When you say 'high speed intake charge", are you saying stick with the moderate intake manifolds likes the standard Edelbrock Performer? Would the Performer limit the higher 360 HP level? I'm basically doing the 360 HP version.

 

Mostly referring to the volume of the intake on the head. 175 to 185cc's vs 195 to 215. This is for a street driver.
The intake matters too. The as cast edelbrock performer will meet you desired HP levels and provide adequate velocity to the heads.

 

Just found some very relevant dyno tests from a very old forum thread @ 2002

 

So, I originally bought the 268H cam back in March and would have my car running now if I didn't get distracted by the next shiny object, a Mike Jones custom grind. I gave him all my specs (similar to everyone living with the L48 bottom end - Trickflow DH175 heads, headers and duals, Eddy Performer, tuned Q-jet and curved distributor), told him I wanted peak HP at 5,000 rpm and a broad torque band and he came back with a grind that looked mild by the duration numbers but he claimed would make 350 HP and 380 ft-lbs. torque. These numbers are about the same as the Comp Cams website gives for the 268H. Just installed it and dialed it in yesterday, here's the cam and card:


Number look unimpressive....

The quality looks awesome, but the delivery was quoted as three weeks and was actually almost seven. It also degreed in 2.5 degrees advanced, but I had the Summit timing set so I was able to retard it 2 degrees. I have yet to read a negative review on his cams, so I'm hopeful for good results. Will post comments after I get it running.

 

Yes and No!! I like your thinking on using the aluminum heads, though I'd lean toward AFR's Enforcer line of heads. Engine Masters did a shoot out of the "budget aluminum heads". Their 195CC Enforcer head not only made "best power" but also benefitted from the use of valve springs that the show's real expert Steve Brulie called out as a step up in quality and durability he didn't expect to see on "budget heads. On the flip side I disagree with your thinking on the use of a smaller cam alternative. Nothing dictates power more so that the cam choice in any combination of parts. Vortec heads are good. The aluminum heads you're talking about are a little better but not nearly enough to make up extra power if you swap in that smaller cam. All bets are off if you do that and this video is completely irrelevant if you go that route.
I put the video up because it shows a package of parts that takes the guess work of potentially mismatched parts out of this. Your aluminum head choice is a minor change, both their choice and yours will yield the 64cc combustion chambers and compression ratio. The flow is likely pretty close too in your choice vs their choice of Vortec heads but a different, smaller cam is a whole other kettle of fish that will invalidate the results seen here for sure. Sticking with Comp Cams: A 268 vs their 280 in the video is a significant change. If you're worried that the cam they use is too much for your gearing a 2,000-2,500 stall converter would fix that in a big hurry..
.

 

There ARE pistons with an effective Quench that are not flat top nor D-dish.
Look at OE L31 iron Vortec truck motors and their many performance variants. As opposed to old L48 pieces, L31 dished crowns have virtually no bevel but have a rather wide (and effective) Quench Band. Same pistons also have preferable thin 1.5, 1.5, 3mm metric ringpak. Please reference 2 photos in link below.
https://www.corvetteforum.com/forums...post1608930451

 

Walter - go back and read the whole thread. With the L48 dished pistons and their crappy quench, maximizing dynamic compression is more important than longer durations. That means get as much fuel in as you can and close the intake valve early. As far as Engine Masters goes, I love those guys but they don't build torquey street motors, they like high RPM screamers.

Also, when I asked the guys at Mike Jones how they made power with such short durations they said: "Our lobe profiles are just more efficient. We have more area where it's needed, and less when it's not. When the piston starts accelerating down the bore, that's when our intake profile accelerates the valve at a higher rate, to efficiently fill the cylinder."

We'll see...

 

Scott,
Mike Jones is not kidding. I just wrapped up my build with one of his custom cams and it definitely delivered everything he said it would. His equipment can grind a profile that most other grinders can not replicate. The cam "numbers" do not tell the story here. They do not drive the same as another cam with the same numbers.

 

No kidding there!
The really important cam duration numbers for cylinder filling are at .100, .200, .300 lift etc.. Not at the seat.
And not enough manufacturers give data there to be able to compare one to another.
As consumers we do the best we can with .050 and "advertised" numbers.
And note that "advertised" numbers vary as well, some are at .001, .004 .006" lift, etc etc.

And IIRC Mike Jones uses some really interesting lobe profiles.
"Inverse radius" or similar.
So they make the power of a much larger "typical" profile, and yet have much smaller "advertised" and .050" numbers which improve torque, driveability and vacuum.


Here is an example where both cams have the same advertised and .060" duration, and lift.
Yet from .100" on up, cam B has more duration, up to 4* or 8* larger duration.
They may drive the same, but,
they will not make the same power.

 

Exactly. The inverse radius cam profiles require a smaller diameter grinding wheel machine. Comp etc dont have the machines that could do that even if they knew how.

 

355 SBC buildup by my engine builder Lorenzo
Nothing fancy. Was a 71 L48.
2 bolt, cast crank, stock rods, Hyper pistons, flattops, stock open chamber 487 heads, CR ~ 9s?, little bowl work, 224/236 cam, QJet, Dyno'd
375HP @5500 393 TQ
Cam is kind of like an L46 350HP cam.
Think how much better it would do with AFR heads on it!
But if you are going to wind it up more, you better beef up the rods at least.

You Tube

 

Interesting that he got an additional 40 hp just by correcting the AFR. Also interesting that the power is still going up but he's stopping at 5,500 rpm because of the stock rods. Another case for not over-camming stock bottom ends. I wonder if a different cam would get you similar power and torque bands but be more efficient? I bet Mike Jones would say 'absolutely.'

 

Also interesting choice of those old tractor wide high friction power-robbing rings. Also curious the OE 487 heads were too sludged to use ? Those replacement 487 heads were breathed on. 2.02./1.6. The cam does seem a plain jane aftermarket shelf piece. I realize this is a street piece.

Perhaps compare to typical local built race 3/8 to 1/2 mile Oval pavement. Max 358". Max bore 4.060", 487 heads milled to rule-mandated no smaller than 70cc, NO porting at all, Max 3-angle (No cut inside bowl), Max valves 1.94"/1.5", Any flattops permitted but mandated Not above deck, mandate later 2101 intake, mandate TWO barrel carb. Max thickness adapter 3/4", Max 500 cfm, Boosters Not raised, Mandated Max lift at valves 0.480" solid flat tappet, Mandate OE crank, weight No less than 52 pounds, clutch-flywheel package No less than 30 pounds.
Most make about 360 HP at flywheel on race gas & Two bbl, with a purpose-ground solid cam within lift rules. Lotsa T&E in 2bbl carb & cam.

 

Yeah I used to rev my 68SS350 Camaro stone stock 300HP L48 350 to ~6000 or so pretty often.... back when it was like 4 years old,,,and I was much younger and ....stupid....then one day it was one time too many. Can you say OOPS?
LOL

Young and dumb....it's how we learn

 

I apologize for this. I'm way late with a response. I don't disagree with your thinking. Fact is this is no small part of why I wouldn't "blow the cash" or effort on an L48 build that doesn't include flat top piston replacement. Back in the day we did it because the engines were "newish" and we were only looking for a simple enough way to bring back some of the lost power the emissions rules had taken away. In a world of 225HP and under SBCs a 268 Comp cam, heads that could get you to 9:1 might have made 300HP. Strong enough to feel like significant improvement and make a move on most cars from the era BEFORE emissions.

That was then......this is now:

Today: a SBC build that fails to generate 400HP and far bigger torque is gonna feel WEAK. Really weak today. We've had more than 300HP and 400Ft Pds as BASE LEVEL V8 power for over 30 years. Every LS powered Pick up, SUV and no small number of cars built since the 1990s has reset the benchmarks of what feels like a lively, decent power engine today. I won't say a C3 with a SBC needs to be a powerhouse ready to take on the C6-C8 cars but it does need to be able MOVE better than today's economy cars and it should run harder than a pick up truck typically does. All of this can be accomplished with the old school tech of a SBC in a car that is lighter than any truck or SUV. It'll never be an MPG champ but it can move with authority. To get it done though "Heads and a Cam" bolted onto an 8:1 compression engine won't deliver. Fortunately, 10:1 even without computer controlled ignition is very do-able on pump gas today. The extra couple of points of compression and ideally slapping in a crank, rods and pistons the will yield 383 from a 4 inch bore and then the cam and heads .......... now you've got DECENT power. Today I won't even consider a 350 build at all. The extra cost of the stroked engines is so very small and yet the extra torque in the street driving RPM ranges is just so much higher that it may be the single best bang for buck in the entire effort to build in more power. But really the extra compression is the big win. 350 or 383.....either way it allows you to go far bigger on the cam without the concern for absolutely demolishing low end torque. An engine either feels snappy and strong in traffic or weak flat and worthless in traffic based on what it has for low and mid-range toque. This is where L48 gets it's reputation as WEAK. The low end power just isn't there and a bigger cam will throw it all away with even just small amount of extra duration. Extra Compression is the way to go to avoid this.

 

Walter - I don't disagree with anything you've said about 400 hp being more fun than 300 HP, or how to get there. My point was that there are dozens of posts on that topic, but there is only one comprehensive post about how to get the most out of your L48 bottom end with dished pistons. There are other posts that talk about it, but mostly they refer to this one. There are members that don't have the skills and/or the money to upgrade the bottom end (or just choose not to) but can manage top end work and a cam kit. That's the point of this post.

Having said that, and having just completed this exercise, there's was a couple weeks when I was waiting for my cam kit that I was looking at the block and thinking, "I could have this out of the car and rebuilt with flat-top pistons by the time my cam shows up". I do have enough skill for that job, so maybe if I'm bored late next winter, I'll do that. Meanwhile, I'm still tuning, but enjoying the gains I got from better heads and a cam.

 

There is one more reason to keep your L48 upgrade on the "mild side" cam wise.
If you go too big in camshaft duration, low rpm Torque suffers, and then you need to add more gear to the car, to rev it up more, just to get the torque back, just to where it used to be.
Obviously the power moves upstairs, but it is what happens just "off idle" that determines how much "gearing" that you need for it to feel peppy.

I look hard at 1200-1500 rpm power for a street car. That is about how high you would rev it to release the clutch, or the torque convertor in an auto. 1 sec later, you are at 17 ft farther, (1 car length), at 18 mph, and at 2400rpm. For a drag-race 60 ft time, of 2.5 sec, you are still only going 30mph, at 4000 rpm, and just hitting the engine's main power band, 3 car lengths from the start. That initial dig, or "push" in the back, is all about torque not HP. It changes drastically if you want to rev it up more, drop the clutch at 3 grand, or put a 3 grand convertor in it.

I wish the aftermarket dyno runs started from idle, but they usually start from 3000, since they focus on peak power. And they have sold the public on "peak HP" not low-end TQ.

For a good street driver, you need to focus on low rpm torque, and that includes the gearing, and cam duration, as a package.

Fortunately the 1970 Chevy Historical specs have dyno sheets starting from Idle, on all their engine combinations.
They give terrific insight on what happens to off idle Torque as you increase cam duration.
It looks like, that at 224* and especially above that, you should add more gear to the car.
Cams bigger than 224* make less power up til 3000+ rpm.

The % of available TQ, at 1200 rpm vs peak, drops from a high of 84% with mild cams, to 68% with a typical larger duration but streetable hot-rod style cam (~230*).

That is 60 ft-lbs less TQ per GM. Or 20% less!
All of a sudden your 350 now pulls like a 283.

Is that really what you wanted when you built a "stronger" engine for your car?


The three 1970 350s, have the exact same peak TQ, but the available TQ at say 1200rpm, at a stoplight pull-out, drops 20% with a LT-1 type cam, with it's rumpity idle.
You can increase your duration from the stock 195*, to about 224*, before the low rpm TQ starts to drop noticeably.
FWIW the majority of musclecars had factory cams in the 210-220* range. Just like the LS5.
The L46 was my favorite SBC driver, and had the biggest cam that did not effect the low-end very much, while it added 50HP to the top end, and rev'd very well.
And it was one of the biggest of the "typical" musclecar cams.

The 224* duration spec is like the "point of no return". Another 7* gains you 20HP upstairs, but costs you 60 ft-lbs off idle.

Many of you will not believe my LT-1 cam duration spec, but Chevy specs the solid lifter engines differently than hydraulics, and I actually measured the duration on mine, while the valves were lashed. This was it's actual "net" duration, above the lash point, with it's valves lashed as spec'd. The famous "30-30" solid cam (Fuelie 327 or DZ-302) is another 8* bigger, or 239*, also as measured. It yields near 7k rpm, but the low end off-idle TQ is much worse, I can't find any chevy Dyno specs on that one. I drove that one for years, and my butt-dyno said it was very soft off-idle, much weaker off-idle than the LT-1. But it sure rev'd great. I had 411s, and it was still weak off the line! It was very demanding to drive on the street.

 

Leigh, I agree with all you said and have said the same for years, even mentioning the very same cyl heads(TF 57cc chamber) and 260HE camshaft.
The Comp 260HE according to Comp's own dyno charts show the 268HE not surpassing it until past 4,000 rpm (I've used the 260 cam three time in the last 38 yrs).
For an stock converter auto with 3.08 gears I would also take a look at the small Isky grinds with; 202*, 208*, & 214* intake durations. (their TQ cam for a 350 is 202/208 on a 110) Some are 108* LS some are 110* LS, at this small it doesn't hurt idle.
In all of these small cams,( from any brand), a consideration can be considered of using 1.6 ratio rockers on at least the intake if using a split pattern or both if a single pattern grind.
I really don't see a need of a split pattern small cam in a street only car with headers and upgraded free-flow exhaust. (my particular TF TW series 1 heads enjoy a nearly 80% exh flow avg).
I appreciate the torque talk!

 

FYI here is the original GM 1970 Dyno Data. It starts from idle, unlike aftermarket dyno data



Here I graphed that data into a more modern format:

What strikes me the most is that the milder cam'd engine, the L48, is stronger than the other two until 3600 RPM. At typical street rpms.

The #1 most common hot rod mistake, is putting a TOO BIG hot-rod cam into your engine, or new engine, like a 230* or LT-1 cam, or bigger, and leaving the stock cruiser 3.08 rear gears in it.

And then being greatly dissapointed in your new engine on the street. It feels 20% weaker, because it is, until 3600 RPM.


The blue arrow represents how much rear wheel TOQUE you could use if you leave 308 rear gears in with a bigger cam. ( The circled spots are GMs recommended gears by engine).

If you just want to drive it on the street, buy a 220* or smaller "TORQUE" cam.
If you want to race it, and use the high rpm range, then buy a bigger "HP" cam.
Even then, 230* is still a decent "street friendly" limit, but you need gears.

Please DO NOT buy a street engine JUST based on it's HP!
If you want a huge jump in low rpm TORQUE, you need more cubes.
That is the reason 383s are so popular now.

This is a very unfortunate consequence of all those 3000+ RPM Dyno charts flying about.
And almost ZERO dyno data that is available from 1000-2500 RPM.
So I dug some up.

How do YOU drive YOUR corvette?

 

leigh, good job on explaining the difference between horsepower, torque, and their relationship with RPM. I would also recommend to anyone to purchase Desktop Dyno before they start any modifications. While not an absolute it does provide an idea of what to expect, high RPM gains along with the low RPM losses.