Boost Pressure question: what is reasonable boost expectation?

Hoping ITA can answer a nagging issue that I've had over the past few seasons: boost pressure shows pretty high. Very traditional setup: roots blown 526 KB hemi, Veney fuel heads. Blower is a pretty nice Critchley built 14-71 hh superman. 37tooth lower pulley, 30 tooth upper: 1.23 drive ratio for blower. About 9000RPM at top end. Combo was put together 3 years ago, have had this issue since day 1.

Boost numbers show over 50psi during the run (anything above 8400engine RPM gives 50psi or more boost). I have been told that is just not very likely--but cannot figure out what is going on. At first i thought it was an issue with my data collection/calibration--but i've checked the boost sensor on multiple occasions and it has been right on (static pressure test: screw the sensor into a known pressure source and see what the computer reads; done at multiple points between 20psi and 60 psi).

Data snip attached; note the top data bar which shows numeric values at the cursor placement (right at the end of the run).

Boost sensor is screwed into front of manifold next to rupture plate (below top blower pulley).

Passes have been relatively good, 6.50s at 220s. 2650lb door car. Fuel system flowed by Randy Anderson. Passes have been getting faster as I have continued to lean out the system, as would be expected when starting on the rich side.

Anyone out there know of what can be causing a backup of pressure in the intake manifold? Where do I go hunting? I do have a fair amount of data for reference.

 

Maybe double check with an actual boost gauge with "memory".
Meaning that it keeps the pressure in the line till you press the relief button. Just a silly way to double check.

Will Hanna should be chiming in soon

 

Great idea--I've definitely questioned the static test vs. dynamic pressures that occur over a pretty quick 6 seconds. I shall go search for such a gauge.

 

It's basically has a pressure relief button like most superchargers have on the front of them. It is in the line so it keeps the highest pressure the blower made till you let the pressure out. You could make your own pretty easily if you can't find one.

 

Peak boost capture kits are less than $ 150 . Spud Miller at Fuel Injecion Enterprises has the kits

 

Is it possible that you have the configuration in the software off?

 

To rb0804: certainly possible, but the fact that the data in the computer matches actual pressure when I test it makes that not likely.

 

I think if you move the sensor to back of the intake you might solve your mystery.

 

I was afraid that might be the solution. On a door car with setback blower, the back of the intake is in a recess in/below the windshield. Not easy to access, and may have to be plumbed through the firewall.

Is the back of the intake the typical location that everyone is using for their data system sensor?

 

Your cam has effects on boost but the graph definitely shows 56# at a lower RPM 8500 mighty stout boost I am impressed!

 

I see your running a RPM data logger. Have you checked your input for your sensor to make sure it matches? 55lbs at 23 over for even a good billet 14 is questionable. Def agree on putting a tattletale on it.

 

Firstly, I don't know jack about top alcohol stuff. That being said over 50# boost does not seem unreasonable to me. The ram air effect you get at speed coupled with a good inlet/injector/shoe can make these things VERY efficient. Good billet standard helix 14s do that easily and I know good 6s that approach 45+ # at similar rotor speeds. I wouldn't call good boost a nagging problem. If you ever get a chance to dyno it, you may find you're in an elite class. Just my $.02

 

You are correct Mr. Kern you don't know blown alcohol door car. You are an expert at what you do know. He states he has a pretty good Superman with Critchley mods. Not a priceless Chuck Ford.
Veney fuel heads. Which Veney fuel head ( probably done well before 9000 ) Which
Verney intake. Port match ? Which Veney rockers. What stage KB. What cam ?
I see Will posted while I was typing. You have failure to flow somewhere.

 

if someone is willing to buy my pretty good Critchley Superman for a priceless Chuck Ford number--I am absolutely willing to sell!

Heads are definitely old--90s vintage very large chamber (182cc), 2.375int/2.000exh. StageV mag intake, port matched to heads. StageV rockers on red stands. Cam is a pretty "normal" alcohol cam--502/500 lift 296/304 duration. KB StageV block.

I would beleive theold intake/head combo just doesn't want to flow the cfm that the newer blower is pushing. With the KB StageV standard height deck, I think I am VERY limited in alternate head options.

I'd be interested in listening if anyone has advice on where to hunt for more flow. Anyone know of any alternate heads that would "bolt on" to allow more flow?

 

Where to start ? Veney heads take Veney intake manifolds . He used a different angle on intake to heads. Unless someone has cut another intake apart it's not going to work. He changed designs many times. Match proper components.
48 degree cam ? 1 and 6 should be the same.
Timing 33 to 35 ? Rocker ratio. 4.5 inch stroke ? How many side bolts on block ? Bore diameter. That is a big intake valve. It should flow very well if everything is right.
That block will take any fuel head ever made !!