Cams

[squint]

I am wondering if there is someone here who could explain to me a little about cams.. what the numbers mean exactly.. and how it translates into torque / HP?..

i just dropped a new 350ci engine into my truck and installed flat top pistons and a 350HP Cam.. The engine guys told me it would put me right in the 350 HP range.. I might have 350HP.. It does have lots of power.. but does not seem to have much bottom end torque.. I am thinking maybe i chose a bad cam.. ?.. Perhaps i should swap it out for something else..

Thanks in advance.

[86 GMG]

bottom end could also be the gear ratio in the rear-end mine is some where around 340 to 350 hp and i thoght the same thing about the bottom end i pulled 3.08's out and ford 9 inch with 3.50 ratio and it woke up and kinda startaled me at first.

[red86chevy]

I'm no expert by any means but hear is what I can tell you.

first of all just because you put a 350hp cam in a motor does not give it 350hp.

The duration of a cam is the duration in crankshaft degreese of how long the valves stay open. Lift is how far the valve is opened. Someone correct me if I'm wrong.

For example a comp 270h cam shaft has 270 degreese of advertised duration. The specs are 224/224 duration and .470/.470 lift. The more duration you have the less bottom end power you will have, but will have more top end power. So to compensate for this you would add more gear in the rear end and add a stall converter If automatic (to where the power band begins) Duration along with lobe seperation angle is what affects your torque.

A big cam in a low performance engine will not have any power. A 350hp cam is probably a small cam. I say this b/c I know in some of the 327/350hp engines in the 60's had a cam with about 218-220 degreese of duration with around .460 lift. If this is what you have it should be a good bottom end cam.

JMO,
Jeremy

[squint]

Thanks for the info.. can you explain a little more on how the rear end and stall converter works.. I want to ensure I am getting the most out of my truck. If i should have different gears.. then so be it.. ( i am not sure what i have now.. )

[Brad_Olson]

David Vizard has an excellent book on cams and cam theory...I can't remember the exact title right now but it's very good reading. A good addition to any bookshelf.

Brad

[red86chevy]

The reason a bigger cam (more duration) needs more stall speed is because the more duration the farther up the power band your hp and torque moves. So in simple terms it allows the engine to "bypass" the lower RPM's so when you hit the throttle the engine immidetaly jumps to the stall speed.

EX. Stock converter.... dead stop...hit the gass... truck begins pulling about 1500 RPMs

3000 stall dead stop hit the gas truck starts pulling around 2800-3000 RPM.


More gear will get you to your power faster. (more acceleration)

Jeremy

[piecesparts]

You need to look at your whole install from the front to the back. What are you running for a carb? To much carb and the engine w ill dog out in city driving. What do you have for an intake on the engine, a single plane will perform great at high RPMs but can be sloppy in low RPM response. What transmission are you running, is it an overdrive tranny or is it a 350/400 auto. This makes a difference on the overall performance of the engine and driveability. A 350 or 400 will cause the vehicle to run in high RPMs at road speeds. The rear end is a major item, a 2:73 or 3:08 will give poor acceleration response but help at highway speeds. This is usually what is behind a 350, 350C, or 400 tranny. If you have a 700R4 then it should be lower rear end gears. In the process of updating my truck and my son's truck we went ot 3:73 gears to get the RPMs up and the engines to function smoothly. What size tires are you running, the taller the more the engine has to work to get them rolling. A good low geared rear end will help there, if you are running a tall tire. I talked to a large contingent of carb suppliers (Holley, Carter, and Edelbrock) about carb sizes---They all said the same thing. For a truck the thought is to keep the air charge (air into the engine) moving. To do that you need to keep the size of the carb down to approximately a 650 CFM unit. If you were running the same motor in a Camaro (lighter vehicle--easier pickup capabilities) a 750 CFM would work. The bigger carb will give you a better topend,BUT you have to get there first. I had a 750 for awhile and they were right I slobbered around on the city streets. The better cam is important to better performance as long as you planned the intake efficiency and operating range to match and the carb size. What do you have your timing set at? You need to look at where the motor is running at TOTAL advance. A generally good setting for TOTAL is around 36 degrees. If you have your initial timing set around 10 to 12 degrees, you are dragging your tail there. What kind of advance springs and weights do you have in your distributor? Look at changing them out for a quicker advance kit. What do you have for plug wires? There are brands on the market that have a very low resistance core in them---that is worth approximately 10 horsepower. Look at Taylor or MSD for a good set. Exhaust is important, if you are putting more in then you need to get more out. A good set of LONG TUBE headers and an open exhaust system is good. I mean Open by limiting restrictions, not open headers. I run 2 1/2" dual exhaust with Flowmaster mufflers and a good "X" pipe to enhance low end power.

[squint]

Wow.. i had no idea all that made such a difference..

I just had the engine built at a shop.. so i dont have all the answeres to those questions..

I have a Carter Competition Series ( 650 i think ) carb.. 350HP cam.
I have 8.5mm Accel Wires.

Not sure what my stall is .. but it seems very low.. I have a Turbo400 3spd Transmission.. not sure what my final gear ratio is.

My exhaust is VERY free flowing. I have 2.5" exhaust all the way back from the headers ( Hooker Compatition ).. and high flow mufflers..

It seems to me like i should maybe work from the back forward.. I wish i had known all this when i put the engine in .. I might have changed the torque converter and got a different cam..

what do you suggest i should look into first.?

[squint]

oh.. and an edelbrock intake.. not sure which one.. it was on it when i bought it.
I will check out the timing when i have a chance and let you all know what its at.. what do you suggest for a cam like this.. ?

[1FaastC10]

Originally Posted by red86chevy

first of all just because you put a 350hp cam in a motor does not give it 350hp.

but in this case, it is very possible that the 350 hp cam put him in the 350 hp range.

For example a comp 270h cam shaft has 270 degreese of advertised duration. The specs are 224/224 duration and .470/.470 lift.

I say this b/c I know in some of the 327/350hp engines in the 60's had a cam with about 218-220 degreese of duration with around .460 lift. If this is what you have it should be a good bottom end cam.

ironically enough, the 270H cam you mentioned is closer to the L79 cam you mentioned later. the actual specs are 222/222 and .477/.477.

i had one in my C10, and in my TA, built very similar to yours. stock heads, flat tops, and that cam. in the C10 i backed it with a built TH350 with a 2200 stall, 3.08 gears, and 28" tires. worked pretty good around town, and didnt do too awful bad on the highway. i later dropped the same engine in my 86 TA, backed it with a stock 700R4, 2.73 gears, and 26" tires. to say it was a screamer would be an understatment. for a 87 octane street car it was damned fast, dead consistent 13.50s both times i took it to the track. the truck was a little sluggish with the stock trans in it, the stall helped quite a bit. with the TA, i didnt have any problems with it, probably because of the weight differenct.

[piecesparts]

You need to figure out your gear ratio first, that way you know if you are getting all of your stuff to the ground. My guess is that you are geared "high" with the tranny that you said you have. At 70 mph what is your RPMs on the motor? The reason I ask, you can use a formula to calculate the rear axle ratio. The output of your tranny is 1 to 1, so that is easy, the tire diameter is needed, the RPMs at a set speed, the speed you choose to use.
Rear axle ratio = RPM X Tire Diameter
MPH X Trans output ratio X 336
This will give you a starting place. If you haven't changed your torque converter from a stock convertor, then you most undoubtedly have a low stall number (around 1600 RPM). With you new engine setup, how does the truck idle at a stoplight. Does it act like it is pulling with your foot on the brake? Does it bog a little when you accelerate from the light (do you have to feather the gas to keep it from faultering when you roll into the intersection)? If so then you are probably in need of a convertor upgrade. With my motor I had to go to a 2400 stall to keep from doing the stuff that I just told you about. ( I am running a 350 cubic inch motor stroked out to 385 CI, with a Comp Cams roller cam setup, Edelbrock Performer RPM, Carter AFB carb, Headers, 2 1/2 " exhaust with a 700R4 tranny, and 3:73 posi rear end, dyno'd at little over 430 Hp)
You keep talking about a 350 Hp cam that was installed---What type is it and what numbers did have on the spec sheet. The guys that put it together for you surely are not goofy enough to talk horsepower only. The setup of the cam would be important also. Did they degree the cam or set it in at NULL? That in itself changes when the cam does it's best work. For a street driven vehicle the setting of the cam close to "0" would be more optimum. Are you planning to race the truck? If not then an advance degree would be needless. Spend some time with the engine builder and see what he can tell you.....

[squint]

idling at a light the truck is definatly pulling.. when i hit the gas it does bog a little... When I say it has a 350HP cam . I dont mean it a cam rated at 350Horsepower.. thats just what they called the cam .. 350HP ( maybe high performance ).. I think I have basically the same setup as you do minus the roller cam setup and not stroked.. I have not dynod it .. but I think its pushing around 350+ HP.. I think i have the same intake / carb and stuff that you have..

I will hit the highway and figure out my RPM's at 70MPH this weekend, then we can work on the rear end..

BTW.. thanks a lot so far.. I am learning so much ..

[piecesparts]

Check to see at what RPM you have to idle the truck at a stop light and keep it running. That will be partly because you are into the transmission stall condition. The cam is making you set your idle up to keep enough fuel and air coming into the engine to make up for your dragging it down on the tranny. The engine exhaust will smell really gassy and rich at the stoplight, also. When you finally get your rear end numbers straight and the engine boys give you the specs on yur cam, you should get with either a good Transmission guy or go to an aftermarket supplier of torque converters and work out what you need. There are many out there and they all have a good customer reference department. I went with "Precision of New Hampshire" http://www.gopnh.com/ These guys build competition converters for racing on a daily basis. I and my tranny buddy explained to them what we had for and engine, rear end gears, idle speed, tranny, and what the vehicle was doing; from that we decided to go for a 2400 stall converter. I already had what was supposed to be a 2200 stall but it was holding me down. That change made all of the difference in the world.

[squint]

My truck idles at 800rpm when in Neutral.. and 600 when in gear..
I set it up pretty good..

I will let you know about the rear end when i get out for a drive..

I only drive once or so a week.. pleasure of course..

[piecesparts]

If you can idle at 800 RPM with the engine in neutral,then you are not pushing an extremely aggressive cam. With the overlap of the higher lobes comes a good ROUGH idle and you have to get the idle up a little to keep it going without the engine trying to die. My guess is that you have at the most good cam for the street and the type and number of cam would clarify that for you. Give us a ring when you get the gear ratio figured out.

[squint]

it not that aggressive.. But it is pretty rough.. when i have it in gear it lunges forwards sometimes.. I will work on getting all of the info.. I emailed my mechanic for the data... I'l keep ya posted..

[Tom]

The old 350hp cam is a slow ramp grind with a lack of low end torque. To overcome that requires big compression. Instead swap in a lunati voodoo 262 cam and reep the rewards

[squint]

do you have a page with specs on the 262 voodoo cam..

what are your thoughts on this cam..

currently my truck runs at about 2200RPM @ 70MPH ... i took it out on the highway the other night and found out. I have 15" wheels.. I cant find a good site that will calculate the final rear end drive ratio..

I still have not heard back from the mechanic either..

[71-longbed]

i would guess you have 2.73's in the rear

[red86chevy]

1faastc10,

The 270 cam i am running is a Comp. Its specs are: Intake valve lift .470" Exhaust valve lift .470". The duration is: Intake 224, exhaust, 224. With 110 lobe seperation.

The "L-79" camshaft that Crane has reproduced to factory specifications is .447, .447 lift with 222, 222 degrese of duration.

Who was your cam made by? I guess different manufactures vary in specs a little. ?

Jeremy

[squint]

Well.. i am STILL waiting on all the details on the cam and everything from the mechanics shop that built and installed the engine.. .. They are not very responsive..

I did a little digging online.. and found something on ebay called the 350HP cam.... so maybe this is what I have.

306/306 duration
447/447 lift
222/222 duration @ .050"
114 lobe separation
1600-5200 rpm power range

http://cgi.ebay.com/ebaymotors/SB-Ch...spagenameZWDVW

let me know your thoughts.. If this is what I have.. what do you guys recomend.. ?

[red86chevy]

The cam mentioned on e-bay sounds almost exactly like the L-79 cam. The L-79 engine was a 327 with 350hp. So they call the cam a 350hp cam, b/c that is what it produced in this engine. This sounds about like the cam you have. I know in the 327 it had a small amount of "rough idle", but i would think it would be fairly smooth in your 350, b/c cams act differently the more cubic inches you have. From the sound of it you do have a 2.73 rear end gear. If you added a 3.55 or 3.73 you would think you put a 454 under the hood. It makes a TON of difference. Also a stock converter with your cam should be fine, but you would be happy with the performance of one with about 2500 stall speed.

Jeremy

[red86chevy]

Also it feels like the bottom end torque is low b/c of your gear ratio. I have a th350 with 3.73 gears and I run something like 2900-3000 at 70mph. Your cam will work great if you put some gear under it. Like I mentioned above if you go from a 2.73 to a 3.73 it will feel like you added 200 hp.

Jeremy

[piecesparts]

I agree on the bottom end torque issue being the rear end gears. I too am running a 3.73 rear set and with my 700 R4 I am running at 2700 RPM with the speedo showing 77 MPH. The change in gearing will give you boost on performance BUT it may also change oyur gas mileage. My son's truck had a 3.08 gear in his rear end and we changed to 3.73s it made a definite difference in performance, he actually gained some on mileage because the 700 R4 in his truck had him running well below the torque curve on the 350 engine. Chevy likes that area around 2200 RPM real well.