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Old 09-19-2007, 10:32 AM   #1 (permalink)
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Compression Ratio on 347

Hi New here,
Im building a 347 stroker, i already have the shortblock( eagle cast crank, forged rods and pistons, stock roller block, main support system, windage tray.

Combo i am looking to get, AFR 185 heads (58cc), trick flow track heat intake(port matched), 75mm throttle body, 30lb injectors, comp cams XE282hr cam, tko 600 trans, 4.11 9in.

Here is my question. The short block was originally built for the stock 58cc iron heads, to give it a 9.7-1 compression ratio, i didnt want it to high because i wanted to run on pump gas. So i want to leave the short block and pistons alone. I am looking to get 400/400rwhp/rwtq, my question is can i do it with this compression ratio(9.7) or should i have the heads milled to give me a 10.5-1 compression ratio.

Will the increased compression ratio benifit me at all, or would milling the heads hurt the flow?

Are my goals realistic?

Thanks
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Old 09-19-2007, 01:55 PM   #2 (permalink)
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Re: Compression Ratio on 347

What octane of pump is available? What's the elevation where you do the majority of your driving?
If your between sea level and 1500ft. then I would use 10:1. If your higher then you may be able to get away with more.
That's with 91 octane. Actually .5 of compression in that build will only get you about 10HP. But it's 10HP...
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Old 09-19-2007, 07:20 PM   #3 (permalink)
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Re: Compression Ratio on 347

I live in Massachusetts close to sea level and 93 octane is avalible here, if the 10hp per .5 compression ratio increase is true i dont know if it would be worth it cost wise, unless it is rear wheel horse power increase.
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Old 09-19-2007, 07:42 PM   #4 (permalink)
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Re: Compression Ratio on 347

Quote:
Originally Posted by umdstang View Post
I live in Massachusetts close to sea level and 93 octane is avalible here, if the 10hp per .5 compression ratio increase is true i dont know if it would be worth it cost wise, unless it is rear wheel horse power increase.

So, to get this straight...10rwhp (11.5 or so at the flywheel) is worth it, but 10 flywheel horsepower isn't?



For what it's worth, I ran 11:1 compression on a Victor Jr headed 347, pump gas. This was at 1100' elevation in Arizona. The cam was designed with this compression in mind however, and that is the only reason I was able to pull it off.

If you're not willing to go custom on the cam, stick to the above advice. If you want to extract all the power and potential out of your setup, a custom cam is the best place to spend the money.

Hope that helps.

Cris
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Old 09-19-2007, 08:04 PM   #5 (permalink)
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Re: Compression Ratio on 347

Never thought of a custom cam interesting thought. any sugestions on where to get it done?

I wasnt really thinkin about rwhp vs fwhp, good point.

The other part of my question is would milling the heads hurt the flow #s ie loosing hp when increasing the comprssion.

Thanks
Brian
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Old 09-19-2007, 08:17 PM   #6 (permalink)
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Re: Compression Ratio on 347

It might on a flow bench.

On a running motor? Not on this planet =).

Another thing you could do, if you milled the heads...is have them angle milled. This changes the valve angle, and with enough cut...there are REAL performance gains. I've got an old set of high ports that were angle milled to just shy of 18*. The performance difference is substantial. You WILL have to have your intake cut to match them if you angle mill though.

For cams, I use Camshaft Innovations - Home. Understand however, Jay's a no BS kinda guy. If you're going to use him...do so knowing that he's done probably 150 motors like yours, among the thousands of projects he's been involved in. Don't second guess...be very clear on your build sheet, and be ready to pay him for his services. When he does a custom cam, he spends an easy 3hrs coming up with the numbers. That's before you ever give him a dime. His time isn't free...but his prices, for what he does, are incredibly reasonable =). Put your faith in him, and allow him to do his job, and the kind of power you're wanting will be a walk in the park. My Victor Jr headed motor made 520+ at the flywheel, and it was a daily driver.



Cris
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Old 09-20-2007, 04:01 PM   #7 (permalink)
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Re: Compression Ratio on 347

Thanks for the help, im seriously going to look into the custom cam.

And im probably just go with a simple flat milling of the heads so i dont have to deal with the intake.

Ill keep you updated.
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