Quick boost question. Just recently I had my car on the dyno with my new 185 pulley and I was logging around 13 pounds of boost. I picked up about 1 pound of boost which was expected. Now for the part I don't understand. Just recently I went to the track to get some more logging done and I was seeing around 1.5 pounds of boost higher at the track than on the dyno... I was thinking this could have something to do with the load on the dyno vs the track??? Any suggestion would be appreciated. It's nothing really major but I don't feel comfortable running my car hard unless I understand what's going on.

I've just recently heard the little chirping noise coming from the front of my SC which just progressed into a ticking noise. The noise seems to be there only on cold start ups. I'm thinking bearings or clutch assembly.

 

That's what happened to my '04 before I had the clutch pack changed out. I had it changed out, and it's much more quiet now, and no chirping before I get into it.

-Chad

 

I was under the impression that you used a dynojet for the last dyno session? If so, then there wouldn't be any load applied to the car on the dyno. If you used a load-bearing dyno, then you're absolutely right: a difference in load settings/specs could greatly affect the outcome. But having the car produce an additional pound and a half of boost at the track is indeed a little strange I wonder if it was due to the extreme grip from the drag radials during the launch allowing the ECU to apply full power? Or could be that the ECU was holding back on the dyno for some reason - possibly heat and air flow defeciency? Was the +1.5 psi gain maintained consistently throughout the whole run? And did you see the same 1.5 increase in all the runs or only some of the runs?

Sounds like symptoms of clutch assembly.... do you feel a rough/violent supercharger engagement along with the noise or maybe getting worse as the noise gets worse? Also, have you checked the idler pullies? Usually their bearings go out first.

 

Belt / clutch slip is my best guess...

 

When I run my car on a 248 H Dyno Jet , That has only 1-36" fan & 10" Squirrel cage. I see 6.8 PSI at 6400 rpm. On the street I've seen as high as 7.6 - 7.8 psi , At the drags I see 8.3 Psi. Repeatedly. I believe it has to do with the increased air flow to the front of the car. Cheers _PTEngineering

 

Thats what I was thinking. More airflow on he track that cant be replicated on a dyno without a wind tunnel...

Do you feel like the bigger pulley and extra boost was productive or counter-productive for your setup?

 

You mean smaller pulley

 

I was speaking of Alans larger pulley. He increased his pulley size and I was wondering if he felt the increase in pulley size and boost was beneficial over the 180.

 

Oh ok. I was confused since you quoted Pat's post

 

What was your psi like with the 180mm? I used to see it climb up to 15.3 with Dashdaq and it drops to about 13psi. Fluctuating off course. Are these real numbers? Or is it just an approximation? Im thinking you should be higher with a 185mm

 

+1

are your afr's keeping up with the extra boost?

 

The only other factor not mentioned, which can effect your PSI, would be DA.

 

+1 to what everyone else is saying.

The greater airflow, true 100% load, and (likely) better-than-inside-the-shop atmospheric conditions are all contributing factors in your real-world boost numbers being higher than the on-dyno boost numbers. Not surprising, IMHO, and good of you to datalog both environments to see the difference.

 

Heres my guess....I think its based on load, Thats why first gear tends to make 1.0 psi less boost than seconed and I tends to .5-.75 more in 3rd. Most dyno's are not set up to see the same load ithat you would see in 4th that you would see on the road.

 

I know this is Allan's Thread, but to answer Mikey's Question. I'm using a new /old stock Innovate LM-1 and it is difficult to understand the graph, even when I stretch it out on the computer Screen. I got the wideband 02 sensor in the header collector, And at the top of every gear I'm down to 10.6 & 10.8 to 1. I'm hoping Allan will help me, when I get my new Purchase of a Zeitronix. Cheers _PTEngineering

 

Boost will fluctuate from car to car due to modifications and sometimes software.
I've personally seen a 1.5lb drop in boost from major exhaust modifications.

Its not necessarily a bad thing. In some cases it just means your motor is operating more efficiently.

 

Mo, this was done a Dyno Dynamics. The boost increase has been consistent both at the track and street pulls, in Mexico of course.

I'm thinking of going with the ASP group of pulley's but my next stage of mods will cost a little more than expected.... I will need to see how my budget looks once I decide what I'm getting done. Worse case I'll purchase them in next couple of months when the man fund account recuperates.

This could very well be the cause of my boost increase. To be honest I never even considered the extra airflow vs the dyno. I must say though this is the first time I have witnessed the varying boost numbers from the track to the dyno.

It's very hard for me to come to a conclusion right now due to the multiple change done at once - pulley, Meziere, and straight pipe. I will be reversing the pumps very soon and I'll hit the track one last time before my cams go in. As my friend stated, I need to get this IAT situation under control before moving forward.

My boost with the 180 was right around 12.5-13 psi in 3rd gear during the lower RPM's at WOT. Most people don't believe these numbers but a very similar modded car, almost identical, has seen the same numbers.

My guess would be that DA didn't range anymore than 1000.

Real-world numbers are always nice to see but sometimes hard to swallow. I'll be adding a few features to my logging system and once finished it will be amazing. I have always felt logging would be key to both success and safety.

Thanks buddy! Just about a month away !!!!

Once you get your Dashdaq/Zeitronix combo you'll be very impressed. The logging capabilities are endless and they sky's the limit. Thanks again Pat and I'm anxiously awaiting the cams .

Very well said. All cars will not boost the same, mods and other factors will play a major role. Actually the next time out I'll log both through the OBD and direct from the surge tanks to compare numbers, that would be interesting.

 

What are you using to monitor boost on the dyno? OBDII or tapped tank? i've seen some slight variations from the two. Nothing big though..

Belt slippage on the dyno should show up. making the HP graph look a bit all over the place. So if you look at your graph that could either rule in or rule out the belt.

Airflow is my guess.. In my situation, I would put one of the fans up high to try to simulate track or real world airflow. When I did this I seen my boost go up about 1psi and taper off less at redline.

As much as it is important to have good airflow directed at the radiator. I like to keep one of the big fans up near the intake.

I had a funky intake cone filter on my C55. For s&g's I would sometimes pick up the floor fan and hold it right on the cone filter. that put me into the 500whp area.. Never really counted those big numbers though.

It would be cool to have some form a a CFM meter to run on the dyno and then at the track. then check the variations

 

YOU CANNOT DUPLICATE REAL WORLD(CFM) AIR FLOW ON A DYNO NO MATTER HOW MANY FANS YOU ARE USING!!!

The dyno would have to be in a wind tunnel and there are only 2 I believe in the country.

As with hp and tq numbers, all other numbers are skewed due to not having the capability to duplicate REAL WORLD conditions and I don't mean DA! DA is one thing that can be corrected!

 

I use the big dyno. The 1320' of black pavement I use ET Streets to strap it down and my printout is on a slip. All the numbers I need right there. Load and airflow are calibrated 24/7 at a rate of more than a sample per ms

Edit: And yes I live my life a 1/4 mile at a time

 

You fukin kill me Ahmad!

Why are people so interetsed in dyno numbers?

It must be the Kool Aid!

 

So yoyr slips are all just signatures of the people that own the cars whos *** you kick that say they have 900hp! Seriously though, if you dyno 600hp but get smoked by a 400hp Subi......who cares what the dyno numbers are really.

 

The key word was "try". Knowing that my filter setup never got any real air, due to its location. The point was to show that more airflow (more than what was normally seen on the dyno) resulted in the boost to increase. So maybe I worded it a bit strange I think we all know you cant dupe real world CFM with a standard dyno fan setup.

 

Good stuff, Ahmad!! haha....

 

My post was in no way directed at you Mike!

You are an extremely well versed person in the tuning world but the majority of MBWorld members are and about dyno and the numbers they show!