Lobe seperation?

[1973mach1]

I have been checking out cams and most cams are about 110 for lobe seperation. I have seen some though that are 108 and others around 112. How does this affect performance? The cam im looking at is a Crower 297 intake / 308 exhaust, duration @0.050 - 234 intake / 240 exhaust
lift - 0.578" intake and exhaust
112 LSA
Powerband - 2000-6000 rpm with a redline of 7000 rpm

Is 112 good or do I want to stay around 110 or do I want less? Does it make much difference?

 

[rbohm]

it depends on what you want from the engine. the wider the lobe seperation, the lower the rpm range of the engine. the reason is the lower valve overlap of the wider lobe centers. turbo and supercharged engines like wider lobe seperation as it cuts down on the amount of fresh a/f charge being blown out the exhaust, and allows higher boost pressure.

 

[Blown4.6]

yep, a larger lobe sep. angle reduces the amount of valve overlap (time when both are open). Both intake and exhaust being open is good at high rpm, with headers when you can actually pull (due to vacuume from the exhaust side) fresh air into the combustion chamber. At idle or low rpm, this doesn't happen, thus the "lope" "lope" "lope" sound. At idle the engine is actually starting to stall. At high rpm, the engine sings!

Modern engines run 112 or 114 lobe sep. angel. This includes super cars such as the LS6 or Viper. a 110 lobe sep. angle is pretty stout for an old muscle car, but pretty standard. If you want to go to a 108, that's very aggressive. You will get lots of "lope" and would benefit greatly from headers.

I don't recomment a 112 unless you are low rpm and maybe towing something.

 

[jcp123]

112 is great for a street car, 110 is perfect for a street/strip. 108, like others have said, is pretty aggressive, and might not be fun on the street at all...

 

[1973mach1]

Thanks for the replies. So if you wanted a FAST street car that sounded mean and could run with the best of them at the track you would go 110ish? The setup I will be running is 4bbl quench heads, stock piston rods and crank, flat top pistons, not sure on intake, probally a 750DP carb, FMX tranny, 2500 or so stall, 3.70, Hedman Headers. Im returning my Hedman headers for a 4bbl one to Summit, I got 2bbl ones thinking I would go with this setup. What size primaries should I get 1-3/4 or 2in? I want something I can still drive on the street at night and the weekends but when people hear and look at it they know its a muscle car. Hopefully run low 13's. I will be running open headers for awhile till I can afford an exhaust. I dont mind though, the louder the better. My brothers running 2.5in pipes with 2 chamber flowmaster mufflers to his manifolds (no cats) and it sounds good but i'd be happy with something even louder. It sounds good on his car, people actually come up to him at stoplights and ask what he's running but for a street/strip cruiser I want louder. Im tyring to get to my 375RWHP mark.


Thanks,
Jim

 

[Blown4.6]

if your goal is 375 to the wheels, out of windsor, I'd go with a very aggressive cam. You already said that you're running headers; so, go with as BIG a cam as possible with your stock torque converter (you're auto right?). If you've got any power options such as breaks or a/c, you may have another problem and will be limited on how big a cam you can use.

For 375 to the wheels, you're going to need something really, really large. I'm talking 235-240 degrees at .050" on a 110 lsa. A little less on a 108 lsa. You'll have to decide if such a cam is compatible with your setup and/or if you want to spend the $ to make it compatible.

 

['69Stang]

You want the 1 7/8" headers and then go with a 110 LSA. If you have 1 3/4" headers you'd probably want a 112 LSA in order for the exhaust charge to have more time to get out through the smaller headers. The Crower cam you listed looks very good. Consider looking into a solid cam for extra performance and getting screw-in rocker studs. Get the compression up to between 10.5:1-11.0:1 to get closer to that 375 RWHP figure. You'll have a tough call on the intakes< I'm sure you want to keep the carb underneath your hoo which only leaves you a few options - Blue Thunder, Torker, or the Holley Strip Dominator.

 

[1973mach1]

if your goal is 375 to the wheels, out of windsor, I'd go with a very aggressive cam. You already said that you're running headers; so, go with as BIG a cam as possible with your stock torque converter (you're auto right?). If you've got any power options such as breaks or a/c, you may have another problem and will be limited on how big a cam you can use.


It's a Cleveland.

Thanks,
Jim

 

[1973mach1]

[QUOTE='69Stang]You want the 1 7/8" headers and then go with a 110 LSA. If you have 1 3/4" headers you'd probably want a 112 LSA in order for the exhaust charge to have more time to get out through the smaller headers. The Crower cam you listed looks very good. Consider looking into a solid cam for extra performance and getting screw-in rocker studs. Get the compression up to between 10.5:1-11.0:1 to get closer to that 375 RWHP figure. You'll have a tough call on the intakes< I'm sure you want to keep the carb underneath your hoo which only leaves you a few options - Blue Thunder, Torker, or the Holley Strip Dominator.[/QUOTE]

Thanks, Would 2in primaries be too big?

Thanks,
Jim

 

[1973mach1]

[QUOTE='69Stang]You want the 1 7/8" headers and then go with a 110 LSA. If you have 1 3/4" headers you'd probably want a 112 LSA in order for the exhaust charge to have more time to get out through the smaller headers. The Crower cam you listed looks very good. Consider looking into a solid cam for extra performance and getting screw-in rocker studs. Get the compression up to between 10.5:1-11.0:1 to get closer to that 375 RWHP figure. You'll have a tough call on the intakes< I'm sure you want to keep the carb underneath your hoo which only leaves you a few options - Blue Thunder, Torker, or the Holley Strip Dominator.[/QUOTE]

Almost forgot, it does have power brakes/front disc brakes. I also has A/C but it doesn't work so I took the compressor and condensor and dryer out to take off a few lbs. So my main concern is keeping my power brakes working good. How large cam wise can you go before your power brakes start being affected?

Thanks,
Jim

 

['69Stang]

I think 2’ are great, but they have to be backed up by a good exhaust system, like a 3” and the right cam to match the whole combination. I think for you application 1 7/8” is perfect. I run 1 ¾” which is probably small for my application, so my cam runs a 112 LSA to compensate for it to a certain extent. A wider LSA will give you a wider torque band, but less peak power. The Crower cam you listed I’m assuming is a hydraulic cam. It should be o.k. for the vacuum for you power brakes, but I’d call crower. You may want to consider a solid cam, they tend to be more mellow for the same duration in a hydraulic due to the lash and produce more all-around power.
I’m running a solid roller that is a 240/240 duration @ .050 and it idles very nicely and gives me enough vacuum for my power brakes.

I think at this point you need to speak with an educated Cleveland cam grinder in order to pull everything together. I can recommend a couple of folks if you are interested.