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| Unknown Stock Slant Camshaft Graph https://www.slantsix.org/forum/viewtopic.php?t=64713 |
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| Author: | hansbuscher [ Mon Apr 06, 2020 6:13 pm ] |
| Post subject: | Unknown Stock Slant Camshaft Graph |
Hello All. Just finished graphing out this cam. Came in a never-run rebuild with a few small issues so I'm checking everything. Will be going into my 2wd, D100, np435, 2.94 gears, no towing or offroading kind of vehicle. Thanks -andrew https://i.postimg.cc/fRMsJLCc/DAUnknown-Slant-Cam1.jpg |
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| Author: | Joshie225 [ Mon Apr 06, 2020 11:12 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
Yup. Looks to be faithful to the original. |
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| Author: | hyper_pak [ Tue Apr 07, 2020 8:17 am ] | ||
| Post subject: | Re: Unknown Stock Slant Camshaft Graph | ||
Made me smile, I thought I was the only one to plot camshafts! I do use excel though, makes it easier to plot accurately. You know this, but multiply by 1.5 for stock lift at the valve.
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| Author: | hansbuscher [ Tue Apr 07, 2020 12:54 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
Thanks Hyper & Joshie Making the graph really helped visualize what the cam is doing. My biggest concern is: https://uempistons.com/p-27-compression ... lator.html "Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees". My heads are 45cc and compression ratio at 9.1. Intake closing appears to be 30* making DCL a wallet crushing 8.7? Retard the cam or am I figuring this wrong? |
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| Author: | Joshie225 [ Tue Apr 07, 2020 1:14 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
9.1:1 is quite high for an engine that hasn't received a lot of head and/or block deck milling. Do you have all the numbers you used to calculate the compression ratio? |
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| Author: | hansbuscher [ Tue Apr 07, 2020 1:46 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
Engine is a rebuild from long ago and never run. Specs: Cylinder Head volume 45cc Piston Head volume 0 Gasket Thickness .040 Gasket Bore 3.52 Cylinder Bore 3.46 Deck Clearance 1.80 Stroke 4.125 Rod Length 6.699 Yes the head has been planed quite a bit. Ya gotta take these rebuilds apart before you run em. #1 rod cap was on backwards. |
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| Author: | Rick Covalt [ Tue Apr 07, 2020 2:26 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
Quote: Cylinder Head volume 45cc
There ya go! 
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| Author: | Joshie225 [ Tue Apr 07, 2020 5:26 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
If this were mine I would choose another cam to lower the dynamic compression and deliver more power. The alternatives are gas better than 87 octane or a compromised timing curve. Of course this is an easy choice for me to say as I can spare $100. |
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| Author: | hansbuscher [ Tue Apr 07, 2020 5:47 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
Thanks Joshie. What cam would you recommend? It seems most cam's intake closing is around the same place. Iv'e read that the "Intake Closing Point ABDC @ 0.050 lift plus 15 degrees" for calculating DC could be dubious as the valve is still open for another 70*-90*. |
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| Author: | Joshie225 [ Tue Apr 07, 2020 8:30 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
It's a little tough to get an accurate intake closing point to then derive a realistic dynamic compression ratio. The best you can do is find the actual intake closing point at the recommended lash. Dynamic compression calculators are a good tool, but it can't replace known real-world results. I am basing my recommendation on my direct experience having run a true 8.5:1 engine with the older stock cam of even shorter duration. I ended up not being able to run 87 octane, but the car ran well on 92. Being heavier a truck needs to be set up a little more conservatively. We have a member here who has had good luck with the Oregon Cam Grinding #819 in a pickup. I have good experience with that cam as well, but in a less apples-to-apples application. What are you running for induction and exhaust? |
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| Author: | hansbuscher [ Tue Apr 07, 2020 8:56 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
I've read some of your posts and you get pretty deep with this stuff. Super Six intake, stock exhaust manifold into 2 1/4" pipe. 3:55 axle, np435 transmission. |
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| Author: | Joshie225 [ Wed Apr 08, 2020 11:31 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
I take that as a compliment. I truly enjoy knowing the principles at work and being able to make sensible improvements. I would use the Oregon Cam Grinding #819 intake lobe, #818 exhaust with a 108° LSA. Install it with 102-104° intake center-line. New 318 valve springs will do fine. The original exhaust manifold is not as bad as some would have you believe so don't worry about it. Do worry about the muffler and the timing curve. You may not like the original Super Six carburetor from a tuning standpoint. They are an emissions carburetor and not so easy to work with. What will make a big difference, if you want to take the next step, is head work. Bigger valves and pocket porting are well worth it. If you're short on money you can just do a bigger intake valve, but pocket port both intake and exhaust bowls. The reason being the intake side is more restrictive than the exhaust and you get more gains working the intake. Nothing radical is needed. Streamline the valve guide bosses, taper the seat to bowl transition and make a nice, gentle short-side radius. Since you have the NP435 I would also suggest you try to find a NP445 aka NP4530. This is essentially a close ratio truck trans and the 2-3-4 gearing is far superior. 1st gear (4.56:1) becomes useful and the rest of the gears are close together so you can drop to 3rd on steep hills without buzzing the engine to the moon or slowing way down. |
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| Author: | hansbuscher [ Thu Apr 09, 2020 1:20 pm ] |
| Post subject: | Re: Unknown Stock Slant Camshaft Graph |
Thanks for the recommendations Josh. I'll give em call in a few days. |
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