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Discussion Starter · #1 ·
The question I have is for the guys here that own or have access to a dyno cell.
I am still in the process of dyno testing our 556 BBC and ran into a few snags, one being we seem down about 100 ft/# on power and changes to timing and or fuel curve only yield like +/-20 ft/# of change. It is a Land and Sea dyno and on their tips page they claim the biggest mistake novice dyno owners make is not enough fresh incoming air. They claim that if you can smell the exhaust you are killing you power. Well trust me when I tell you that my eyes water when I am adjusting the barrel valve. Our next step is to build some kind of fresh air system to blow down on the carb/throttle body.
My question is has anyone run into this problem and if so did clean air make that much of a difference?
 

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Although I do not have my own dyno at this time, if you are that fat, you will be down on power. Are the headers equipped with EGT's ?

As far as having fresh air in the dyno room - yes!!!
If your exhaust is not being directed to the outside in some fashion, the air in the room is not only being heated but also diluted.
 

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On our dyno we pump in fresh air directly on top of the carb/carbs from another room. We have a squirrel cage fan in the other room and ducting to the dyno and then some "accordion" type duct about 18" diameter with a pan on the bottom that we can raise/lower to get right on top of the engine, although it is not sealed to the carbs. I have forgot to turn on the "carb" fan on occasion and I have seen upwards of a 30hp drop. We have a pretty well sealed exhaust but you still get some back in the room, you just have to attempt to seal the carb as best you can and give it plenty of fresh air.
 

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When I was working at my last job, we pumped fresh air in just above the motor and had a large exhaust fan that pumped the exhaust out the top of the building.

I've seen similar things to mattson as far as power when you forget to turn the fans on.
 

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Superflow states you must exchange the air in the room 8-10 times a minute. Thats a big fan specially if the room is big.

I have a 800mm 10 blade fan on my dyno cell and it pulls 1/2"H2O pressure drop with the door closed.
 

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Most dyno cells have intake and exhaust ventilation. With the exhaust side pulling slightly harder to keep a negative pressure in the cell. If the cell has good ventilation there should be no need for fresh air plumbed to the intake, unless you need to run with conditioned air.
Also ask when the last time the load cell was calibrated, this should be done monthly.
For a quick check, power up the dyno with the engine not running and you should see 0 ftlbs of torque. If not that would be a good indication that the dyno is out of cal.
 

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Discussion Starter · #7 ·
Thank you all for the feed back. It is what we were thinking and will be revamping the whole dyno cell. Today I am going to MacGyver some sort of fresh air system to blow down on the velocity stack. ( I have a 4’ dia fan to try)
As far as EGT yes we have them and that’s part of the big problem. I didn’t want to weld in any fittings to I drilled/reamed 0.250 dia holes and slid the thermocouples in and held them in place with retainer clips. Problem with that is they are not sealed up. The motor is running VP M5 methanol and when I am adjusting the barrel valve my eyes tear so that will tell you what the air is like. Add that to the fact that the present cell exhaust system is getting tired and leaking. The air the motor is sucking in is way less the clean or fresh. My EGT’s have been low (like about 900 degs).
I will keep you posted on my findings as I plan on not changing my set-up just feeding the motor clean fresh air.
 

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Superflow states you must exchange the air in the room 8-10 times a minute. Thats a big fan specially if the room is big.

I have a 800mm 10 blade fan on my dyno cell and it pulls 1/2"H2O pressure drop with the door closed.

where and what shop are u in melbounre

looking at getting my engine dyno soon-

i am in essendon 3040-

Thanks

Nick--
 

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Discussion Starter · #11 ·
You HAVE to have proper ventilation in the dyno cell. Your air intake should be seperate from the air in the room so that you can keep it controled for repeatability when testing.
Kind of funny, this dyno is 4 years old and mostly has been testing under 500hp motors. I put our methanol drinking 556 BBC on it and all kind of things show up like dirty air, bad water control valve, tired exhaust system. One by one things are getting fixed and corrected. I have a set-up to blow fresh air in from outside so tonight I will not change anything from our last pull besides air quality and see what happens.
Seems everyone agree poor air = poor results.
 

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I think I'd go after the exhaust fan first because blowing air into the throttle body is another way to "trick" yourself unless you are somehow able to coincidentally achieve a net pressure of zero above what the engine wants to breathe in on its own.

10 times per minute is the right target to shoot for with room air changeover.
 

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Kind of funny, this dyno is 4 years old and mostly has been testing under 500hp motors. I put our methanol drinking 556 BBC on it and all kind of things show up like dirty air, bad water control valve, tired exhaust system. One by one things are getting fixed and corrected. I have a set-up to blow fresh air in from outside so tonight I will not change anything from our last pull besides air quality and see what happens.
Seems everyone agree poor air = poor results.
Even on low HP engines if the room is set up that poorly you're not going to have good testing.
 

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Ultimately what it comes down to in the dyno room is consistency and repeatability. We do push (at WOT probably not) clean air to the engine from elsewhere in the building and we also pull outside air through our room by way of a large vent on one end and an exhaust fan on the other end. The reason we don't use outside air to the carb is that it's just not consistent through the day, and yes the dyno does correct for differences in air, but you will end up chasing the tune from morning to afternoon. Differences in air temp/quality throughout the day is just another of the variables that you have to gain control of if you want that consistency and repeatability.
 

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Ultimately what it comes down to in the dyno room is consistency and repeatability. We do push (at WOT probably not) clean air to the engine from elsewhere in the building and we also pull outside air through our room by way of a large vent on one end and an exhaust fan on the other end. The reason we don't use outside air to the carb is that it's just not consistent through the day, and yes the dyno does correct for differences in air, but you will end up chasing the tune from morning to afternoon. Differences in air temp/quality throughout the day is just another of the variables that you have to gain control of if you want that consistency and repeatability.
So why not duct air from a controlled area outside the cell without pushing it in?
 

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Discussion Starter · #16 ·
Well the posts on here and some of my web reseach turned up some great info.
1st What I call dirty air, yesterday I did a MacGyver and built myslef a 3' diameter duct out of plastic that I connected onto a big ass fan. I blew that across the intake and it helped somewhat but with our eyes tearing you can guess that is was not nearly enough.
2nd. According to Stahl headers a dyno cell exhaust system needs to be 8 - 10" diamters. They say 8" will support 400 per tube. We have 5' of 4" dia connected to the header which connects onto 6" dia that has to run straigh up 25' and come out the roof. I didn't put a pressure gage on it but I think it was like 2 huge mufflers.
All that being said I have a good base tune-up for our motor and enough fuel pressure curves so tonight the motor comes off the dyno and tomorrow night it goes in the dragster frame. I will fine tune it from there. This whole dyno experience has been very enlightening.
 

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Well the posts on here and some of my web reseach turned up some great info.
1st What I call dirty air, yesterday I did a MacGyver and built myslef a 3' diameter duct out of plastic that I connected onto a big ass fan. I blew that across the intake and it helped somewhat but with our eyes tearing you can guess that is was not nearly enough.
2nd. According to Stahl headers a dyno cell exhaust system needs to be 8 - 10" diamters. They say 8" will support 400 per tube. We have 5' of 4" dia connected to the header which connects onto 6" dia that has to run straigh up 25' and come out the roof. I didn't put a pressure gage on it but I think it was like 2 huge mufflers.
All that being said I have a good base tune-up for our motor and enough fuel pressure curves so tonight the motor comes off the dyno and tomorrow night it goes in the dragster frame. I will fine tune it from there. This whole dyno experience has been very enlightening.
Sounds like you learned allot Paul. BTW, What kind of peak HP did you get from your alky 556?
 

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So why not duct air from a controlled area outside the cell without pushing it in?

I don't know of anything that says you can't do it that way. The main point I stress is that we test the same every time, and we happen to use a fan in our setup. I'm a fan of "conditioned" air, it is more consistent (at least in Kansas) and it makes my job a little easier.
 

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Discussion Starter · #20 ·
Sounds like you learned allot Paul. BTW, What kind of peak HP did you get from your alky 556?
Learned a lot would be an understatement. Just under 900hp but didn't run the rpm's up to see where peak Hp would be or fall off. My goal was to tune for peak torque first with just the main by-pass pill, then add in the high speed by-pass and tune for peak Hp. With all the issues we ran into we have been going nowhere fast so we decided to pull the motor off and put it in the frame and tune it from there. I have good data for my fuel curve with different size pills and nozzles so I can work it out from there.
Even with the problems and learing curve we went thru it was still pretty sweet to fire it up and do a pull. Now I want to see it boogie down the track.
 
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