Bone's Engine Pull - Part Deux

[1000hpOdyssey]

vacuum problem

Good ideas Roy,
Until someone figures this out, those of us with Roe blowers are going to be maxed out at 700 hp.

 

[Prof]

While I would love to have 700 hp, I can't handle what I have very well.

But I want this blower to not get stalled over something that I know others have faced with other blowers.

I may renew my 30 year old relationship with Don Prudhomme to see who he thinks might be able to address our issue.

 

[Bone]

Bone,
Since you are going to run a larger lower pulley and a smaller upper, you will end up with more boost than I am running. What do you plan to do to decrease the turbulence induced vacuum behind the throttle body? I am thinking about taking Tony's suggestion and trying a splitter in the Roe intake to keep the air from just slamming in the back wall.:dontknow:

First, "turbulence induced vacuum" are you saying you are worried that the air flow will be come turbulent and not stay laminar? I am an Aero Eng by degree and haven't heard that term before. The differential of air pressure by some extent can make a lower pressure area (not necessarily a true vacuum). Is that what you are concerned about? Or are you finding that term next to flux capacitor and pulling my leg? A high Reynolds number is the best indicator for turbulent air flow. Some simple thin fins could keep the air from separating from the boundary layer if needed. Something like this you would have to flow in a chamber. Is this where you are going with the comment. I am just a caveman here, late at night, with a beer, trying to understand.

Second, the I.M. for the Roe is on the pressure side of the Compressor not the vacuum side. Air will be under pressure during boost on that side and not just 'slamming'. Or are you crossing the terms intake and throttle body? Sean already has a baffle plate in the IM, what he uses to make the A/F ratio on all cylinders close to exact.

Did David Weaver find any issues during his test runs?

 

[1000hpOdyssey]

vacuum problem

At 12 lbs of boost Weaver measured 2" of vacuum behind the stock throttle body. Same vacuum with or without the air filter. Changing out the stock tb for the Roe tb decreased the vacuum to 1". The working hypothesis is that the vacuum is being created by turbulent air flow. :dontknow: I don't know. :dontknow: I am just trying to get more hp. Do you think 1" of vacuum behind the tb is a problem? So far, the vacuum issue is the only explanation I have for why my dyno graph goes horizontal at 695 hp. Thank you for sharing so much information and so many pictures in your build threads.

 

[Stagethree]

I may renew my 30 year old relationship with Don Prudhomme to see who he thinks might be able to address our issue.

That will work.

The "Snake" fixing a Viper! :burnout:

 

[Bone]

At 12 lbs of boost Weaver measured 2" of vacuum behind the stock throttle body. Same vacuum with or without the air filter. Changing out the stock tb for the Roe tb decreased the vacuum to 1". The working hypothesis is that the vacuum is being created by turbulent air flow. :dontknow: I don't know. :dontknow: I am just trying to get more hp. Do you think 1" of vacuum behind the tb is a problem? So far, the vacuum issue is the only explanation I have for why my dyno graph goes horizontal at 695 hp. Thank you for sharing so much information and so many pictures in your build threads.

Are you running rich and not getting enough air?
"vacuum to 1"" - 1 inch of water? And where after the TB?

 

[1000hpOdyssey]

vacuum problem

1" of vacuum as measured by the vec map software. It is my understanding that it is 1" measured as a water vacuum measurement. A/F is set at 11.6 - 11.8 at wot. According to the vec graph I received from Weaver it is right on. My wide band A/F shows the same. I hope I am not hijacking your build thread with this discussion. Since you are also building for a higher boost Roe application, you may experience the same flatening of the hp curve at around 700 hp like I did. I do not know for sure why that happened. :dontknow: The rest of my mods (similar to what you are building) should make for more hp. I appreciate your thoughts.

 

[RedSrt007]

There is a large difference between 1" of Vacuum or Hg and 1" of water. I spent over 3 weeks measuring high and low pressure areas on these trucks, and also the car to figure out restrictions in the intake system. If you have 1 Hg of vacuum at the filter, you have too much restriction....especially with a forced induction vehicle.

 

[Bone]

I'm with you guys now, the pressure inside the TB before the charger.
Not necessarily a disturbed airflow in the sense of turbulent airflow.

1" of vacuum as measured by the vec map software. It is my understanding that it is 1" measured as a water vacuum measurement. A/F is set at 11.6 - 11.8 at wot. According to the vec graph I received from Weaver it is right on. My wide band A/F shows the same. I hope I am not hijacking your build thread with this discussion. Since you are also building for a higher boost Roe application, you may experience the same flatening of the hp curve at around 700 hp like I did. I do not know for sure why that happened. :dontknow: The rest of my mods (similar to what you are building) should make for more hp. I appreciate your thoughts.

My curve was still climbing and limited by my RPM limit.

This is an open thread, just about anything (Mikey) is applicable. I'm sure more people are getting good info from it than we know. Learn from my (our) mistakes and profits. If someone asks a question, there are probably 10 more thinking the same thing.

11.8 is perfect.

What belt did you get 93.5 inches, 7 rib? Or did David take an 8 rib and cut a rib off? Did he add any more tensioners than per the Roe Kit? I already have one extra for slippage, non-standard to the Roe Kit.

 

[Prof]

I love getting grease all over my brain! This thread rocks!

Here I thought all of my brain cells had gone up in smoke in the 80's...but now I see some renewed growth up there! Now I will probably go bald!

 

[1000hpOdyssey]

I do not know the length of the new belt. David did the brake in with the 6 rib belt Roe supplied. For final delivery, David used an 8 rib cut down to a 7 rib, but on this past Friday the 8th rib flew off. Maybe damaged when they cut the one rib off. :dontknow: The rest of the belt still looks ok. David is thinking about having a custom 8 rib made to sell with his new DW Special billet lower pulley. No extra tensioner and no slippage that we can seen.

 

[Prof]

I do not know the length of the new belt. David did the brake in with the 6 rib belt Roe supplied. For final delivery, David used an 8 rib cut down to a 7 rib, but on this past Friday the 8th rib flew off. Maybe damaged when they cut the one rib off. :dontknow: The rest of the belt still looks ok. David is thinking about having a custom 8 rib made to sell with his new DW Special billet lower pulley. No extra tensioner and no slippage that we can seen.

So the eight rib would be the same width as the seven rib provided by Roe?

 

[Bone]

So the eight rib would be the same width as the seven rib provided by Roe?

Probably not.
David and I have been looking for a 7 rib belt at a specific length for awhile now. We found 6 and 8 ribs but no 7, unless you custom order it, which is some bucks. Easier to get an 8 rib and cut a rib off at the moment.

 

[1000hpOdyssey]

There is a large difference between 1" of Vacuum or Hg and 1" of water. I spent over 3 weeks measuring high and low pressure areas on these trucks, and also the car to figure out restrictions in the intake system. If you have 1 Hg of vacuum at the filter, you have too much restriction....especially with a forced induction vehicle.

What can we do to fix this. :dontknow: Any ideas?

 

[Prof]

What can we do to fix this. :dontknow: Any ideas?

Could we do a group buy and get 8 rib belts for all of us that will be needing another belt at some point in the future? That might make it affordable for the high boost guys to get three or four and the rest of us pick up a couple of spares...

That would spread the cost and provide a solution to future needs...

Roy

 

[Bone]

Could we do a group buy and get 8 rib belts for all of us that will be needing another belt at some point in the future? That might make it affordable for the high boost guys to get three or four and the rest of us pick up a couple of spares...

That would spread the cost and provide a solution to future needs...

Roy

Roy,

Our (Roe) setup is a 7 rib. Now with a larger crank pulley and/or a smaller charger pulley, it would change the belt length needed. Also, I imagine it will be quite a big order on the belts to make the cost per belt lower. Sean may know better than anyone on this.

David Weaver is making a custom crank pulley for our trucks. It is not out yet in production. John has his first one. Now Sean can grind a smaller SC pulley. So there will be different options in the near future with different belt lengths needed.

It has been fustrating to talk to different belt makers and companies to find a proper belt fit. Just a non-standard size unfortunately in 7 rib.

Dave

 

[1000hpOdyssey]

8 Rib Belts

Great idea Roy. :elefant: I will talk to David Weaver about making an order. Since he is selling the larger lower pulley, he might coordinate a buy with a supplier.

 

[SnakeDoc]

Great idea Roy. :elefant: I will talk to David Weaver about making an order. Since he is selling the larger lower pulley, he might coordinate a buy with a supplier.

Hey John, about to catch my flight back to Texas. I hope Cody gave you a call yesterday. I should be able to call you this afternoon. I got some really good advice while in California that I think will help out situation.

For all that are unclear, I logged the stock map sensor with the VEC to see the vacuum. Here is a screen shot of the log file. This is measured behind the throttle body, before the blower.

I have yet to pull the trigger on producing the larger billet crank pulley till I get the belt situation figured out. I am in contact with Gates to have a custom belt made. I am still waiting to hear back from them. I will keep you posted.

Thanks, David Weaver
www.americanracingtech.com

 

[1000hpOdyssey]

Roe Blower Vacuum Issue

Attached is the VEC graph showing the vacuum that we have been discussing in this thread. Do any of you gear heads, tuners or engineers have any suggestions? :dontknow: Thanks.

 

[Muzzy]

That graph doesn't seem quite right. The problem I see is that you are getting the data from the MAP sensor. I would like to see what the MAP voltage is over the same RPM range. It looks like the MAP signal is being clipped at about 2500 RPM. I am willing to bet the sensor voltage is being pegged at 5V from 2500 RPM and on. Are you using a stock MAP sensor or 2/3 BAR sensor? It would be better to see an actual vacuum/pressure gauge hooked up. What that reading taken when the engine was under load or just revving it while parked?

-Muzzy