Camshaft Selection
Ultrashock
05-25-2006, 11:18 AM
Depending on how much free time and how much money I have, I plan on purchasing a new camshaft for my truck.
When looking at cams what do I have to look for? Im loooking to keep it daily driver but looking for better performance and gas mileage. What is the difference between hydraulic flat tappet and hydraulic roller tappet? Whats the advantage to buying a full out kit complete with the cam lifters etc., as opposed to just the cam?
When looking at cams what do I have to look for? Im loooking to keep it daily driver but looking for better performance and gas mileage. What is the difference between hydraulic flat tappet and hydraulic roller tappet? Whats the advantage to buying a full out kit complete with the cam lifters etc., as opposed to just the cam?
curtis73
05-25-2006, 12:27 PM
Good questions.
First of all, is this for your blazer listed in your sig? If you have a roller cam, chances are the current lifters are fine. They can be switched out at will since they don't have to be wear-matched to the cam. So if your current rollers are doing fine, leave them in there. You can always change them later if they start failing. If you have a flat cam, you must install new lifters. You can't put new lifters on an old cam, nor can you put a new cam on old lifters.
Some things to consider. If your current cam is not a roller, converting to roller is expensive. Its one of those things where you say, "hmmm, the cam is only $300," but then you have to buy retrofitting roller lifters because the bores are different. Then you need pushrods, thrust bearing or retainer plate, distributor gear... it ends up being well over $1000. Going the other way is easy. Most roller engines will accept flat cams and lifters with no alterations. The problem with that is that (while you save a little money) you are giving up all the superior qualities of the roller setup. Rollers not only reduce friction, but they have a longer life. The big limiting factor in flat lifter cams is the ramp speed. As the cam rotates it encounters a nearly flat cylinder. If the lobe's ramp is too steep it won't lift the lifter, it will just shear off. With a roller, the ramp can be much steeper since its encountering a wheel. So, for a given duration cam, a roller provides more average lift faster while providing dramatically reduced friction. More power, more drivability, less friction... truly a free lunch. The only drawback to hyrdaulic rollers is that they're heavy... but you won't notice it unless you're spinning the motor to 7500 RPMs, which won't be happening on a street truck. If this is for you 92 S10 it should already have a roller cam.
When choosing a cam, look at the overlap. Often times cam manufacturers don't publish that number, but its the amount of time that the exhaust and intake valves are open at the same time. I won't get into it too much here since we're dealing with just a step or two above stock, but two main numbers determine overlap; duration and LSA or lobe separation angle. In general, less overlap makes better mileage and also supports good torque. Your stock cam probably has an LSA of about 116 degrees. Many performance cams fall in the 112-108 area. More overlap has its benefits at higher RPM levels at the expense of idle quality and low end torque.
You should be fine with a cam in the 114 LSA range, but I'd entertain 115-112 depending on the overlap. Your cam manufacturer will be the best there... you can trust them to make a good recommendation. The TBI system in that S10 (if that's what you have) can't operate well if you have too much overlap. The poor vacuum signal which makes carbed cars have a rump rump idle will start to piss off the EFI sensors and your mileage might get worse because of it.
Your stock cam is also probably about 191intake/196exhaust duration at .050" lift. If you bumped that up to about 196/206, or even 200/210 you should get a nice push in power without much of a penalty in MPG, but like I said a cam manufacturer's tech line will give you good advice.
First of all, is this for your blazer listed in your sig? If you have a roller cam, chances are the current lifters are fine. They can be switched out at will since they don't have to be wear-matched to the cam. So if your current rollers are doing fine, leave them in there. You can always change them later if they start failing. If you have a flat cam, you must install new lifters. You can't put new lifters on an old cam, nor can you put a new cam on old lifters.
Some things to consider. If your current cam is not a roller, converting to roller is expensive. Its one of those things where you say, "hmmm, the cam is only $300," but then you have to buy retrofitting roller lifters because the bores are different. Then you need pushrods, thrust bearing or retainer plate, distributor gear... it ends up being well over $1000. Going the other way is easy. Most roller engines will accept flat cams and lifters with no alterations. The problem with that is that (while you save a little money) you are giving up all the superior qualities of the roller setup. Rollers not only reduce friction, but they have a longer life. The big limiting factor in flat lifter cams is the ramp speed. As the cam rotates it encounters a nearly flat cylinder. If the lobe's ramp is too steep it won't lift the lifter, it will just shear off. With a roller, the ramp can be much steeper since its encountering a wheel. So, for a given duration cam, a roller provides more average lift faster while providing dramatically reduced friction. More power, more drivability, less friction... truly a free lunch. The only drawback to hyrdaulic rollers is that they're heavy... but you won't notice it unless you're spinning the motor to 7500 RPMs, which won't be happening on a street truck. If this is for you 92 S10 it should already have a roller cam.
When choosing a cam, look at the overlap. Often times cam manufacturers don't publish that number, but its the amount of time that the exhaust and intake valves are open at the same time. I won't get into it too much here since we're dealing with just a step or two above stock, but two main numbers determine overlap; duration and LSA or lobe separation angle. In general, less overlap makes better mileage and also supports good torque. Your stock cam probably has an LSA of about 116 degrees. Many performance cams fall in the 112-108 area. More overlap has its benefits at higher RPM levels at the expense of idle quality and low end torque.
You should be fine with a cam in the 114 LSA range, but I'd entertain 115-112 depending on the overlap. Your cam manufacturer will be the best there... you can trust them to make a good recommendation. The TBI system in that S10 (if that's what you have) can't operate well if you have too much overlap. The poor vacuum signal which makes carbed cars have a rump rump idle will start to piss off the EFI sensors and your mileage might get worse because of it.
Your stock cam is also probably about 191intake/196exhaust duration at .050" lift. If you bumped that up to about 196/206, or even 200/210 you should get a nice push in power without much of a penalty in MPG, but like I said a cam manufacturer's tech line will give you good advice.
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