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Technical info for camshaft
https://slantsix.org/forum/viewtopic.php?t=63346		 Page 1 of 1
Author:  frank79912 [ Mon Feb 25, 2019 4:07 pm ]
Post subject:  Technical info for camshaft
I know this subject is getting old but.... besides the usual info on duration. Somewhere I remember a calculator for lobe separation and for the slant 6 it comes out to be 107 degrees on the intake - stock cam specs for hrdro cam ,but at a loss on exhaust - stock spec is 111 degress. Also, anything over .425 net valve lift is rumored causes a dead spot off idle . Any ideas ? Basically is to take a stock hydraulic (188 @ .050), add 15 degress duration @.050 and .050 more lift then the stock .375 and keep the stock lobe separation then install at 102 centerline without have to cut a lot off the head or deck.To keep the low end but give it a little more help - it will loose power under heavy load /high gear until it hits 1200 rpm then keeps pulling now.
Thanks Frank
Author:  Joshie225 [ Mon Feb 25, 2019 4:13 pm ]
Post subject:  Re: Technical info for camshaft
What's the question?

Also, don't confuse lobe separation (degrees between intake and exhaust centerlines) with intake centerline (degrees before TDC of maximum intake valve lift) as you appear to have done in your second sentence.

There is no truth to more valve lift causing an off-idle flat spot.

DadTruck did the most research on juice cams for heavy vehicles and has good results for his efforts. I wouldn't hesitate to follow in his footsteps so long as the compression ratio increase is observed.
Author:  Rick Covalt [ Mon Feb 25, 2019 4:50 pm ]
Post subject:  Re: Technical info for camshaft
You will have the head off to change the cam if it is the peanut head anyway. Planing the head a little will help performance and economy. 2 more cents
Author:  DadTruck [ Tue Feb 26, 2019 5:33 pm ]
Post subject:  Re: Technical info for camshaft
Quote:
a calculator for lobe separation and for the slant 6 it comes out to be 107 degrees on the intake
the lobe separation calculator that I am familiar with is a 2 axis chart published by David Vizzard, and yes for a 225 a lobe separation of 106 or so is
in line with recommendations.

a couple views of the David V chart are at the link below

https://www.google.com/search?q=david+v ... 17&bih=857

And as Josh mentioned, don't confused LSA (Lobe Separation Angle) with ICL ( Intake Centerline )

LSA is fixed when the cam is ground, LSA is the distance in camshaft degrees between the max lift of the intake and exhaust cam lobes.

ICL set during the camshaft installation process, when the cam is 'degreed' and is the point in crankshaft degrees where the intake valve reaches maximum lift.
Exhaust centerline can be calculated but exhaust centerline cannot be set independent of the Intake Centerline, unless you have a twin cam motor, so with a slant
set the Intake Centerline and the Exhaust Centerline falls where it is.

and yes raising the compression on a slant really helps,
understand how to cc the combustion chambers and measure piston recession
then trim to get the compression up to the 8.5 range for static compression, for regular gas, you can go much higher but
may need premium.

and below is a link to a hydraulic cam thread that I participated in back in 2011 ( wow 8 years ago) still running that cam in the D150 today have 30K miles on
it, was a nice boost from the stock cam for drivability and power and runs regular gas.

https://www.slantsix.org/forum/viewtopi ... 19&t=43301
Author:  frank79912 [ Tue Feb 26, 2019 6:44 pm ]
Post subject:  Re: Technical info for camshaft
Yes - I understand the difference between lobe separation and center line and to raise compression .The main question is if a cam has lobe separation on the intake - 107 ish is the optimum calculation - install the cam at say straight up - would there be any difference is when the cam was ground the lobe center of the exhaust was changed? If you install the cam at 102 wouldn't that adversely effect the exhaust opening too soon? Looks like most just copy the intake lobes ramp. And about 165 is about as much compression you can have and get away running 87.
Thanks for the report on the lift because it was told to me to keep below .425 or low speed /off idle response is slow due to drop in velocity.
Has any one tried the Aussie long tubed intake to see if its better or worse then the stock 2bbl intake ?
Author:  DadTruck [ Tue Feb 26, 2019 8:09 pm ]
Post subject:  Re: Technical info for camshaft
Quote:
And about 165 is about as much compression you can have and get away running 87.
I would get the static compression up in the 8.5 range and not try to target a specific cranking compression.

as an FYI my 83 D150 has an 8.5 static and a cranking compression up in the high 180's and runs fine on regular gas with a
fairly aggressive advance curve.

here is useful compression ratio calculator:

https://www.rbracing-rsr.com/compstaticcalc.html

once you know your existing piston recession , this calculator calls piston recession 'Deck Height' and
the existing heads combustion chamber in cc's, you can insert values to see how decking the head or block
can get you to your desired static compression ratio.

cutting the block is very straight forward, cut the block by .010 raises the piston ( decreases piston recession) by .010
knowing how much to cut head requires an additional simple calculation, to reduce the combustion chamber by one cc, you need to mill the head
.0068
reduce the combustion chamber by 5 cc's requires a cut of .034 ( 5 x .0068)
as one cuts deeper into the head the ratio changes, but for a light cut like you are doing the ratio given is fine.
Author:  Joshie225 [ Tue Feb 26, 2019 9:57 pm ]
Post subject:  Re: Technical info for camshaft
Quote:
Yes - I understand the difference between lobe separation and center line and to raise compression. The main question is if a cam has lobe separation on the intake - 107 ish is the optimum calculation - install the cam at say straight up - would there be any difference is when the cam was ground the lobe center of the exhaust was changed? If you install the cam at 102 wouldn't that adversely effect the exhaust opening too soon? Looks like most just copy the intake lobes ramp. And about 165 is about as much compression you can have and get away running 87.
Thanks for the report on the lift because it was told to me to keep below .425 or low speed /off idle response is slow due to drop in velocity.
Has any one tried the Aussie long tubed intake to see if its better or worse then the stock 2bbl intake ?
You say you understand the difference between LSA and ICL, but then contradict yourself. There is no lobe separation on the intake. There is separation between the intake and exhaust lobe centerlines. That angle is set when the cam is ground and is independent of the cam-to-crank phasing which determines the intake centerline (ICL).

The 107° number is a best guess from David Vizard's work on intake valve to cylinder volume ratio. The idea is less breathing (smaller valve) or larger cylinder (more demand) requires more valve overlap for good scavenging. If the LSA is decreased the exhaust valve opens and closes relatively later and is therefore open longer into the intake valve opening increasing overlap.

Almost every slant built needs a healthy compression ratio increase. Not all of them need longer valve timing. Get the timing curve, intake and exhaust correct before you do anything. A cam is a waste of time if the exhaust is restrictive. I did quite a lot (over 2 seconds in the 1/4 mile) without a cam swap in my '67 Valiant.
Author:  drgonzo [ Wed Feb 27, 2019 6:13 am ]
Post subject:  Re: Technical info for camshaft
I agree with everything that Josh said. A bump in compression and a re-curved distributor made a night and day difference on my 225 with stock 1968 cam.
Author:  frank79912 [ Wed Feb 27, 2019 4:35 pm ]
Post subject:  Re: Technical info for camshaft
My mistake is terms , What I meant to say keeps coming out wrong . If you have cam with lobe separation that are the same -the published is a average of the two , and you advance to cam, at what point does the exhaust open to early .I have a grinder that can grind the intake for full lift @106 degree, then cut the exhaust "retarded" to max lift at 111- so when the cam is installed in advance for the intake ,the exhaust does not open too soon.When does it become a issue or does it ever matter on the exhaust side ?
Author:  frank79912 [ Wed Feb 27, 2019 4:37 pm ]
Post subject:  Re: Technical info for camshaft
And yes its going to get compression, just a hydraulic cam cut to stock solid cam specs . The factor 83 is only a bump stick.
Author:  Joshie225 [ Thu Feb 28, 2019 8:56 am ]
Post subject:  Re: Technical info for camshaft
The #1 most important valve timing event is the intake closing point. If you close the intake valve later then more mixture is pushed back out at low speeds on the compression stroke and you lose low end torque (all else constant), but more is trapped at higher speeds moving the torque higher in the engine's speed range. Every other valve timing event has less impact on the way the engine behaves. Opening the exhaust sooner starts blow-down earlier and costs a tiny bit of low-speed torque. It's not a big deal.

What you should do to avoid wasting time and money and having a poor-performing engine is to first is read about engine performance fundamentals. If you can find a copy of David Vizard's Performance with Economy that's a great resource. But until then read this: http://www.elgincams.com/campaper.html
Author:  and739 [ Thu Feb 28, 2019 11:39 am ]
Post subject:  Re: Technical info for camshaft
Thanks for the link, Josh.
Lots of knowledge for things I've often heard of but have never been explained.
Good stuff there.
Author:  frank79912 [ Tue Mar 05, 2019 4:29 pm ]
Post subject:  Re: Technical info for camshaft
I got a video so you'll can hear what is sounds like - can figure out how to post it .
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