Max Wedge heads

[Voss]

Many thanks for all the info and hints in this thread. I must say this forum is really great!  

I'm currently using premium 98 pump gas (95 is regular fuel here in Sweden, but I use premium 98). I have not observed any pinging, but I have just got the car and only driven it a few miles. The engine runs strong and fires right up (even in cold weather as it is here now). So there are really no issues with the engine. The guys who done the rebuild seems to have done a good job.

I won't tear down the engine at this point. However, I aim to restore things back to original on this car so I want the 906 heads since they are after all what supposed to be there. But I will try to figure out what's done to the internals of this engine before doing any rebuilds back to original. What Challenger340 posted about the pistons is very interesting (btw, thanks for all your info)... I will definitely check that out when I remove the heads next winter.

I will do a compression test next weekend when I'm at the car... What would be the expected psi reading assuming original pistons and original 516 heads? And what would the psi reading be for original pistons and original 906 heads (all original 440)? I'm trying to figure out if I can use the compression readings to understand what's done to the engine without tearing it down...

/Andreas

Trying to guess an accurate Static Compression Ratio, from a Compression psi or "effective" pressure, is not a very accurate method to determine Pistons present ?
Very hard to guess a compression reading without knowing the Camshaft events ?
How big is the Cam ? Overlap ?
How well is the Engine sealing ?
What Compression method ? ..4 Bumps...1st bump 75% of the 4th and final bump ?
too many variables to doing it right here......

If your intent is to have the 906 Heads at all costs for Vehicle number legitimacy, IMO, PULL the Heads and LOOK at the Piston heights to be sure.

Thanks for the info, now what you are saying makes perfect sense... A static compression reading won't tell that much about the internals, agree on that...   Besides measuring, is it possible to identify the pistons by any numbers/marking or something like that? And what would the measurement down hole at TDC be for a stock engine (to have 10:1 C.R. with stock cam and pistons)?

[Challenger340]

The Factory original '68 to '70 Pistons(non 6 Pack)..... from memory were about .060" Downhole,
however.....
that was WITH using a Steel Shim Head Gasket @ .022" thick.

The factory used to advertise the Comp Ratio as 10.1:1 for the above Pistons, and it would have been, based upon a Ma'Mopar "published" Volume for the 2843906 open chamber head as 79.5 CC,
which,
because of the HEMI's DOMINATION of the Super stocks ranks...
... was quickly adopted by NHRA, and other Drag Race sanctioning bodies of the period, as "Legal" minimum sizing on the Magnum Wedges.

In the REAL World However,
Because most of the 906 Heads of the time, came in around 82-84 CC's as produced with no Valve seat recession, actual Compression from factory on the Engines "as delivered" was only around 9.8 to 9.9:1 using the steel shim Head Gasket.

Anyways, and back to your question.....
Simply reproducing that .060" Piston downhole @ TDC these days, will NOT necessarily duplicate that Compression Ratio, or the Performance, due to variances in 40 year old 906 heads, and the lack of Steel Shim Head Gaskets(dunno if still around..or if you wanna use them anyways), and changes in Engine Swept CC Volume with Boring & Honing Cylinder Oversizes.
Long Story Short.....
You would need to BLUEPRINT your Engine.....and 906 Heads...Camshaft...etc., etc.

The GOOD news..
is that if you do undertake Blueprinting back to factory specs, on a SuperFlow 902 Engine DYNO with minor Head work, these Engines WILL produce around 400hp/500Trq using stock manifolds and 2 1/4" exhaust.....
I can pm you Dyno Sheets from my Shop as proof( the last 6-pack example we did churned 425hp and 530Trq using Flat Tappet Repro Cam !)

I applaud your efforts in this area, to RESTORE not just the Car, but the factory PERFORMANCE as well.....
I will Not mince words here...
I find it an absolute SHAME, that far too many "restored" numbers matching Musclecars.....are absolute TERDS once the loud pedal is mashed due to the owners lack of continuity & diligence in the Engine Dept.
I'm OLD...... I DROVE these things.... and RACED them....back when still fairly "factory" and "untouched".....so I dunno whether to LAUGH or CRY sometimes with some of the "award winning" restored Cars I've seen these days.....some can't get outa their own way.

[BSB67]

Many thanks for all the info and hints in this thread. I must say this forum is really great!  

I'm currently using premium 98 pump gas (95 is regular fuel here in Sweden, but I use premium 98). I have not observed any pinging, but I have just got the car and only driven it a few miles. The engine runs strong and fires right up (even in cold weather as it is here now). So there are really no issues with the engine. The guys who done the rebuild seems to have done a good job.
I won't tear down the engine at this point. However, I aim to restore things back to original on this car so I want the 906 heads since they are after all what supposed to be there. But I will try to figure out what's done to the internals of this engine before doing any rebuilds back to original. What Challenger340 posted about the pistons is very interesting (btw, thanks for all your info)... I will definitely check that out when I remove the heads next winter.

I will do a compression test next weekend when I'm at the car... What would be the expected psi reading assuming original pistons and original 516 heads? And what would the psi reading be for original pistons and original 906 heads (all original 440)? I'm trying to figure out if I can use the compression readings to understand what's done to the engine without tearing it down...

/Andreas

Trying to guess an accurate Static Compression Ratio, from a Compression psi or "effective" pressure, is not a very accurate method to determine Pistons present ?
Very hard to guess a compression reading without knowing the Camshaft events ?
How big is the Cam ? Overlap ?
How well is the Engine sealing ?
What Compression method ? ..4 Bumps...1st bump 75% of the 4th and final bump ?
too many variables to doing it right here......

If your intent is to have the 906 Heads at all costs for Vehicle number legitimacy, IMO, PULL the Heads and LOOK at the Piston heights to be sure.

Thanks for the info, now what you are saying makes perfect sense... A static compression reading won't tell that much about the internals, agree on that...   Besides measuring, is it possible to identify the pistons by any numbers/marking or something like that? And what would the measurement down hole at TDC be for a stock engine (to have 10:1 C.R. with stock cam and pistons)?

Here are the stock replacement piston compression heights used over the years: 2.06, 2.03, 1.99, 1.93.  Generally, these in an uncut block go: .020, .050, .080, and .140 in the hole, respectively.    The 2.06 is the six pac piston, and 2.03 is the 68-69 piston.  The 2.03 piston has not been available new for over 20 years.  Frankly, the 2.03 piston with a 906 head is a poor choice any ways with today's gas. 

I too am a bit embarrassed when the restored car guys hit the track and turn 15's, but that's just me.  The only way my car would win a prize at a car show is if I was the only guy entered.