Just realized I might've done a stupid thing...

[Cuprum-74]

Well, I might have done a silly stupid thing....

1 year ago I was rebuilding the motor I went ahead and bought a Cam from summit.

It was the Mutha Thumpr Camshsaft.

This is for a roller 1990 LA360, with flat topped pistons. estimated comp. ratio is around 9.6-7 to 1
I have stock 308 swirl port heads that have been milled a little.
with 1.5 Roller rockers.
Roller timing chain.
the bore is still 4.0 inches
(I was lucky and found a low mileage motor)
3.23 rear end. and 2200 stall convertor in an A999 tranny.

Specs for the Mutha' Thumpr: (Grind 291THR7)
Valve lift (std. Rockers) int. .522 Exh. .509
Duration: Int: (.050 in.) int: 235 exh: 249
Duration (Seat to seat): int: 291 exh: 311

*Should've realized then that might be a problem there Bob'

As I am putting the motor together, and putting it in the duster and getting it ready to run during my spring break. I'm staring at my power break system that I installed in the duster.

It dawned on me, I might have put in a cam that will not generate enough vacuum. I should've went with one of my first choices:
Lunati voodoo 20200710 or 20200711


So... My options I think is to ditch the power brake setup and go standard brakes. Or pull apart the motor and put a different cam in...

 

[CUDA69]

Do the brake vendors offer a vacuum pump for this problem?

 

[moper]

If the motor's still being assembled - now's the time. I think you are about 10° too long ont he duration, plus that line of cams is not going to give the best vacuum because you bought it for noise. So the choices IMO are replace it with something else, or ditch the power brakes. I honestly can understand why a muscle car needs power brakes. I don't like them nearly as much as manual for pedal feel and controlled braking. Just me tho...

 

[inkjunkie]

Have power steering? If so, how about hydroboost brakes? They are what is in my diesel pickemup truck...

 

[krazykuda]

You could also try a set of Rhoades variable duration lifters. They bleed down at idle and take out approximately .025" of lift and 15° of duration. They "pump up" by 3500 RPM and give full lift and duration of the cam.

they will increase idle vacuum. smoother idle, better low end and mid range torque and horsepower. I've been using them for over 25 years without any problems.

You will need part # 1068 for the hydraulic roller lifter for your engine.

I installed them on a 284/484 MP cam that would idle choppy at 1100 rpm with 8" vacuum, after installing the rhoades lifters, I was idling much smoother at 800 rpm and 11" vacuum.

rhoades main page:

http://www.rhoadslifters.com/


Part numbers:

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


Read the second article on how they work.

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

 

[Cuda68Scott]

I saw a 340 duster at a car show awhile back that had an electric vacuum booster to make up for his engine shortcomings. He said it did the job.

 

[fishmens67]

2x on the rhoads lifters, they work!

 

[69conv]

Autozone sells a vacuum canister for $70 that might solve your problem. #5201. Just plumb it in and it holds off idle vacuum.

 

[Dezduster]

I removed the power brake system from my 72 340 Duster. I used the mopar performance aluminum master cylinder. No regrets lighter cleaner underhood asthetics and run any cam you want. Engine on off its always the same.

 

[jimmyray]

i removed the power brake system from my 72 340 duster. I used the mopar performance aluminum master cylinder. No regrets lighter cleaner underhood asthetics and run any cam you want. Engine on off its always the same.

x2

 

[duster360]

X3. I bought an adapter kit from summit racing, went to the local parts store and picked up a master cylinder for an 85 dodge diplomat. Works perfect.