I'm building a 427 BBC for one of my cars. Time to think about what cam for it.
Car specs are :
3300 lbs ( not a chevelle . Sorry)
4 speed manual ( G force 101a ) with 2.75:1 first gear. Mcleod RXT clutch 30 lb flywheel
Currently has 4.10 dana 60 gear set. Might go down to 3.54
29 inch tall rear tire
Engine specs are a little unusual .
New Blueprint Gen VI style 4.25" siamesed block
3.76 Callies Compstar crank one piece seal ( I hate leaks. Hate them )
6.535" Molnar rods
36cc dome racetec pistons for 11:1 compression
AFR 265 heads cnc chamber.
total seal gapless rings
Edelbrock pro flo 4 fuel injection with 60 lbs injectors
4603 Morel lifters
Limited at 7K RPM
As you can see by the little heads this is NOT a max power engine. I'd like to get it close to 600 HP but I'd also like it to get 15 MPG or better. This is a 99% street engine that MIGHT see some drag time but the local track sucks and I dont want to build a car for that purpose. It'll need 7-8 inches of vacuum at idle to get the injection to work right. I'm thinking in the 245-250 range at .050" and mid .600 lift at most on 110's.
What do you think for a cam. Again not max effort but I'd like as much oomph as I can get given the design considerations.
Hydraulic roller. 97.3% street or more but some track time.
That Clay smith cam is a terrible grind. Way too short on the duration unless its a 396 and that 107 LSA ? The lift doesnt take advantage of the AFR heads flow characteristics at all. Thats a lousy cam for 265's. Ive run a few sets of those ver the years and they really like mid .600 lift and 240@050' or better duration. Ive run less and more and they respond pretty well to the 240-250 range.
The engine is going to be built to rap up to 7K as needed. Biggest issue is going to be sufficient idle vacuum to operate the injection junk. That my biggest mystery.
That cam is an EXCELLENT grind if used for what it is intended for. Run very well on engine for a max HP rpm of 6000-6500. If you want it to make peak HP at 7000 rpm it will need more camshaft. You won't need anything above 245 duration at .050" and nothing over .630" lift.
Mike Jones and Chris struab are the cam guys most talk to here. Mike Lewis AKA Wolfplace also can spec you out a cam as well. If looking for off the shelf I have a few I would look at but I don't want to just dump some links you can find your self.
Here's a recommendation, probably a little more stick than you're after, and it's a solid roller, bump that comp up a bit and go E85...........you never know if you don't have a go
Here's a recommendation, probably a little more stick than you're after, and it's a solid roller, bump that comp up a bit and go E85...........you never know if you don't have a go
Unfortunately we dont have E85 here or it would have been built for it.
Its all in the AFR. With the old 496 13:1 AFR cruise I would hit 13 MPG but it wouldnt transition off idle worth a crap so I'd keep it 12.5 to do everything well. The fuel injection will do it automatically and I'd expect 14-15 MPG with a lean cruise. Remember theres 29 inch tires back there. Makes a difference.
You may still have wishful thinking without overdrive.
I have 28 inch tall tires, 3.73s in the back and managed 11.8 I think it was.
I have the proflo 3 XT set up. Running that trip at 14.9afr going 65ish
I have a big cam and a 489 and make about 6 inches of vacuum. It doesn't seem to care and works great
Mike You will be fine with the Pro Flo 4. I run Pro Flo 4 XT and have 8 inches vacuum at idle. Idles fine at 900. Cam is 248 @ 50 and 650 lift solid roller.
recommendation from Crower. Still in the parts gathering stage but this looks a little too high on the duration for enough idle vacuum in a 427 to me.
Howards cams recommendation. Looks a little better.
The AFR 265's have such good exhaust ports in the CNC version I'm not sure how having 6-10 degrees more duration on the exhaust benefits my 427. Most BBC cams being closer to 10 or more. Looks like most of the cam's I'm seeing recommended are cut and paste stock port cams. I think it is easier to recommend a cam if you dont actually look at what the customer has.
Mike, that cam should see 11-12" Hg, although mine is a solid flat tappet ( 243/251, 155/161@.200" so maybe the same intensity) .
I was going to recommend a cam similar to a custom grind I got from a member here 233/236 @/050, which I never ran . The trouble with the AFRs is that most BBC cams are ex duration heavy due to weak ports. Honestly, I'd have Chris or Bullet grind me a custom, in that mid 230's range, setting the lobe centerline where you'd prefer. With mid 230s duration you can get tight, like 108, and still have some Hg at idle. A custom grind is *only* $100-150 more. That's what I would do.
The old Comp 288AR is a great mild solid roller grind, but a bit too much. Good heads dont require "too much" cam, which is why I'm spying 230s for this build. Isky used to have many single pattern cams; I recall reading Ron's piece on why single patterns made more TQ. I'd call Isky, then Straub.
I settled on a Goldilocks grind yesterday. Its a Lunati 20110875. Might be a little bit more than most folks would go but the specs are a little lighter than I was willing to go. To be honest if it holds enough idle vacuum, and I think it will , it should be just about right. I'm the guy who would rather have too much cam than too little but this one looks like its got all the bases I want covered covered. The 11:1 compression and almost too good exhaust port should work well for it.
I think your'e right under 3500. It is a 3500 lb car with 2.75 first gear and a 4.0 rear. It is a 427 and I'd expect a peak of 6500 ish with that cam which is totally reasonable Should rev quick once its in its powerband and keep enough vacuum at idle to run the injection correctly especially with a 30 lb wheel . Might even be able to keep the 60 lb injectors although we'll see.
If you do something quicker, it takes less time. We make power by making cylinder pressure......quicker you can get it in and close the valve the better. The late events will hurt the average power from idle to max....but hey it's hotrodding....it's trial and error. I have used the same math now for 30 years. It's been right for 30 years.
Our L72 Chevelle was pretty tame by comparison. When leaned out and making no power, it could do 15 mpg Imperial. When jetted where it could actually run, it was down to the 11-13 mpg Imperial range. With the bigger engine, mileage will only go down from there. Our 2005 Corvette with 3.42 rear gears and everything else stock with a six speed runs consistently right around 35 mpg Imperial. After a lifetime of big block Chevies, I really am sold on LS power.
The good thing about the pro flo injection system is I can lean it out on the fly from my cell phone. I dont need to make power all the time. Driving to work at 5:30 AM I'm probably not going to get into a early morning grudge race. Coming home maybe I will but the system is moderately adjustable on the fly without having to hook up the laptop. Its not Holley HP adjustable but it still looks pretty good. Ive spent a lot of time talking to the Edelbrock Engineers about how I could use their system with Nitrous and their company line is don't do it. BUT knock the timing back a few degrees and program in 11.5 or richer with a WOT switch and a wet system and the system will handle it. A lot of the cam specs above are from what they recommended given my situation and their equipment.
I can only go so far with gearing. The cam wont like to run the engine under 2K would be my guess. I know my old 496 wouldnt run worth a flip under 2500 with its 254/264@.050" cam. Overdrive was out of the question and most of my driving would never see OD anyway. I dont drive on the highway. I MIGHT go down to 3.54 gearing to make my goal but its going to have a 1:1 ratio coming out of the G Force tranny no matter what.
Well, Here it is. Ended up going with a Richmond SS 5 speed and RXT dual disk for the overdrive. Gen 6+ 427 with AFR 265's, Holley sequential HP injection ( Edelbrock fumbled ) , Callies crank, Mollnar rods 240/245@.050 Lunati juice roller .612" lift 11:1 compression yada yada yada.
Got the injection programmed to my cam profile and I THINK all the settings are spot on. Fires right up and sounds great. I just can't get it out of my driveway over the foot of snow. 8" of vacuum at idle and it purrs at 750 RPM . Dry nitrous injection and I'm putting a PWM Holley Methanol kit on it as soon as it comes in. The HP computer controls all of it.
I was kicking around buying a custom cam for it but I'm running out of time. I might be taking a job in another state soon and I'm in a hurry to be able to get it on the trailer. One of those options if California and I might have to find a pre smog car to transplant everything into if I want to street drive it. Getting tired of these cold winters.
Someone had posted and then removed the post that I needed 18" of vacuum to run on the street . "At least 18 inches" . Ive NEVER had a car that had anything over maybe 13-14 inches of vacuum in 36 years of engine building and even then I usually ended up changing the cam to something more aggressive.
"do you really want your motor to be a low end dog, shaking, stinking, hard to start and not capable of handling a power brake booster."
Look closely at the above picture and keep in mind a few things.
1. I dont have a vacuum brake booster. Whatever experience youve had with vacuum brake boosters does not in any way translate into the world of hydroboost. Imagine a world where the best brakes you can imagine were doubled in efficacy. Thats hydroboost. They dont use vacuum. They use hydraulic fluid from the power steering pump.
2.Low end dog? I'm running AFR 265 ovals with 11:1 compression , sequential fuel injection , a 2.88 first gear and 4.10's out back. It hums along at 14:1 AFR at idle and doesnt shake or stink. The Holley HP system is that good. I fully expect this car to handily run mid 10's or better and still get better than 15 MPG all day.
3. As mentioned its fuel injected. Theres a couple of things you may not be aware of. Say I'm steering and braking hard. Normally with a carburetor that 750 RPM idle speed would make the engine stall under load. With the stepper motor idle control it just lets more air and fuel in to compensate for the load. A/F ratio stays the same , RPM doesnt change etc. Theres no bucking or shaking and certainly no stinking. Now normally all things being equal a carb is going to make a little more power top end from the latent heat of evaporation cooling the intake charge more than point injection is capable of. I'm running water/methanol injection which will do the same thing and with the power and fuel efficiency of fuel injection it will put this over the top as a street engine.
The low 240's for duration isnt a big cam. Medium ish maybe for a 427. Last cam that was in here was a 260/264 grind for a 496 and I'd rate it a little bit more aggressive even considering the cube differences. Ran great on the street. Ive run cams well into the 270's on the street and never had an inkling of issues. Ive also run the low 220's cams everyone said were the ticket and I was miserable. Car wouldnt run better than an 11.5 and it ran out of steam at 5400 . I expect a street duty 427 to peak at 6400 or thereabouts and shift at 6500. The idle quality I could care less about . I still want the house to shake when I fire it up in the garage.
Good thread over on bullet about head selection and George Bryce is on there. To paraphrase George, the better the head moves air the less camshaft you need.
Mine peaked at 6800 and ran right through 7200. near 160 durations @.200" will do that on a small mill. Funny, I think my cam is much stronger, and I pull 11"Hg.
An engine that holds on like that is telling you that it is bound up. When you see an engine hold on for over 300 rpm the the power numbers vary up down or stay the same that is telling you most likely it has an issue in on the exhaust side more than likely. In a solid lifter application, the quick reduction in valve lash on the exhaust will confirm if it is exhaust.
The only case where I have seen that it could be an intake manifold was a dyno test on a GM Crossram on a DZ302. The engine peaked at around 6500 rpm at 450HP and just stayed there till 7500 rpm. No change. Lash change, header change, and a recalibration of dyno yielded the same result. She would not move.
A well tuned combination should run past peak HP while falling off just a little for about 300 rpm then start to fall. The best engines accelerate quickly to peak....the goal is to reach the peak, not hang out there...then shift, allow the rpms to drop to given rpm that the gearing will take advantage of and allow the engine to accelerate back to peak. An engine that is climbing in rpm should be climbing in HP numbers, not staying the same.
An engine that holds on like that is telling you that it is bound up. When you see an engine hold on for over 300 rpm the the power numbers vary up down or stay the same that is telling you most likely it has an issue in on the exhaust side more than likely. In a solid lifter application, the quick reduction in valve lash on the exhaust will confirm if it is exhaust.
The only case where I have seen that it could be an intake manifold was a dyno test on a GM Crossram on a DZ302. The engine peaked at around 6500 rpm at 450HP and just stayed there till 7500 rpm. No change. Lash change, header change, and a recalibration of dyno yielded the same result. She would not move.
A well tuned combination should run past peak HP while falling off just a little for about 300 rpm then start to fall. The best engines accelerate quickly to peak....the goal is to reach the peak, not hang out there...then shift, allow the rpms to drop to given rpm that the gearing will take advantage of and allow the engine to accelerate back to peak. An engine that is climbing in rpm should be climbing in HP numbers, not staying the same.
Chris and Chris - always good information from two different POV's. THNX Gents!
PS My 427 had some damn good head at one point. That my "causality" and I'm sticking to it. Those worked 074 rocked. ( and blew rocker bosses off at the same time which is why they're gone!) Point of fact is it pulled past peak with a weaker Crane Commander CC304, but same great heads.
One reason I ordered a pro built mill this time - I want good heads! The best 781s money can buy in fact. Work well with a baby cam compared to what I've been running.
I watched this thread and never commented. He had his mind set on a big hyd roller with low vacuum, lumpy idle , etc. I didn't run much more cam than the 240/245 on 112LSA that he's running in that 427 in the 540" motor. And yes Gene, that 233/236 .600/.610 CamMotion cam would've been ideal. It is what it is!
As Vince and I found out through trial and error, you swap in bigger and bigger cams and see very little if any gain at the track tells you something. Then you start going smaller and smaller and realize you haven't slowed down.
I'm sure you are referring to the OP not me, but with solid flat tappets and 170/370 springs, no efn way . Which is why I have 20K on this iteration of the 427 and it still shows 205 psi across the board and zilch cam wear. PS, also set rod side clearance on the wide side for same effect. Roller is different I'd guess. With a solid flat tappet that holds RPM to 8000 rpm, it aint about personal preference, its about proper engineering and keeping those lobes well lubed PRINCIPALLY from crank spray. ( + edm oil holes in my case)
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