion chambers to hit my target compression ratio.

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polara pat
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PostPosted: Tue Feb 19, 2008 11:08 am 
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Without actually measuring your piston to deck height and chamber volume you might just as well piss in a gopher hole and guess,,,,,or even just guess,
Sandy has a good method for checking deck height and CC volume, then go to this site and plug in all the data. http://www.csgnetwork.com/compcalc.html Maybe Sandy will help you with his link since I'm running out the door.

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sandy in BC
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PostPosted: Tue Feb 19, 2008 12:17 pm 
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http://www.slantsix.org/forum/viewtopic ... chamber+cc

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68barracuda
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PostPosted: Tue Feb 19, 2008 9:29 pm 
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WEEELLLLL no gopher holes over here......lots of meerkat holes over here in South Africa and my bladder is way to small :P :P


I was hoping not to have to pull the head but OK I know it is the best and only way to do things.

Thanks guys

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Dart270
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PostPosted: Wed Feb 20, 2008 6:17 am 
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If you really have 8.8 (I doubt it), then 0.070" mill should get you to high 9s or 10:1. If you have what a stock US 225 looks like (8:1 or so), then you'll want to mill about 0.130".

HOWEVER, I would strongly recommend measuring piston-deck height and head chamber volume as others have suggested. Most stock 225s are below 8:1 comp.

Why such a small cam? Not much above stock, really. If you want to use that cam, then make sure you do a good porting job on the head and bigger valves, and set compression around 9.5:1. Headwork is where you'll see the biggest gains. If you really can run on 95 octane, then 10:1 should be no problem. Really, you might run higher comp, but it depends a lot on how much time you want to spend tuning ign timing and carburetion.

If you will run a stock converter automatic, then this is a good cam choice.

Lou

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68barracuda
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PostPosted: Wed Feb 20, 2008 8:33 am 
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Quote:
If you really have 8.8 (I doubt it), then 0.070" mill should get you to high 9s or 10:1. If you have what a stock US 225 looks like (8:1 or so), then you'll want to mill about 0.130".

HOWEVER, I would strongly recommend measuring piston-deck height and head chamber volume as others have suggested. Most stock 225s are below 8:1 comp.

Why such a small cam? Not much above stock, really. If you want to use that cam, then make sure you do a good porting job on the head and bigger valves, and set compression around 9.5:1. Headwork is where you'll see the biggest gains. If you really can run on 95 octane, then 10:1 should be no problem. Really, you might run higher comp, but it depends a lot on how much time you want to spend tuning ign timing and carburetion.

If you will run a stock converter automatic, then this is a good cam choice.



Lou

Hi Lou Thanks for the reply

Yes My Converter is stock.

With said stock converter - what is the best option after this I notice Erson has a bigger cam

270 seat to seat, 220 at 0.050, .465 lift wich they recommend for std converter app - Good choice - and at that what CR please ?

I found a erson dealer over here Yay!! Talking of erson - what is their url please?

Thanx again

Fanie

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68barracuda
 Post subject: Double posts sorry
PostPosted: Wed Feb 20, 2008 8:58 am 
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For interest sake

What is the compression pressure as recorded when doing a compression test for the different known cr's ?

Fanie

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Dart270
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PostPosted: Wed Feb 20, 2008 9:00 am 
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Fanie,

If you have already bought the 264/215 cam, then I'd just go with that, but that Erson 270/220 looks nice too and should work with a stock converter and up to about 10:1 on your pump gas. On either, you'll have to spend some time on ign advance curve and carb tuning, as I said.

I would not use a bigger cam than that Erson with a stock converter.

Lou

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68barracuda
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PostPosted: Wed Feb 20, 2008 9:31 am 
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Hi Lou,

Have not bought yet - bussy getting in quotes - the guy who will be doing the head work loves erson cams - and the erson price is better than comp

Already did the recurve, but will have to again once head with higher cr is in place!

Am looking at the 9.5 - 9.8 area worried about future fuel quality

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Fanie Gerber
It's never junk, it's just a part you're not currently using

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Joshie225
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PostPosted: Fri Feb 22, 2008 10:07 am 
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Just as a data point I calculated the compression ratio of my stock 1973 vintage 225 and got 7.7:1. The head was milled .080" to get from 62cc to 50cc chambers and the block will be decked .100" to get the pistons up to -.077". With a .040" thick head gasket that gets me just over 10:1.

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BigBlockBanjo
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PostPosted: Sat Feb 23, 2008 10:27 pm 
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Hey Josh...would you mind sharing your engine specs ''when original'?? (Deck height, which head gasket)
Just curious....because my stock engine had about the same compression as yours.....Just wanted to compare. :)

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