Having fits with DCR
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Having fits with DCR Working on my stroker build and trying to figure out where to degree the cam. I know I can raise and lower DCR by advancing or retarding cam. I have a Rollmaster timing set. I've used different calculators and they give me different results, all of them way too high of a DCR I think. The odd thing is when I ran a slightly smaller cam, the same heads and roughly the same SCR on my stock LS1 I got crazy high DCR numbers even though it ran fine for two years.
Here's where I'm at: Calculated SCR would be 11.47 using .045 gaskets with my 4" stroke, 6.125 rod, 58cc chambers and -8cc pistons. The pistons are flush with the deck so I'd want to get the quench down to at least .045 using those gaskets. Intake advertised duration is 276*, exh. 285*, 111* lsa+2*, ABDC is 43.5*. Using a calculator I get something like 10.4 DCR and that's almost exactly what I got putting in the numbers for when it ran as a 5.7 and it ran fine on pump gas. Am I missing something?
Here's where I'm at: Calculated SCR would be 11.47 using .045 gaskets with my 4" stroke, 6.125 rod, 58cc chambers and -8cc pistons. The pistons are flush with the deck so I'd want to get the quench down to at least .045 using those gaskets. Intake advertised duration is 276*, exh. 285*, 111* lsa+2*, ABDC is 43.5*. Using a calculator I get something like 10.4 DCR and that's almost exactly what I got putting in the numbers for when it ran as a 5.7 and it ran fine on pump gas. Am I missing something?
Yeah that's way off. I don't have the calculator in front of me, but with IVC of 43.5* at 050?, and intake duration of 276, I would expect DCR closer to 8.5. Wish I had access to it so I could try to run the numbers for you.
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What's the gasket bore diameter and cylinder bore? You need to use the advertised IVC, not the .050 IVC to calculate DCR. 276/285 111+2 cam would have an AIVC of 67. What DCR are you aiming for? Do you have Microsoft Excel?
***uming 3.898 bore & 3.92 gasket bore, I get SCR of 11.44, DCR 9.0, quench .045.
***uming 3.898 bore & 3.92 gasket bore, I get SCR of 11.44, DCR 9.0, quench .045.
Last edited by JimMueller; Aug 16, 2014 at 02:31 PM.
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It's a stroker so the bore is 3.903 x 4" stroke and gaskets would be 3.910. Ya I have Open Office which runs Excel. I want a DRC that runs 93 pump gas so below 9 or even closer to 8.5 would be nice. Don't think that's going to happen and keep quench in reason. I tried a different calculator and got the 9.1. My old cam when it was not stroked running it through the calculator came out even higher than this at 9.2 DCR.
If I retard the cam 2* I think it comes out to 8.87 which I'm sure I can tune around. Just don't want it to dog or buck at low RPM. I have a 58cc chamber because a jackwad shop was supposed to mill .020 off stock 243s and it ended up being 58cc chambers which is far more than 20 thou
If I retard the cam 2* I think it comes out to 8.87 which I'm sure I can tune around. Just don't want it to dog or buck at low RPM. I have a 58cc chamber because a jackwad shop was supposed to mill .020 off stock 243s and it ended up being 58cc chambers which is far more than 20 thou
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Thanks to Jim for getting me a very complete calculator. Using the sheet I get 11:44 SCR and 9 DCR (67 AVIC). My old setup with stock stroke/bore was 11.7 SCR and 9.28 DCR. I ran that for two years and after careful tuning only got very small occasional knock under some throttle transitions. Seeing all the components except the rotating assembly and cam are the same and it will be 0.27 lower I think I'm going to try the cam install straight up. If I can't run it I'll pull the balancer, spew some antifreeze and retard it two degrees to 8.8 DCR.
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I get 11.48 and 9.01 with my calculator and zero deck and .045' gasket. That's a pretty small cam for a 383 (assuming 226/235 or close). You want your IVC to be much closer to 49-50 degrees @ .050... you're at 42 degrees. If you want torque, you can keep it in the 47-48 degree range. That means I'd run something much closer to this:
235/242 113+3. It'll drive nice with 12.5 degrees of overlap and make a ton of avg power with an IVC of 47.5 degrees. I'd then switch to a .040" gasket as you want your quench as close to .035" as you can get. .040" is better than .045". With that quench, you end up with 11.62:1 CR and a DCR with that cam of 8.71:1. I'd keep DCR around 8.7:1 for maximum safe power on 93.
235/242 113+3. It'll drive nice with 12.5 degrees of overlap and make a ton of avg power with an IVC of 47.5 degrees. I'd then switch to a .040" gasket as you want your quench as close to .035" as you can get. .040" is better than .045". With that quench, you end up with 11.62:1 CR and a DCR with that cam of 8.71:1. I'd keep DCR around 8.7:1 for maximum safe power on 93.
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Verdad Gallardo Yeah, that's a great cam in a 3.622" stroke motor. With the 4" stroke, you need a later IVC by about 6 degrees on avg. And you can add around 6 degrees of duration int/exh and end up with a very similar performing cam. Hence my advice for 235/242 which is exactly 6 degrees more intake and exhaust and puts your IVC in an optimal area for a torquey 383... especially with an 8.7:1 DCR.
Although, there is nothing wrong with the smaller cam you have - you're just not running optimal quench, compression, overlap, or valve events for the 4" crank. But it will make a ton of torque at the expense of some HP.
I would run the .040" gasket and retard 4 degrees if you want to run that camshaft. It would put your DCR at 8.8 and your IVC at 47.5. I know the Rollmaster provides 2 degree increments, so that would work out fine. I doubt you'd lose much torque but would gain HP.
Although, there is nothing wrong with the smaller cam you have - you're just not running optimal quench, compression, overlap, or valve events for the 4" crank. But it will make a ton of torque at the expense of some HP.
I would run the .040" gasket and retard 4 degrees if you want to run that camshaft. It would put your DCR at 8.8 and your IVC at 47.5. I know the Rollmaster provides 2 degree increments, so that would work out fine. I doubt you'd lose much torque but would gain HP.