Thread: Cam Help Please

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You Guy's are both good guys, and we all make mistakes.
And I wish I knew as much as either of you.
Back when I was taking chemo I went over to get
my friend to help me figure something out on my car.
He started laughing at and said are you kidding me you
taught me that, he thought I was fooling around.
Problem was I had a brain fart weather it was the drugs or
just being tired I don't know. I just had to laugh it off
because I knew he was right. Anymore i think I'm stuck in
one big fart. HE! HE! HE! Gotta laugh what else can I do. Kurt

Hey guys, thanks for all the replys. I thought for a moment there we were going to have to seperate Tech and Denny. I am learning to degree cams and using the intake lobe centerline method is the only way I know right now. This cam is being used in a beautiful '86 GMC short bed daily driven 357c.i. with Patriot 195 aluminum heads, Holley street dominator/650 cfm 4150 carb, Hooker Comp. 1.625 headers. I want a nice streetable truck
Thanks again for being here for guys like me.

peace Bud

And then of course, there is the real way of finding what the true actual lobe centerline is

Bud, Denny have been clawin' at each other for years. Sometimes he's right and sometimes I'm right. What's important is that the OP gets the answer he was lookin' for, whether he likes it or not.

Originally Posted by jerry clayton

And then of course, there is the real way of finding what the true actual lobe centerline is

Do tell.... I would like to hear your technique.... don't just tease us like that

-Chris

Originally Posted by skids72

Do tell.... I would like to hear your technique.... don't just tease us like that

-Chris

I think what Jerry's sayin' is put the cam in the motor and use a big degree wheel and dial indicator to find the opening and closing points and centerlines.
You can't do this properly usin' a lifter because there is no nice, flat surface to indicate from. If you already have a dial indicator, turn a 6" long steel fixture to drop into the lifter bore to ride on the lobe at one end and dial indicate off of on the other end. Turn one end of it to 0.842" for checkin' Chevies and the other end to 0.875" for checkin' Fords.

If you don't already have a dial indicator, buy one of these tools and have it all in one piece....
http://www.jegs.com/p/Proform/753485/12552/-1

If a guy will just pay attention and follow the instructions given here by the "Camfather", he'll be "in like Flynn"....
http://www.iskycams.com/degreeing.php

It's OK to have a spirited debate between experts in the interest of finding the right answer but Denny and Tech1 are both my best sources of good information for engines so let's keep it friendly, please! This is the best thread I have seen relative to a question I have. It took me a long while and a lot of searches to find out what cam is actually in my short block SBC 350 which was set up by a local circle-track racer. Three years ago Tech1 gave me good advice for choosing a cam with good low end torque but I hated to put in a cam with less duration than the stock cam for a '76 Corvette 350 so I wanted a Comp 268H (actually pretty hot, what I have has less duration than the Comp 250H) but the machine shop guy refused to install a Comp cam saying he had too many wipe outs with Comp cams so I let him choose a "Crane" cam which I thought was slightly more duration than a stock Z28 or the 327 SBC 300 HP cam. To my surprise the spec sheet the machine shop gave me for my cam did not match anything Crane had as a Crane cam and even the part number was written over so for a long while I did not know what it is. Finally I learned that Crane bought out Blue Racer cams about three years and evidently what I have is the lowest duration Blue Racer cam which had a different part number slapped on the box when Crane bought out Blue Racer. I have a set of both 1.5 and 1.6 ratio rockers from Speedway and have the 1.6 rockers installed now. When I finally got a guy at Crane who recognized the cam as one of the former Blue Racer cams he emphatically recommended the 1.5 rockers and Joe Gibbs BR break-in oil seeming to warn about the wipeout problem with modern oils. I now plan to drain out my oil and use the Joe Gibbs BR for break-in and then use the SFR 100 additive for oil changes after that. After that long intro here is the question: what is the difference in the 0.050" duration if I use 1.6 instead of 1.5 ratio rockers? It is easy to calculate the added lift but without a degree wheel it looks like Tech1 may have a way to estimate the added duration with the 1.6 ratio rockers? Here are the specs for the first three low end cams for the old Blue Racer cams:

APPLICATION AND BASIC RPM CAM USE
GRIND NO.
CAM PART NO.
LIFTERS
Deg. Dur. @ .050 Cam Lift Int./Exh.
Deg. Adv. Dur. Int./Exh.
Deg. Lobe Separation
Running Clearance -Hot-
Int./Exh.
Gross Valve Lift
Int./Exh.

(My Cam)
HYDRAULIC - Smooth idle, good low end torque,
economy and throttle response. Use as stock
replacement.
BASIC RPM 1000-3200
Street CD194-11C 975213
C37-16
99277-16
C817C-16
194/204
256/262
112
.000
.000
.398/.420

Next hotter cam
HYDRAULIC - Good idle, good low end torque
& throttle response. Works well with minimal
modifications.
BASIC RPM 1500-4000
Street CD204-11C 975850
C37-16
99277-16
C817C-16
204/214
270/280
112
.000
.000
.420/.442

HYDRAULIC - Good idle with lope Good all
round performance with basic intake and exhaust
modifications, strong low-mid range torque.
BASIC RPM 2000-4800
Street CD214-11C 975848
C37-16
99277-16
C817C-16
214/224
280/290
112
.000
.000
.442/.465

Sorry about the loss of the column alignment but all the numbers are there. The full table is given at:

http://www.cranecams.com.au/pdfs/blu...et_14-5-07.pdf

Note that the lift of the first cam with 1.6 rockers will be higher than the second cam with 1.5 rockers but still less than 0.500 in range of most hot rod cams. I have Z28 springs in GMC 882 heads.

The simple thing is to just use the 1.5 rockers and avoid lobe wipe as much as possible with basically a stock cam which might give good economy and hey, 200 HP ought to be enough to move a Model A? Or, I could use the 1.6 rockers on just the exhaust valves as shown on Ryan's Engine site to give more torque. I could change to the 1.6 rockers on the exhaust valves after break-in. Finally I could just leave the 1.6 rockers on there now but that gives higher lift than the second cam and I have no idea what the duration would be so maybe I would encounter pinging with a short duration high lift situation? This is just play stuff for me in the winter because the "sensible" thing to do would be to use the 1.5 ratio rockers for the best economy but I have slightly higher compression, headers and an Edelbrock intake so why not push the cam to a little more performance. I was surprised that Tech1 can do such good estimation with just the numbers so what can you do with the 112 centerlobe on the specs marked "My Cam"?

Don Shillady
Retired Scientist/teen rodder

Hi DennyW,

Well I do not plan to change the cam that is in there now, I am just wondering if I should run the 1.6 rockers with the lowest cam on the list as to whether the lift will be too high. I note that the Crane cam for the SBC 305 on the Chevy cam list is up to 0.465":

http://www.kendrick-auto.com/chevrol...y_cam_spec.htm

Mainly I wonder how much more duration I will get with the 1.6 rockers?

Best Wishes for a Happy New Year!

Don Shillady
Retired Scientist/teen rodder

Hi Don. The seat to seat duration of a cam will not change by using different ratio rocker arms, but the duration measured at a different lift will change slightly because of the different RATE OF LIFT afforded by the different rocker ratio. 0.050" lift will be achieved just a tad sooner on the opening ramp and just a tad later on the closing ramp.

Taking all the clearance characteristics into consideration and having seen so many dynosim results, I wouldn't be too interested in changing from 1.5 to 1.6 unless I was looking for that final 5 horsepower in a drag race motor.

By clearance I mean piston to valve clearance, rocker slot clearance at the stud, spring coil bind clearance between the coils at full lift and clearance between the bottom of the retainer and the seal on the valve guide or the top of the valve guide if you're not running positive control seals.

And like I said, I have seen on average a 5 hp increase on a ratio change on the software program I play with. You can pick up more than that by changing the phasing of the camshaft in relation to the crank (advancing or retarding the cam). Every motor you put together will be different and even if you have nailed the cam timing events for that particular motor, you can usually find some additional hp or torque by phasing the cam differently because of under-scavenging or over-scavenging with the cam in a straight-up position. I highly recommend using a 2-piece timing cover and some sort of aftermarket cam timing change device to make it easy to dial the motor in to whatever characteristics you're looking for.

Tech1, thanks for your reply. Denny just reminded me about the clearance issue which I had ignored. I have set the valves cold and did not notice any clicking or binding so at low speed the eyebrows in the pistons seem to have enough clearance with the 1.6 rockers but the heads were shaved enough to bring the pockets to 73 cc so the valves are lower now. I guess the "sensible" thing is to put the 1.5 rockers on and take what I get. Your point is that the actual opening and closing will not change even though the 0.050" duration may increase a bit. Actually the '76 Corvette 350 was pathetically detuned below 200 HP with the best option for 210 HP so with higher compression, better manifolds, turbo mufflers (2 1/4" pipes with an H crossover), 3.55 rear gear and 73 cc heads maybe I can get over 200 HP and 25 mpg with the 700R4 OD. My wife keeps asking me if we will get good mpg with the engine and I always say, "Oh Yeah" knowing all along that 25 mpg would be great! Who knows, by next summer gas could be back up above $3/gallon again? Since we last compared notes I had the exhaust system installed with the H-pipe and if I can finally get the wiring finished soon I should be able to start the engine. Actually the cam I have now is close to what you recommended three years ago for low rpm torque. You and Denny have been a big help on the driveline and IC2 has helped with the wiring so far so maybe I can get it going this summer?

The article from Carcraft Denny cites above shows some additional HP from just using the roller tips which I have for the 1.5 rockers, but now I am mostly worried about the clearance issue. I know about plastigage but it looks like I would have to bolt/unbolt at least one head and turn the engine over, right? On the higher exhaust lift of 0.420" the higher lift would be 0.420 x (1.6/1.5) = 0.448". Apparently the engine can be turned over with this clearance now but I have no idea how close the valves would be with just a little float, so I guess I will take a little improvement with the roller tips and be safe with clearance and best chance at higher mpg. Anyway this is a good exercise in cams and I did not take precautions for measuring clearance.

Don Shillady
Retired Scientist/teen rodder

Don, I wouldn't be worried about PV clearance until I was using a 0.500"+ lift. I also wouldn't want to be pulling heads off to do the "clay on the piston" method of checking. That's a great way when you're mocking up all the parts you're going to use and you're checking PV before final cleaning and assembly, but I wouldn't want to be tearing off the carb/manifold and all supporting parts and pieces after it's all together for the final time. If you want to check the clearance, do this:

Order up this valve spring compressor online.
http://www.jegs.com/i/Manley/660/41830/10002/-1

Order checking springs online...
http://www.jegs.com/i/Comp+Cams/249/4758-2/10002/-1

Order some clothesline rope online. (or get some at the hardware)
http://housewares.hardwarestore.com/...ne-177097.aspx

If you don't have a dial indicator and magnetic base, here's one on ebay...
http://cgi.ebay.com/Hydraulic-MAGNET...3A1%7C294%3A50
This is not the quality of a Starrett or the like, but for a home workshop, I would think it would work fine. The dial has the proper 1.000" travel, 0.100" revolution and 0.001" graduations it takes for this kind of work.

You can check one cylinder only or the two end cylinders on one bank to check for deck slope or you can do the four corners.

Remove the spark plug of the hole you're going to check. Actually, turning the motor over will be much easier if you remove all the spark plugs. Remove the valve cover. Remove the rockers and pushrods for that cylinder. With a socket and long bar on the harmonic damper retaining bolt, turn the motor in the direction of rotation (clockwise standing in front of it) until the groove in the inertia ring of the damper is about 90 degrees (1/4 turn) from the timing pointer on the timing cover. Thread in the clothesline through the spark plug hole, leaving a tail of line out to grab and pull out of the cylinder when you're through. With a cheater bar and socket on the harmonic damper retaining bolt, turn the crank clockwise to smash the rope up against the valve faces. This method assumes no available air compressor. If a compressor is available, put shop air into the cylinder to hold the valves up.

Slide the Manley tool onto the rocker stud with the short end over the valve and install the rocker nut. Now, using the armstrong method, compress the valve spring and remove the keepers. Release the tool and remove the retainer and spring. The valve will not fall into the bore because it's being held up by the rope. Remove the other spring/retainer. Install light pressure "checking springs" with the retainers and keepers. Install pushrods and rockers. Remove the rope. Roll the motor over clockwise to TDC with both valves closed. Back off each rocker nut until there is some play in the rocker. Jiggle the pushrod up and down with your thumb and forefinger as you tighten the rocker nut. When you have removed all up and down play in the pushrod, tighten the rocker nut another 1/2 turn. Do the other valve the same way. Now the lash is set. Turn the motor over clockwise to just short of one complete revolution (like maybe 20 degrees before top dead center). This will be approaching the overlap period. Now, see Isky's instructions from here.....scroll down to THE ISKY "LIGHT SPRING" METHOD OF CHECKING V/P CLEARANCE.
http://www.iskycams.com/camshaft.php

Back in my circle burner days with a limited stock, we were limited to a .500 lift cam, reasoning was that with a flat top piston no one would be out spending money on eyebrowing pistons to run a big cam.... So I'm gonna go with Tech on the non-issue with valve to piston clearance. Seems with stock springs it would coil bind from exceesive lift before it ever got to a valve hitting a piston...

Anyway, not being a sbc guy, my experience with the 1.6 rockers was trying them once on the same circle burner.... The driver claimed (you know how drivers are!), that the only time he felt any power increase was with 1.5's on the intake and 1.6's on the exhaust...... I suppose cuz we had to run those junk cast iron exhaust on the car, maybe the longer arms on the exhaust helped with the scavenging a bit????????

Could you maybe just run the valves on a cylinder to full open, measure the height to the retainer with the valve full open, use Tech's prescribed method of removing the valve spring and bring the same piston to TDC, install the reainer (no spring) and lower the valve til it does touch the piston top, then again measure the height to the retainer and compare the diffierence??? Done that a time or two (yes, I'll admit it) after changing cams on an engine with an unknown piston height, decking, etc.???? Tech's the expert on this stuff.....not me.....

Dave, when I first put that answer together, I included clothespins on the stems to keep the valves from dropping into the bore and doing exactly what you said. Then I thought to myself, no, a lot of different guys will be reading this, so I'd better tell him the bulletproof way to do it.

Tech1, Thanks for documenting the clearance procedure in great detail, it adds a lot to this thread but you have just pushed me toward installing the 1.5 ratio rockers. Actually I was so lazy that I was trying to rationalize leaving the 1.6 rockers on there since they are already set (and probably with enough clearance?) but surely changing the rockers is easier than the full clearance procedure. I have seen the "rope trick" before. The guy who rebuilt my tiny 4-cyl MG midget engine knurled the valve guides instead of replacing them and one valve would stick so he put the rope into the intake port, took off the valve spring and attached an electric drill to the valve stem to rotate it fast. This worked so well that the valve later sucked oil pretty fast so I do not ever want to just knurl the guides again, just full replacement thank you! I think Dave put his finger on the 1.5/1.6 combination. The circle track guy who built my SBC 350 and polished the exhaust ports in the heads said the same thing and recommended his experience with 1.5 on the intake and 1.6 on the exhaust. However he was racing in a class that used SBC 400s but required iron manifolds and stock iron heads. In fact I traded him a set of camel-hump heads (with no accessory holes) for $200 off the machining bill so the idea of using the 1.6 rockers on only the exhaust is probably a good idea with restrictive exhaust manifolds but as Denny pointed out above the cam I have already has longer duration and higher lift for the exhaust valves. The car Craft article Denny cited above shows that in that test the use of just roller tips did give some added HP, probably in the 5 HP range on my mild engine just as Tech1 said too. Today I am itching to work on the car but it is 38 F outside here (warm for Dave!) and I have just been felling pretty good after getting over a miserable cold so I will wait until the temps get up to where my small heaters in the garage can get up to 60 F or so. Just so you don't think I have not done anything I am attaching a top view of the Zip water pump, alternator, fan and the limited clearance to the Model A radiator. It looks like the only way I can turn the motor over to set the valves with the 1.5 rockers is with the ratchet on my long handled torque wrench with only about a 15 degree turn on each ratchet. It is really tight in there now that I added the lines to the trans cooler at the bottom of the radiator. I note the use of Tech1's favorite rubber hose for the radiator, maybe someday I will add the metal version but I just want to get it running for now. I had to shim the Alternator mount carefully with a few washers to get the fan belt in there and still clear the fan blades! No, I do not want to take that all apart to use plasticgauge! Thanks to Tech1, Denny and Dave for considering this problem but the compromise for me is to replace the 1.6 rockers with the 1.5 rockers to be sure of clearance and better mpg. As I recall a stock Model A motor was rated at 42 HP so as Denny said above a nearly stock SBC 350 should be pretty good at 200 HP and hey, I have chrome on the outside of the engine which was almost as good as real performance when I was in H.S.! Thanks for taking the trouble to document this information.

Don Shillady
Retired Scientist/teen rodder

Here is another interesting fact. In checking out the flow of the GM 882 heads on the site Tech1 recommended recently, we can see that it really does no good to go beyond 0.400 lift since the flow at even 0.500 lift is essentially the same as the flow for the 0.400 lift! This goes back to my original question as to how the rocker ratio changes the 0.050" duration, probably very little. With the GM 882 heads we are probably just talking about a tiny effect and I note that the present Blue Racer cam is slightly bigger in lift than the original Chevy 300 HP cam so I just better change back to the 1.5 rockers to be on the safe side of the clearance problem and take what I get. I will save the 1.6 rockers in the case that I ever upgrade the heads.

http://www.purplesagetradingpost.com...fo/heads1.html

Don Shillady
Retired Scientist.teen rodder