Blow-Off Valve Spring Pressure?

[HarperRacingBangkok]

I am building a Vortec-supercharged 1UZ for my drag race car (see photo) and am nearing completion. I have a question for this experienced group: I have a Tial 50mm blow-off valve (see photo) that has a 14 pound spring in it (intended for a turbo). My understanding of supercharged engines is that this spring is too stiff to allow a good idle rpm. I expect a maximum of 8-10 pounds of boost. I have ordered 3, 4, and 5 pound springs to test. I would appreciate any feed-back and/or advice on the matter of blow-off spring pressure. For a full story, with photos, of my build up, please visit my Racing Projects Blog ( http://drjeffbangkok.squarespace.com/racing-projects-blog/ )

 

[HarperRacingBangkok]

FYI . . . . . you guys weren't much help on this, but the Corvette guys had a great (and technical) discussion on this topic over at Corvette Forum on centrifugal supercharger [Tial] blow-off valve spring pressure: a 3 pound spring recommendation won the argument.

http://forums.corvetteforum.com/c5-forced-induction-nitrous/2264176-tial-50mm-bov-which-spring.html

Doc

 

[HarperRacingBangkok]

I did a search on line and learned a lot about supercharger and turbo boost management, there are some differences. I have ordered the 7 pound spring.

I "finished" the assembly of my 1UZ last night, but didn't start it . . . it was just too late for any of us to be in full command of our senses. We will start it up, and trouble-shoot the inevitable little "issues," tonight. I appreciate all the help and interest I received from this site, even though my car isn't a Lexus. I didn't know where else to go on-line for good reliable info without the BS. You guys have been honest and and I appreciate it. Please feel free to offer a critique of how I have done things.

Here are the pics of the completely assembled Vortech V-9 supercharged 1UZ in my race car.

The complete story of the build-up can be found on my web page: http://drjeffbangkok.squarespace.com...projects-blog/

 

[spf_lexus]

I went thru the EXACT same problem with my procharger. I also use the same 50mm tial that you are using and the solution was a special order 3psi "supercharger" spring. I called direct and they referred me to the 3psi thats not advertised on their site. It pissed me off because their site says "turbo/supercharger applications". I bought every damn spring until I decided to quit messing around. After installing all issues disappeared and throttle response as well as BOV actuation response imporoved. Only downside to the tial is its non-recirculating and you constantly hear a rush of air at part throttle and idle but it sounds absolutely brutal during a 7k decel


with your output you may need a muzzle for it's bark! great project btw