74Dusted
Stock Piler of 340's
Jack is right, at an idle a 6-71 Blown 340 should be and normally has about 12" of vacuum (Intake/"Pressure" side of the system).
Crack the throttle open and it instantly moves from Vacuum to Boost.
Strange problem with 6-71
- Thread starter Coyote Jack
- Start date
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Jack is right, at an idle a 6-71 Blown 340 should be and normally has about 12" of vacuum (Intake/"Pressure" side of the system).
Crack the throttle open and it instantly moves from Vacuum to Boost.
funwithfuel
Well-Known Member
So, how did things shake out. What did ya find?
Valvebounce
Well-Known Member
The blower can't make boost at idle, because the throttle blades are closed. So it cant get any air to pump into boost. Open the blades up, and that huffer starts puffing.
I run a 1400cc per rev toyota blower on a 1500cc in line 4 pushrod motor.(all non mopar obviously) The instant the pedal hits the floor, the needle hits 11psi. Everytime.
Does seem strange.
It can only be a leak on the discharge side of the blower. (Or a faulty gauge?) If the leak was on the intake side of the pump. it would try to make boost at idle. and it wold run like sh1t as there would be a lean condition. Actually it would be lean all over.
But if it's leaking on the discharge side of the pump, that charge must be leaking somewhere? And if it is, it's explosive! Even if it's the pop off valve, what's leaking out will want to explode at the nearest hint of a spark.
the only other thing would be a problem with the blower itself. Is the new pulley properly keyed onto the main shaft of the supercharger?
If not, the pulley might be going around, but the blower aint. Hook the carbs off, unhook the coil, and get a mate to crank the engine over while you look down the top. See if the rotors are turning?
Blowers rule. The torque never fails to make me smile.
Horsepower sells cars.
Torque wins races!
I run a 1400cc per rev toyota blower on a 1500cc in line 4 pushrod motor.(all non mopar obviously) The instant the pedal hits the floor, the needle hits 11psi. Everytime.
Does seem strange.
It can only be a leak on the discharge side of the blower. (Or a faulty gauge?) If the leak was on the intake side of the pump. it would try to make boost at idle. and it wold run like sh1t as there would be a lean condition. Actually it would be lean all over.
But if it's leaking on the discharge side of the pump, that charge must be leaking somewhere? And if it is, it's explosive! Even if it's the pop off valve, what's leaking out will want to explode at the nearest hint of a spark.
the only other thing would be a problem with the blower itself. Is the new pulley properly keyed onto the main shaft of the supercharger?
If not, the pulley might be going around, but the blower aint. Hook the carbs off, unhook the coil, and get a mate to crank the engine over while you look down the top. See if the rotors are turning?
Blowers rule. The torque never fails to make me smile.
Horsepower sells cars.
Torque wins races!
Valvebounce nailed it. It is an intermitant problem with the gauge Sometimes the vac and boost are there and sometimes not. I did find one very minor leak around a fitting though. I took the car to the Atlantic Nats in Moncton this weekend and other than blowing a voltage regulator things were great. Thanks guys, it is always better to get a bunch of ideas.
Jack
Jack
leblanc
member 2883
You made it back with no problems? Great to hear.
Cool. Glad you figured it out. Now quit crappin around and post a burnout video.
67Dart273
Well-Known Member
I could SWEAR you said "it runs like it has no boost"
Sounded to me like a lot more than a "gauge" problem
Mad Dart
Nothing to see Here!
Yup if the Boost Gauge don't work you will instantly loose the affect of moving the ground quicker! Funny how our brains work. Haaa
Just playing around Jack!
Valvebounce
Well-Known Member
Yeah that was the bit that made me think it was fault with some part of the blower set up too.
I ended up taking my boost gauge off and not bothering to refit it. It never changed, and was just another distraction tbh.
I ended up taking my boost gauge off and not bothering to refit it. It never changed, and was just another distraction tbh.
Yup, you did see me type that. I'll swear the gremlins were having fun with the car. I had a spark plug wire off at the cap so I was down to 7 cylinders. That robbed me of some HP right there. However the plug wire came off must have effected the timing as well as it was at 22 degrees instead of the 28 I was running before. Minor little problems add up to big HP loses and that is why it felt like there was no boost. The gauge was my clue something was wrong. So after checking everything I could think of the performance is back to where it should be and the gauge is still bad. Time for a new one. There was one other problem I found that was stopping the car off and on this weekend but had nothing to do with boost. It had me scratching my head. It ended up being a loose wire at the battery terminal. Just a bunch of little stuff that happened over the long winter we had and that I didn't know about before now because I have been so busy and not able to drive the car.
Jack
Mad Dart
Nothing to see Here!
A bunch of little things will add up for sure. Glad it is fixed and an easy fix at that!
funwithfuel
Well-Known Member
that's what I love about this site I never get an opportunity to stop learning
I'm glad to see that you got your car running the way you want and fix all your small problems that added up to a one larger oneand I got an opportunity to learn how superchargers work on cars vs diesels
This is not an all out race application. The car will probably never see the track. So taking that into account I figured 1500 cfm was a little much. It was running rich with the 750's and is a little lean with the 600's. I am going to up the jets to compensate. Running down the road a little lean is o.k., a little lean at w.o.t. is not, so the change in the jets.
Jack
Jack
bOb shingler
Well-Known Member
you might have killed the strips with the smaller carbs by leaning it out. why did you do that anyway?
Are you running power valves or are they blocked and just jetting?
Power Valves, Yes.
I am going to look at the strips this winter Bob. Just to make sure they are o.k. I do have boost now.
Jack
I am going to look at the strips this winter Bob. Just to make sure they are o.k. I do have boost now.
Jack
Do you have them boost refed? have you ever put a vacuum gauge on the base plate of the carbs to see how much vac your blower is pulling? I had a one with teflon strips and it pulled a ton of vac at idle and went up from there, I ended up plugging the power valves and jetted up, when you get to drive it get a long piece of vac hose and hook up a gauge and drive it to figure out where your vacuum map is and if you can use pv's. Just my two cents for what it is worth.
As I posted above, I do have power valves and the carbs are boost referenced. They were blower carbs from the factory. I like your idea of running a hose to my handheld vac gauge to look at while driving. It's a great way to check the mounted boost gauge I have.
Jack
What I have done is have someone ride along with you and record the vac readings at different times, like cruise and when you get on it then you can tailor your pv's to come in when you want, kinda like a fuel switch. I also mapped the vac readings thru out the rpm range, I like to have alot of data for some reason. And see where your boost is during the drive, too bad it is winter...
Yup, not a whole lot I can do until spring. I will be working on other parts of the car though. A few little gremlins to find.
Jack
Jack
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