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boost question

6K views 44 replies 14 participants last post by  scott foxwell 
#1 ·
I had my fuel system flowed for 15lbs of boost, I talked to mooneyham, gave them cubic inch, blower size and rpm, they said to overdrive the blower at 35% to make the 15lbs, then I looked at the BDS book and it shows 20% over for 15lbs and then I looked at The Blower Shop book and it says 35% also. So my question is who is closer to being right? I know there are variables and its not exact but I want to be close when it goes on the dyno. what are you guys runnin your blowers at and how much boost?
 
#2 · (Edited)
And some one here is suppose to know what you need without an engine size or a blower size how?? What fuel. Is the blower stripped? 18 strips, or 6 strips.(tips and sides or just tips)
There may be some good info here, but not a one has ever shown me they were worth a shit as a pyschic.
 
#4 ·
BDS is being a little optimistic. I'd go with TBS and Mooneyham. With an open exhaust and a good set of heads, along with a long camshaft your boost will be lower than BDS is showing.

Remember, boost is the RESTICTION to flow. Its the pressure that builds up in the manifold. The better the engine breaths, the more air that it will pass. BDS's numbers are based more on "street" and average marine builds. Short cams and lousy heads, and a restrictive exhaust will show more boost at the same blower on something that can breath.
 
#11 ·
I see it as just volume of air being push in, not a restriction. It is how much air you are putting in to a defined space, closing the valve and then compressing it. That is why all the factors matter. Blower size, striping, pulleys, and RPM define how much are is being pushed in to the manifold. Intake runners, valves and cam events say how the air transfers to the cylinders. Then the bore and stroke define where it is all stored until the intake valve closes and the final compression takes place.

Just how I wrap my brain around it.
 
#17 · (Edited)
Mark, you making the assumtion that the boost is caused by the entire system filling to full boost pressure, and backing up from there. That the only way you can have 50psi in the manifold is to have 50psi in the cylinder first. Bad thinking!
But lets just say for the sake of arguement you're right. That could only happen at 7000 if the cam was open long enough. If is takes X time to COMPLETELY fill the cylinder at 50psi at 3500, you now have 1/2 that much time at 7000. AT 8000?

Look at wizbangs post about valve size as ooposed port size. Its really the entire system. Huge valve and small port, huge port small valve, it still comes down to TIME! Like Info said, you can always open the valve longer. It really doesn't help to open it further if the valve diameter is the limiter. Once the curtain maxes out, its done.

CFM is right. The BAE will produce much lower boost levels at the same blower speed, and make considerably more power than the very same setup on a stock 454. Using your BOOST theory, the 454 with 50 psi should kick ass on the BAE at 35psi. Same blower, same speed. Never happen
The BAE has the fuel/air in the cylinders, the 454's is backed up in the manifold.
The cylinder pressure on the BAE might be fairly close to the manifold pressure when the intake valve closed. The 454's isn't even close.



 
#22 · (Edited)
The BAE will produce much lower boost levels at the same blower speed, and make considerably more power than the very same setup on a stock 454. Using your BOOST theory, the 454 with 50 psi should kick ass on the BAE at 35psi. Same blower, same speed. Never happen
The BAE has the fuel/air in the cylinders, the 454's is backed up in the manifold.
The cylinder pressure on the BAE might be fairly close to the manifold pressure when the intake valve closed. The 454's isn't even close.
Exactly. Another good extreme example in the opposite direction:

Put a baby Weaind 174 on a Suburban 454 and it's easy to make 5psi boost.

Put the same Weiand 174 (edit in: with same rotor speed..or double it I don't care...lol)) on the BAE and let me know how much boost you can make at full song.

In fact, the 174 on the BAE will cut hp vs the BAE N/A because the BAE will move more air on it's own than a 174 will. So throw out the 174 with the BAE, but keep it on the Burban. Who's still making more power by using more air ? The Burban at say 90% VE vs the BAE at say 120% ?

Edit in: Quick summary question: So 454 Burban with 5psi. BAE with 0 PSI. Who's making more power ?

Last note for now, I'd rather talk VE vs compressed air volume.

Looking at VE% speaks volumes....no pun intended. LOL.
 
#32 ·
Hass we ahve kick this topic up and down the block so much it has almost become comical.
I stopped looking at A/A motors as having different air flow requirements than N/A motors long ago. It takes some work to make a N/A engine 100% V.E. and even more to make it 100+%. Its NO DIFFERENT with the A/A engine, IF you look at the enigne as just operating in a higher than 14.7 psia world. The N/A guys are trying to accomplish atmospheric pressure in the cylinder by the time the intake closes. Maybe even a little more.

Do you really believe you can accomplish 100% manifold pressure in the cylinder by the time the intake closes, at 7000 rpm on a 540cid using 366 peanut port truck heads and the stock 366 truck cam.

It may seem extreme to you, but if it requires extreme to get the point across, thats what it takes.
You think Brad Anderson and Alan Johnson sell heads because they are shiney? Or light. You think they could make 8000 HP with stock 392 hemi heads?

Maybe if you did have a freek'n knob you would look at the whole deal differently. The knob is exactly what Sleeper says it is. A crutch!
I guess if you have the knob it allows you to check you brain along with your hat. All you need to do is have a strong wrist.



 
#34 · (Edited)
Now Bob, lol, I never mentioned peanut port heads, knobs, crutches or any of that. And believe it or not, Turbocharging isnt an easy way to anything except emptying your wallet and burning up a bunch of parts & cash if someone was as brainless as you seem to insinuate.
As for the BA or AJ heads, and even the mention of the peanut port heads(which nobody but you have suggested) The only thing that was ever claimed is that you CAN make more power than any of us need in a jetboat with an out of the box set of decent heads, and a relatively small cam. The BA & AJ are also designed to move huge amounts of nitro -alky in the intake tract. How big are those ports when they are over half filled with a liquid fuel that wont compress?
BUT, back to the topic at hand, with a piston traveling down the bore and 20-30psi in the intake tract I believe that it does a better job of filling the chamber than what you would lead most to believe. Does it ever reach EXACTLY what is in the intake ? Even with a wildly ported set of heads? Doubtful, but I would bet that its close.
This is were I wish that I had way more time & $$ on my hands as I would love to build an engine around the idea of putting a set of Peanut port heads(since you brought it up) on a turbocharged engine and show you just what actually could be done with the proper planning & building around them , I think youd be amazed. But maybe not.LOL
 
#35 ·
Airflow wise: Peak torque occurs at the RPM the cylinders are filled the best. As RPM's increase torque drops off due to less time to fill the cylinders. HP numbers increases with RPM's due to the increased number of power strokes per minute and offsets complete cylinder filling. You eventually top out on HP when it quits breathing.

Torque numbers are lower if you rob some of it to turn a blower etc. One thing that fascinates me with turbos is the torque climbing with the HP.
 
#36 ·
Other than their TF heads, I can tell you that every head AJ designs isn't just "put the biggest port/valve in it and go". Ports and valves are application specific, just like everything else. It just so happens that when you're making 4000hp they need to be big but rest assured, they're a specific size. The other side of the coin that is always interesting to me is, look at the relative ex. valve size for the amount of HP they generate. Not very big, is it.:)bulb
 
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