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I'm finally rebuilding my engine!


AThomas

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I'm in the middle of my engine buildup for my soon-to-be CMC Camaro. (Yea! Progress!) I got lucky. All the pistons were good except one (It looks like someone had dropped a carburetor stud into the engine at some point and it beat up the top of the #5 piston). I had the block/crank/rods inspected and cleaned and the one piston replaced with a stock-type unit. My crankshaft only needed to be polished and was still within the factory clearance specs so STD bearings worked just fine. The block was touched with a hone, but the bore was also still within spec to reuse the original pistons. As filthy as the engine was when I removed from the car, I was figuring that it was junk, but it turned out to be in great shape internally. This is my first engine build, so I'm glad things are going fairly well so far.

 

Anyway, I've disassembled the heads and they seem to be in really good shape too, but the exhaust runners are caked with carbon buildup. I mean this is some really nasty stuff. I've been spraying the runners down with carb cleaner about once a day, but it doesn't seem to be loosening it up any. I've tried scraping it with a very dull screwdriver and cleaning it with a wire wheel on a Dremel, but this is slow going. Also, I don't want to give the appearance that I've done any porting (as it isn't specifically addressed in the rules, I'm assuming porting is a no-no). What is the best method to remove this stuff?

 

Also, where can I find a list of compression ratios for 3rd gen 305's?

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You can find lots of information, including compression ratios, here:

 

http://www.f-body.org/tech/tech.htm#ThirdGen

 

I feel your pain, I'm just now installing a freshly rebuilt 305 for CMC. Mine sounds like it was a bit more expensive than yours, though =)

 

The rules dictate that you must stay within "stock" compression limits, and since you don't need a bigger bore and are keeping stock pistons, you probably won't have any issues.

 

My build, on the other hand, is .030 over and is using aftermarket as-close-to-stock as I can find pistons, so I'll probably be a little over "factory" compression.

 

Third gens (according to the url above) top out at 9.5:1, but I'm not sure what overboring and milling on the head will result in. I would expect 10:1 to be on the high-end of "acceptable" (and my build should be under that), but there's no posted absolute max.

 

edit: I already asked, porting is dissallowed.

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Hummm, I'd like to understand more thoughts on compression limits. Does 7.7.4 apply to compression ratio? If so that gives you a band of +/- 0.05 on the CR, with per that list of 305 engines a nominal of 9.5, so the max allowable is 9.55:1.

 

To be blunt, I would not have thought 10.0:1 is anywhere close to acceptable.

 

Other thoughts or clarifications?

Jeff

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Hummm, I'd like to understand more thoughts on compression limits. Does 7.7.4 apply to compression ratio? If so that gives you a band of +/- 0.05 on the CR, with per that list of 305 engines a nominal of 9.5, so the max allowable is 9.55:1.

 

To be blunt, I would not have thought 10.0:1 is anywhere close to acceptable.

 

Other thoughts or clarifications?

Jeff

 

There is a disparity there, then, because if your compression ratio is 9:1, then you have +- .5, which is a much wider gap than +-.05.

 

There is no way you can keep within +-.05 with an allowed +.000 to +.030 over bore. +.030 alone gives you around +.15:1 compression ratio, which blows the +-.05:1 right out of the water.

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What rule are you guys looking at?

 

8.16. Engine Balancing / Rebuilding

Engine balancing is allowed. Lightening of parts beyond the minimum required to balance is prohibited. Boring/honing is allowed up to 0.060 over. Head/block milling is allowed but only as far as required to square/clean the surface area. Compression ratio must remain within stock tolerances for the make/model/year of the engine.

 

I don't see any mention of .5 or .05. Is there another part of the rules that state something different that I don't see?

 

I'm using the rules downloaded from the CMC site as of today.

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What rule are you guys looking at?

 

7.7.4 Tolerances

Unless otherwise specified, all published measurements infer a tolerance of + / - one-half of the last specified decimal place. All rounding will be done to the nearest decimal place that is specified in these rules. In a case where a measurement falls exactly on the halfway mark it shall be rounded up or down in favor of the competitor.

 

So, that would make 9:1 = 8.5:1 to 9.5:1

And 9.5:1 = 9.45:1 to 9.55:1

 

edit: I'm not saying this is what I think, I'm saying this is the literal interpretation of the rules.

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Yeah, that is the rule I was pointing to. Good point by Doug on the simple difference between a factory manual that calls out 9:1 vs. 9.5:1.

 

I'm very curious to hear what others have done or thought based on the rules as written.

 

Jeff

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I brought this exact point up months ago when when the rule was introduced and never saw any clarification. It's a good argument for simply setting a maximum compression ratio, which is easy to tech, and leave it at that.

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Great discussion. It sounds reasonable that comp ratio should not fall under 7.7.4 and should instead have its own tolerance (1/2 a point for example). Open to suggestions for '08 from all of you master engine builders.

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One suggestion would be to take a poll of all the legal configurations that people are running, add a couple tenths on top of the highest "reasonable" (verifyably legal) setup, and set the max to that.

 

I'm still trying to figure out all the factory and current measurements for the CR calculators I've found to see if an extra .5:1 is really unreasonable within the scope of the rest of the rules. It seems reasonable in my head, but the math should tell.

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Yes, it is very easy to make that big of a change to CR on a rebuild, especially on the Ford now that there is a wide variety of legal cylinder heads. For example, the nominal chamber volume of legal heads ranges from 60 to 67 ccs. Add in the effect of an overbore, thinner head gaskets, decking the heads or block, and you can get to 0.5 point or higher very easily.

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i think head gaskets are addressed in the rules. must be OEM thinkness.

 

8.17. Fasteners/Gaskets

Fasteners are unrestricted provided they serve the same function. Gaskets are unrestricted.

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As a practical matter, most people have no idea what the factory spec is when they need to buy head gaskets. Do you have a list of the OE head gasket thickness for every year, make and model that's legal in CMC so we can tech that?

 

edit: Well, there you go. Moot point.

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Head gasket thickness was why I asked about CR to start with. Since I'm running stock parts and I haven't had the block decked or the heads milled, gasket thickness is the only place I have left to make anything up if it doesn't measure out like it should.

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8.17. Fasteners/Gaskets

Fasteners are unrestricted provided they serve the same function. Gaskets are unrestricted. Head gaskets must be the same compressed thickness as OEM stock.

 

i was thinking of the 2006 rule. didnt realize it changed for '07.

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