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Old 02-10-2011, 12:46 PM
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I understand that more cubes = more power in general, however it would be due to a shorter stroke that the numbers would show better results at a lower CI in our application if that sounds correct?

Problem that I'm having now is figuring out the actual compression running 781 heads. We want to be running at roughly 10.25-10.5:1 compression

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  #17 (permalink)  
Old 02-10-2011, 01:04 PM
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Quote:
Originally Posted by Wattsy
I understand that more cubes = more power in general, however it would be due to a shorter stroke that the numbers would show better results at a lower CI in our application if that sounds correct?

Problem that I'm having now is figuring out the actual compression running 781 heads. We want to be running at roughly 10.25-10.5:1 compression
That'll take some big domes- something on the order of 35cc to get you to 10.4:1, w/119cc chambers, zero deck, 0.041 gasket (and quench), 0.030" over 454 block w/a 427 crank.
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Old 02-10-2011, 02:09 PM
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Quote:
Originally Posted by cobalt327
That'll take some big domes- something on the order of 35cc to get you to 10.4:1, w/119cc chambers, zero deck, 0.041 gasket (and quench), 0.030" over 454 block w/a 427 crank.

That sounds about right, can this be done with the stock rod length as well, or am I going to have to use the 6.535 rod? I know that I would on a tall deck truck block, however I don't know if just the tall domes with standard 6.125 rods would work on a standard deck. As I'm waiting on the pistons, and the blocks in the mail, I'm kind of SOL on measurements, any experience with this?

Only reason I ask is because I have a nice set of steel rods sitting here and don't want to send them back.
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Old 02-10-2011, 02:35 PM
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To add to this, the pistons we're thinking of using are IC-9917 41cc domes rated at 11:1 on 119cc heads OR IC-766 which are 37cc domes rated at 10.7:1 both on 6.135 rods, is this all I have to worry about along with gasket thickness/bore?

The heads that I'm using are 781's and I'm opening up the valves to 2.19/1.88 which will slightly increase the chamber size of the head as well. Logically to me, this would lower compression, however doing the math down on paper, it's raising it? I'm just completely lost in the sauce now and do not understand this.

Last edited by Wattsy; 02-10-2011 at 03:02 PM.
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  #20 (permalink)  
Old 02-10-2011, 03:04 PM
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Quote:
Originally Posted by Wattsy
To add to this, the pistons we're thinking of using are IC-9917 46cc domes rated at 11:1 on 119cc heads OR IC-766 which are 37cc domes rated at 10.7:1 both on 6.135 rods, is this all I have to worry about along with gasket thickness/bore?
Those pistons will work with that combination, but are fairly heavy. What are the rods you have?? Hopefully not 3/8" bolt stock rods.

If you really want to turn the rpm fast enough to really make this 427 shine I would recommend either IC772(37cc dome) or IC989(38cc dome) for use with 6.385" rods. They are a lot lighter than the heavy piston you are planning to use. They put the compression ratio closer to where you want to be also.

If the rods you have are 3/8" bolt rods I wouldn't recommend you go over 6500rpm or so, with the longer rod(which has 7/16" bolts) and lighter piston 7800rpm would be no problem. You are going to need to rev it if you expect it to be a powerhouse and outrun the guys with 454 or 489/496 engines.
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Old 02-10-2011, 03:06 PM
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Quote:
Originally Posted by Wattsy
To add to this, the pistons we're thinking of using are IC-9917 46cc domes rated at 11:1 on 119cc heads on 6.135 rods, is this all I have to worry about along with gasket thickness/bore?
That piston (44.7 cc dome on the 0.030" over piston) will work for your application: 6.135" rods, 3.76" stroke, open chamber heads, etc.

You can recompute the CR and see if you get what I did: ~ (about) 11.5:1, w/all parameters as above.

The domes are solid, so they can be machined smaller if need be.

The rods are OK, too, ALA they're 6.135".
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Old 02-10-2011, 03:14 PM
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Quote:
Originally Posted by ericnova72
If the rods you have are 3/8" bolt rods I wouldn't recommend you go over 6500rpm or so, with the longer rod(which has 7/16" bolts) and lighter piston 7800rpm would be no problem. You are going to need to rev it if you expect it to be a powerhouse and outrun the guys with 454 or 489/496 engines.
We're wanting to set our rev limiter at 7000rpm as anything higher would be out of the powerband we're shooting for (I believe 6500 is peak). The rods I have are 6.135, 7/16 cap screws, made with 4140 forged steel. Would these be legit for what we're shooting for? The weight comes out to 685 +/- 2 grams per. I'm guessing I'm going to have to balance those a little bit more, but they should be pretty close.
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Old 02-10-2011, 03:18 PM
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Quote:
Originally Posted by cobalt327
That piston (44.7 cc dome on the 0.030" over piston) will work for your application: 6.135" rods, 3.76" stroke, open chamber heads, etc.

You can recompute the CR and see if you get what I did: ~ (about) 11.5:1, w/all parameters as above.

The domes are solid, so they can be machined smaller if need be.

The rods are OK, too, ALA they're 6.135".
How many CC's are raised by going .30 over on a piston? if that's the case, I'd choose a smaller CC (such as 33/34) to reach my desired CR of 10.5:1.
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Old 02-10-2011, 03:19 PM
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Quote:
Originally Posted by Wattsy
We're wanting to set our rev limiter at 7000rpm as anything higher would be out of the powerband we're shooting for (I believe 6500 is peak). The rods I have are 6.135, 7/16 cap screws, made with 4140 forged steel. Would these be legit for what we're shooting for? The weight comes out to 685 +/- 2 grams per. I'm guessing I'm going to have to balance those a little bit more, but they should be pretty close.
You will want to balance this engine. The piston and pin weigh 909g(!) together.

6500 rpm red line seems kind of low-ish for a 11.5:1 427 BBC.
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Old 02-10-2011, 03:21 PM
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FF............. good call.

now.. the options?
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Old 02-10-2011, 03:26 PM
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Quote:
Originally Posted by Wattsy
We're wanting to set our rev limiter at 7000rpm as anything higher would be out of the powerband we're shooting for (I believe 6500 is peak). The rods I have are 6.135, 7/16 cap screws, made with 4140 forged steel. Would these be legit for what we're shooting for? The weight comes out to 685 +/- 2 grams per. I'm guessing I'm going to have to balance those a little bit more, but they should be pretty close.
They will work for what you are shooting for. At that rpm level (65-6600)I would expect maybe a 550-560hp engine.

The parts I was referring you to would lead to a 650+hp engine, but you would need to turn it 7800rpm. I don't think I would be wanting to take a 900+ gram piston w/pin that high.
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Old 02-10-2011, 03:32 PM
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Quote:
Originally Posted by ericnova72
They will work for what you are shooting for. At that rpm level (65-6600)I would expect maybe a 550-560hp engine.

The parts I was referring you to would lead to a 650+hp engine, but you would need to turn it 7800rpm. I don't think I would be wanting to take a 900+ gram piston w/pin that high.
That's pretty much spot on our goal (550-600hp) 7800rpm is def. out of the range. Our cam range is only up to 7,200 anywho and keeping at 7 to stay safe. What's it going to come down to when balancing this thing?
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Old 02-10-2011, 03:36 PM
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Quote:
Originally Posted by Wattsy
That's pretty much spot on our goal (550-600hp) 7800rpm is def. out of the range. Our cam range is only up to 7,200 anywho and keeping at 7 to stay safe. What's it going to come down to when balancing this thing?
Hopefully you won't have to add weight (Mallory metal added to a crank cost$), but it wouldn't surprise me if you did.

The machinist will weigh all the components, even the rings, and will come up w/a "bob weight" to use to balance the crank and rotating assembly.

You'll want to bring the damper and flex/'wheel, too.

At the RPM you're shooting for, I'd expect them to use the standard 50% factor.
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Old 02-10-2011, 03:40 PM
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IC-988 is a bit lighter(70 grams, 844 grams w/pin) and has 38cc dome. Would make balancing a bit easier and gaurantee it wouldn't need any mallory in the crank.
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Old 02-10-2011, 03:49 PM
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Quote:
Originally Posted by ericnova72
IC-988 is a bit lighter(70 grams, 844 grams w/pin) and has 38cc dome. Would make balancing a bit easier and gaurantee it wouldn't need any mallory in the crank.
I cannot even say w/certainty that the 909g piston would need heavy metal- BUT- the lighter piston sure could help things in that regard.

The lighter slugs also would be more "rev-able", to boot. Less load on the crank and bearings.

But this will drop the CR down to 10.7:1, so be sure the cam is compatible w/that CR.
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