Builder used different cam than specified.
01-19-2016, 07:10 PM
#131
Registered
iTrader: (3)
While I do stand behind my original cam recommendation to 79 for his build, I am not going to go as far as saying the cam the builder chose was simply WRONG, because it has a blower.
We have all been taught, even some of the phone operators at cam companies, that a supercharger cam should be 114 or wider LSA. That just isn't always the case. There are many guys out there running roots/screw blowers, on pump gas, with 110/112 LSA's, and making excellent power.
BDS blowers recommends 110 LSA cams, and back in the early days of supercharger development at B&M, they also found 110 LSA cam in a big block to make the most power on the combos they worked with. Harold Brookshire who started ultradyne cams, designed the Voodoo series of cams for lunati, and revamped many of their cams, and generally in the camshaft design business for a lifetime had this to say
Blown engines are quite different from unblown ones; clean air and fuel starts entering the combustion chamber as soon as the intake valve cracks off the seat, generally around .001" of valve lift. Unblown engines don't start putting clean air and fuel into an engine until a little while AFTER TFC. Before TDC, the piston is moving upwards and pushing the exhaust gases out the exhaust port, there is no air/fuel intake until after TFC and the piston starting down on the intake stroke.
This is just for blown gas engine, as blown alcohol engines require different cams, as do turbo-charged engines.
Because gas burns HOT, pumping a lot of fuel into the combustion chamber causes a very hot cylinder head, and detonation problems. The more racier blown gas cams are on 108-110 LSA, and use the intake overlap to COOL the combustion chamber down. Needless to say, they don't make that good of a gas mileage. They also have all of the normal actions of tighter LSAs, plus a lot of torque. Tight LSAs don't make good street engines, too snappy.
Wider LSAs make flatter torque curves and deliver better mileage, particularly at lower boosts---6-8 lbs. The blower will add lots of power.
When you get up in real racing blown gas engines, 36 lbs of boost lets you accomplish with 116 LSAs what you used to do at 110 with 8 lbs of boost.
I generally go with wide LSAs on the street with low(6-8 lbs) boost, moving to tighter LSAs (108-110) with higher boosts and racing use, then back to very wide LSAs with very high (24-39 lbs) boosts.
I also tend to pay lots of attention to those who make this their field of expertise.
UDHarold
Every combo is different, and I don't believe there is a one size fits all cam for all applications. The cam a guy might run in his weekend cruiser chevelle, might not be the came the guy who trailer his car to the track runs in his engine, or the offshore engine, etc. I also don't think just because a cam has a 110 LSA, it will revert, and a 114LSA wont revert. Theres more to it than that.
Years back a friend of a friend ordered some blower cams from Tommy at Cheif engines. Once he got the cams, he noticed they were 110 LSA . All the guys said he must have made a mistake, so he called tommy. Nope, he reassured him thats the cam he runs in his stuff. Still, his friends told him that cam was wrong, until it came to dyno time.
Things like cylinder head style, blower style, boost levels, RPM range, operating range, compression ratios, all play a part in the cam selection. I know the original cam I suggested worked well in this combo at hand, but it would be ignorant of me to say, that something else, may not have worked better, without trying it.
We have all been taught, even some of the phone operators at cam companies, that a supercharger cam should be 114 or wider LSA. That just isn't always the case. There are many guys out there running roots/screw blowers, on pump gas, with 110/112 LSA's, and making excellent power.
BDS blowers recommends 110 LSA cams, and back in the early days of supercharger development at B&M, they also found 110 LSA cam in a big block to make the most power on the combos they worked with. Harold Brookshire who started ultradyne cams, designed the Voodoo series of cams for lunati, and revamped many of their cams, and generally in the camshaft design business for a lifetime had this to say
Blown engines are quite different from unblown ones; clean air and fuel starts entering the combustion chamber as soon as the intake valve cracks off the seat, generally around .001" of valve lift. Unblown engines don't start putting clean air and fuel into an engine until a little while AFTER TFC. Before TDC, the piston is moving upwards and pushing the exhaust gases out the exhaust port, there is no air/fuel intake until after TFC and the piston starting down on the intake stroke.
This is just for blown gas engine, as blown alcohol engines require different cams, as do turbo-charged engines.
Because gas burns HOT, pumping a lot of fuel into the combustion chamber causes a very hot cylinder head, and detonation problems. The more racier blown gas cams are on 108-110 LSA, and use the intake overlap to COOL the combustion chamber down. Needless to say, they don't make that good of a gas mileage. They also have all of the normal actions of tighter LSAs, plus a lot of torque. Tight LSAs don't make good street engines, too snappy.
Wider LSAs make flatter torque curves and deliver better mileage, particularly at lower boosts---6-8 lbs. The blower will add lots of power.
When you get up in real racing blown gas engines, 36 lbs of boost lets you accomplish with 116 LSAs what you used to do at 110 with 8 lbs of boost.
I generally go with wide LSAs on the street with low(6-8 lbs) boost, moving to tighter LSAs (108-110) with higher boosts and racing use, then back to very wide LSAs with very high (24-39 lbs) boosts.
I also tend to pay lots of attention to those who make this their field of expertise.
UDHarold
Every combo is different, and I don't believe there is a one size fits all cam for all applications. The cam a guy might run in his weekend cruiser chevelle, might not be the came the guy who trailer his car to the track runs in his engine, or the offshore engine, etc. I also don't think just because a cam has a 110 LSA, it will revert, and a 114LSA wont revert. Theres more to it than that.
Years back a friend of a friend ordered some blower cams from Tommy at Cheif engines. Once he got the cams, he noticed they were 110 LSA . All the guys said he must have made a mistake, so he called tommy. Nope, he reassured him thats the cam he runs in his stuff. Still, his friends told him that cam was wrong, until it came to dyno time.
Things like cylinder head style, blower style, boost levels, RPM range, operating range, compression ratios, all play a part in the cam selection. I know the original cam I suggested worked well in this combo at hand, but it would be ignorant of me to say, that something else, may not have worked better, without trying it.
01-19-2016, 07:34 PM
#132
Registered
Thread Starter
I absolutely agree that the builders cam may make more power. If I had money to play, I would have dynoed it. I also would have tried it in the boat had the dyno runs been impressive. At this point, I gotta go with a cam that many on OSO have successfully used. I could not find one person on OSO that used his cam at all. I don't have the money to gamble.
01-19-2016, 08:59 PM
#133
Registered
79,
I only read a few pages so this may have already been mentioned. Why don't you call Comp and ask their opinion on the cam based on your application ? Call them and tell them what you have with the blower etc. and ask for their recommendation. Don't tell them anything else and see what they say. I bet they will spec a cam with a lot more lobe separation for the blower.
I would personally never change a cam request without talking to the customer first. If I thought that the cam they chose was wrong I would explain my reasons and let them make the decision if they insist. I would never change it without talking to them first.
I only read a few pages so this may have already been mentioned. Why don't you call Comp and ask their opinion on the cam based on your application ? Call them and tell them what you have with the blower etc. and ask for their recommendation. Don't tell them anything else and see what they say. I bet they will spec a cam with a lot more lobe separation for the blower.
I would personally never change a cam request without talking to the customer first. If I thought that the cam they chose was wrong I would explain my reasons and let them make the decision if they insist. I would never change it without talking to them first.
01-20-2016, 05:44 AM
#135
Registered
Thread Starter
79,
I only read a few pages so this may have already been mentioned. Why don't you call Comp and ask their opinion on the cam based on your application ? Call them and tell them what you have with the blower etc. and ask for their recommendation. Don't tell them anything else and see what they say. I bet they will spec a cam with a lot more lobe separation for the blower.
I would personally never change a cam request without talking to the customer first. If I thought that the cam they chose was wrong I would explain my reasons and let them make the decision if they insist. I would never change it without talking to them first.
I only read a few pages so this may have already been mentioned. Why don't you call Comp and ask their opinion on the cam based on your application ? Call them and tell them what you have with the blower etc. and ask for their recommendation. Don't tell them anything else and see what they say. I bet they will spec a cam with a lot more lobe separation for the blower.
I would personally never change a cam request without talking to the customer first. If I thought that the cam they chose was wrong I would explain my reasons and let them make the decision if they insist. I would never change it without talking to them first.
01-20-2016, 06:55 AM
#136
Registered
iTrader: (1)
Quick snipit on LSA;s, including marine and SC'd:
http://www.enginelabs.com/engine-tec...-relationship/
http://www.enginelabs.com/engine-tec...-relationship/
01-22-2016, 04:17 PM
#138
Registered
Thread Starter
I swapped the cam myself. I had the gaskets and a degree wheel. It was faster than taking the motor back and picking it up a few days later. He will still credit me the cam.
01-22-2016, 05:28 PM
#139
Gold Member
Gold Member
