hmm intersting

 

Sure a cam profile can help move more air at slower engine speeds but that becomes irrelevant in a combination with a centri. The blower doesn't care what cam the motor has in it with regards to airflow. If the blower is moving x amount of air at 3500 engine rpm with one cam, it is gonna flow x amount of air at 3500 with a different cam. I'm sure there are extreme cases that could show a change in blower volume, but for what you're talking about, this extreme circumstance doesn't apply. The simple outcome of a cam swap would simply just show up as a different number on the boost gauge.

I just can not understand your relentless quest to convince yourself that the -94 race blower can be set up to perform well at low engine speeds. One of these days you just need to accept the fact that these new bread of race blowers are designed to perform at very high impeller speeds. Procharger didn't release this new technology to cater to the daily driven 5000+lb truck guys with engines that are cam'd to peak torque well below 6500 engine rpm.

Your fetish for the -94 is obvious and that is cool, but why you are trying to figure out a way to make it work outside of its design parameters is beyond me.

Back to the basics......motorcars run best when all the components work in conjunction with either other. It's all about putting together the best combination of pieces.

Also, like I've already stated, speeding the blower up to help with it's lacking performance at low rpm is only going to result some very high boost numbers as you approach shift rpm which plays right into the hand of the one major design flaw in the ls architecture. We all know what that is........the ability to keep the heads down.

If race car with big rpm solid roller camshaft, crazy loose converter, steep gear ratios and light weight is the game, buy all means.....give me the -94.

 

You're right. I know you are. But there is more to it than blower CFM.

Cam selection can really effect cylinder pressure at desired RPM. To that end I could fatten mid range in a huge way with the correct cam, and let the blower do what it does up top. That's why spec's for different power adders look so drastically different. A 'blower cam' is not a 'blower cam' across the board. For most mild combinations, yes, they are fairly interchangeable. For what I am trying to accomplish that is not the case. You can be moving the same air at the same RPM and have drastically different torque numbers. For instance you want to do everything you can with a PD cam to reduce cyl pressure at low RPM and assist it at high RPM. By putting in a cam that also increases mid range cyl pressure, you arent necessarily reducing its ability to flow air. In fact you can increase both. That would be the goal with one of these blowers. Reduce boost across the board and pulley down. Make it hit its sweet spot at a lower engine RPM, while combined with a fatter mid range from the cam, and all the sudden you have an engine thats flashing the converter harder and getting itself into a sweet spot for the blower even quicker. Of course there is only so much you can do... but it would all add up.

My obsession with the -94 is simply that its a far more capable blower that is also more efficient. Why wouldn't I want to try to try use that? Also, yes, I'm greedy, and 900 to the tires (would be less in my truck anyway) isn't enough to warrant a change in power adder. The 2650 will lay down that number easily. If it's a procharger that ends up on the truck the F1a wont cut it.

The long and short of it is this. I will be tuning an F1c-94 this spring. I'll let you know how laggy it really is.

 

Thats cool man. Glad you decided to go the -94 route. As hard as I've tried to talk you out of it, it will be a great source of data for everyone.

Now the big question is how are you gonna drive it? You know a 6 rib will have to be in the trash can and I really can't see an 8 rib doing too much good either. Are you gonna do a HOB dedicated drive with serpentine or a cog setup.

If you wanted my opinion on that topic, the cog is the only way to go. As long as the brackets are right, blower support is right, pulley alignment is right, belt tension is right and a large enough BOV capacity.......the cog will never give you an issue and they make belts that are plenty streetable.

A good analogy would play out like this. You choosing to do a serpentine setup and fighting a few battles with it only to end up going cog, would be the same as me starting with a 4 bolt iron factory block and spending a gazillion dollars trying to get it to work, only to finally ruin it and everything else around it to start over with an aftermarket 6 bolt setup. Catch my drift? Learn from my stupidity.

 

Nah I haven't made the call myself. When I say tuning I was talking about Kurt's truck.

Believe me, I am soaking in all the info you give me. I trust your opinion. I also know that the new blowers are far more capable and efficient. It would be awesome if I could make one work for me. I guess the best way to describe it is I haven't ruled it out yet, but I am far from a decision. Seems an F1c would be a better fit for me. Let's not forget this idea is still in second place to a larger more capable PD unit.

If I go procharger it will without a doubt be a direct drive unit. I would sell my current 8 rib stuff to help fund it. I's be a little nervous about the cog drive on a street truck though.

 

Just think of the thousands of guys who have run cog driven 6-71 and 8-71 on the streets over the last 30-40 years. No issues.

Several years ago I inquired about running a gear drive on the street and I couldn't find anyone that would confirm it was a good idea. The real issue I was finding is that those units only hold 4 oz of oil and the plastic pucks in the drive system where giving folks lots of problems that weren't talked about much publicly.

Now days, it seems that there have been several guys to have done it with no issue. When you think about the 4 oz capacity of oil, you have to remember, the big blowers only hold 4 oz as well and they seem to survive no problem.

Regarding the plastic pucks, there has been some R&D done that has produced several different flavors (think durometer) depending on the application and that problem seems to have disappeared.

After having run the cog set up on my truck and seeing how reliable it is (I've never had one single issue with a belt), I've actually changed my mind and prefer the cog drive over the gear drive due to the simplicity of being able to change pulleys. I can change blower speed almost as quickly as the turbo guys can turn there little ***** or whatever. lol

 

Alright, I'm going to attempt to make what I type make sense here.

All devices that move air should have what I call a blower curve if the designer did their home work (blower/fan/pump/any type of pump, they all should have some type of curve). Usually they are are 2D graph that outlines a blowers performance at specified parameters (you can add more parameters, but then that makes the graph have a bazillion dimensions or lines that suck). Google is great resource for this.

There are 2 parameters that we really give a **** about in terms of your paragraph as it relates to combustion. They are mass air flow (Kg/s), and back pressure (psi/kpa/inH20..) on the down stream side of the blower. The blower curves that I have personally created are set up to be at a specified blower rpm, with Mass air flow and back pressure as the Y and X axis (usually there a many curves on these graphs to deal with different conditions, in my case I did many different speeds as the system had a variable speed blower. I feel like this still applies here). Once the curve is created, you just need to measure boost pressure to figure out how many Kg/s you are flowing. My limited knowledge about speed density tuning is that all one is doing when adjusting the fueling vs. mani psi is manually adjusting fuel to match the other axis of the blower curve (no MAF = no Kg/s reading). If you had said 'blower curve' for your Speed Density system at a few different engine speeds you could nail the fueling in the tune first time.


For simplicity of typing I will limit the rpm to what ever constant blower RPM a constant engine RPM of 3500 dictates. This is all assuming the BOV is closed and not leaking hp gold into the atmosphere...

The low down on blowers / blower curves as I know them are pretty simple, again, constant RPM is key:

- as the down stream pressure ('boost') goes up, the kg/s goes down.
- as the down stream pressure goes down, the kg/s goes up.
- blowers are almost always more efficient when spinning faster as leakages are less of a factor, this only holds true until you hit the geometry limits of your system then **** is whack.
- there is always an upper, down stream restriction limit at which a given blower will 'fall off' and not do any thing cool. basically it will be maxed out hp wise and you won't get anything more out of it by spinning it faster.
- every blower has a curve, even positive displacement blowers and pumps
- temperature and altitude above sea level (ambient pressure) can have dramatic impacts on the curve.


That being said, I feel like from the blowers point of view the motor is just a restriction (in the case of your paragraph the cam helps dictates the amount restriction, which I agree with). If you put a bigger cam in, your down stream restriction will go down, thus decreasing the 'boost' pressure and increasing the kg/s through the system as you moved yourself to a different point on the blower curve. A smaller cam will increase the restriction, upping the 'boost' pressure and move you to a different point on the blower curve which will have a consequently lower kg/s flow associated with it.

Long of the short is I agree that a cam swap at a constant RPM will change the boost numbers, but I disagree that the system will flow the same amount of air (also assuming your x = x in the original paragraph). If you notice it on the boost gauge, you're flowing a different amount of air. I can't comment on how much, because I doubt any one got their little mits on the air flow curves of a pro charger. It would likely be more than you think as air moving devices typically have crappy efficiencies due to the low viscosity, even more so at low speeds.

Something like this would actually be mega interesting to know, as a guy could optimize the blower speed vs. engine speed for the type of driving and get the most out of the setup.


Make any sense??

 

Great post!

What I was saying ties into that beautifully. I can spec a cam to REDUCE boost and INCREASE airflow while simultaneously increasing mid range power at the sacrifice of crazy RPM. More airflow doesnt always mean more RPM, especially with a power adder like a blower. I think that would work beautifully with the -94 series blowers because it would allow you to pulley down and get into the sweet spot of the flow and efficiency map you describe that much faster.

And speed density tuning is done my manifold pressure and RPM. You are more or less dictating the engines volumetric efficiency based on those 2 factors, therefore telling it how much fuel it needs.

 

Perfect sense....and to hell with "curve chart"......

Put that bitch on the the water pump, max the blower out and see if there are any pieces on the floor.

 

..... still waiting for pictures of a crank that yard saled all over the dyno......