Now this is not my design, but thought that I should share this with some who are building a blown motor and need to put a pop off valve or pressure release valve somewhere in the intake. this is the intake, no provision has been made for a pop off valve. the photos are simple but I think you can see the idea behind it. I decided to use 3/8 bolts so on the side of the intake under the blower mout I drilled two holes and taped them for 3/8 bolts, then drilled some 5/16 and continued up until 3/8 and then filed them out to make an opening. Then I just used a piece of flat 1" wide strap, two 3/8 bolts two springs ( hardware store variety) and glued some rubber to the back of the 1" strap to seal the hole. heres the mocked finished product. I will take a photo of the blower on top, you cant see the valve at all. hope some one can use this. flatoz.
I can not see the pictures as I am at work, but from what you are describing, it is similiar to what I used on my blower set up. It is not really a pop off valve, but is a "sneeze plate". It is in case you get a backfire in the manifold, it will blow this plate off instead of trying to go anywhere else. They work really well when seting up and tuning the motor. It would probably work to relieve excess pressure if the springs were weak enough. I used chevy valve springs on mine and just tightened them until I felt comfortable with them. Several times as I was trying to get the carb dialed in, it backfired and shut the motor down(loss of boost and vacumm) and I started the car right back up after the springs pulled the plate back down and it re-sealed. I have since put 15#'s of boost on the motor and they have never released any boost, but if it backfires, it is sudden enough to blow the plate off.
Hey Corey, I love your tech work, its awesome and practical. I really think though you should do a "putting my blower on a modal A" tech post Danny
goober, I sourced the springs from a machine shop, but hardware store would do, just find a spring that you feel that the tension is not hundreds of pounds. then it really is just a matter of tightening the bolts down until your happy that the intake is just sealed. so any small backfire will have an easier way to escape. I spun mine up pretty high on the weekend without any disasterous results , well sofar... well you know me dan, part agricultural...
Figure the amount of boost you want to run, add 25%, then calculate the area of the pop off. Such as 1.5" in area, 8 lbs of boost + 25% =10 lbs. X 1.5 =15. You will need at least 15 lbs. of spring pressure per end to seal under full boost.
As a preliminary test before fitting to the engine, and you want to test the valve, make some blocking plates to seal the ports (for both the top and bottom of the manifold ). Allow for a fitting on one of the plates (I'd use the top one over the plenum) so that you can use a air supply (with a gauge) to allow you to test the 'blow-off valve'. As mentioned above, if you want to run say 15 PSI boost, allow about 25%, and using a regulator on your air supply, pump about 18-19 psi into the plenum, which should allow you to finetune the spring pressure by simply winding (equally) the two bolts either in or out. When the valve starts to release the air at the desired pressure, your ready ROCK. Trust this assists. Cheers, and BTTT, Drewfus
damn smart. I see alot of people spend money for things instead of spending a little time and thought to come to a solution. keep up the good work.
Hey Drewfus, do you have a photo of the drivers side of the motor to show just how hidden it is? yes mitchell.
If you have a backfire, you can have 45 lbs. instantly. Maybe I should re-phrase, when you have a backfire.
Flatdog, I am running a slant six, 225c.i. motor with that kind of boost. I do not do it all the time as it will lift the head and puke oil out. I only do 15#'s when I am dead serious about outrunning someone. Normally I run between 4-8#'s and do not have any problems.
I have been told that the set up I have will pump out up to 15 lbs boost, I dont have a boost gauge at the moment, I have one on the way from the states. I will probably shit myself when it arrives, but drewfus will vouch for the fact that not having one has let me lean a little harder on it than I probablys should.
It's not going to hurt anything untill you get detonation or start lifting the heads At least that is what I keep telling myself. You can go to Dyers Blower website and they have a good page of blower sizes, motor c.i. and they tell you what kind of boost you can actually get into the motor without a lot of modifications.
Nice to see a six year old post that is still relevant and being used! Just a thought..I would use studs, cross drilled ,with castelated nuts and split pins, as the pressure on the spring is the only thing stopping them winding out, I.e. there is a low torque load on the bolts, they could vibrate loose. same idea as early ford radiators mount bolts and springs.
Hey Ben, I can see what your saying, I just used 3/8 bolts, and no loctite either and 6 years later there hasn't been a problem. I check them every now and then ( maybe 4 times in 6 years) but also think of the standard torque settings for a lot of bolts on a flathead motor, I think the timing cover bolts are 17lbs! and that has the cam on it and the dizzy ( 8BA) spining on it and the vibration of the motor too. but I do like your idea of the studs.
The Jalopy Journal
