Looking for Info / Specs on Obsolete Mopar Piston

Here is one more idea to throw in the mix. Just bear with me a bit on this one. Back in '73 in the 1st Arab oil embargo, gas prices doubled overnight, and lots of the hot rod guys wanted smaller cams but ran into the problem the OP is having: too much DCR if they took their high CR engines and put small cams in them to save fuel. So there were a series of cams made back at that time which had pretty short .050" durations and short overlaps and 114 LSA, BUT which had a long slow ramps down to advertised duration so that the intake valve closure was late and bled off enough pressure to get DCR down. Crane had such cams and I bet others did too.

The rollers tend to have fast ramps which is part of what they are good for. Ditto for something like and XE or a VooDoo; those are going the wrong way on ramps. So a slow ramp (below .050") flat tappet would be very good for this.

If there ever was a time for a custom cam, this is it IMHO. This is when I would be picking up the phone and calling someone like Racer Brown and seeing what he could do.

I wish I could run some DCR numbers on this idea and some example cams specs to do this, but it is 'bedtime for bonzo' LOL. Out on the road working long days.....

nm9stheham said:

Here is one more idea to throw in the mix. Just bear with me a bit on this one. Back in '73 in the 1st Arab oil embargo, gas prices doubled overnight, and lots of the hot rod guys wanted smaller cams but ran into the problem the OP is having: too much DCR if they took their high CR engines and put small cams in them to save fuel. So there were a series of cams made back at that time which had pretty short .050" durations and short overlaps and 114 LSA, BUT which had a long slow ramps down to advertised duration so that the intake valve closure was late and bled off enough pressure to get DCR down. Crane had such cams and I bet others did too.

The rollers tend to have fast ramps which is part of what they are good for. Ditto for something like and XE or a VooDoo; those are going the wrong way on ramps. So a slow ramp (below .050") flat tappet would be very good for this.

If there ever was a time for a custom cam, this is it IMHO. This is when I would be picking up the phone and calling someone like Racer Brown and seeing what he could do.

I wish I could run some DCR numbers on this idea and some example cams specs to do this, but it is 'bedtime for bonzo' LOL. Out on the road working long days.....

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I sent an email to Racer Brown based on your suggestion.
I'll report back with their response.

1970 TA said:

I sent an email to Racer Brown based on your suggestion.
I'll report back with their response.

Click to expand...

Very cool.

Sometimes it easier to get Jim on the phone than by email. If you call him, make sure you call AFTER 5 pm eastern time. It's nice to talk to the guy who is grinding the cam.

FWIW... I just ran a 274 advertised duration cam with 114LSA and 114 ICL and with a .051 head gasket (Felpro 8553 PT), came up with a DCR of 8.19. So that is getting where you need to go pretty easily. A thicker head gasket would be another item that you could interplay with intake closure angle to get the DCR you want.

You are not starting all that far off as the engine sits so it looks very doable IMHO.

nm9stheham said:

FWIW... I just ran a 274 advertised duration cam with 114LSA and 114 ICL and with a .051 head gasket (Felpro 8553 PT), came up with a DCR of 8.19. So that is getting where you need to go pretty easily. A thicker head gasket would be another item that you could interplay with intake closure angle to get the DCR you want.

You are not starting all that far off as the engine sits so it looks very doable IMHO.

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What value of "intake valve close ABDC" did you use that gave you 8.19 DCR?
How would this cam affect driveability?
RPM band would move down? Idle quality and idle vacuum would improve?
Or do I have those backwards?

71 ABDC.

I would expect idle quality to be decent with the 114 LSA; if the exhaust duration was kept to 274 also it would not have too much overlap to make the idle rough. I am thinking you could get around 14" of idle vacuum properly tuned. With the cam you have now, it must be a rough idle.

Just making a guess relative to the cam you have now (228 @ .050"), the RPM band would move down a bit. This is not a basically torquey kind of cam, but you still have a lot of compression left to keep the low RPM torque good. If you could get near to a 60 degree difference in advertised versus .050" durations, then your advertised would be in the mid-210 range and that is not a wild cam at all.

The keys are the slow ramps and the wide LSA and no ground in advance in the cam. The old Crane cam I had like this had and advertised duration that was 60 degrees longer than the .050" duration.... not a lot of companies have such slow ramps anymore. Which is one reason why I suggested Racer Brown; he might have such things; their EH18 is in the neighborhood, tho' the ramps are a bit faster than I would want for a street cruiser.

The other company to ask is Crane. I see they still have some slow ramp cams in their standard catalog, and made those old long duration cams as their 'HE' series back in the day. Something like an H 272-2 is getting pretty close if the ground in advance is taken out in the cam setup; it would have a 67 degrees ABDC intake closure. (With a 114 LSA and 2 more degrees advertised duration it arrives at that 71 degrees ABDC number, so you can see that it is not far off.)

Just wanted to give an update on where I'm going with this engine refresh.
I talked to Jim at Racer Brown and he didn't recommend doing a custom grind cam to reduce the DCR. He said I needed to get the SCR down to about 9.5 for a street motor.
I talked to a local engine builder (Opel Engineering) that knows Mopar engines well. He said to bring in the pistons and he can machine the domes to achieve the desired compression.
Depending on how much the piston weight is reduced, he said you may have an "overbalance" condition and wouldn't need to rebalance the crank.
As I completed the teardown of the engine, there were two different head gaskets used, one side a 1008, the other a 8553PT.
With the current cam that is in the engine, I can achieve the following SCR / DCR combos:
Assuming the advertised 10.7cc dome volume.
Given the two choices above, is one preferred over the other? (remember these are open chamber heads).
What is the relationship between weight and cc volume for the forged pistons I have?
I'm trying to get an idea how much the piston weight will be reduced.
Would you do the crank rebalance?

Use 2.67 grams per cc for this grade of silicon-aluminum alloy. That would be around -21.4 grams for the 8553PT's and -28.6 grams for the 1008's.

Your bobweight will change by the same amount as the material milled off of one piston. I would absolutely rebalance with the amount of weight removal above. I have no idea waht is meant by an 'overbalance' condition.....????

The 1008 and 8553PT are very similar but the 1008 is a more consistent compressed thickness.

OK on the cam... yeah, I suppose it is not worth the price. Someday, Ima gonna call Crane to see if they still have those old HE grinds around....

In response to doubts in previous post referring to "overbalance"--when the amount used on the bob weight is calculated at 51% or 52% rather than the standard 50%. Some believe for very high RPM operations it enhances horsepower or balance (something to that effect).

dibbons said:

In response to doubts in previous post referring to "overbalance"--when the amount used on the bob weight is calculated at 51% or 52% rather than the standard 50%. Some believe for very high RPM operations it enhances horsepower or balance (something to that effect).

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Ah, that makes all the sense in the world; it works out to around 51% in this case. That seems appropriate for a circle track engine, but I can't say if 51 vs 50% is going to show vibrations very badly on the street at low RPM, or not; I just always assume that the standard 50% factor is used for a good reason.