I am building a 427 that is 30 over. It will have Edelbrock heads 100 or 110cc oval , performer intake, M21 transmission and 3.55 rear. It will be a performance street car. Hoping to get as much Hp and torque possible with a rough, but idle under 1000 rpms. I have received a wide range of cam durations from different sources, 206/212 , 232/232, 236/ 242. I have heard not to over cam the engine, but I don't know what that would be for a big block. Second I read the Edelbrock heads flow 290 cfm intake but, only 110 cfm exhaust. Is this true? If so a greater exhaust duration may be best. Thanks for any information.

 

Suggest a car forum is a lousy source to get reliable and specific cam recommendations. Call a legit cam maker and tell them exactly what you have and what's planned & expected. The smaller, less-known cam grinders can be more personable. Most offer a tech sheet for customer to complete; good for grinder as well as you.

Mike Jones (owner-operator)
Jones Cam Designs
Denver NC
(704) 489-2449

Charles Reichard (owner-operator)
Camcraft Cams
Canton NC
(828) 681-5183

*what seems to you an apparent disparity between intake & exhaust flow rates is truly quite typical; don't sweat that one.

 

Those 100cc heads are great for getting some more compression.

What pistons are you using? I believe those heads have 2.19 intake valves...so you have to be aware of piston to valve clearance on the 10.25 ratio style pistons as they were designed for 2.06 valves. The larger valves can get into "radial" clearance issues with more aggressive cams. The forged 11.0 pistons used in 425HP versions had larger valve pockets to handle the larger valves.

Are you planning to use a hyd roller or a flat tappet (either solid or hyd)?

Your trans and rear gear makes for a "long geared" combo...so getting it rolling out of the hole is going to be a little tougher...but once rolling it will be good.

How high are you planning to rev it? What are you comfortable with? Those heads will pull strong on a 427 easily to 6500+...so you could plan power to max out in the 6000 RPM range and still have a comfortable cruiser.

Will it have headers? What carb and intake?

Not sure which ones you're looking at but Edelbrock shows the 60499 head flows 299/210 @.600" lift...so you're at around 70% ex to intake flow. It will like some added duration on exhaust side.

Tell us some more and we can help.

JIM

 

Here's my $0.02. I wouldn't ask anyone including camshaft manufacturers for a recommendation. It's too subjective. What I've done is to buy and download Desktop Dyno and plug in the numbers. Don't just look at peak horsepower but the average horsepower in your RPM range. I based this on RPM drop between shifts. Also the horsepower at 1000 RPM's is important too for a steet car to have good driveability. One of my cars makes about 63HP@1000RPM's with a start up ratio of 9.5 and the other is about 55HP@1000RPM's with the startup ratio of 10.7. While Desktop Dyno is not an absolute, it's a good tool. Also YouTube has videos of cars idling which you can get an idea from also. I'll start you off at one at the bottom. For some reason it's one of my favorites, LOL.

 

I totally agree with Fly skids up on a couple of his points there! Time spent on Desktop Dyno is well spent and you can learn a lot from it. Hours and hours of time were spent on my parts before buying started. The newer Desktop Dyno also has a bigger library of cylinder heads and cams shafts to pull from. I love playing with this software as you can frequently find horsepower.

We have a 1968 Corvette 4 speed with a 427 that started life with solid lifters. I went and copied the L88 engine design and built a clone of one. The engine we built is a standard bore 427 with 12.25-1 compression ratio on using a cast iron cylinder head (GM part #: 3931063) that matches the pistons. People like to remind me that Chevrolet claimed it was 12.5-1 compression but if you run the numbers it was 12.25-1 and GM exaggerated a bit and rounded it up to 12.5-1 versus the sound of 12.25-1.

After speaking with Comp Cams and a couple others I soon became disappointed. My car has a 3.36 rear axle ratio which is fine with the torque that a tweaked big block can make. The problem was that Comp Cams would not make suggestions unless I agreed to change the rear end ratio to a 3.70 or the dreaded 4.11's. I had to have my engine builder call them and order the cam that I wanted. I am using a Comp Cams CB 275 Dual Energy with a set of 1.7 double roller rocker arms on top. After using play dough on all 8 cylinders we learned that I still had lots of room between pistons and cylinder heads, almost .125". I can drive this car year round with High octane fuel, I am not buying racing fuel, I can retard the ignition on the fly to accommodate the fuel quality.

I don' think the guys at Comp Cams are helping us fairly on this one. A BB with this cam can be a beast and it is totally different in a SB engine. With my 3.36 rear end I am able to spin the tires more than halfway down the track (Literally) and still get a nice E.T.. What good would a 4.11 do in my situation? I outran several highly collectible Corvettes with their 4.11 rears and fancy engines. The software says I should be in the mid 10's in the quarter mile with 3200 pounds. I have been using a device called a GTECH Pro and it shows me doing 0-60 mph in less than 4 seconds, it pulls hard while running wide open and easily goes into the triple digit speeds on the highways.

The cam I got works very nicely in my engine package. The car can scream and it scares the heck out of passengers not used to brutal acceleration. I can lug the car by cruising along in 4th gear at 25-30 mph and speed right up to highway speeds without shifting. It goes (Much) faster however with a good downshift. With my 3.36 rear end I got to wave, as buddies pulled off for fuel on the trips we took. With a high compression 427 engine I think the 3.36 is very near the right way to go. This engine is happy just chugging along or doing 1/4 mile runs and has way more power than I could ever use without hurting someone. On a day trip the fuel consumption becomes apparent as the guys with the 4.11 rears started seeking gas on our way home. I went another 50 miles to my home and still had a quarter of a tank left with a BB. The BB makes the C3 a real power house and one fast car.

The Cam I am using is not "HUGE" or anything unusual, I had an engine expert suggests that it was a tad smaller than he would have chosen. When we built this engine it seemed that there was a lot of guessing, CC was not comfortable selling this cam to someone without a race oriented 4.11 rear in their car.

The recipe for "Fun with a 427" is: Lots of Compression, Good heads, Forged bottom end and a healthy camshaft all served on a Four Bolt Block.

 

Cam selection is one of the most important decisions you’ll make when building a performance engine.
Bigger isn’t always better unless you’re building a full time race car reving the engine to high rpm.
If you plan building a quick cruiser then a smaller cam may be the better choice.
Your use of the car and driving style comes into play when your building a street car, especially with a big block.
Check the cam specs to see what the cams rpm range is to see where it builds power.
For example, the cam in my 496 comes on at about 1500 rpm and builds power up to 6000 rpm.
Peak torque on my engine is at 4900 and peak hp is at 5900.
I built the engine for low and mid range torque because it will be used primarily on the street as a cruiser.
Just remember to make everything work together for your use of the car, the camshaft choice is especially important.
A cam that produces tq/hp at a higher rpm range can make your engine and car a real dog at the lower rpm range which could be extremely disappointing on a street driven car.
One other thing to consider is how the cam effects the engine vacuum at idle.
Some cams will cut the vacuum down to levels that will affect the power brakes and you may need to install a vacuum pump.

 

You might want to look into Straub Tech cams. I put one of his AFR head cams that is a 229/229 at 50 in my big block. The car has over 20" of vacuum at idle and the rpm is around 750-800 at idle. The car made 572 hp and 604 tq on the engine dyno, where I broke it in and tuned it up.

 

Another vote for contacting Chris straub at Straub Technologies. Chris is fantastic at designing a cam just for your motor. I have a straub cam in my 496bb and couldn’t be happier.

 

Just to answer a few of the questions asked about my engine build. I am not doing the build another guy is doing the work , but he will not make suggestions as what to use. Block is 4 bolt 30 over with a 427 crank. The piston rods and the Wisco pistons are forged steel with about 10:1 ratio. The tappets will be hyd roller and roller rockers at 1.7 ratio. My driving rpm range will mostly be 2500-5500. It has headers that measure almost 2" OD, I'm not sure of the brand. Small 2" exhaust with stock mufflers. The Edelbrock heads 60455 or 60435. I'm not sure if one is any better than the other. I'm using the performer intake with the divider cut down some. I have hood clearance issues with the standard hood. the carb is a 750 Holley. I'm looking for mainly lots of torque. Thanks

 

Sounds like a good street engine.
You can search the forum through Google for intakes that fit under the hood, which should help you see what others have done to make everything fit under a stock hood.
I believe others have used that intake and made it fit.
There are several drop base air cleaners that will help, also the big block hood provides a little more clearance as does the L88 hoods.

 

Ok your specs:
Std BB Hood - That means you are extremely limited to stock height intake manifolds, and they are a low-rise type to fit the low C3 hood. High rises will not fit. And you will also have to use the stock GM AC Delco 2" drop air filter. Almost nothing else will work. They will cost you 20Hp past 5000 rpm but they fit. The performer may fit if you trim the carb mount some. The 569 intake can handle a 1/2" spacer and still clear. But That is a say a 3.63" carb pad height. The published height info on the repop LS6 is wrong, I measured an original at 3.16. With the 1/2" spacer that is 3.63" I am not at all confident you can get a Performer to fit. It is over 1.25" too tall at 4.85". A stock 1970 454 that I measured had 1.25" of air cleaner to hood clearance, with the first cat iron intake listed, Qjet, and the stock 2" drop open element air cleaner. So maybe 4.1" total could work, or a little bit more. If you are able to get the Performer to fit, please let us know how.


These are the ones that fit. Most everything else is 1" too tall. The top two is the cast iron oval The third is a 68-69 only aluminum oval port for a Q-Jet. The LS6 is a Square port for a Holley, used often on oval port heads. The Torquer is a single plane, for a Holley, will lose low rpm TQ.

Heads - Edelbrock are a great choice and worth more HP than the stock ones. Likely worth 20-30-40HP vs stock heads.

Cam - HR is a great choice. Knowing your intended RPM range is a perfect first step for choosing a cam. With a 5500rpm or slightly less power peak, you do not need or want that big of a cam. Stay under 230* @ .050 duration. Even 224* might be better. Ask about the idle vac. A 224* will likely have 15" of vac at idle, and all the vacuum stuff will work well. Keeping the cam duration on this smaller side also keeps the low end TQ up, which is very helpful on the street. More than 224* really starts to kill both the idle vacuum and the low end TQ. Less duration would build more TQ at 1500-2000, like a 215*, but I would not go that low on a BB unless you plan never to rev it past 5000-5300. A 230* should make peak HP near 5800-6000 rpm, and you may not want that big. A stock hydraulic cam is 214*. A 224* might hit your sweet spot. The HR profile will also help build TQ. My 454 dyno'd at 490HP with a 230* cam, and 550lb TQ. At 5300-5600 rpm the HP was flat, due to the cam and the 569 intake. Your 427 could be similar, just at say 5700-6100 with that cam. You'd have the same airflow at that speed.

With a 230*+ your idle vacuum will drop to like 12", reversion goes up a lot, as does the slightly rougher idle, and peak TQ drops like 50lbs and low speed TQ drops more than that. Your HP may climb another 10 HP or so. Maybe 20, maybe not. Gas mileage takes a dive too. It's still a big block tho, only now with attitude! That's the duration number where drive-ability tends to start to fall off badly. Go past that and it will be a lot of work to drive. At that number and smaller it is still pretty smooth. As the reversion goes up, the cars really respond to a free flowing or open exhaust, and really get choked down with restrictive exhaust. A huge overlap 530 HP L88 would get choked all the way down to 430HP with factory '69 2.0" exhaust, due to the reversion. With open exhaust they scream.

Headers - Are worth roughly 30HP on a BB vs the factory manifolds, vs a dyno run I saw. On a 500ish HP BBC.

Exhaust - Factory 2.0" exhaust and factory mufflers is going to choke 50HP out of your BB. I am quoting Duntov himself. You should consider that part carefully. The 70-74 BB had 2.5" exhaust which helps a lot, fits like factory, and flows better. PYPES has a mandrel bent 2.5" system which fits well, and flows better, but does not look stock. But the factory quiet mufflers are the biggest restriction. The N11 off-road mufflers are available and are some better. My local Corvette shop loves the Magnaflow mufflers for a C3. They flow very well, fit well, and have a growl but are not too loud. And you get your 50HP back. Going to 3.0" will help even more, but only by about 10HP. A lot more effort, and greatly diminishing returns.

Gearing - 3.55s w/ a 2.20 CR box. - A little long legged in first. Only a 7.8 ratio. 5300rpm by 55mph. But with a torquey BB you should be fine. If you could find a 2.52 ratio W.R.. box, it would be peppier off a stoplight at part throttle at 8.9 overall. But with a BB you will smoke the tires either way at full throttle. It is like a 70 lb or 15% TQ boost. But only if it hooks. At full throttle the street tires are the limiting factor, in first, as well as second gear, with a BB. The tires should hook in third once you are past 70 or so!

I raced a high revving LT-1 for 27 years.
Big Blocks are different. We say "shifting is optional" LOL

Have fun!
.