stock_mach

I just back into the LS world again. I got a 99 FRC. I really don't know much about the car bc the previous owner didn't know much as well. The car runs very well and was well kept up. but anyways its has longtubes with a catted mid pipe and borla out the back, has a ls6 intake, and a vortech V2 on about 8 pounds of boost when the belt don't slip. I drive this car everyday but I want to put a good cam in it. I want something that's very streetable but performs well and sounds good. Thanks for any info!!

ws6fitz

Check out Speed Inc. They have a good selection of blower cams that will fit your needs!

stock_mach

Thanks man Ill check them out

mjs1012

iTrader: (36)

brute speed blower cam is another good one.

jeffro_93

iTrader: (16)

ECS baby blower cam is also another good one. Very streetable, no lope, and made 745 to the wheel on 91 octane, with stock heads and intake on my ls2, with 15psi

stock_mach

Thanks for the info guys! I do want me a good sound though to

mjs1012

iTrader: (36)

the brute speed/epp cam i mentioned before has a decent lope to it.

(SS)

iTrader: (1)

I would make a call to martin@tick performance. He's been doing really good with his custom cams.

99Bluz28

iTrader: (35)

Cam Motion has a full line of blower cams.
I'd check it out.

pm sent.

Make sure to look at the C33-620, C33-627, C33-647

Bob@BruteSpeed

iTrader: (16)

Thanks! Here is a link to this cam, and there is a soundclip of how it sounds at the link. Bob

Bob@BruteSpeed

iTrader: (16)

Here's a link to my old Camaro with this same cam profile. Bob

stock_mach

Thanks yall for the info!!

Sales@Tick

iTrader: (3)

IMO you need something smaller than a 230's duration camshaft for good street manners and overall power.

Here is what I'd recommend:

223/239 .617"/.610" 114lsa.

This is a custom cam with 3 degrees of valve overlap. It will drive like stock and have a nice lope at idle. It will also make great torque under the curve and pull like a larger cam up top.

A blower motor makes peak power(torque and horsepower) at a higher piston speed than a N/A or turbo motor. Higher piston speed=higher rpm. Higher piston speed at peak power means less effective time in crank degrees to evacuate the cylinder. Meaning we have to open the exhaust valve sooner to keep spent exhaust gas from polluting the intake charge at higher RPM's. This causes power to fall off and plummet before it really should.

To combat this we open the exhaust valve earlier with added exhaust duration. We must keep overlap in check when this is done though.

Since blower motors have pressure above atmospheric(boost pressure) behind the face of the intake valve and atmospheric pressure(90-100kpa depending on density altitude) behind the face of the exhaust valve, the pressure differential during overlap is huge.

High pressure always moves to areas of low pressure. Added valve overlap in a blower motor is not beneficial because of this.

Hope this helps in your decision.

stock_mach

That help a lot man! Ill be giving you a call soon! My choice is made

Sales@Tick

iTrader: (3)

My first sentence sounds contradictory now that I've re-read it.

Intake duration and the ICL of the cam will determine 90% of where the torque and horsepower curves peak. Where the intake valve closes(directly related only to intake duration and intake center line) is 80% of your torque production under the rpm where torque peaks. Then the exhaust events affect torque production after torque peak much more than intake duration.

This is why when I said, "I feel you need a cam that isn't in the 230's duration" I'm sure I confused some of you.

Exhaust events and where the exhaust valve opens is critical on a blower motor. This is why I use much more exhaust duration than intake duration. This gets the exhaust valve open sooner.

Keeping intake duration small and using a wider exhaust center line will keep valve overlap low even if exhaust duration is much larger.

BigKID

iTrader: (4)

Would this statement apply to positive displacement blowers/compressors or just centrifugal?

Sales@Tick

iTrader: (3)

Where a blower makes peak power is directly related to volumetric efficiency of the engine and how the pulley diameters are configured.

Since a blower is driven by engine speed, as RPM rises, so will positive manifold pressure. It takes engine power to turn the blower. The faster the blower turns the more power it takes to turn.

Consequently though, the faster it turns the more positive manifold pressure it will create and more power will in turn be produced.

But, there will come a point where even though more positive manifold pressure is being registered by the map sensor in the intake manifold, power output will not rise. It will start to decline. At this point the power it takes to turn the blower has nullified the added manifold pressure turning the blower faster is creating.

If we had a larger engine or an engine that produced more VE, or a better set of cylinder heads, camshaft or intake manifold and/or could turn the engine a higher RPM and produce more VE we could utilize the added manifold pressure and the engine could actually consume it into the cylinder on a given intake stroke. Once that cylinder is filled at peak VE though, no more air mass will fill the cylinder and what is "left over" will be registered as positive manifold pressure in the manifold. It's not really "left over", but it's related directly to VE and what each cylinder can consume in terms of air mass.

If the cylinder could consume more air mass, manifold pressure wouldn't be as high when we turn the blower faster as the cylinder would be consuming that added pressure and turning it into added power that would over come the added power it takes to drive the blower faster.

Hopefully I haven't confused anyone yet. Haha.

Boost is a measure of efficiency(some will say restriction...whatever). The more VE the engine has, the less manifold pressure will be registered for a given power output.

As boost rises, power will rise. This is why if you have waste gate creep with a turbo car, the power will continue to rise and not peak and begin to fall off until boost stops rising.

This isn't a turbo car though and is taking engine power to turn the blower.

Answering your question now with that said, since a PD displacement blower in general cannot produce the air mass that a large centrifugal can, the point where drive power exceeds power added from manifold pressure will occur much sooner. In fact, most PD blowers are so tapped out in terms of producing manifold pressure that they make peak boost extremely early due to being so small and spun so fast. They fall of much sooner due to the amount of power it takes to drive them and no added manifold pressure being produced to offset the drive loss.

This is why they peak sooner and fall off sooner than a centrifugal.

If you had a very large PD blower though like a Whipple 4.0 or a KB 3.6 this wouldn't happen until very high manifold pressure.

Hope this helps!

BigKID

iTrader: (4)

Thank you for the explanation. I was thinking about it in more basic terms and how the torque curves generally look between a PD and Centri given all other aspects of the setup are equal. The PD would have a flatter curve which peaks sooner where as a centri would have a steeper curve that peaks later. This is why I was curious about the piston speed/rpm statement. If I understand correctly, as rpm rises, ve rises which uses up the excess cfm created by the supercharger (boost). However, a pd blower will reach a point of diminishing returns due to its rotating mass, parasitic loss and inability to create adequate cfm in the higher rpms and cant keep up with the increased cylinder ve as rpm rises whereas a centri does a better job of this.
Now appling this back to cam science, would you still want as much exhaust bias for a pd blower since it cannot keep up in the upper rpms where the early exhaust opening is most beneficial? Or would it work the opposite and actually help extend the rpm range?

Sales@Tick

iTrader: (3)

First off, I have to applaud your knowledge and understanding of these concepts. You're a natural.

You are 100% correct with everything you stated in your last post.

To answer the question of the earlier exhaust valve opening event, through the testing I have done and trends I have seen with my camshafts opening the exhaust valve earlier on a PD set-up does help to extend the torque curve further into the RPM range.

Opening the exhaust valve earlier will nearly always result in a power curve that carries further into the RPM range. Since a PD blower makes such astronomical torque in the lower RPM ranges, worrying about bleeding off cylinder pressure too soon on the power stroke and starting to blow down the piston too soon is not an issue.

I like to keep the intake valve close event "early" to keep low speed torque production high and then use the exhaust opening event to extend the power curve.

I've found that PD blowers, especially the small ones don't like excessive valve overlap. This holds true for 80% of PD blower applications in all but the largest PD blowers.