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#2425392 - 12/29/17 12:45 PM Higher compression ratio options when starting with 7.5:1?
prochargedmopar Offline
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Registered: 01/21/17
Posts: 228
Loc: Granbury TX
Man, these deep dish pistons and 70cc heads are killin my comp ratio.
I’d like to get it up to 9:1+ being I’m gonna run e85.

Is it ok to mill the heads down to 58cc from their current 70cc? (sb sidewinders)
What is the minimum piston to head clearance I should run turning 6200rpm max?
Steel rod/forged piston combo?
Do we really need to align hone when installing main studs or is it a money making scam?



Edited by prochargedmopar (12/29/17 01:35 PM)
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#2425421 - 12/29/17 01:58 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
astjp2 Offline
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Its probably better to change the pistons to match the combination than start milling thing, you may get too thin. Or just put a blower on it. Tim
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#2425433 - 12/29/17 02:38 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: astjp2]
prochargedmopar Offline
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Ouch, this.


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#2425434 - 12/29/17 02:40 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: astjp2]
prochargedmopar Offline
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Originally Posted By astjp2
Its probably better to change the pistons to match the combination than start milling thing, you may get too thin. Or just put a blower on it. Tim


Yes it’s going to have a blower and turbo but I would like it to start without nitro.
;-)
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#2425454 - 12/29/17 03:35 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
prochargedmopar Offline
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New pistons would get expensive unless they made them the same weight as what ive got because it’s already been balanced.
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#2425471 - 12/29/17 04:13 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
451Mopar Offline
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Registered: 05/19/08
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The mains have to register to the block, not the studs. Might have to ream the bolt holes in the caps? If the block is stock, the deck heights may be all over the place to where the piston to head clearance might be different front to back and side-to-side.
I like to have the mains align honed as part of the machining along with having the deck cut square to the crank centerline. I normally run about 0.040" piston to head clearance, and know other that run tighter than 0.035", but I don't want to push it. I don't pull the engine apart each season to check bearing wear.

I would not mill too much off the block/heads or the intake will land on the blocks end rails and the intake side of the head (or intake) will need to be milled to fit correctly. Besides, that much milling might cost almost as much as new pistons.

If using heads studs too, ream the bolt hole where the rocker arm oil supply flows too.


Edited by 451Mopar (12/29/17 04:14 PM)

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#2425640 - 12/30/17 12:57 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: 451Mopar]
prochargedmopar Offline
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Loc: Granbury TX
Deep sigh*

Thanks for the advices.
Most I found was .002-.003 difference in deck height on all 4 corners.

I had planned to mill the intake but milling the head side seems like a better idea.
I’ll have to check price.

There is no interference between the main caps and studs.
I will check on the head stud clearance.

All this business makes me want to call Clegg and get balanced rotating kit.

Wish I would have did better calculations on comp ratio before balancing.
I would have stuck with regular fuel or sucked it up and got a rotating kit.
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#2425645 - 12/30/17 01:08 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
WO23Coronet Offline
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Registered: 01/08/08
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How much of a difference would a thinner gasket make in your calculations? Doesn’t Cometic make a .028” gasket?

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#2425653 - 12/30/17 01:21 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
Cab_Burge Offline
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Registered: 08/23/03
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What type of precision measuring tools do you have access to?
The reason I'm asking is if you can get, beg, borrow, rent or steal, JUST Kidding on the theft, a decent dial bore gauge or a decent set of inside and outside micrometers so you can check the I.D. of all the main bearing bores with the mains caps and bolts torque down with the bolts and then recheck them after installing the studs to see if the studs affect the I.D. or out of round of those main caps scope
If they check good, less than .00025 differences, I would run it as long as you have at least .0027+ main bearing to crankshaft clearances thumbs
If your really going to add the turbo or super charger later or sooner, within the next year, leave the short block alone now as far as the compression ratio twocents
On your deck height differences if you didn't use the same rod and piston in all four corners you may be seeing the difference in the rod lengths, not the deck height differences shruggy I've seen .008 difference in rod center to center lengths out of the same stock 1968 H.P. 440 and similar results with stock street hemi motors and 340 motors puke shruggy
With a true 7.5 to 1 compression ratio you can run regular pump swill with the blower up to 4.0 lbs. of boost and still make a hoop of power compared to the same motor N/A work
As far as piston to head minimum clearances with the blower I would shoot for .045 to .055 cold to the closest part of the piston and heads, check all eight pistons at TDC and rock the piston so each side of the piston rotates as tall as it can get when changing directions on firing scope
I run E85 in my bracket car with 14.5+ to 1 compression ratio, it works very well in this application, better than race gas ever did thumbs
Get that boost mounted and working soon thumbs boogie devil
Good luck on your deal thumbs


Edited by Cab_Burge (12/30/17 01:29 AM)
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#2425658 - 12/30/17 01:39 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: WO23Coronet]
prochargedmopar Offline
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Registered: 01/21/17
Posts: 228
Loc: Granbury TX
Yes, they make one.
Trouble is I would only have about .030 piston to head clearance with that gasket which doesn’t include rocking of the piston so maybe less.
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#2425664 - 12/30/17 01:49 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: Cab_Burge]
prochargedmopar Offline
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Loc: Granbury TX
Yes, I have a dial bore gauge and mics’.
Haha, roadkill was driving the 318 offroad challenger in a rock storm on 87 octane and found it to have 7:1 compression when they pulled the engine apart.

Just spent over $800 for a carb conversion and EV hat from HP Innovations.
Committed to e85 now.

Do you think 8.5:1 would work with e85 if I milled the heads only?

I don’t like the fact I can’t let it sit for more than 2 weeks but it is cool to be forced to drive it regularly when it finally gets done. lol



Edited by prochargedmopar (12/30/17 01:57 AM)
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#2425665 - 12/30/17 01:55 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
prochargedmopar Offline
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Loc: Granbury TX
This with heads milled only.


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#2426045 - 12/30/17 06:37 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
prochargedmopar Offline
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Registered: 01/21/17
Posts: 228
Loc: Granbury TX
10:1 with 70cc head.
Balanced assembly


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#2426046 - 12/30/17 06:39 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
prochargedmopar Offline
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Registered: 01/21/17
Posts: 228
Loc: Granbury TX
11:1 70cc head.
Hmmmmmm
408 cubes.
Dbl. Hmmm


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#2426334 - 12/31/17 11:49 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
Superfreak Offline
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Registered: 11/08/08
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My CP blower pistons were that much so for a complete kit that is a great price.
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#2426342 - 12/31/17 11:59 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: prochargedmopar]
Superfreak Offline
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Registered: 11/08/08
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If you are concerned about spending $1500 on a rotating assembly why would you waste a boat load of $$ to go with a blower and a turbo? Either one will make more power than a stock block will handle and if you have an aftermarket block you can make power where the car will need a ton of money put into it to. shruggy twocents
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#2426564 - 12/31/17 03:24 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: Superfreak]
ou812 Offline


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416 we did earlier this month....
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#2426833 - 12/31/17 08:36 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: ou812]
Cab_Burge Offline
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Come on now Brian, what did it make on that pull? work
Is that on your dyno in Indio? If so what time of year was it and how was the weather work grin devil


Edited by Cab_Burge (12/31/17 08:37 PM)
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#2426866 - 12/31/17 09:35 PM Re: Higher compression ratio options when starting with 7.5:1? [Re: Cab_Burge]
ou812 Offline


Registered: 01/31/03
Posts: 5334
Loc: SoCal
Originally Posted By Cab_Burge
Come on now Brian, what did it make on that pull? work
Is that on your dyno in Indio? If so what time of year was it and how was the weather work grin devil


Really? [ Moparts Family Site - Keep it Friendly ] does the time of year matter? We go off of software as you should know. That engine will make over 950 horsepower however his carburetor was not prepared for that much power with only single needles and seats. With a roller cam it would exceed a thousand horsepower. Not hard to do when you know what you're doing!
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#2426932 - 01/01/18 12:27 AM Re: Higher compression ratio options when starting with 7.5:1? [Re: ou812]
Cab_Burge Offline
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Registered: 08/23/03
Posts: 29967
Loc: Bend,OR USA
If I'm remembering your shop location correctly it is right at sea level, correct?
I have seen the density altitude at Thermal airport(150 Ft. below sea level) be right at 8700 Ft in the mornings in June, I have also raced at the old street races in Indio in March when the D.A. was probably around 1200 Ft. shruggy
The motor knows how thick or thin the air is regardless of the Pro Charger, correct shruggy
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