Looking for constuctive feedback on this combo for healthy street duty. BBC 427 +.030, TRW 9.5-1, Edelbrock RPM Air Gap, 3310 750cfm rebuilt by DaVinci, Hedman headers w/1.75x3", Flowmaster 2.5", Proform HEI distributor, Heads are cast iron(number unknown but were original closed chamber PASS heads that have been pocket ported with 2.19/1.88), roller rockers, cam is Comp Cam XE242H 232/236 @.050 and .515/520, TH400 with Hughes 2500 stall and 3.73 gears. Looking for decent vacuum for brakes. Thoughts?

That is a decent sounding street engine but it will be a bit short on vacumn. I estimate 13 inches at best so you will need a vacumn cannister for sure. I went with a hydroboost system that runs off the power steering instead.

What do you feel is the minimum required for the brakes?

For one stop very little( the booster holds alot with the one way check valve on the outside of it)but for stop and go traffic you need good strong vacumn. I suppose 13 would be cutting it close. You would hate to pull away from a light and need to panic stop and nothing there. I believe guys should put as much thought into braking systems as they do engines. A vacumn pump woud be the way to go ( I dont know much about canisters) and probably not too expensive either. Good luck Paul.

Paul,
Are those vacuum pumps electrically operated?

Thgat is a decent sounding street engine but it will be a bit short on vacumn. I estimate 13 inches at best so you will need a vacumn cannister for sure. I went with a hydroboost system that runs off the power steering instead.
i don't agree at all with this. i've not had an engine that has produced more than 12 inches and i've never had a problem with power brakes. i get about 10.5 inches of vacuum with my current 406 and have not had an issue with power brakes at all. no cannister either. 230/236 is nothing for a 427, imo. i'd go bigger if it were me. :)
i would call that combo a fairly "MILD" combo, not a "HEALTHY" one. it will have daily driver type street manners though, if that is what you are looking for.

Of course it's one of those things many of us could argue until the cows come home, but all other things being equal, open chamber heads and mild pop up pistons to arrive at about the same compression will give you noticeably more flow and the ability to more effectively do more cam in the future. This closed-chamber-caused limitation is made worse since the lift on your cam is relatively mild.

Closed chamber heads with larger valves have trouble pushing the flow between the head of the valve and walls of the combustion chamber. At the very least, I hope that when the larger valves and porting was done that relief cuts in the combustion chamber were also made to make those larger valves worth the trouble. If not, adding the larger valves and porting may not provide all the benefit they could/should.

71malibu406 - You do not drive across the Narrows bridge in stop and go traffic either! :p

Follow the links to my ride........ 13 inches at idle was not enough for where and what I drive.

Ive seen some electric ones on ebay and jeggs, I believe there are some mechanical ones out there to that look like a fuel pump and run off the cam lobe (I know chevy used them on there 3.8 liter celebrity), that is if you have an electric fuel pump.

Will have to look the cam up, but that said, I have pretty much the exact same motor with a few less cubes. You will have 431CI, mine is 408CI, 23 CI should net 23 HP and another 30 FTLBS of torque. Back to the brakes issue. Running a Comp NX279HR hyd roller, 279/294, 230/242,. 537/.541, on 113LSA. Same CR, mine may be a little higher (9.7/1). I get 165PSI cranking compression and pull 13" vacuum. No issues at all with my brakes. Last cam I had in the car was a flat tappet hyd 286/296 on 112LSA. Motor had a lot more lopey idle and only about 11.5 -12" vac. No issues with the brakes with that cam also, of course I never used it in daily stop and go driving either, but still no apparent problems.

Way back in the '40's and '50's, cars had fuel/vacuum pumps made in one piece so that the windshield wipers would work better than intake manifold sucked vacuum wipers.

Tall buggers with a bunch of hoses attached to it!!

pdq67

I road in a Ford wagon that had those vacuum wipers at speed that weren't worth crap. They'd slow down due to the lack of vacuum.....Dangerous things.

I have a similar combo, I'm running a Crane H284 cam and I have no problems with vacuum.

Edd,looks like you have a nice streetable combo that would have a lot of low-mid range torque and upper rpm grunt to approx 5600-5800 rpms in a 427 with good breathing intake & exhaust. Not that i am any expert but i would think your 427 setup would put out at least 400-425hp & 430-440 lbs torque and with 373 gear & auto should be a blast to drive.

I would not worry about your power brakes as i was running 228 deg dur @ .05 on a 112deg L/S in a 396 that had 12-12.5 inches vac @ idle. The power brakes in my 69 chevelle were fine feeling 85-90% as good @ idle as with my stock 396 with the whimpy 325hp cam had with 18 inc vac @ idle.

Your running only 4 more deg int dur @ .05 (which isnt much more )in a motor with 30 more cubes so i would bet your idle vacuum would be a little better in the 13-15 inches vac @ idle range so dont sweat it.

But you do have to make sure to crank in plenty of initial timing like 16-18 deg btdc with the vac advance unhooked @ plugged with idle set low while setting the intial timing with that cam.

This is important because these aftermarket perf cams need a lot more initial timing than the stock gm cams do which is a fact that seems to be overlooked at times and people chase their tales with tunning issues because of this. If you run too retarded with intial advance the motor will run very luggy/lazy with low idle vacuum,loss of power,run hotter,waste fuel,etc so keep this in mind crank in plenty or intial timing as mentioned above.

An after thought is watch out for your cylender pressure getting too high with that fairly short dur in a 427. Yes your comp is supposed to be approx 9:5 but mine was supposed to 9:6 with new pistons but after decking the heads/block it can increase closer to 9:8-10:1 which is what happened to me.

I am running a new cam with a little less int dur @ .05 since recent rebuild with 222 deg deg dur @.05 in my now 402(.030 over 396). Unfortunately the cranking comp went from 170 with the old 228 deg dur cam to 220+ psi with the new 222 int dur cam which now put me in detonations realm when i get on it. It doesnt detonate while crusing but i will have to retune/retard my intial/total timing to stop it which will very likely result in lost power/perf or i will have to run octain booster with every tank of fuel to keep my perf. Later I had wished i stayed with the prior cam int dur specs but it was too late then and i dont want to go throught the hastle of a cam change. The motor does run great with the new cam and has plenty of umph but its the detonation and having to loose power by retarding the timing to stop the ping @ full throttle or to dump an additional $6-8 in every tank full on top of the $3.15 per gal i am already paying that's the problem with the new cam i am currently running.

So with that said consult with cam mfg to ensure this will not happen to you with that cam thats only 4 deg more dur than my is which could be a detonation issue. If it were me i would run at least 236-245 deg int dur @ .05 with 427 cubes becasue it will still be very streetable,make more power but will bleed off a little more cyl pressure too to help avoid detonation issues that may crop up with your 232 deg int dur @ .05 cam in a 427 that could build a fair amt of cyl pressure so make sure your est 9:5 comp is really going to be 9:5 after all machining work was done.

Get in touch with Harold @ Lunati cams for good advice .

Scott

Still confused on what cam you have, is this the XE268H, 224/230, .515/.520 on 110 LSA? This cam will work power brakes just fine. If you are really concerned, step to a Marine Cam, these are often set up with 112LSA (or wider) to decrease overlap slightly. Engine vac will be higher. My NX279HR has a 113LSA and still has a very healthy sounding idle quality. If my cam was ground on a 110LSA, it would be far too radical due to overlap.

I have finished building an extremely similar combo except mine is .060 over. Same carb, 215 (closed chamber) heads with 2.19/1.88 valves, the valves were unshrouded as mentioned above, roller rockers for what thats worth, 1.75 inch dynomax headers, 2 3/4 full length exhaust, flowmaster 40 series mufflers (they came on the car), and an UD 272/282 solid flat tappet. This is in front of a 3000 stall th350 with a 3.55 gear posi 12 bolt. It should run fine :)

Daniel

Comp Cams part # 11-242-3, I think is the one. The specs of 224/230, .515/520 are correct. This will almost be a daily driver but only on weekends. I realize that by todays standards that this is considered mild but was just looking to have some fun in a 69 Chevelle that I have had since new. Thanks to everyone for great responses. I have really learned a lot from this Tech Forum. Thanks again.

ED,that will be a nice cam for your motor with plenty of umph and very streetable.

I am going to send you some cam install info i put togther in case you could get something usefull from it considering all the wiped out new cams we have seen on this site. Let me know if you get it and if you find it at all usefull.

scott

Electric vacuum pumps are NOISY. I like the hydroboost option better.

i would also add that the extreme energy cams are very noisy. the magnum line up is much quieter. that cam will be very responsive. we put one in my dad's 427 this year. power is great, noise not so great. my dad always says we need to run the valves one more time.tom