Checking Intake Manifold Fit After Resurfacing Heads
This is odd sounding.... sounds like you have pistons like the Speed Pro L2316's... what pistons DO you have? Is this without a head gasket in-between head and block? Even then, this sounds odd... How much has the deck been cut so far, if any? Standard early 340 pistons stick around .018" above the deck and the open chambers should clear around them.
Not sure how to answer this....[/QUOTE]
Specs on the pistons below.
They are Race Tec forged customs. I had the compression height made to 1.840 to match the TRW 11.5:1's that they replaced. They were originally made flat with no chamfer around the OD like the TRW's. On the first mockup of the engine, the piston to head travel was about 0.020 to 0.030 using an 0.054 gasket. The pistons were hitting at the edge of the diameter of the open chamber around the valve pocket side of the piston. I had the pistons machined to add a 37 degree chamfer to the edge to match the TRW profile. Now my piston to head is measuring 0.060 to 0.070 using the 0.039 gasket.
The deck surface of the block has never been cut.
Thanks for everyone’s responses.
I agree that the distributor / cam gear is not an issue.
Here’s the situation I’m dealing with.
Street driven car for cruise nights. 3:55 gears with 727 Torqueflite. Turbo Action converter, 11 inch, 2500 rpm stall. I’m trying to maintain decent low rpm torque.
I rebuilt this 340 over the winter, it’s +0.030 (4.070).
New forged Race Tec pistons, flat tops, compression height = 1.840, so pistons are above deck 0.020.
Valve pockets are 7.6cc, 0.295 deep.
Top ring down = 0.250
Reusing the Mopar Purple Cam, P4452761, adv dur = 268/272, installed at 107* ICL. Intake close at 61*.
Heads are open chamber “O” castings with tulip 2.02’s, stock, no mods. I thought they were 72cc (I remember measuring one of the chambers before taking them into the machine shop and it was 72cc.). Maybe I misread the burette, because now they all measure 77 to 78cc.
The problem: With my original parts combo (Felpro 0.039, cam @ 107 ICL, pistons +0.020 above deck, 72cc chambers), the calculated SCR = 9.4, DCR = 7.67 (using the Pat Kelly DCR Calculator). I get similar numbers using the Wallace Calculator. Substituting 78cc for chamber volume, SCR = 8.83, DCR = 7.22.
If the heads are shaved 0.020, reducing the chamber volume to 74cc, yields a SCR = 9.2, DCR = 7.5. Cranking psi predicted to be about 147 psi
I’m thinking at these specs, I may be able to run mid-grade / 89 pump gas.
The heads are going into the shop tomorrow. I’ll have them cc a chamber to see if my numbers are correct. Depending on their results, we’ll make a decision on taking some material off the deck surface
This is odd sounding.... sounds like you have pistons like the Speed Pro L2316's... what pistons DO you have? Is this without a head gasket in-between head and block? Even then, this sounds odd... How much has the deck been cut so far, if any? Standard early 340 pistons stick around .018" above the deck and the open chambers should clear around them.
Not sure how to answer this....[/QUOTE]
Specs on the pistons below.
They are Race Tec forged customs. I had the compression height made to 1.840 to match the TRW 11.5:1's that they replaced. They were originally made flat with no chamfer around the OD like the TRW's. On the first mockup of the engine, the piston to head travel was about 0.020 to 0.030 using an 0.054 gasket. The pistons were hitting at the edge of the diameter of the open chamber around the valve pocket side of the piston. I had the pistons machined to add a 37 degree chamfer to the edge to match the TRW profile. Now my piston to head is measuring 0.060 to 0.070 using the 0.039 gasket.
The deck surface of the block has never been cut.
Thanks for everyone’s responses.
I agree that the distributor / cam gear is not an issue.
Here’s the situation I’m dealing with.
Street driven car for cruise nights. 3:55 gears with 727 Torqueflite. Turbo Action converter, 11 inch, 2500 rpm stall. I’m trying to maintain decent low rpm torque.
I rebuilt this 340 over the winter, it’s +0.030 (4.070).
New forged Race Tec pistons, flat tops, compression height = 1.840, so pistons are above deck 0.020.
Valve pockets are 7.6cc, 0.295 deep.
Top ring down = 0.250
Reusing the Mopar Purple Cam, P4452761, adv dur = 268/272, installed at 107* ICL. Intake close at 61*.
Heads are open chamber “O” castings with tulip 2.02’s, stock, no mods. I thought they were 72cc (I remember measuring one of the chambers before taking them into the machine shop and it was 72cc.). Maybe I misread the burette, because now they all measure 77 to 78cc.
The problem: With my original parts combo (Felpro 0.039, cam @ 107 ICL, pistons +0.020 above deck, 72cc chambers), the calculated SCR = 9.4, DCR = 7.67 (using the Pat Kelly DCR Calculator). I get similar numbers using the Wallace Calculator. Substituting 78cc for chamber volume, SCR = 8.83, DCR = 7.22.
If the heads are shaved 0.020, reducing the chamber volume to 74cc, yields a SCR = 9.2, DCR = 7.5. Cranking psi predicted to be about 147 psi
I’m thinking at these specs, I may be able to run mid-grade / 89 pump gas.
The heads are going into the shop tomorrow. I’ll have them cc a chamber to see if my numbers are correct. Depending on their results, we’ll make a decision on taking some material off the deck surface
Might it not be cheaper, easier, better, to just change the cam's ICA to adjust the Dcr?
I've installed the cam 1* advanced @ 107*.
The shop I'm using knows these numbers, but they don't always work out due to block deck variation / other factors. That's why they resurface the deck side and do a test fit before adjusting the intake face.
New piston vs TRW before chamfer addition
Impression in clay from interference prior to adding 37 degree chamfer
