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-   -   camshaft question (http://www.hotrodders.com/forum/camshaft-question-173135.html)

crussell85 02-16-2010 08:12 PM

camshaft question
 
Here we go:
1993 Chevrolet K1500
383 Stroker
Flat Top Clevolite Pistons with 5cc valve relief
Scat 9000 Crankshaft
Scat 4340 Cap screw rods
Brodix -8 Pro Cylinder Heads
Edelbrock Multi point Conversion Kit
Shorty Headers with 1.5" pipes and 2.5" collectors
True Dual Exhaust 2.5" pipe to mufflers then 3" exit
3.48 gears with stock converter

I am looking for a camshaft for this engine. I am looking for the perfect camshaft for towing, off roading, and regular driving, while holding some fuel mileage (not a big concern, just a weekend warrior). I would actually like to know how to spec out a camshaft or if anyone could lead me to some information. I am not opposed to swapping the torque converter for another one. Right now I have the GM Performance 14097395 specs are located here http://www.summitracing.com/parts/NAL-14097395/ So if anyone could suggest a camshaft and maybe explain or show me the way to an explanation of how to spec out a camshaft I would appreciate it.

SSedan64 02-16-2010 09:57 PM

That's the same Cam GM uses in their RamJet350 and HT383 Crate engines. I don't think it's a bad choice for what you plan to do with it. It's designed for Vortec Heads/Flow pattern so I'm not sure what will be the best choice with your Brodix Heads. A Cam Co. would be your best bet. :thumbup:

PS. The -8 Pro Head isn't a good choice for what you plan to do>> http://www.brodix.com/heads/-8.html

techinspector1 02-16-2010 10:51 PM

The first thing you need to know to spec a camshaft is the exact static compression ratio of the motor. You need to know this so that you can choose the proper intake valve closing point to trap just the right amount of fuel air mixture to make good power without detonation on the available fuel you have to run. Just looking through my Crane catalog, I'll give you some for-instances....

Powermax H248-2, power range 800-4600 rpm's, advertised duration 248/260, 0.050" duration 192/204, lobe separation angle 112, intake valve closes at 23 degrees after bottom dead center. This cam is recommended for use in a motor with 7.75-8.75 static compression ratio. If you average the SCR in this case, you can see that a motor with 8.25:1 SCR needs to close the intake at around 23 degrees ABDC.

If you closed the intake valve earlier than that, you might trap too much mixture and introduce detonation. If you closed the intake valve later than that, some of the fuel air mixture could be blown out the (still open) intake valve by the piston coming up the cylinder on the compression stroke. When the piston blows mixture out through the open intake valve, it travels back up the intake tract and disrupts the signal at the carburetor venturi. The venturi sees mixture going both ways and it doesn't know whether to sh** or go blind, so there isn't a good homogenization of fuel/air being blended.

Now, let's move up on the cam selection. The H260-2 Powermax has an operating range of 1200-5000, advertised duration of 260/272, 0.050" duration of 204/216, lobe separation angle of 112 degrees, intake valve closes at 29 degrees ABDC. This cam is recommended for use in a motor with 8.0-9.5 static compression ratio. If you average the SCR in this case, you can see that a motor with 8.75:1 SCR needs to close the intake valve at around 29 degrees ABDC.

For the last example, let's use the 284H12 Energizer. Operating range 2800-6200, advertised duration 284/284, 0.050" duration 228/228, lobe separation angle 112 degrees, intake valve closes at 41 degrees ABDC. This cam is recommended for use in a motor with 9.5-11.0 static compression ratio. If you average the SCR in this case, you can see that a motor with 10.25:1 SCR needs to close the intake valve at around 41 degrees ABDC.

Now, this little bit of knowledge isn't going to allow you to choose a camshaft for your motor. There is so much more to it than this, but we have to start learning somewhere.

Go to the various cam grinder's websites and read everything you can. Come back here and ask questions. Read some more. That's the way we aquire knowledge.

Start by reading this page on Performance Camshafts by Dimitri Elgin. He's the main force behind Elgin Camshafts and is, in my opinion, a very smart man....
http://www.elgincams.com/campaper.html

One of my pet peeves is the newbie that has the 8.0:1 motor and wants a lumpy camshaft. It should be clear to you even with the little bit I have outlined here for you that this AIN'T GONNA HAPPEN. A lumpy camshaft, as a general rule, will have quite a lot of duration. A lot of duration closes the intake valve later, so you need more SCR to compensate and keep the balance between SCR and intake valve closing point. Bottom line: If you want a lumpy cam, coordinate the components in the motor to reach the proper SCR to match the cam.

ap72 02-17-2010 07:54 AM

Assuming about .040" quench he's a little over 10.5:1 compression.

So towing is out of the question unless you have some DEEP gears.

crussell85 02-17-2010 05:58 PM

Quote:

Originally Posted by ap72
Assuming about .040" quench he's a little over 10.5:1 compression.

So towing is out of the question unless you have some DEEP gears.

Can someone explain why towing is out of the question? Is higher compression worse for towing, is it due to heat?

Why is the brodix -8 PRO heads a bad choice of heads. I did a fair amount of research before I purchased these heads. The have 2.02 intake and 1.60 exhaust, 185 cc intake runner and 67cc combustion chamber.

techinspector1 02-17-2010 06:36 PM

10.5:1 static compression ratio is gonna require a cam with a 0.050" duration of around 235 degrees. Such a cam is gonna make power from 3000 to 6500 rpm's. So, gettin' "up on the cam" is gonna take some pretty short gears to tow within the posted speed limits. For instance, towing at 3500 rpm's with a 4.56:1 final drive and 28" tall tire will have the vehicle going 63.9 mph.

Now, let's look at another scenario. If you had finalized the SCR of the motor at, for instance, 8.75:1, then you could have used a cam like the one in the example above, making power from 1200 to 5000. Now, with the same tire, 3.10 gear and turning only 2350 rpm, you would be going the same 63 mph. You'd be "up on the cam" and everything would be hummin'.

SSedan64 02-18-2010 02:19 AM

Quote:

Originally Posted by crussell85
Why is the brodix -8 PRO heads a bad choice of heads. I did a fair amount of research before I purchased these heads. The have 2.02 intake and 1.60 exhaust, 185 cc intake runner and 67cc combustion chamber.

In your 1st post your intended use is Towing, Offroading & everyday use.
This requires lots of Torque at lower engine speeds.
The Brodix -8Pro heads make power in the mid to upper rpm range
Cubic Inch--Compression------Camshaft------------ RPM-------Application
355-406---- 9.1 Minimum--Hydraulic/Flat Tappet- 3500-6500----Street/Pro Street
From Brodix's site>> http://www.brodix.com/heads/-8.html
This Info may be using the larger 2.08"/1.60" valves so you could be Ok with the smaller valves. Check with Brodix & see what they say.

crussell85 04-14-2010 07:09 PM

OK, I have read a few books now and know a little more about selecting a camshaft. The thoughts that I am having is that I need less duration because I am holding the intake and exhaust valve open together to long and am dumping raw fuel out the exhaust.
From what I have researched and read this is the cam (08-465-8) I came up with http://www.compcams.com/Cam_Specs/Ca...?csid=206&sb=0
It is also one that comp cams recommends in their cam selection software. I ran it on my Desktop Dyno and it is showing a great amount of improvement. I was just wanting some feedback or a straight up yes or no before I would commit to buy. Thank you. The cam that comp cams recommended when I filled their form out on their website and they emailed me back was the 08-502-8.

crussell85 04-15-2010 07:05 PM

anyone? anyone?

cobalt327 04-16-2010 05:43 AM

Quote:

Originally Posted by crussell85
The thoughts that I am having is that I need less duration because I am holding the intake and exhaust valve open together to long and am dumping raw fuel out the exhaust.
From what I have researched and read this is the cam (08-465-8) I came up with http://www.compcams.com/Cam_Specs/Ca...?csid=206&sb=0
It is also one that comp cams recommends in their cam selection software. I ran it on my Desktop Dyno and it is showing a great amount of improvement. I was just wanting some feedback or a straight up yes or no before I would commit to buy. :smash:

What you're running into w/the cam you've selected, is a cam w/"short" duration and basically no overlap in combination w/a static CR of over 10:1 being too high of a 'dynamic' CR. There will be enough "efficiency" of the small cam to actually cause the 10:1-10.5:1 CR (or whatever it is, exactly) to cause detonation. When that happens, power takes a nose dive and parts breakage will happen.

You need to lower the static CR, OR choose a larger cam, duration/overlap-wise and the gears and torque converter to make it all work together.

The cam Comp spec'ed for you presumably has specs that will allow your CR to be compatible w/the cam and the rest of your combination of parts and gear ratios. It would be a better choice, IMO than the cam you picked. Is there a reason for not going with Comp's recommendation?

Here are the specs, from them you can see how the cam Comp suggested will not have as high of a DCR as the "little" cam you picked for yourself.

252XFI HR13 #08-464-8
Intake open 17BTDC close 55ABDC
Exhaust open 69 BBDC close 15ATDC

Comp's choice: XR269HR #08-502-8
Intake open 26BTDC close 62ABDC
Exhaust open 74 BBDC close 22ATDC

I hope this helps you, and doesn't just confuse the issue more.

Good luck.

crussell85 07-22-2010 06:15 PM

I am learning, I think? I have been reading on and off when I have time. I know now more about the duration and overlap and all of the other good,confusing stuff. I am no camspert but I am closer than when I started this post. I was cruising around the www.summitracing.com site and seen this. I ran the cam through the hotrodders search feature and seen that another person had asked about the cam but I was just kind of curious. I see that cobalt said in that post the he don't like to select cams for people because the person that asks always knows better and basically doesn't want to admit that their setup is not "setup". But anyways here is the link, so let me know if you would. I understand the compression ratio is high for what I am wanting to do, but lets just say for the the way engine is setup right now would it be a cam in a list of options?

http://www.summitracing.com/compare.aspx
http://www.summitracing.com/compare.aspx

techinspector1 07-22-2010 06:21 PM

Your links are bogus.

crussell85 07-22-2010 06:49 PM

http://www.summitracing.com/parts/TFS-31402000/

sorry about that, i checked them and they worked on my computer

techinspector1 07-22-2010 07:05 PM

Quote:

Originally Posted by crussell85
http://www.summitracing.com/parts/TFS-31402000/

sorry about that, i checked them and they worked on my computer

Too short for 10.5 SCR. (needs 235-240).
Too short for 10.0 SCR. (needs 225-230).
Just right for 8.75-9.75 in my opinion.

crussell85 07-24-2010 05:29 PM

just out of curiosity will a retro cam work in an oem roller block as long as I use the old style timing set and a thrust button?


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