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Just Joined and Looking for Helpful Advice

2K views 15 replies 9 participants last post by  AutoGear 
#1 ·
New member here and somewhat a hot rod novice. We own a 57 Bel Air that we cruise and show during the season in Michigan and later this fall in Arizona.

We just repowered the 57 with a 355 in front of a 700R4. Typical for the tri fives and most big body chevys but the 283 was crap and the TH350 trans just cranking too many RPMs on the highway. Have not been on the dyno yet but I think we are somewhere around 350 hp at the flywheel.

Did a disc/drum conversion but the 355 doesn't make enough vacuum to power the set up. Put vacuum pump on and made some improvement. Swapped out the 8" single diaphragm booster for a 9" and made a bit more improvement. May go to an 8" dual diaphragm booster if someone an advise it will do the job.

Planning on heading to the 2015 HR Power Tour in June and will be at the Tri Five Nationals in Bowling Green, KY in August. Sounds like a great summer coming up.
 
#3 ·
Yes, another 57 Bel Air but its a beauty. Considering a '63 Olds Holiday Coupe 2DRHT as a survivor orphan badge just to be different.
We did change the pedal ratio as required by lowering the attachment point as directed by CPP in their conversion kit. I just ordered the 8" dual diaphragm booster and will advise all of results. I am blaming all this on the choice of the cam set up (comp cam XR276HR-10) that resulted in too low Hg at the intake manifold (12" Hg versus a required 18" Hg). Comp's dyno on a similar set up shows the Hg results to be below the need vacuum.
 
#6 ·
are you sure you used the correct master and valve for the disc/drum set up?

im not a fan of vacuum boosters. you can always run a hydroboost, but they can be pricy

im running willwoods with no power assist. stops on the proverbial dime.

a T56 Magnum holds great behind the 383, and lets me cruise on the freeway at low rpms.

 
#8 ·
Swapping the cam this fall

We are going to resolve this issue this fall by swapping out the cam. May do it sooner if we get the time. For the moment the vacuum pump is doing the job but it does vibrate. Will try a vacuum canister in the interim to see if it does the job but the cam swap has to happen. If we were running a stick shift it would be okay but the 700R4 doesn't like the lope the cam produces. It sounds great but not easy to cruise around town.:thumbup:
 
#9 ·
Not sure what the rest of your engine specs are,or'exactly what your looking for powerwise,but,when it comes time for cam swap,we've used the XR264 in a couple of Vortec headed 355's.Only 1 saw a dyno.It made 375 HP & 410 ft/lb torque.Good vacum.It's not your cam tho if you're looking for a lopy idle.
 
#10 ·
Cam specs and planned swap

The cam we have now is the comp Xtreme Energy 276 Hydraulic Roller. Lift is .502/.510 and comp's engine dyno in 356 ci develops 375 hp. Planning to swap out for what my builder originally wanted (Comp talked him into the 276) is the Xtreme Energy 264 Hyd Roller with .487/.495 lift on same set up getting 335 hp. We are running full length headers, 2.5" Pypes exhaust, Weiand Stealth intake and Holley 670 carb and HEI. Comp ration is 9.5:1.
 
#12 · (Edited)
The cam we have now is the comp Xtreme Energy 276 Hydraulic Roller. Lift is .502/.510 and comp's engine dyno in 356 ci develops 375 hp. Planning to swap out for what my builder originally wanted (Comp talked him into the 276) is the Xtreme Energy 264 Hyd Roller with .487/.495 lift on same set up getting 335 hp. We are running full length headers, 2.5" Pypes exhaust, Weiand Stealth intake and Holley 670 carb and HEI. Comp ration is 9.5:1.

. Surprised Comp recommended a bigger cam than expected, they are usually rather conservative and recommend something a tad smaller than what the car owner was hoping for...


. When looking at Comp's dyno results, need to take into account the heads and compression ratio they used for that particular cam test... sometimes the compression ratio is 8-8.5 and the heads just stock Chevy midling-performance heads..


. I don't believe you specified the heads you're using, but with good heads and your 9.5:1 compression ratio I figure the 276 cam to be good for 425-450 HP and the 364 cam for about 400-425 HP... assuming headers and free-flowing dual exhaust system, 4 bbl. carb. and high rise intake manifold...


. An engine produces more vacuum each time when you take your foot off the gas at high RPMs than it does at idle, and a vacuum storage canister can store that higher vacuum for when the vacuum booster brakes need it...
.
 
#11 ·
The best answer instead of swapping all this vacuum stuff, and cams etc is to just go to a junkyard sourced "Hydroboost" system. This is a power steering pump that also supplies the power assist to your brakes. They work SO much better than vacuum brakes, it will get that huge booster off the firewall, and you can keep the cam in your engine.
 
#13 ·
Do you think that people only drive their cars at 3500rpm+? Vac. canisters are great EXCEPT for slow speed stop-and-go driving. Downtown traffic, or a parade? You'll get 2 or 3 good stops before the 'can is depleted. If you have a clutch car; no worries, punch the clutch and clear out the 4bbl. On an automatic; You're MUCH better off for an actual street cruiser car; to not crutch the system. Instead; you should correct the problem. If you deplete the vacuum can; and you need to stop the car in a hurry...its going to get shaky. If I had a wife or kids who were going to drive the car...this is a non-starter.

2 ways to fix the problem:
1. smaller cam. It'll reduce the bragging rights, calm the idle, probably make more power where the car is driven. Its not exactly a joy to do a cam swap with the motor in the car however.
2. keep the ham-fisted cam; get rid of the vacuum gobbledygook and go to an OE style hydraboost. More consistent brake performance, cleaner firewall and OE technology. Order the parts new from Napa and have it done on a Saturday.

I vote option 2; but If I wanted a more tame engine; option 1 would be fine with me and the fellas here can certainly help you with a stout cam so your '57 isn't a *****cat either.
 
#15 ·
Option #3 would be to lose the power brake booster entirely, and go back to manual brakes, with the disc bake upgrade you will stop just the same...all a power booster does is decrease the amount of pedal pressure the driver has to supply, it does nothing to decrease actual stopping distance.

So many people think it helps you stop better....it doesn't, it just makes it so granny's and soccer moms don't need a lot of effort to press the brake pedal.

Getting rid of any booster really cleans up the firewall. ;)
 
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