Higher compression ratio options when starting with 7.5:1?

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?

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

Ouch, this.

Yes it’s going to have a blower and turbo but I would like it to start without nitro.
;-)

New pistons would get expensive unless they made them the same weight as what ive got because it’s already been balanced.

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.

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.

How much of a difference would a thinner gasket make in your calculations? Doesn’t Cometic make a .028” gasket?

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
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
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
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 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
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
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
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
Get that boost mounted and working soon
Good luck on your deal

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.

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

This with heads milled only.

10:1 with 70cc head.
Balanced assembly

11:1 70cc head.
Hmmmmmm
408 cubes.
Dbl. Hmmm

My CP blower pistons were that much so for a complete kit that is a great price.

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.

https://youtu.be/u_nTKaaD_Os

416 we did earlier this month....

Come on now Brian, what did it make on that pull?
Is that on your dyno in Indio? If so what time of year was it and how was the weather

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!

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.
The motor knows how thick or thin the air is regardless of the Pro Charger, correct

If you dyno an engine at sea level, or 5000ft. up, it does not matter...it's called a correction factor.
His uncorrected HP on that pull was 895.
His car has already run 9.90's in full street trim at 780HP...much faster than some Dusters out there with 750HP BB's....

I am going to ask you nicely to leave my posts alone...I do not need you trying to correct me. This is not your Post, and nothing has been directed at you except for me being stupid enough to actually try and explain something to you.

Back to the OP, I would keep the 7.5:1 if you are turbo'ing this thing...

9 to 1 compression works great with E85 turbo supercharged or whatever. I would not be afraid to do that up to 18 PSI of boost. Use an NGK number 7 spark plug that is non projected as a starting point.

What # indicates the 7?

Will it even run/start on e85 with 7.6:1 comp.?
Have you ran it that low before on E?
This is suppose to be a street car with only a few 1/8 or 1/4 blasts a year.

Or these?

Holy Smokes,
Custom pistons from Diamond?
$1160!!!!!

And they still can’t make them 522g so I would need another rebalance.
Said new materials and machining techology would put them in the upper 400 gram range.

I really don’t want a low comp. laggy/peaky motor in my 3400# car.

hmmmmm

Fail to plan, plan to fail.

Less than 9:1 is harder to make power with using E85...it won't like it.
Plug is NGK -7 non projected. Similar to the -8 and -9 but hotter.
Never get a light piston using BOOST!

I’m sure you’ll be fine since you’re going with boost. Not optimal but you should really be able to crank the boost to it. Once boost hits it won’t be laggy at all

Local machine shop said both heads done is $162 to deck heads to specified cc of 58.
$75 to mill intake sides.

final compression will be 8.3:1
This may be the way i go.

Yup,
I bought the rotating assembly parts 14yrs ago.
Just now deciding to use them (this past year collecting more parts)
Would have been fine with the magnum heads, 93, and the blower.

Can you afford the loss of P/V clearance? Also, correcting intake face, pushrods?

I really think you should just live with it. With boost, 7.5:1 is not that big of a deal. Good lord, every Mopar engine built after ‘72 was around that ratio N/A. You need the deck thickness in the heads to deal with the boost. I really don’t understand why you’re so twisted up about this

Because from what i understand after google searching e85 requires a high compression ratio.
And can also run with a much higher compression increasing efficiency.

If this was race only I’d get the next size up turbo and have at it.

Yes, I’ve only got a .505 lift cam 230/240.
One of the last items to purchase for assembly is pushrods.

I can sell you some CP bullet series pistons and rings for less than that. Changing pistons is THE only way to go, because you really need to leave the heads unmilled.
9:1 is really where you should start....

Also, what are your engine specs...like crank, rods, cam, etc....?

How much?
Need comp. height of 1.545
Chevy .927 pin dia.
Valve reliefs
And a weight of 522 grams

Diamond tech said his pistons because of new technology and machining processes would be lighter.
I’d prefer not to rebalance.

6cc reliefs with flat top would be perfect.

30 over 360
Cast crank turned down 10 on mains and to chevy size 2.1 on rod throw.
6.25” chevy I beam eagle rods
Everything was balanced a couple weeks ago, took massive amounts out of counterbalance.
.480/.480 .230/240 115lsa blower cam
1.6 roller rockers should bring lift to .501ish
Main and head studs
.040 mls gasket
main girdle bought still need to machine main caps flat at work on mill

Heads.... And yes, I know the .100 lift #’s aren’t right. lol
And it’s going into this 3400# beast with 3.55 gears.

This

Verified combustion chamber volumes today.
Used the cattle syringe, scrounged up plexiglass, and washer fluid trick.

Knowing exactly(within .2 to .5 CC) how much each chamber holds is way better than hoping you know you what it is

Yeah, even 1-2 CCs is better than my original mental calculation that had me at min. 1.5 compression points off the mark.

Now the decision between $950 pistons and a $1400 stroker kit.

The $450 difference plus cylinder block bore and cleanup
will basically get me a 2nd engine.
8.24 to 1 comp using my current rotating parts and home porting the stock magnum heads.
I could run it with the Holley street dominator single plane on pump gas and a turbo.
Drop it in my dart to use as a megasquirt testbed.

I’m practicing my first efi Shenanigans with this Sniper tbi setup.

Be careful on the pistons you use in a "kit"....very few will be boost friendly!

I’ve been offered this kit with 15.5 cc dish pistons which is normally $1440 +ship but a 5% discount.
So it would be $1443 to my door.
Also be around 9.7:1 comp ratio.

Not sure if the Icon forged are up to the task.

Stronger than a cast 9000 series crank OR the main saddles?
How bout with the long arm of the law swinging around inside the stock block?

Actually the compression would be 9.1:1
That’s perfect.

TIESON ENGSTRUM
“Thanks for the info. The pistons will have a 1.465" compression height so based off the factory 9.599" deck, pistons will sit .011" in the hole. The compression with factory deck height and 4.000" bore will be right at 9.1:1. If you have the block decked to zero, compression will be right at 9.4:1.”

Icon pistons are made with 2618 aluminum, which is the more ductile alloy normally used in high stress situations. The other alloy, 4032 or VS-75, is less ductile but still strong. This is what the lower cost forged slugs are usually made of. Federal mogul now calls its alloy "FM4032"

Icon is the forged piston line from Silv-O-Lite, which has been making pistons forever and also makes the Keith Black line of hypereutectic pistons.

R.

Interesting

No problems with the Icon pistons in my 470 @12 lbs.

What heads are you running?

Home ported r.p.m's

I think a lot of guys go off of pressure for rating blown motors when volume should be the major concern, a standard 6.71 blower may make 12 Lbs. of boost at 600 HP at 6000 engine RPM and by changing the blower and slowing it down with 8.71 or 10.71 will make 200 HP more at the same or less pressure and RPMs
Same thing on turbo sizes