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post #1 of 14 (permalink) Old 04-12-2012, 02:04 PM Thread Starter
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Compression Ratio question

Hi All , I'm from europe and I have '88 GT coupé 5.0 HO T5 and prepare it to drag racing. No large and expensive mods. Car is stock rigt now. I buy 8.8" 4.10 FRPP ring and pinion , GT40 heads and GT40 intake. My idea is "Low-cost lightweight small block car" with time around 11 to 12 seconds. And major question is - how much high compression ratio engine withstand without troubles ??? Mainly pistons , rods and crank. I would like to 11.0:1 compression ratio with stock short block and lightly ported GT40 heads. I have s special high octane racing fuel for high CR.

Thanks for advice and opinions.

1988 GT 5.0 T5 4.10 - ET 13.460
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post #2 of 14 (permalink) Old 04-12-2012, 05:16 PM
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Re: Compression Ratio question

Welcome, jabko. Compression will not hurt the engine if you are using good fuel. However, your engine and new heads with 11:1 pistons will still not make enough power to hit the 11-second range. That will take around 400 rear-wheel HP. You may want to consider keeping the stock short block as it is and using a power adder like N2O or boost to hit 11s with 400hp at far less cost.

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post #3 of 14 (permalink) Old 04-13-2012, 01:36 AM Thread Starter
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Re: Compression Ratio question

Thank PSIG, 11 seconds is a bit of a dream, but maybe 12 is real. For me it is 300 +/- RWHP sufficient. There is no track with penetration, only the concrete and the biggest problem is traction.

I can not use Boost. I'm in class "Naturally aspirated V8". N2O is a good thing for me, but this system I have only for the carburetor and the big problem is filling of bottles.

1988 GT 5.0 T5 4.10 - ET 13.460
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post #4 of 14 (permalink) Old 05-04-2012, 02:38 AM Thread Starter
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Re: Compression Ratio question

One little question, Have GT40 heads same position of threads for P/S as standart HO heads ???

1988 GT 5.0 T5 4.10 - ET 13.460
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post #5 of 14 (permalink) Old 05-05-2012, 09:04 AM
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Re: Compression Ratio question

Yes. I do not recall offhand if the thread diameter is the same, but I think so. There are inserts if you need the other size to make it work either way.

David

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post #6 of 14 (permalink) Old 06-08-2012, 02:45 PM Thread Starter
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Re: Compression Ratio question

Hi , so my heads are here , but I'm little surprised , on heads is only "GT" casting - NOT "GT40"

Please help with identifying of these heads. I clean it and take a pictures of details.

1988 GT 5.0 T5 4.10 - ET 13.460
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post #7 of 14 (permalink) Old 06-08-2012, 03:09 PM
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That's correct. "GT" is cast into gt-40 heads. The ford part number should start with "f3ze", and there should be 3 vertical bars on the end (front/back) of the head.

Some have reported casting numbers of f"1ze" & "f2ze", too.

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post #8 of 14 (permalink) Old 06-10-2012, 04:34 AM Thread Starter
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Re: Compression Ratio question

Thanks , and still one question , how much I can downground this heads with safe piston-to-valve clearance ???

1988 GT 5.0 T5 4.10 - ET 13.460
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post #9 of 14 (permalink) Old 06-11-2012, 12:17 PM
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That depends on what cam you're using, what crank, rods and pistons you are using, and what size rocker arms you're using.

You may not even need to deck the heads. Check them with a straight edge. Unless of course, you're trying to get a little more compression and you want to deck the heads.


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post #10 of 14 (permalink) Old 06-11-2012, 02:41 PM Thread Starter
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Re: Compression Ratio question

Sorry , all is stock HO engine , crank , rods , pistons , cam , lifters , rockers.

I want only (I have only) GT40 heads "F3ZE" casting and GT40 intake with 65mm throttle body but I need higher compression than stock engine.

Maybe in the future I buy high lift rocker arms.

How much I can downground heads for high compression ??? 0.04" is maximum for "closed intake valve to deck clearance"

BTW: this GT40 heads have 68 ccm combustion chambers ???

1988 GT 5.0 T5 4.10 - ET 13.460
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post #11 of 14 (permalink) Old 06-11-2012, 03:53 PM
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The book I have says those heads have 60-63cc chambers (just a couple cc's smaller than the stock e7 heads).

As far as how much can be taken off, I don't know. Talk to the shop that is going to do the work. They might know?


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post #12 of 14 (permalink) Old 06-12-2012, 01:00 AM Thread Starter
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Re: Compression Ratio question

Unfortunately, there is no speed shop where I could ask.

I am here only one who makes V8's.

1988 GT 5.0 T5 4.10 - ET 13.460
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post #13 of 14 (permalink) Old 06-12-2012, 06:46 AM
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Re: Compression Ratio question

I would look to get pistons for your compression. Milling the head will raise it a little, but not what you want at 11:1. Milling .040" to get maybe 5cc (from 65cc to 60cc) will only raise your compression 0.5 (about 9.5:1). You can't mill enough to get 10:1, so I would save the money for cutting the heads and wait for pistons.

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post #14 of 14 (permalink) Old 06-13-2012, 04:24 AM Thread Starter
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Re: Compression Ratio question

Yes, I understand, maybe better than pistons is 347 stroker kit.

But no time to wait for parts.

1988 GT 5.0 T5 4.10 - ET 13.460
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