who got what.....

[The Pope]

Quote:

Originally Posted by Shelby-Rampage >engine mods ? My engine is low miles so for now I’m leaving the bottom end stock. As for mods, the main things are…Weber twin 38 carb, B&M blower, mild MP cam, MP spark computer, and lots of polishing. My next mod will be a water injection setup so I can run cheaper gas. Also I’d like to get a smaller 8psi blower pulley soon. That and I’d like to upgrade the brakes and exhaust too.

mild cams increase cylinder pressure, something you want to bleed off. Blowers work off RPM, something you want to increase. Higher boost levels heat the air up so there is more detonation chances.

Why not just go out and buy a Comp Cams 280M cam for it? 280 degrees duration with some overlap will make the engine rev up and will bleed off pressure. Then with more breathing your boost PSI will drop down. Turbos will just spin faster to match flow, the super charger can't, more flow will reduce boost.

[Shelby-Rampage]

Quote:

Originally Posted by The Pope mild cams increase cylinder pressure, something you want to bleed off. Blowers work off RPM, something you want to increase. Higher boost levels heat the air up so there is more detonation chances. Why not just go out and buy a Comp Cams 280M cam for it? 280 degrees duration with some overlap will make the engine rev up and will bleed off pressure. Then with more breathing your boost PSI will drop down. Turbos will just spin faster to match flow, the super charger can't, more flow will reduce boost.

This particular roots blower (B&M) is limited to about 6000 RPM’s according to it’s manual. Spinning the engine faster than that will probably just lead to parts breakage. Therefore a high RPM cam isn’t of much use to me in this application. I'm using a MP 765 cam. The 765’s specs are .430/460 lift, 240-248 duration, 24 overlap…not much over stock actually. It does make good torque at lower RPM’s, which is what I like.

As for detonation….These roots blowers produce a lot of heat into the motor. So to deal with the detonation associated with running the stock n/a compression ratio, I wired in a detonation sensor, switched to colder plugs (RN9YC), put in a 160 degree thermostat, richened the Weber 38 carb, wired the fan to run all the time, and 12 degrees timing for now. That and to be on the safe side I’ve been running a mix of high octane fuel. No detonation so far, but the cost of the fuel mix is getting prohibitive. I’m getting ready to try a water injection setup soon which should allow me to run cheap gas.

In my Rampage, which is pretty light, the whole setup feels reminiscent of a strong V-8 car. Or maybe like my T-II Shelby Z, only with a flatter power band. With the gearing I have it all matches together pretty well. It’s a lot of fun for an occasional tire burnout and pulls great though the whole RPM range, especially when the boost starts to come in at about 2500-3000 rpm and the blower starts to really whine. I built this thing as more of a show car than a drag racer. Right now it’s only making about 5 psi at 4k with the stock B&M pulley.

Eventually, I’d like to build a turbo short block using turbo pistons and get a smaller pulley for the blower. That and add a header and open up the exhaust some.

Anthony
1984 Dodge Rampage Supercharged
http://www.cardomain.com/memberpage/557514/6

[The Pope]

going to higher boost from a smaller blower pully spins the blower faster. Roots blowers are fine with RPM, its high boost pressures that can hurt them. Not made to compress air they pick it up and through it. Going to a pulley that adds a faster spin to the blower should come with a larger cam for more breathing. More flow will just stress the blower less. The 280 cam is a 460 lift, 280 duration, 80 degree of overlap cam. The cam breaths so much I would fear to use it with out a blower. But with it it will scream. Thats how blowers are the best for all out power, with a turbo your always cam limited.

[Shelby-Rampage]

Keep in mind the limitation to this roots B&M blower is about 10-12 psi. I’m currently running the stock 5 psi pulley. I'm planning on going to the smaller 8 psi pulley eventually, not any higher.

As for cam overlap, again you don’t want much with a blower. Quoted form the B&M blower manual: “High overlap camshafts are actually detrimental to a supercharged engine’s performance. The longer the exhaust and intake are open at the same time, the more usable air/fuel mixture is blown out the tailpipe. When choosing a cam profile to work well with a supercharger, moderate duration is desirable, but high overlap is undesirable. The best choice is a “torque” type camshaft.”

This is why I think a mild cam like the MP 765 is best suited for this particular application. Too much overlap can be detrimental to the amount of boost that the blower can produce. In other words, a high overlap cam will lower the blower’s boost.

Using the stock B&M 5 psi pulley that came with the kit or even a slightly higher boost (smaller) 8 psi pulley, you’re not going to produce an abundance of boost that will stress the blower. With boost numbers in this range I don't see a need to kill off boost with a high overlap cam. So when using a lower boost pulley like the ones I mentioned I’d keep the cam profile moderate at best.

[The Pope]

Quote:

Originally Posted by Shelby-Rampage Keep in mind the limitation to this roots B&M blower is about 10-12 psi. I’m currently running the stock 5 psi pulley. I'm planning on going to the smaller 8 psi pulley eventually, not any higher. As for cam overlap, again you don’t want much with a blower. Quoted form the B&M blower manual: “High overlap camshafts are actually detrimental to a supercharged engine’s performance. The longer the exhaust and intake are open at the same time, the more usable air/fuel mixture is blown out the tailpipe. When choosing a cam profile to work well with a supercharger, moderate duration is desirable, but high overlap is undesirable. The best choice is a “torque” type camshaft.” This is why I think a mild cam like the MP 765 is best suited for this particular application. Too much overlap can be detrimental to the amount of boost that the blower can produce. In other words, a high overlap cam will lower the blower’s boost. Using the stock B&M 5 psi pulley that came with the kit or even a slightly higher boost (smaller) 8 psi pulley, you’re not going to produce an abundance of boost that will stress the blower. With boost numbers in this range I don't see a need to kill off boost with a high overlap cam. So when using a lower boost pulley like the ones I mentioned I’d keep the cam profile moderate at best.

Have you ever worked with a roots on any other car? Yours is no different than any other roots, just smaller. Overlap makes big power. Top fuel cars have so much overlap they are still firing fuel in the tail pipes and produce 800 lbs of down force from the exhaust on the rear tires. A torque cam will make your tires explode and then start running out of breath. The Comp will smooth out the boost hit and make tons more top end. It will also reduce the chance of ping. The nice thing about a roots is that you can run a cam that is normally too big and it works better. When you add a sprayer, fill it with alki so it will be chemically cooled. Or OMG nitrous loves roots, it seams to fix them lol.

[supercharger2.2]

Quote:

Originally Posted by Shelby-Rampage Keep in mind the limitation to this roots B&M blower is about 10-12 psi. I’m currently running the stock 5 psi pulley. I'm planning on going to the smaller 8 psi pulley eventually, not any higher. As for cam overlap, again you don’t want much with a blower. Quoted form the B&M blower manual: “High overlap camshafts are actually detrimental to a supercharged engine’s performance. The longer the exhaust and intake are open at the same time, the more usable air/fuel mixture is blown out the tailpipe. When choosing a cam profile to work well with a supercharger, moderate duration is desirable, but high overlap is undesirable. The best choice is a “torque” type camshaft.” This is why I think a mild cam like the MP 765 is best suited for this particular application. Too much overlap can be detrimental to the amount of boost that the blower can produce. In other words, a high overlap cam will lower the blower’s boost. Using the stock B&M 5 psi pulley that came with the kit or even a slightly higher boost (smaller) 8 psi pulley, you’re not going to produce an abundance of boost that will stress the blower. With boost numbers in this range I don't see a need to kill off boost with a high overlap cam. So when using a lower boost pulley like the ones I mentioned I’d keep the cam profile moderate at best.

my manual also says the same thing it also says running a mixture of 50%water 50% alki is all you need they say running 100% alki makes no difference on this set up

[Shelby-Rampage]

Quote:

Originally Posted by The Pope Overlap makes big power. Top fuel cars have so much overlap they are still firing fuel in the tail pipes and produce 800 lbs of down force from the exhaust on the rear tires. A torque cam will make your tires explode and then start running out of breath. The Comp will smooth out the boost hit and make tons more top end. It will also reduce the chance of ping.

Too much valve overlap causes a "blow-down" effect in the cylinder. This is fine for a high-revving N/A car that only needs to operate in a narrow powerband like a drag racing engine. A high overlap cam would effectively bleed off cylinder pressure at lower engine speeds, which is exactly opposite of what you're trying to accomplish in a street-driven application with a blower.

With a street-driven blown car you want either a stock or mild cam or better yet a purposely made “blower cam” of which most don’t have excessive overlap. A high overlap cam used with a blower reduces ping because it’s bleeding off boost, again something I don’t want to do in this case.

My application is a 66 cubic inch blower on a 4 cyl that’s making 5 pounds of boost., not a Top fuel car that’s making 40-50 psi. Instead of bleeding off boost, I need all I can get with this thing…lol.

As for a torque cam making my tires explode, that’s exactly what I want with this particular vehicle. If I wanted to build a truly fast car for racing I’d go with a turbo, it’d be cheaper to build (parts cars) and I’d go faster by making more boost. I made this as more of a show/cruise car and spinning the tires through the gears is a plus to me.

I’m not saying you are necessarily wrong, but in this application I’d stick with B&M’s recommendations on camshaft selection. Here is a link to the B&M manual I was referring to concerning camshaft selection:
http://www.pnw-sdac.org/HowTo/BMBlower/1989/07.jpg
http://www.pnw-sdac.org/HowTo/BMBlower/1989/10.jpg