Dual pattern cams in towing applications

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travis
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Dual pattern cams in towing applications

Post by travis »

I was reading somewhere (can’t remember exactly where) that the reason most cam companies recommend dual pattern cams in heavier towing applications is to help control heat buildup in the exhaust system. Is there any truth to this?
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Re: Dual pattern cams in towing applications

Post by novadude »

travis wrote: Mon Oct 14, 2019 12:08 pm I was reading somewhere (can’t remember exactly where) that the reason most cam companies recommend dual pattern cams in heavier towing applications is to help control heat buildup in the exhaust system. Is there any truth to this?
I am no expert, but it seems to me that the earlier exhaust opening should (in theory) put MORE heat into the exhaust system. Remember, as the gasses expand and do work on the piston, temperature drops. Later EVO would also give more time to transfer heat through the cylinder walls and piston - In Theory. Real world, I doubt you'd see much difference, assuming that the valve events are close to what is needed with both the single pattern and dual pattern cams. JMO.
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Re: Dual pattern cams in towing applications

Post by PRH »

IH used a backwards dual pattern cam in their 304/345/392 v8’s.
260/252-adv
188/178-.050
.445/.401-lift
110.5lsa
111 int c/l
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Re: Dual pattern cams in towing applications

Post by CamKing »

Increasing the exhaust duration can reduce temp in the cylinder, but will also reduce pressure, and power at lower RPM's.
For a towing application, where power below peak is more important then power past peak, increasing the exhaust duration is the wrong way to go.
If the engine has to pass a smog test, where they check the NOX levels, then the longer exhaust is a good idea, because it will reduce the cylinder temps, and reduce the NOX.
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Re: Dual pattern cams in towing applications

Post by novadude »

CamKing wrote: Tue Oct 15, 2019 10:08 am Increasing the exhaust duration can reduce temp in the cylinder, but will also reduce pressure, and power at lower RPM's.
For a towing application, where power below peak is more important then power past peak, increasing the exhaust duration is the wrong way to go.
If the engine has to pass a smog test, where they check the NOX levels, then the longer exhaust is a good idea, because it will reduce the cylinder temps, and reduce the NOX.
Reducing cylinder temps puts more heat into the exhaust system, no? I think this is what the OP was asking (cooler exhaust from dual pattern).
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Re: Dual pattern cams in towing applications

Post by travis »

novadude wrote: Tue Oct 15, 2019 1:02 pm
Reducing cylinder temps puts more heat into the exhaust system, no? I think this is what the OP was asking (cooler exhaust from dual pattern).
That sounds right to me...longer exhaust duration and/or earlier exhaust open point means less time that the hot exhaust gasses are sitting inside the engine and less cylinder wall exposed to the exhaust heat, so that heat has to go somewhere.
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Re: Dual pattern cams in towing applications

Post by travis »

PRH wrote: Tue Oct 15, 2019 9:49 am IH used a backwards dual pattern cam in their 304/345/392 v8’s.
260/252-adv
188/178-.050
.445/.401-lift
110.5lsa
111 int c/l
Off the top of my head, I seem to remember that the IH 6.9 and 7.3 diesels used almost the exact same specs, except on a 104 lsa.
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Re: Dual pattern cams in towing applications

Post by travis »

CamKing wrote: Tue Oct 15, 2019 10:08 am Increasing the exhaust duration can reduce temp in the cylinder, but will also reduce pressure, and power at lower RPM's.
For a towing application, where power below peak is more important then power past peak, increasing the exhaust duration is the wrong way to go.
If the engine has to pass a smog test, where they check the NOX levels, then the longer exhaust is a good idea, because it will reduce the cylinder temps, and reduce the NOX.
This makes more sense to me, and also matches my experiences. What prompted this question though is that if you look through many cam companies catalogs, they list single pattern cams for “light towing”, but their stuff listed for moderate to heavy towing tends to be wider lsa with more and more exhaust duration/widening lsa as the towing weight gets heavier...which always seemed back asswards to me but I’ve been wrong before. And it’s not just one or 2 cam companies that do this.
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Re: Dual pattern cams in towing applications

Post by Mummert »

Headers, headers. If your exhaust works narrow up the lobe centers and and drop the exhaust duration. Last cam I had was 202@.050 on a 108 installed on a 102. It was to revvy. I was gonna try a 192@.050 on a 103 installed at 98. But the truck had so many miles and the front end was shot, needed everything, and ended up selling it.
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Re: Dual pattern cams in towing applications

Post by PRH »

You wanna see some exhaust heat...... try a late production Mopar 400/440 with the pistons 1/8” down the hole, net CR near 7.7:1, and your typical 10deg split white box special dual pattern cam........ that’s too big and too wide.

The ex manifolds are glowing so bright it seems like you can almost see through them.

Oh, and after you’ve worked it hard for a while........ don’t lean on the fenders........ it’ll burn the skin off your arms.
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Re: Dual pattern cams in towing applications

Post by Old School »

PRH wrote: Tue Oct 15, 2019 4:30 pm You wanna see some exhaust heat...... try a late production Mopar 400/440 with the pistons 1/8” down the hole, net CR near 7.7:1, and your typical 10deg split white box special dual pattern cam........ that’s too big and too wide.

The ex manifolds are glowing so bright it seems like you can almost see through them.

Oh, and after you’ve worked it hard for a while........ don’t lean on the fenders........ it’ll burn the skin off your arms.
What are the specs on the cam you use to prevent that?
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Re: Dual pattern cams in towing applications

Post by travis »

Back when I was in high school my parents upgraded their mid ‘70’s dodge chassis Winnebago motor home (318, and apparently really low gears because top speed was barely over 60 mph) to a slightly bigger ‘77 or ‘78 Winnebago with a 440. That sucker could definitely make a set of manifolds glow! And it pinged relentlessly no matter what fuel you put in it or where you set the timing.
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Re: Dual pattern cams in towing applications

Post by PRH »

Yup...... the worst of all worlds.

Lotsa ping....... lotsa heat.

But on the plus side........they also got awful gas mileage.
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Re: Dual pattern cams in towing applications

Post by FC-Pilot »

PRH wrote: Tue Oct 15, 2019 5:32 pm Yup...... the worst of all worlds.

Lotsa ping....... lotsa heat.

But on the plus side........they also got awful gas mileage.
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Re: Dual pattern cams in towing applications

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travis wrote: Tue Oct 15, 2019 5:08 pm Back when I was in high school my parents upgraded their mid ‘70’s dodge chassis Winnebago motor home (318, and apparently really low gears because top speed was barely over 60 mph) to a slightly bigger ‘77 or ‘78 Winnebago with a 440. That sucker could definitely make a set of manifolds glow! And it pinged relentlessly no matter what fuel you put in it or where you set the timing.
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