Bruthish

Easy part: how much does .020 more cam lift effect your motor?

Back story:

I had a NOM 350 I pulled out of my '71. I know nothing about it as it was in there when I bought it and the owner knew nothing.

So I decided to pull the motor and install new gaskets, get the heads worked, clean'er up, and install a new cam. When I pulled the cam it did not occur to me to look at the serial/grind # on the end of it until after I ordered a new one. It is HIT-280-NC which equates to a Crane Cams item.
Here are the specs:
Basic Operating RPM Range: 2,200-5,200 RPM
Duration at 050 inch Lift: 224 int./224 exh.
Advertised Duration: 280 int./280 exh.
Valve Lift with Factory Rocker Arm Ratio: 0.460 int./0.460 exh. lift
Lobe Separation (degrees): 114

I BOUGHT Compcams Magnum 280H...here are the specs:
Basic Operating RPM Range: 2,000-6000 RPM
Duration at 050 inch Lift: 230 int./230 exh.
Advertised Duration: 280 int./280 exh.
Valve Lift with Factory Rocker Arm Ratio: 0.480 int./0.480 exh. lift
Lobe Separation (degrees): 110

So is there much difference between these two cams to notice a difference?

cardo0

U have 13% more vlv overlap and 4% more vlv lift with that Comp cam - meaning it will rumble a lot more at low rpm and would be difficult to drive with high freeway gearing (low ratio differential gears). But it will pull significantly harder through the mid range up to red line.
IMHO that Comp cam is not a street cam - more of a racing cam. If u read further on its specifications it should say at least 3.90 rear gear set ratio and a higher than stock stall converter plus headers are required.
FYI 280* (long duration) cams are hard on the whole vlv train and the spring life is short - cam lobe wear is greater making cam life short too, as low as 50k mi.

Hope this helps ya,
cardo0

TheSkunkWorks

In and of itself the .020" alone isn't worth all that much, but the real differences are the Magnum has more total area under the curve from .050" to .050" and a significantly tighter LSA. The Crane will run a good bit smoother, while the Magnum is going to lope and make more peak power. Where you index the intake CL in relation to your CR will definitely affect bottom end torque, so do your DCR homework.


TSW

Bruthish

Thanks for the response! I am not a engine guru by any means and I can see a little is actually a lot when it comes to cam selection. I chose the magnum cam based on the data on their website. I wanted it to rumble yet still have vacuum. This is not going to be a daily driver what so ever...weekends at the most, so highway is not really a concern. The motor is mated to a 4-speed but I am not sure on the rear ratio, but I am confident it is a stock one.

Gordonm

That Magnum cam is fairly mild. It will provide a little rumpity rump for sure. It could take a little more compression than what you have stock but should work OK. For a daily driver it is a little much for stop and go driving but for a weekend car it will be fine. I ran a cam with 248@ .050 in a 350 with not a lot of compression and it ran fine. I did have 3.70 gears with a stick but it was good on the street. The L82 cam had 222 @ .050 duration so you are only a little more than that cam and that was put into thousands of daily driven cars.

Bruthish

Since we are talking cam selection and before I put the Magnum in, I went strictly by their "cam dyno" app that allowed me to input everything in. It is a 4-bolt 350 block with no boring. It has TRW flat top pistons with 4 valve reliefs. The heads are the LT1 heads from '71 ...casting# 487X with the 1.94/1.5 valves and 76cc combustion chamber. They are getting worked over now with 3 angle valve job. I am using the Performer dual plane intake and long tube headers. Of course I want POWER and to SOUND GOOD. According to their dyno app I should push 350HP and around 390TQ...does that sound right?

Lt1er

I never heard of small valves and 76cc on 487X heads, but who cares.

Big cc heads on a 350 is not a good thing. Compression is power. Those little valves and poor flowing heads are not worth putting a dime into fixing them. That performer manifold is for low performance vehicles like pickups.

Bruthish

Hey, that's what they came with and I measured to be sure....so I guess they just have small valves. Regardless, they are for sure "smog" heads due to the large CC. But I have read from experts like John Lingenfelter that these are one of the 4 best GM STOCK heads to use, and since I am on a budget I am using them. I know that no matter what I do to them, they will probably never flow as well as aftermarket nor vortech heads. Also, with the performer manifold, it is what came with the engine.

I am all ears though if you have ideas.....as far as I know the machine shop has not touched my heads yet so I can pick them back up.

Lt1er

Original questions: .020 more lift is really nothing. like changing the rocker arm ratio from 1.5 to 1.6 It is a very minor change in total lift, but it does help fill the cylinders as the rpm rise.

I prefer wider LS numbers for several reasons especially on small motors like 350 - 355 ci Modern LS... motors run very little overlap with LS numbers as high as 116 - 118.4 or some big number like that. They have very smooth idles and it really adds to the gas mileage of the vehicle.

So the 280 mag cam only adds 6 degrees to the intake, but the 110 ls number is going to give it more radical sound, poor low speed performance and bad gas miliage. One saving grace is small valves and low flow heads will be less effected.

If the shop is replacing the valves maybe inquire about replacing them with 2.02 or 2.05 intakes and 1.6 exhaust. Manley also sells race flow stainless valves that have a tulip stem and a radius higher flowing back of the valve.

You could also install the magnum cam retarded by 2-4 degrees and it would help low speed performance by cutting down intake reversion.

lastly I hope that you bought a matching spring set for the new cam.

my motor was built by a guy here on the forum probably 12 years ago. it is a solid cam with 114 LS and 1.6 roller tip rockers

Bruthish

Thanks for the input! I am not going to have them do any extensive work to those heads...I took them in to be checked for warp, magnufluxed and cleaned, and do the valve job and seals. Trying to do it with minimal cost as I am just not sure what I plan on doing with this car. If I decide to put another $1000 grand into it, I will def buy aftermarket heads. This motor was in in my '71 with the Crane cam and it seemed to have a lot of power.

Thanks also for the tip on retarding the cam 2-4 degrees....I am sure that would help.

v2racing

The LS engines don't need as much overlap or duration as the Gen 1 because of their superior heads. You can't really compare a Gen 1 and an LS on cam needs.

Having small valves and less flow is no saving grace, it is only a disadvantage. It will not make for better mileage or power. No saving grace here.

The 280 is not that big of cam and with proper tuning will not be that bad on gas. I get decent mileage with a lot more cam. I and many people I know have run larger cams in 350's and got decent all around use out of them. The 4 speed is the saving grace here.

Retarding the cam will have no affect on reversion. Reversion is a positive pressure wave traveling backwards through the exhaust port into the combustion chamber and out the intake port during overlap. Moving the installed cam timing does not change overlap so in effect does not change reversion. There are several things that affect reversion besides overlap but not installed timing on a single cam that holds both intake and exhaust lobes. Retarding the cam timing will help make better bottom end power to a small degree, because retarding the intake helps bottom end, but as you retard the intake you are retarding the exhaust which will hurt the bottom a little and help top end power. You are usually best off to install the cam within a couple degrees of the grinders intentions.

AZDoug

The first cam is sorta close to an L-46 cam.
The L-46 is aNice street cam with the right gears.

The second cam has too much duration for car with normal 3.xx gears, in a 350 CI or less motor, IMO.

The lift is somewhat irrelevant, lift doesn't affect drivability, it just allows more HP.

Doug

pauldana

So so correct!!! right on....

pauldana

Just another $1,000.... lol...... try more like $3-4K in valve train.... heads ~1500+.... springs~300...... RR's~500..... Push rods~100....Retro roller lifters~500.......porting and polishing and port matching~1,000.....you get the idea.... :-)

Way more than $1,000 for a good running valve train.... way more.... good luck ,,,, p:-)

DRIVESHAFT

Dont be so sure. Retarding a cam closes the intake valve (among other things) later.
What that is guaranteed to do is lower cylinder pressure, which will make less power.
Think about how DCR is calculated based on the intake valve closing point.
At very high engine speeds a retarded cam can help a bit due to giving additional time to fill the cylinder, but not at low RPM.

gkull

Dynamic Compression Ratio determination is iffy at best. That is why you see different calculators come up with different answers.

Here is a simple reason as to why:

Motor A has a small carb, small port dual plane, 165 cc 487x heads with 1.94/1.50 valves and a 280 mag cam. You start rotating the motor over and you might be only filling the cylinder less than 80%. The intake flow restrictions keep the motor from reaching some mystical on paper DCR

Motor B has a 750 double pumper, big single plane, AFR 227cc Eliminator full ported heads with 2.10/1.625 valves. Now install the same 280 mag cam or better yet some drag racing solid roller lobes with the same open and closing event numbers and the motor is now pumping at 100% It will detonate on equal octane fuel even with the same magical DCR numbers Racing motors can actually exceed 100% cylinder filling over a certain rpm with a tuned intake tracks that actually are ramming in additional air.

Use them as a guide line not the gospel truth.

At work I degree in every cam. We also make cam degree changes on the dyno trying to get better results. A road racing motor with 5 or less gears need a broader TQ curve. Often the Amercan V-8's respond well to somewhat retarded cam timings. We are never after just high peak numbers. we are after the highest average numbers

TheSkunkWorks

I didn't mean to open a new debate on the value of DCR, and anyone who has followed in-depth posts of mine concerning DCR likely knows that I don't tout DCR as being the holy grail of engine design. It's just another gauge on how a cam matches up with the compression ratio. That said, for a mild street pump-gas mill IMCO if you don't get it in the ballpark you could well end up with dog (if too low) or an engine which will bang itself to death (if too high).

FWIW, I use the same formula as the calculator found in the DCR primer below, again with the qualification that it's not everything; just a guideline as George suggests. And, the wilder is a build the more attention I pay to things like cylinder pressure than DCR...

http://www.empirenet.com/pkelley2/DynamicCR.html

DRIVESHAFT

As long as your dealing with average power output, and you pull the engines over a wide enough RPM range, what your saying is entirely plausible.
Its rare to get HP & torque outputs from an engine dyno at speeds below 3000 rpm, maybe 2500 if your lucky, so below that you really dont know how far down on power you were from retarding your cam.
If our goal is to improve low rpm torque, then retarding the cam is the wrong way to get there. It will make less low RPM power.

Here is a page on Comp's web site that you can refer to.
http://www.compcams.com/Pages/413/ca...ion-angle.aspx

63mako

With your pistons and heads you basically have an L82 engine without the forged bottom end. They are a 9 to 1 compression engine. A 280 cam needs compression. I think if your using what you have and you already made a cam purchase you need compression to match the cam. Since the heads are off mill the heads .030 and use the steel shim .015 head gasket. That should get you up over 9.5 to 1 which will be a much better match for your cam for hardly any expense. The heads will limit the HP you can get out of the engine but matching the components as well as you can will get you the most bang for the buck. The 230 duration will help with cylider filling but a split duration cam would be better with a stock head.

v2racing

You are correct about retarding the cam. It will lose bottom end. I have to quit answering posts so late at night. If you read my reply backwards (retarded as advanced) then what I said makes sense.

Advancing the intake helps bottom end, advancing the exhaust helps top end. Still not huge gains to be made by moving both lobes at the same time, that's why I have what I want in the end ground into the cam.