572 Hemi: Pump gas compression with no squish/quench

I need to read more about Hemi builds, but now I'm wondering,
since there is no squish area, do you have to run less
compression ratio than a 572 wedge ? For pump gas that is.

Or if you have the compression on the Hemi, do you also need
more cam duration than the wedge, to bleed off some pressure ?

As an aside, I think that in general, bigger bores are more
detonation sensitive than smaller bores, and a 572 Hemi has a
big bore as well as no squish.

I don't overthink that stuff. Normal line-of-thought is 9.5 for iron heads and 10.5 for aluminum heads. And all that quench crap? Well, Hemis and Mountain Motors don't have that and they run pretty good.

Just was wondering what exactly is your application for this motor. This 572 Hemi you using Iron or Aluminum block and what heads.

Hemicar, still collecting parts. Have an old KB alum block,
will eventually get Stage V heads. 1970 Chall 4-speed / Dana
3.54 is the goal. Drive it everywhere hopefully.

With a 4.5" bore there is a "quench ring" around the outside edge of the Piston/head that hangs over the bore.

We run as high as 12:1 on pump gas in a Hemi...NO issues, and I am not alone in this. many others have as well.

A friend has a 572 that was built by FHO. It made just under 700 HP on the dyno. It is a pump gas 9.5 to one. I looked at the build and there is plenty left to make a lot more HP from this motor. He built it to put the motor in a 1968 Charger and drive it any place like hours of driving. It is a World Aluminum Block and Stage V Heads. The cam lift is very small and I talked to Tim of FHO about the lift and it was the right choice for this motor and what my friend wanted to do with the motor. I would have to look at the specs of the cam on the card to give you any information on the cam, do not remember what exactly they are since I have not look at the specs of the build for years. Since you live were you have to drive to get any place this might be the kind of build that might suit you. 700 HP seems plenty for a driver.

One of the reasons Chrysler went to the Hemi in the 50's was because it could run a higher compression ratio than other engines with the same octane fuel. A lot of motorcycle engines run the Hemi chamber so they can run higher compression ratios as well.

W/r/t "it could run a higher compression ratio than other engines with the same octane fuel"
Source of this is?

Late IVC to "bleed off some compression" is very effective... until about 2,000 RPM. The engine has its full static CR (and more if VE > 100%) during the entire torque range.

I built a Mopar Mega iron block 572 C.I. pump gas hemi motor several years ago, it has EFI with dual 4150 1150 CFM dry throttle bodies, it had right at 10.8 to 1 true compression ratio and made 799 HP on Oregon 92 octane non ethanol pump swill on a DTS engine dyno in Chico, CA with a set of CNC ported Stage V heads form Tim at FHO
It's going into a 1971 Challenger with a 727 with 3,23 gear with 29 inch tall rear tires, no O.D. or lock up torque converter
I'm going to help my customer get it running, it is a complete ground up build from front to rear. The car was strip completely by a thief several years ago while stored at a friends of his house
Hemiroid motors are a pain in the butt to get the exact true compression ratio, I use a 100 CC burrette to measure the volume in the cylinders with the piston dome down enough to have from .010 to .050 clearance above the dome to the block deck and then calculate the true down volume off of the specs for that motor
Good luck on your build

11:1 on my 604 Pump Gas Hemi.

Seems like the squish in a Hemi is in the piston dome on either side of the valve notches. How close can you make them fit the chambers? .040"-.060" clearance, smaller radius than the chamber.

Mine is at 10.4-1, I feed it 91 octane as that's the best stuff you can buy around here. I have in a pinch had to put some 87 in the tank as the closest 91 pump is 21 miles away

Thanks All.

I don't think I'm being nit-picky on the compression issue,
just cautious.

Here's a lttle more info. I don't want to take the motor
over about 6000. This should assure some good low RPM street
manners. In view of this, I won't need huge intake ports,
manifold, or carb. So all that limits cam duration to something
maybe around 250 degrees ? Less ?

That is not a big cam, so what can I get away with for
compression with aluminum heads, polished chambers and
piston tops, and zero quench ?

Well I know it takes real gas to run a 12/1/2 high dome hemi piston with iron block and heads and huge duration cam, old school build I did years and years ago from old parts I had laying around and that motor is still in my Challenger. I do not know were the Feds and each State is going with their corn syrup gas. I read about they are now doing tests on this 10% Eth. to see if there is any bad side effects and all of us know it eats gaskets and hoses. I have seen were it has a shelf life of about 4 week before is starts to separate and becomes crap and evaporates and gums up a carb. Never could figure out why corm is used for gas and not to feed Humans and Animals but Government seems to want to appease the tree hugger. Also read that there is going to be 100% plant life gas in the near future.

I will not argue the shelf life or the damage it does to hoses in time. I ve always said if the government is going to make us use it, it should at least have alot more octane like 100.
But....when corn is used to make ethanol the chief byproduct is Millersgrain. It's a very hi energy livestock feed. Cattle love the stuff, it's like feeding a kid candy, they can't get enough of it.

With no lead and other things taken out of gas and improvements in refining why is a food source being used to run a Vehicle. In the Dakotas alone there is something like 250 years of Oil still in the ground. North America has plenty of oil to be processed, the Alberta Tar Sand has plenty. Texas still has plenty, Sask. in Canada is becoming a big producer but we have to have this 10% Corn Syrup added. Just wait till we are made to have an Electric Vehicle in the next ten years and you will have charging stops everyplace. Who will be making the money then it is not GREEN looking at everything it take to get it done.


Getting back to the topic, 11.1 maybe the high and 9.5 the very low 10.5 in the middle, so 10.5 to 11.1 is were I think you should try for. Who are you going to get to build your motor. is that Washington on the West or East Coast you are from. Cab Burg states that he is in Oregon so if you are on the west coast you could talk to him. East Coast has plenty builders like Susquatch on Moparts also.

There is no special trickery to run 12:1 in a Hemi....on pump gas...Keep timing in check and make sure its not lean, and keep engine temp reasonable.

It's not the same corn.
All you need to know: corn = Archer-Daniels-Midland = Iowa primary = ethanol subsidy.

W/r/t "Seems like the squish in a Hemi is in the piston dome on either side of the valve notches. How close can you make them fit the chambers? .040"-.060" clearance, smaller radius than the chamber"
In some British bikes it is, but the dome shape has to be really accurate. Making it out of an existing piston would need more positive deck or a head mill (!!), and removing some of the dome volume at 12 o'clock to keep the CR.
Even if you don't get actual quench (something no wider than about .060"), you can get squish (higher turbulence) by simply making the piston dome radius curve away from the chamber wall as it approaches the plug - the charge will flow to the larger volume.
You might be able to build some swirl into that as well, but:
1. would you want to?
2. which direction?

Gold Star, Manx, G80 500 singles are much easier to work on!

Hemicar, I'm west coast. I am definitely going to hire
someone else to build this motor for me, but I will have input
on the design parameters. I would like to get a little better
handle on the cam. I "feel" 10:1 is probably safe ! If you
found the specs to that 9.5:1 572 that would be great but
I don't want to be a pest.

Cab, do you recall the cam in the 10.8 572 you built ?

Dragula, what is a typical cam you use in a 12:1 pump gas Hemi ?

Gsmopar, same question if don't mind, cam in your 11:1 Hemi ?

Quickd100, I really like that truck of yours, always like
reading about it. What cam in your 10.4 motor ?

**********

As long as I'm here typing, I'll throw this out. Because
of my design limit of 6000 RPM or so, and the fact that
it will be an aluminum block, I'm considering a hydraulic
roller cam and using titanium valves. The hydraulic cam
would take up lash from block growth, and the Ti valves
would allow using fairly light valvesprings to help out
the hyd lifters.

I don't really care about overall horsepower with this
motor, no specific goal, it will be healthy enough.
I look at it as being a torque generator.

Again, I want to say thanks for the guidance, there is
an amazing amount of collective knowledge on Moparts
compared to many other websites !

I will stop in on Monday to see this friend of mine that had this 572 built and it was done by FHO a few years ago and try to get some specs you have asked for. I also will stop in and see another friend that built a 605 World Block FHO ported Stage V heads and ask him about how much compression he has in this street motor. I believe the Cam Shaft has 630 lift but not sure on the duration. It made around 830HP on the dyno on real good gas but he pulled back some timing and other things to run on pump gas and to make it more streetable. Still is a beast in his 68 Runner. You might want to talk to FHO and ask Tim what he would recommend for a Cam and Compression. There are plenty on here that have had more hands on experience than I do building this kind of street Hemi motor. My stuff is smaller cubes 430 to 450, high rev, big duration, and lift cam and 12 1/2 compression high dome pistons with planed heads making more that 12 1/2 to one compression and not really fun making it not ping on the street unless real gas is added to the gas tank. Would rather put good fuel in than take some things out of the motor. But I have been interested lately in building a bigger motor keeping the RPMs down and taking some weight out with an all Aluminum Motor to have my Challenger making the car weigh in just over 3000 lbs. and run on pump gas.

FWIW here is what I am using in my 572" .It is more cam than you need though.
CP 10.5 to 1 pistons . CNC ported Stage V heads. Comp Cams solid roller from Dwayne Porter approx. .670" lift 270* duration 112 LSA .
Runs fine on pump gas no knocks or pings or run on after shut off.
Mark

Tim of FHO was very helpful on getting me parts for my 472. It was in a car I bought and never ran quite right. He sold me a set of stage V heads, intake and a comp cam he had them grind. That cam isnt very wild but 3000 and up it acts completely different. Runs good. You might want to give him a call.

I bought the cam from Tim at FHO along with all of the top end parts, it is one of his custom Comp Cams grind, grind # FHO57224X2
I'm sure Comp won't sell that cam grind to anyone other than Tim
It idles nice, has plenty of vacuum at 1000 RPM idle for this cars power brakes and it made 704 Ft. Lbs. torque at 3500 RPM at WOT on the DTS engine dyno with peak torque of 730 Ft. Lbs.at 4900 RPM, at 3500 RPM it made 469 HP and made 798 peak HP at 6500 RPM where we stop the pulls at do to it would start to loose HP after 6500 RPM
AKA aside this customer is a show car guy who wants a real nice driving 1971 Hemi custom clone Challenger to drive here in central ,OR, and a car his wife can drive also without worrying about the car doing donuts when they step on it to WOT
Me being me it was really hard to not shoot for the moon on both torque and HP on this build, I was hoping for 800 to 850 HP around 7000 RPM at WOT.
This motor has beehive valve springs from FHO with only 450 Lbs. opened pressure with .600 valve lift
I had Comp grind me a solid roller cam for it first with different specs than Tim FHO grind but they sent me a core with six bolts on the front for the timing gear and I sent it back, bottom line is I got into a tiff with them on that core and ended buying and using this one from Tim
The customer is happy with these results, he may be greatly surprised and hopefully loves the results of this motor in his car no matter what the dyno sheets show

Well I don't think you'd like my cam. Bullet solid roller, .767/.686, 288/292@.050 113 center. I didn't pull it past 6800 rpm, the power was still climbing. With the old heads it made 852.8hp@5800rpm.

subscribing....

It'll probably be awhile before mine is operational, I'm still in the data collecting stage and can see that will never end, but it should end up between 10.2 and 10.7:1.

My 572 hemi is 11:1 and no issues at all on pump 93. Been 9.54 at 140.4 mph at 3800 lbs naturally aspirated on pump gas.

A true 10:1 with iron heads here & a VERY small cam. 93 octane daily driver. 30 deg spark advance.

528ci, 235 @ .050, laziest easiest-starting Hemi you'll ever see, lol. It actually does good on gas though, and its no slouch at the strip either.

This is a great thread, good info, thanks again Gents.

Any more cam/compression combinations ?

9.5 to 1 with stage V heads, StageV rockers, crane 248@50 .630 lift 112 lsa, stageV intake port matched and ported for magnafuel shear plates, 2 quickfuel 770 vacuum secondary carbs with annular boosters on the primaries and downlegs on the secondaries. Desktop dyno showed it at about 650 hp and 700 tq. Engine has only ran for 5 minutes since it was built.

Here's a visual aid:

Dwayne Porter spec'd Comp Cams solid roller 276°/284° @ .050", .672"/.651" lift, 112 LSA
Mild lobes w/ light springs (PAC 1243) and good lifters (Isky Red Zones)

ZIPPY, I don't think that's enough squish to do any good.

Agreed h.e., it's not going to do much of anything with this piston. Especially once I put a gasket on it.
I've got roughly 13cc of dead space around the edges (I CC'd and did the 1" down measurements etc) and although I could cut the block, I have
no desire to push any limits.

As they say a picture is worth a thousand words, so anything to help visualize the stuff I figure is a good idea.

Cam wise I'm going to start with 276/280@.050 on 112, .420 lobe lift. Not 100% sure on rocker ratio or gross valve lift yet.
A local horsepower God tells me the cam is about 20 degrees too big for my application, so it will be interesting to put that thought to the test.
What I have should be good enough to get it running and decide if I like it, at least.

Zippy...is your shortblock assembled already? I hope you mocked up the valvetrain and checked pushrod clearance on the block and heads before you started putting it together.
I had a LOT of time in checking clearance and grinding for the pushrods on my KB block. Dan Costello also mentioned it would likely be an issue w/ the World block also. I haven't built the World block hemi I have here yet so can't comment for sure.

Hey Chip,
No it's not assembled yet, this was a mockup without rings to look at what I could, with the pieces I had.
It's back apart now and the lower end is out for balancing.

Thank you for that advice...folks also PM'd with similar statements, so I am expecting to correct problems.

Couldn't mock up any valvetrain yet since my parts collection is incomplete. And I think I want something better
than stock rockers so I will go shopping pretty soon.

Rich

I saw one of the Sox and Martin SS/A cars in the tear down barn at the 1974 NHRA Winternationals , Jake King had removed the stock castings around the pushrod tubes in the block and heads. Where is the surprised Imogy, help!
I had to grind the KB aluminum street hemi block on three of the 7/16 single tapered exhaust pushrod in the stock machined grooves in that block, all the others cleared fine.
Mock up and check every part up before final assembly on every Hemiroid motor !

I had to do a lot of clearancing on my KB block for a typical straight 3/8" pushrod. Only slight clearancing on the heads, but even the head gaskets needed grinding on so the pushrod didn't rub them.
Probably had the heads on and off the motor 40 times, lol.

Hemienvy I PMed you the information on my friends Cam Shaft, World block, Stage V heads street style the 572. I was wondering what Stage V heads you own. I was at the other guys house today and he can not find his Cam Specs to his 605 but will look for them.

I am not an expert on Hemi's but do street drive a warm wedge with manual transmission. Compression that is OK for a short blast on the strip may not work for extended street driving. Heat builds up cruising and a manual transmission can let the engine lug under load. I was conservative by standards of the board with 10.2 CR and tight quench on 496 wedge. 243 @.050 fast mechanical cam. The car also has a stout cooling system that keeps temps right on the 180 stat when rolling... even driven hard. With the conservative CR I still have to watch timing. Transition from light cruise (50 deg) to WOT (34 deg) needed some care to prevent rattle. I have gradual timing curve vs RPM at WOT to prevent rattle coming out of the corners when hot lapping the road course.

First time I noticed the cruise rattle was on I8 along the Mexican border. Cruising at sea level in OD, about 95 degrees F and just starting to climb the coastal mountains. I pressed the pedal a little more and that cleared it up... I also enjoyed a fast trip to ~4,000'. When I got home I took 2 degrees timing out in that transition area.

Point is, cruising (and road racing) needs a little bit conservative CR and tune.

Heat builds up cruising
... until the thermostat opens

Cylinder head temp and intake air temp have a big effect on detonation. Even with water temp well controlled, metal of the head and intake air can get hot after a long period of running.

Good Morning Hemicar,
I just logged on after a few days and saw all your PM's so I sent you one.

Thanks to all who posted here, there's a lot of good info. Can only talk about it so much,
I need to get with a builder. I think I'm in the ballpark at least.

Repeating it doesn't change the laws of physics. Heat doesn't "build up".