vacuum question

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SoulSurvivor

SoulSurvivor

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I built my '70 340 motor 040. over, 915 2.02. heads with three angle valve work, KB 10.2 hypereutectic pistons, Comp Cams XE268 cam, super comp roller rockers, Edelbrock performer RPM intake and Edelbrock 800cfm performer series carburator. The car pulls very hard and I am happy with it's performance.
Why do my power brakes feel like I'm pushing on a brick until the motor is warmed up?
 
Go back to the details info about the cam. Many performance cams will not support power brakes. This is the main reason I'm planning to sell or trade what I've bought for something closer to stock. Decided I'll keep power brakes and cruise control.
 
Throw in a set of Rhoades lifters part # 2018
 
PB's require around 13 - 14 inches minimum of vacuum to function properly. My bet, with that cam, is you're right at the borderline.

I run the HE268 and I have the same issues.

I would put a vacuum gauge on it and tune to the highest reading you can get, I did, and it helped some.

I am doing away with my booster and going manual.
 
Bad Sport said:
PB's require around 13 - 14 inches minimum of vacuum to function properly. My bet, with that cam, is you're right at the borderline.

I run the HE268 and I have the same issues.

I would put a vacuum gauge on it and tune to the highest reading you can get, I did, and it helped some.

I am doing away with my booster and going manual.
Click to expand...

^^^^^^^^ Xs2
 
I bought a vacuum pump and I now have 22 inches of vacuum and my power brakes work like a dream
 
Thanks guys. When I was building the motor and the drive train all the way back to the rear axle I didn't think about the brake booster or the affects of my build.
But your answers pointed me in the right direction. Thanks again.
P.S. I never thought about stopping. Just accelerating. Fast.
 
The problem usually only manifests at first start and idle. Once the car is moving and the engine starts pulling a vacuum,mine works fine. And so long as the check-valve is working there have been no issues.( 292/509Mopar cam). Is your idle timing perhaps lazy?
 
AJ/FormS said:
The problem usually only manifests at first start and idle. Once the car is moving and the engine starts pulling a vacuum,mine works fine. And so long as the check-valve is working there have been no issues.( 292/509Mopar cam). Is your idle timing perhaps lazy?
Click to expand...
Timing is fine if not advanced just a bit for the 1/4 mile. But you described my symptoms. Once the car is moving and the engine is at operating temperature the brakes are fine.
 
krazykuda said:
Throw in a set of Rhoades lifters part # 2018
Click to expand...

How come? The lifters I installed are the ones that came with the cam. And I've heard that comp cam lifters tend to not pump up after while. Or they are bad out of the box.
 
I know you said your timing is fine. But fine is kinda broad. That cam likes quite a bit of idle timing. And the lack of vacuum to the booster is telling me your motor may want more idle timing, or more idle speed, or a combination of the two.
On my combo;
At about 18* idle timing and 900rpm things got better.Eventually, I got the timing and idle down a bit. Eventually I swapped that cam out for a Hughes 223* cam. Never missed that Purple cam. Yeah I lost some top end power, but the torque down low made up for it. Managed a 106mph on street tires.
When that 223*cam dropped two lobes, I put in a Hughes 232* cam. That summer was a bit disappointing,until I got the tune right. I still kinda miss that 223.
As to the Rhoads,They are a specialty lifter.I have never run them, and with the small cams Ive been playing with, never felt the need for them. Check them out if you like. Theyre not for everyone.
 
SoulSurvivor said:
How come? The lifters I installed are the ones that came with the cam. And I've heard that comp cam lifters tend to not pump up after while. Or they are bad out of the box.
Click to expand...


Rhoades pioneered what they call "variable duration" lifters. He puts a groove in them so they bleed down at low RPM and "pump up" by 3500 RPM. They take out about .025" lift and 15° duration at idle and give the full lift and duration of the cam by 3500. They are also anti-pump up. The Rhoades variable duration lifters work better than the others. He patented his groove design which works the best...


Here's their main page:

http://www.rhoadslifters.com/


Part numbers, you want 2018:

http://www.rhoadslifters.com/Pages/PartNumber.html


Here's the page with articles on how they work. The second one is the better one to read.

http://www.rhoadslifters.com/Pages/Articles.html


I've used Rhoades lifters for years. It took me 3 years of looking into them to even try them and now it's all I use. They give better low end torque and horsepower, better fuel economy, without sacrificing the top end. They work with large or small cams and std./high volume- and/or high pressure oil pumps.


I installed a MP .484/284 cam in my 68 340. It barely idled at 1100 RPM at 10-11" vacuum. After installing Rhoades lifters, I had it idling smoother at 800 RPM and 13" vacuum. I'm running a stock 340 with the MP .484/284 cam, stock converter, and 3.91 gear, Holley spread bore Mechanical secondaries and it doesn't bog off the line...

I put them in a 318 with 9.2 compression, stock 340 cam, 360 heads, 4 bbl, dual exhaust and it idled at 22.5" vacuum and got just under 18 MPG highway. I drove it over 300k miles with a set of Rhoades lifters in there.... They last and Rhoades stands behind them.

I got a new one with a pin hole where it didn't machine, back in the 80's. I called Rhoades and described the defect and they sent me one without even asking for the old one back.


They work. Some people don't think that they do, but if you ask people who have used them, they work...


Here's a link to them at Summit Racing:

http://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=rhoades 2018



And this is when it's just starting to smoke 'em. I can roast them all the way to 6500 RPM as long as I want to....

View attachment Barracuda 2.jpg
 
No disrespect to Krazy, But,Yeah, as a streeter, I kinda like all my cam at/from, Right off idle . Even that purple sob.Same reason I use the DP750. I want it. and I want it now.lol. Like I remarked, my cams have all been small ones.Once I got the tune into the combo,they drove nice. I also thought about the Rhoads,briefly, with the 292cam. But in the end, it all came around.Id rather save the money for tires.
 
Do you have a one way check valve in the line that limits the flow of vacuum back to the motor?
My old Corvette has one from the factory, may give it a try before spending $ on a electric vacuum pump.
 
To S
I think I addressed that in post#10. Is it even possible on a Mopar to plumb the booster with a fitting that doesnt have a check valve in it?Ive never seen one. Not saying they dont exist.
 
AJ/FormS said:
No disrespect to Krazy, But,Yeah, as a streeter, I kinda like all my cam at/from, Right off idle . Even that purple sob.Same reason I use the DP750. I want it. and I want it now.lol. Like I remarked, my cams have all been small ones.Once I got the tune into the combo,they drove nice. I also thought about the Rhoads,briefly, with the 292cam. But in the end, it all came around.Id rather save the money for tires.
Click to expand...


None taken.

No disrespect to you, but you have totally missed the point of the Rhoades lifters. THEY GIVE YOU MORE LOW END AND MID RANGE POWER WITHOUT SACRIFICING TOP END. If you use standard lifters, you make LESS torque and horsepower under 3500 RPM.

By giving you more at the low end, you now have more "area under-the-curve" which is the ability of the engine to do work. This is what gets the car down the road...

It's like having an adjustable cam. You get a little smaller for the low end and mid range, then keep the top end. You get to have your cake and eat it too.


There's potential gain for people who recognize it. If you don't buy into it, then don't use them.
 
AJ/FormS said:
To S
I think I addressed that in post#10. Is it even possible on a Mopar to plumb the booster with a fitting that doesnt have a check valve in it?Ive never seen one. Not saying they dont exist.
Click to expand...

Yes you did.
The Chevy one way valve just fits in the vacuum line like a fuel filter, two clamps done.
I think it will fix his problem.
 
To krazy
Yup I understand the science behind the Rhoads perfectly. I run small cams for their streetability. I dont need hp at 6000. I need tq at 2200 to 4000ish. If I cammed my motor for 6000 I would need somewheres around a 250* plus cam, which the Rhoads would bleed down, as you say 15* to 235*, which is a roughly 2 or 3 cam sizes. I just start with the 235*, and call it done. The small 235* cam is plenty for the street, being able to roast the 295s from just off idle to 60 mph. Even the 223* I had was nearly as potent.So,Now if the Rhoads could give me a 223* at idle and a 250* at the other end, well, Im still not interested.
For a guy who spends some significant time at the track, wants to post some dynomite times, and then cruise around on the weekend, I totally get it.
But Im not interested much in that. My car is set up for bombing around,and posturing, and, the occasional blast to the end of the runway. A 235* cam is real good at that.It already has more low end and midrange than the chassis can handle, and I dont need the top end.
And lest you say that my chassis needs upgrading; She goes 93 in the eighth, with a 1.9 60 ft. So yes and no. Its all I want. And at my age I should probably be wanting less soon.
Again Im not trying to argue. I just think theyre not on my must have list
And thanks for explaining it to the OP, and the links.
 
I have the electric pump on my drum brakes, works just like advertised, I may be putting manual disc up front and it will be for sale if you or anyone wants it.
 
You know that little vacuum can on your dist? Hook it up to manifold vacuum and readjust the carb. Ill bet you get 15" at the same idle rpm your at now, unless your trying to idle at like 600rpm or something low like that. Take it out for a test drive and if it pings at light load, you can use a 3/32 allan wrench in the hole where the hose hooks up and give a turn or 2 clockwise to limit the rate of advance. The cam I use in my Classic Cruiser 360 has way more duration that that comp cam, and they pull 17-18" at a 850 idle. You just need to dial the tune in a bit.
 
MRL Performance said:
You know that little vacuum can on your dist? Hook it up to manifold vacuum and readjust the carb. Ill bet you get 15" at the same idle rpm your at now, unless your trying to idle at like 600rpm or something low like that. Take it out for a test drive and if it pings at light load, you can use a 3/32 allan wrench in the hole where the hose hooks up and give a turn or 2 clockwise to limit the rate of advance. The cam I use in my Classic Cruiser 360 has way more duration that that comp cam, and they pull 17-18" at a 850 idle. You just need to dial the tune in a bit.
Click to expand...
It is connected to the carburetor now. I've adjusted the timing and vacuum advance to the point that it doesn't ping. And the idle RPM is at 900. The distributor is one of those MSD pro Billet dists with mechanical and vacuum advance. It was expensive. The brakes work when the engine is cold. Just takes some muscle. But after about 5-10 minutes everything is fine.
 
AJ/FormS said:
To krazy
Yup I understand the science behind the Rhoads perfectly. I run small cams for their streetability. I dont need hp at 6000. I need tq at 2200 to 4000ish. If I cammed my motor for 6000 I would need somewheres around a 250* plus cam, which the Rhoads would bleed down, as you say 15* to 235*, which is a roughly 2 or 3 cam sizes. I just start with the 235*, and call it done. The small 235* cam is plenty for the street, being able to roast the 295s from just off idle to 60 mph. Even the 223* I had was nearly as potent.So,Now if the Rhoads could give me a 223* at idle and a 250* at the other end, well, Im still not interested.
For a guy who spends some significant time at the track, wants to post some dynomite times, and then cruise around on the weekend, I totally get it.
But Im not interested much in that. My car is set up for bombing around,and posturing, and, the occasional blast to the end of the runway. A 235* cam is real good at that.It already has more low end and midrange than the chassis can handle, and I dont need the top end.
And lest you say that my chassis needs upgrading; She goes 93 in the eighth, with a 1.9 60 ft. So yes and no. Its all I want. And at my age I should probably be wanting less soon.
Again Im not trying to argue. I just think theyre not on my must have list
And thanks for explaining it to the OP, and the links.
Click to expand...



You still missed the point, but that's ok.... O:)
 
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