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Author Topic: Ideal DCR for new build? Pinging issues...  (Read 3320 times)
dsrtjeeper
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« on: March 14, 2017, 02:51:49 pm »

It is my understanding that DCR should be closer to 8 to run 91 octane safely. I've suffered pinging at high loads with my current combo with very low total timing and I'm looking to solve it. Car has been tuned numerous times.

Current combo:

4.3 bore
3.4 stroke
5.315 rod
Flat tops with - 5cc valve reliefs
61cc chambers
-.010 piston to deck
.030 head gasket thickness
4.1 head gasket bore

Camshaft specs:
224/232 @50
108 icl
112 lobe seperation
Intake closing 40*
Cold cranking compression is 195-202 psi

Run those numbers through your favorite DCR calculator and look at the DCR value. It's pretty high. If I drop my CR to 10:1 and change Intake closing to 50*; DCR drops back close to 8.

--------------------------------------------------------------------------------

I'm building a new 347 combo and would like to get it more 91 octane friendly. The main difference will be using 5.4" rods.

I'm open for suggestions on changing cam to bleed off more cylinder pressure, different head cc's, head gasket thickness and/or piston dish. I'd like to retain good quench.

Thanks!
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juiced coupe
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« Reply #1 on: March 14, 2017, 04:40:43 pm »

Since you live in a hot/dry area, whatever you have will be a little more sensitive to detonation than many other parts of the country.

While you could have a cam custom ground to bleed off some cylinder pressure, I think that lower the compression would be the best route.

Theoretically, doing it with a reverse dome piston and smaller chamber is the more efficient method.

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Doing more with less, or something like that.
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You might need some Titanium rods and a flow bench!  LMAO on floor

I honestly don't get it.

I'm sweating, my heart is racing, my clutch foot is twichin', and my right arm punched the computer screen doing an involentary 2-3 shift while reading all that. 
dsrtjeeper
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« Reply #2 on: March 14, 2017, 04:56:53 pm »

Since you live in a hot/dry area, whatever you have will be a little more sensitive to detonation than many other parts of the country.

While you could have a cam custom ground to bleed off some cylinder pressure, I think that lower the compression would be the best route.

Theoretically, doing it with a reverse dome piston and smaller chamber is the more efficient method.



So maybe a 58cc chamber and 12cc's or so dish? I'd like to maintain good quench.
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woody
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« Reply #3 on: March 14, 2017, 04:59:41 pm »

dish volume has no effect on quench. Keep the piston at 0 deck, use a .040 x 4.100 head gasket and get the correct dish volume
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dsrtjeeper
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« Reply #4 on: March 14, 2017, 05:07:13 pm »

dish volume has no effect on quench. Keep the piston at 0 deck, use a .040 x 4.100 head gasket and get the correct dish volume

Thanks Woody. Are you agreeing that I need to lower the CR as well?
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David Claflin
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« Reply #5 on: March 16, 2017, 06:03:56 am »

Did you try running your calculator with the cam retarded? With a smaller cam you could probably get away with that, especially with a long runner intake
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1990 Red LX, 306, 75MM, ported gt40's, Holley SMII, accufab longtubes, 3" exhaust, 4.10's, 318RWHP/316RWTQ
1985 LTD LX 302, ported TW's, XE-264 cam, ported Holley SMII, 75MM-R TB, MAC 1 3/4" longtubes, 4R70W, mach 1 brakes
1988 GT long term project
dsrtjeeper
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« Reply #6 on: March 17, 2017, 02:37:24 pm »

Did you try running your calculator with the cam retarded? With a smaller cam you could probably get away with that, especially with a long runner intake


A friend did. Retarding 2* will put me at a 110 icl. He believes that this will help bleed off some cylinder pressure. It's intertesting that you refer to the cam as small. One builder told me that I could put down around 400hp to the wheels with 58cc AFR 185 heads and a Systemax intake. CR would be 10:1.
Thoughts?
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David Claflin
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« Reply #7 on: March 18, 2017, 09:51:38 am »

If you don't want to go to a bigger cam I wouldn't hesitate to retard that to a 112 ICL, like I said the long runner intake like the later valve opening. That cam Jay did for my 306 had a 113, stock is 114 or thereabouts.
What head gaskets are you using to get .030? I presume you meant 4.030 bore?

http://www.wallaceracing.com/Calculators.htm
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1990 Red LX, 306, 75MM, ported gt40's, Holley SMII, accufab longtubes, 3" exhaust, 4.10's, 318RWHP/316RWTQ
1985 LTD LX 302, ported TW's, XE-264 cam, ported Holley SMII, 75MM-R TB, MAC 1 3/4" longtubes, 4R70W, mach 1 brakes
1988 GT long term project
dsrtjeeper
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« Reply #8 on: March 18, 2017, 01:04:50 pm »

If you don't want to go to a bigger cam I wouldn't hesitate to retard that to a 112 ICL, like I said the long runner intake like the later valve opening. That cam Jay did for my 306 had a 113, stock is 114 or thereabouts.
What head gaskets are you using to get .030? I presume you meant 4.030 bore?

http://www.wallaceracing.com/Calculators.htm

I'm not opposed to changing cams; I'm just hoping that I don't need to. Yes; 4.03" bore. Head gaskets are Cometic .030" compressed MLS.
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David Claflin
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« Reply #9 on: March 18, 2017, 11:06:26 pm »

The new cars, LS and Hemis run the ICL in the high 1 teens, to compensate for the high compression, and run a small cam that will pull well in the upper RPMS
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1990 Red LX, 306, 75MM, ported gt40's, Holley SMII, accufab longtubes, 3" exhaust, 4.10's, 318RWHP/316RWTQ
1985 LTD LX 302, ported TW's, XE-264 cam, ported Holley SMII, 75MM-R TB, MAC 1 3/4" longtubes, 4R70W, mach 1 brakes
1988 GT long term project
dsrtjeeper
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« Reply #10 on: March 18, 2017, 11:57:09 pm »

The new cars, LS and Hemis run the ICL in the high 1 teens, to compensate for the high compression, and run a small cam that will pull well in the upper RPMS


If only our cars had knock sensors.

So the new combo will be as follows:

347 with 10:1cr
5.4 rods
14cc Dished pistons
4.060 head gaskets /.041 compressed
58cc AFR 185 heads
1.6 let's
1 3/4 shorties
Rpm Performer 1 intake fully ported by Panhandle Performance
2.5" exhaust with H pipe

Would you mind plugging this combo into your EA? I'm curious. Does the program suggest cam specs?
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BirdMan
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« Reply #11 on: March 19, 2017, 05:46:55 am »

I am putting together a carbed 347 for the street also.  I have a CI 235/248*@.050 TLSR and plan on running 91 octane also and with compression of 10.51 the DCR of 7.78.
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David Claflin
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« Reply #12 on: March 19, 2017, 07:46:27 am »

The new cars, LS and Hemis run the ICL in the high 1 teens, to compensate for the high compression, and run a small cam that will pull well in the upper RPMS


If only our cars had knock sensors.

So the new combo will be as follows:

347 with 10:1cr
5.4 rods
14cc Dished pistons
4.060 head gaskets /.041 compressed
58cc AFR 185 heads
1.6 let's
1 3/4 shorties
Rpm Performer 1 intake fully ported by Panhandle Performance
2.5" exhaust with H pipe

Would you mind plugging this combo into your EA? I'm curious. Does the program suggest cam specs?

It does make suggestions, but it keeps saying to plug in those numbers and try again. What is the lift on the cam you have? If memory serves it came from Ed, was it in a Lunati box, or Comp?
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1990 Red LX, 306, 75MM, ported gt40's, Holley SMII, accufab longtubes, 3" exhaust, 4.10's, 318RWHP/316RWTQ
1985 LTD LX 302, ported TW's, XE-264 cam, ported Holley SMII, 75MM-R TB, MAC 1 3/4" longtubes, 4R70W, mach 1 brakes
1988 GT long term project
dsrtjeeper
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Location: Phoenix, AZ.

« Reply #13 on: March 19, 2017, 11:57:19 am »

The new cars, LS and Hemis run the ICL in the high 1 teens, to compensate for the high compression, and run a small cam that will pull well in the upper RPMS


If only our cars had knock sensors.

So the new combo will be as follows:

347 with 10:1cr
5.4 rods
14cc Dished pistons
4.060 head gaskets /.041 compressed
58cc AFR 185 heads
1.6 let's
1 3/4 shorties
Rpm Performer 1 intake fully ported by Panhandle Performance
2.5" exhaust with H pipe

Would you mind plugging this combo into your EA? I'm curious. Does the program suggest cam specs?

It does make suggestions, but it keeps saying to plug in those numbers and try again. What is the lift on the cam you have? If memory serves it came from Ed, was it in a Lunati box, or Comp?


Lunati box and lift is .590/.590.   
Thanks!
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dsrtjeeper
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« Reply #14 on: March 19, 2017, 12:43:29 pm »

I am putting together a carbed 347 for the street also.  I have a CI 235/248*@.050 TLSR and plan on running 91 octane also and with compression of 10.51 the DCR of 7.78.

Love your avitar! Those old Fords are so simplistic and make the perfect hot rod platform.

That's a pretty stout cam for the street. Will you be running a 5 speed and power brakes?
That cam must have really dropped the DCR.
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