Pistons .010 inch ABOVE Block Deck - Opinions ?

[AMX69PHATTY]

Wanted to ask opinions on having an AMC V-8 built with the Pistons protruding .010 inch out of the block above the deck surface.

Pistons are .030 over cast dish top stock type replacements and the narrow rim around the perimeter is the only area .010 above the block deck. The new pistons were less tha $100. Targeted compression is 10.2:1 as original in this 1969 343 block. To get this compression with the 3/16" dished top pistons a 304/360 3.44 stroke crank offset ground .010 was used yielding a 3.46 stroke and 1.73 throw, stock 343 rods and mildly ported and relieved 1970 304 heads milled .050 with 2.02 / 1.68 valves at about 57 cc's. Intend to use Fel-Pro Blue Head gaskets, .045 compressed thickness. Top dead center stack-up is 1.730 throw, 5.875 Rod, 1.581 Piston Compression Height = 9.186 and 343 deck is 9.175 so pistons are .011 above the deck. Running the numbers give 10.2:1 compression. With the .045 compressed gasket thickness the piston rim is .035 away from the head. Piston to valve clearance checks out at .100 + with a #31702 Lunati cam, .496 / .496 & 228 / 235 @ .050 installed strait up although the cam card says as ground it is 4 degrees advanced. Target is 500 HP on high octane pump gas with a little CAM2 Purple added for some lead content. This motor previously made 420 HP with only about 9.00:1 compression with the same cam, which was way to little compression for the cam. Even with such low compression the car ran 12.60 @ 109 off the brakes though the air cleaner and exhaust on pump premium, Holley 850 DP, Torker, 1-5/8 Headers, 727 Automatic, 3500 B&M Super Holeshot. 3.73 Gears, MT 26 x 8.5 Slicks, MSD 6T, stock distibutor with UniLite conversion and recurved for 0 degrees at idle and 35 degrees at 3500 rpm.

So am I nuts ? Will the pistons .010 above the deck cause any problems ? Is a 500 HP 367 C.I. AMC V-8 on pump gas just nuts or what ? The combination has already made 420 HP with the way too low 9.0:1 compression and hopes are that the 10.2:1 will make all the difference and allow this combination to show it's full potential. (:-P)

[jeepsr4ever]

You will need .040-.045 at least above the top of the cast piston for quench. Look around and see if you can find some thicker gaskets.

[Holeshot]

...or have the .010" ring turned down to eliminate it. Then shoot for the .045" piston to head clearance.

You also have the distributor curved wrong, go for 18 advance & 20 initial.

As far as the "I'd go with it" advice, that is DEAD wrong, as you already know!!!

The Ross pistons from Maddog have SBC combustion chambers & will never be correct. You need flattops direct from Ross, $500 something with pins, be sure to get the ones with 1/16" top rings, instead of the thick stock ring size.

[SwampRat]

I wouldn't be scared of it, cast pistons do have a lower expansion rate than forged pistons and if the RPMs weren't sky-high and with steel rods I say it would be fine.

[AMX69PHATTY]

Well my 367 Engine build up has come to a screaching halt.

Using clay I found there is only .050 Exhaust Valve to Piston Clearance.
#-o
Understanding is there should be .100 minimum.
Knew it would be close because limits were pushed.
Heads milled .060, short 9.175 early block, 304/360 Crank offset ground .010 for a 3.46 Stroke.
Zoellner Cast Pistons, $88 from Maddog, are .020 shorter than stock, 1.581, with a 27cc dish.
Need to gain a minimum of .050 Valve to Piston clearance.

Maybe have the Piston Valve reliefs machined deeper ?
Like to avoid buying new pistons, exspensive, and would need customs.
The Maddog Ross units give to much compression, 1.596 Comp Ht. 21cc Dish.
Let alone stick out above the deck .026, so that's no good.
Would need a compression hieght of 1.560 with a 21cc dish.
If somehow could come up with shorter Rods, then would loose compression.
Target Compression is 10.2:1 same as original '69 343 4V motor.
Takes me back to having the Piston Valve reliefs machined deeper.
Wonder how thicj the cast piston tops are and if there's enough meat ?
Man, what am I gonna do ......... ?
Opinions ?
:-|

Oh, and by the way, when I use the specifications for the Maddog Ross AMC 360 Pistons,
assembled in a stock 360 bored .030 over with 58cc heads,
I only come up 9.65:1 compression whereas thier listing says 10.2:1.
Get 10:1 if deck is milled .015 to 9.193 hieght with .002 piston deck clearance.
Anyone have DeskTop Dyno to check and see what compressin they get ?
111!!!

http://mywebpage.netscape.com/SketchKT/AMC+AMX+Comp+Ratios.jpg

[Holeshot]

Any progress on this plan? I still suggest biting the bullet & getting some forged pistons, they come up on ebay for around $300 pretty frequently (I would rather use used forgings than new cast pistons). Since you are building the 360, your choices are more than with the 390/401, since you will be using the smaller wrist pin. You can use SBC flattops and get the valve reliefs machined just as you need them. Isky used to rent out the milling tools for doing that using your valve guides as the arbors. They may still rent the tools out. Not too sure if you'd be safe milling cast pistons for the needed piston to valve clearance, I certainly would not ever feel safe modifying cast pistons. I always use the 1/16" top ring groove size pistons, thinner rings are more performance oriented. Always use full-floating pins & forced oiling to the pins. You probably know all this already, but for those that don't, there it is.

What did it cost for the offset grind of the crank? A SHORTER stroke would yield MORE horsepower!!!! But at a slightly higher RPM, 500 or so more.

Are you building this to meet stock specs for NHRA/IHRA, or what (claimer?)?

What are you using for cam, intake, carb, exhaust? (modeling your engine in Dyno2000)

If you DO go for forged pistons, and DO use 390/401 rods, you can push your redline way up & go a different way with the cam/carb/intake, & make a bunch more ponies. May or may not need custom pistons, most likely can find an off the shelf item that can work.

Also, Total Seal gapless rings are more costly but offer around 10% more power (0% leakdown versus up to 10%).

Putting in 2.08/1.74 valves can offer more HP if you are moving that much air, and, of course, with porting can be worth 50-100HP more.

500~575HP would probably be about the max, so all the extra expense will get you between 50~100HP. But the forged parts would allow safer high RPM op & the option of safely adding up to a 350HP shot of NOS if you get the block O-ringed. That would be just under 1000HP on the bottle!!!

A cheaper way to get 1000HP is to go turbo with low compression forged pistons & forged rods. Metering the fuel would probably be the biggest challenge, financially. A "home brewed" setup is quite easy to do but going with all the newest gadgets would be salty. Turbo works better with the smaller engines, 290, 304, etc., since they have a thicker cylinder wall.

[AMX69PHATTY]

Some progress, I'm hesitating some due to the Piston / Head / Valve Clearances and deciding on a direction.
Also I've been distracted by a little front end body work since I have freshly rechromed bumpers and a new grille.
A big part of the decision process is the fact that I'm currently unemployed since mid July.

The Short Block is already assembled and has been balanced, this and costs are why I hesitate to get new pistons.
Also, the clearances are pretty close to recommended minimums, they're right there at the edge of being ok.
Changes would be big bucks only to gain .010" or a few thousands more clearance.
Checking with a strait edge and feeler gauge, the pistons protrude only about .007" due to reconditioned Rods.

Thanks for the Isky Tool info, they said they still rent the tool, I agree modifying casts is questionable.
Have tried to contact Zollner in Fort Wayne to get there opinion, haven't got anyone on thephone yet.
There pressed in pins and stock width Hastings cast iron rings, not file fitted.
I'ts been an "economy build", motor had been together this way and made about 425 HP at the flexplate.
And that was with only 9.0:1 static compression which wasn't enough for what the cam "wants".
Changes made were to increase static comp to a little more than 10:1 so the combo could realize it's potential.
The $88 Zollner Pistons are the same as the old TRW's that had been in the motor,
so really the only thing changed from before was the .010 offset grind on the crank.

The offset grind to a stock 304 Crank cost me $100, and it was cross drilled - $75.
Intention is to only run the motor out to 6000 rpm shift points.
Target E.T. is 12.00 sec @ 111 mph, and 3.73 gear, 26" Slicks, 7% converter slip = right around 6000 @ 111mph.
When it was together this way before with only 9.0:1, through the exhaust, best was 12.60 sec @ 109 mph.

Nah, it's not a full race car, it's a driver hobby street car that I run at the track occasionally for fun on Tune & Test nights.

Cam at valve: .512 - 230/280 & .530 - 245/295, 110 Lobe Centers,
110 Intake Centerline installed strait up or 106 advanced 4 degrees crank.
Previously this cam was installed Strait Up, but now I have it in there 4 degrees advanced,
and would like to advance it to 6 or 8 degrees, just need to figure out how to do that.
The cams a little to much for my stall / gear and wish to make that up by advancing it,
getting more valve clearance due to the exhaust closing sooner, and higher dynamic compression.
It's actually a stock AMC cam that was reground by Chet Herbert, done 20 years ago in the 80's !

Holley 850 DP, 1" 4 Hole spacer, port matched Torker, 27cc Piston Dish, mildly ported 48cc iron Heads,
11/32" stem StnStl 2.02 / 1.68 Valves, Roller Rockers, 1-5/8" Headers, 2-1/2 Exhaust, 2 Chamber FlowMasters,
MSD 6T, Unilite Trigger, B&M 3000 Stall, TorqueFlite 727, AMC 20 3.73 Posi, 26x8.5 MT Slicks.
3250 lbs with driver and pump gas with a little CAM2 added to get a little lead in the fuel.

I've already been real close to my target of 12.00 Flat quarter mile on pump gas through the exhaust
running the motor out to only 6000 with this combination, 12.60 and with only the 9.0:1 Static Comp.
So the goal has been to get the same combination back together with more like 10.2:1 compression
like I think the cam wants, advance it, get that little more additional HP, 25-35 maybe, and get to 12.00 flat.
If it runs under 12.00 it would need to be caged, and I don't want to do that.

I'm curious to see what DD comes up with. It chassis dyno'd before the milled ported heads at about 280 HP.
And that was at something like a little over only 8.0:1 compression even !
So the milled ported heads bumped compression to about 9.0:1 and gained about 35 HP !
Please let me know if I omitted anything needed for DD.
Glad to see ya got your PC fixed and workin' !

Thanks for your help, I'm curious to see what DD comes up with.

:t: