I have been reading a lot of dyno and build up articles and it just made me wonder.....why don't big blocks make more power then they do it basic stock components or usual street hardware??

Here is my example....I just read an article where they were rebuilding an L72, thats a 427/425hp. I don't understand why that motor did not make more power from the factory... The one they rebuilt had lower compression, now at 9.8-1 and a modern solid lifter cam that was similar to the factory L72. After tuning they got 455hp on an engine dyno which was better then stock with less compression but....I still think it should make way more then that.

If consider the big block heads are HUGE ports, 2.19" valves sitting on top of big cubes with a bottom end that will spin to 6500, what is holding them back??

If you built a 10-1 compression, 427" small block with heads that were half the port volume of a BB and a cam with 242*@.050 and a lift of .520-.550 it would make well over 500hp.

I have built several big blocks myself including a 1970, LS6 for my dads Chevelle and other then tons of tq in the low to mid, I have never been that impressed with them. Granted I haven't set one up with killer hardware like Brodix heads or a big roller cam but it just seems like they should make more power then they do..

Food for thought or interesting debate.

 

BTW, I am fully aware that builders are changing heads and installing large roller cams and getting 600hp at the crank with em, I am just curious why they don't make more power with stock type heads and normal hyd cams.

A friend of my dad's just dynoed his 70' Chevelle. It had a std bore 454, oval port/semi closed chamber heads(stock ports, 3 angle VJ), 292h comp cam, RPM intake and a 750 DP, the car had a 2500 stall and a 12bolt rear end, 3.73 gears and dynoed 290rwhp. I thought the owner was going to cry. Granted thats probably 375hp at the crank or so... I would expect more. Not sure of the tune up or anything but..

 

I've always figured most have a real low volumetric efficiency.

They are so big that mediocre builds yield enough guts for most folks purposes... so why bother working the high end? Stomp the pedal at idle and yank your ears off seems to be the name of the game. Idle down the highway... right below the torque curve, and stomp it, no downshift just GOOO!

 

This is true most people are interested in just good torque these days.
Big blocks don't make as good of hp per cube as small blocks the
crank rods and pistons are heavy in comparison to the small block
and soak up some of the power. You know they use small block chevys
for starter motors on big blocks to try and get all that mass spinning.

 

It has a great deal to do with the heads.

The 468 in my vette made 602 on an engine dyno with Edelbrock oval ports that flowed 282 at .600, 11:1 compression This was with a relatively large solid roller (.651 lift / 255 ish duration). We swapped in a set of AFR's (flowed 368 at .600) and the motor has WOKE up. I would guess 650 - 675 would be reasonable.

The 540 in my camaro made 707 on a motor dyno; it's 10:1 with a hyd. roller and a nice set of Brodix heads.

I would say that one of the largest differences between the small blocks you are talking about and the big blocks you are talking about reside in the ability of the head to flow what the cam will flow.

Jim (427hotrod) has a crazy set of heads on his 540; I think he made 823 on an engine dyno.

I personally will always choose the big blocks...

Bryan

 

Big blocks= easy way to make big torque and big hp.

 

I don't agree with the premise. A BB will always make more power (especially torque) than a SB if the builds similar,..same displacement, duration cam, etc.

Yeah, you can build a pretty snotty SB that makes 550 HP at 6500 RPM,..but this engine would be absolute mush below 3000 RPM, which is where a street car lives 90% of the time. Now build a 550 HP BB and you have an engine that would be a blast from idle all the way up.

Like I've said before,..the heads are the diff. Large SB heads have 220cc intake ports. Mid-sized BB heads (O-ports) have 290cc, and there's bigger (square ports) if you wish to get rowdy.

A big intake valve for a SB checks in at 2.05. Big for a BB is 2.25 or bigger.

If comparing SB-427 to BB-427, the only advantages to the mouse would be weight, both overall and rotating. But's that's quickly nullified by the cavernous BB heads that make huge torque and HP with ease.

I'm sure the mouse boys will serve up their thoughts,..

 

I was out on the lake a couple weeks ago with the neighbor and
his 25 ft boat that weighs 4500 pounds we ran 70 mph with ease
on rough water the engine only turning 5800 rpm. its a punny little
496 with none that fancy nos, blowers ,turbos, tunnel rams, just a
stocker. Sure made me think about another big block

 

Yes we will, and the statement above is hogwash, my 406ci makes 550HP and it makes over 450ft/lbs at 2000RPM and goes up to 510Ft/lbs. Hardly mush at under 3000RPM, I drive it on the highway in 5th gear at 1600RPM and if you floor it from there it just takes off, no stumble or nothing,

When you are talking about intake runner and valve size the only thing that really matters is flow measured in CFM and the small block Vic Jr.s outflow many big block heads.

Now I might agree with your statement if it was posted 20 years ago when a small block was a 350ci and to get 550HP you would have to put in a huge cam that would indeed make it mush under 3000 RPM. Times have changed and with roller cams and big inch small blocks you can have the best of both worlds

 

If you built two motors with identical compression and cam duration and one was a 427 smallblock with gm heads and the other a 427 bigblock with gm heads which would make more power???

Actually that L72 has ports too big for a 455 horse motor. Put the port dimensions into a torque computer and those L72 head are trying to make that 427 achieve peak torque at 7225rpm. Peak horsepower would be well over 8000rpm. However those typical performance 186 smallblock heads from the 70's on a 427 would probably put peak torque at not much over 3000rpm (dont have the port dimensions at hand).

Now if the L72 had the cam, manifold and compression to match the head, it would make a solid 700 horsepower & 530ftlb. The same cam and compression in a 427 with 186 heads might only make 500 horsepower & 530ftb (just guessing here)

 

There was an article in Car craft, within the last 12 months, (it may have been Hot Rod) where they built a SB and a BB to the same displacement to try and settle this technical issue. if I remember right, the outputs of the two motors were pretty much similar, and the mag conclusion was "there are SB guys, and there are BB guys" you can get there either way. I guess you have to consider the increased wt with the BB as the most obvious negative. I would guess that since the BB runs a lower RPM most of the time, that from a durability standpoint the BB will be a better long term street option.
I personally like my 454 and its available low rpm TQ. I guess that makes me a BB guy.

 

I mean, I love the tq and low rpms of a good big block, hell we own one.. To reiterate my question, WHY? THis is not a BB vs. SB debate, I KNOW a big block will make MUCH more power easier and cheaper then a SB, I just don't under stand why they don't make more power with traditional parts. I mean even the stock oval port, 119cc chamber LS5 heads have HUGE ports and valves, 10-1 comp and the ability to rev to 6k. Why don't they make more power? Is it just the cam that holds them back? Do they need MONSTER cams to make those big heads work? I have not looked up any flow numbers on any of the BB heads but you know those GM Rectangular ports are 300+cc with 2.19 intake valves...I would THINK those things would flow HUGE amounts of air stock, like 300+ cfm at .500 lift or something crazy like that.

I mean even the ZZ502 I think should make more then 500hp. Its 9.6-1 comp, a mild roller cam and good flowing heads on top of 500 cubes... I would think that thing would make 550hp...maybe its the mild cam thats killing it.

This is what prompts my curiosity. My LS1 with only 346", stock heads that flow around 230-240cfm and a good sized cam(237/242@.050 and .603/.608 lift) makes 400rwhp. Assuming 18% DT loss thats what? 470 crank hp...out of a small motor. Granted stock LS1 heads flow well but 230-240cfms is NOTHING compared to what a 300cc BB head would flow. I guess I am just not seeing it.

I do have a buddy with a 496", Full works Edelbrock heads and a hyd. flat tappet that made 611hp on an engine dyno but there was a lot of work done in that motor.

 

You're contradicting yourself in your arguement. In one sentence you want only stock components, in another your modding a SB to the max. A 427 SB is not a stock 350 SB.

One thing I notice with dyno sheets is that a BB regardsless of the build will usually have a flat (or near flat) torque curve, at or near 400ftlb.

A stock SB will have a rise, then peak and then decline.

 

Hot Rod Ragazine did a build a few years ago with a 406 sb vs a 406bb it was close but the bb won in hp tq and the drag race they did. there is always the $$ arguement, bb is more sb costs less also, SBhp+NOX=BBhp for about the same $$ as bb alone. do what makes you happy because you cant beat everybody, every day.

 

I love BBs, they are really ,but I run a SB stroker 383. WHY ?? I like the fit in the C3. I dig the simplicity of the 60's cars and having some breathing room in the engine compartment is a real pleasure. Next time around a big inch SB, maybe a blower or turbo (there goes the simplicity) maybe a Big inch LS. Now theres an engine !!

 

I was merely using the 427"SB in comparison to the 427/L72 build up I had read about. I mean, you have to have a GOOD set of small block heads that are worked over pretty well to get 275-300cfms at .550-.600 lift. Those same heads with a decent matching street cam on a 383 would make 500hp pretty easy with the right induction. To me, I would think any of those big retangular port 300+cc heads should flow ATLEAST 300 cfms considering how big the ports are especially, from the articles I have recently read, basically stock headed(rect port/closed chamber) 427-454s with atleast a 230@.050 and .550 lift cam are not making near 500hp... hell some of them are only breaking 400-425hp. Maybe those old style heads are just junk....big ole holes that just don't flow.

A few years ago, I built a 1970 LS6 454 for my dad's 59' It was a numbers matching motor and we had made a few changes. Mainly flat top pistons to get the compression at 10-1, a change to a hyd cam with 244*@.050 and .550 lift on a 110lsa. The rect port heads had a 3 angle VJ with stainless 1 piece valves. It was fully blue printed and balanced with the 7/16" dimple rods, 4340 steel crank and was bored.030. We got the motor together, and in the car, we broke it in, tuned it as best you can without an AFR meter and the engine ran really well but it just did not seem that strong to me. Considering it was in a 3200lb 59' vette with a 4.11 rear, it just was not that fast.. My LS1 would RAPE the ole vette. We did a follow up compression check and it had between 188-190psi in all 8 holes. Definetly could have used some good dyno tuning but...

I have another 461" BB in a 4200lb pontiac GP. It has ported 69' Oval ports with light work on them, its got flat tops and a mild 270H comp cam, hyd flat. The motor makes a lot of tq and runs perfect. Its definetly out of steam by 5000rpm. This through a performer intake and stock BB manifolds. I love the torque, especially with the 3.90 gears, has nice roll from a 60 punch. Its torquey but I would be suprised if it broke into the 13s.

 

To me the question is more like What Is Power? HP is a function of torque and RPM. What spins the wheels and what you feel in the seat of your pants is TORQUE. There is to much emphisis put on HP. TORQUE is power, HP is what keeps pulling you through the traps at 7000 + RPM, not what gets you off the line. HP numbers can be very misleading.

 

I think if I buy these heads I should make well into the 700 hp range. I am just curious if you can rev a big block to 7500 like a small block safely. Im sold if I can rev it to 7500.


http://www.jegs.com/webapp/wcs/store...tegoryId=10187

This rotating assembly should be pretty strong. Although I would think the 427 would be a better choice for high rpms applications. Thats what l-88's are.

BB-Chevy 540 2-Piece Rear Seal Balanced Competition Assembly,

 

I own both a small block and a big block. I think there are two reasons big blocks may seem less powerful that one might expect.

1. Law of diminishing returns: It is harder to get 454 hp with 454 cubic inches that to get 350 hp with 350 cubic inches.

2. It is cheaper and easier to performance mod a small block than a big block. I rebuilt my big block a few years ago and just went stock. The selection of performance parts available for a big block is not as great as a small block (someone may argue this, but I did say AS GREAT AS A SMALL BLOCK). Also, small blocks are easier to get to and work on, better for the shade tree performance enthusiast like myself. I rebuilt my small block at almost double stock hp.

My final 2 cents worth: I love them both, I concentrate my performance work on the small block because of ease and cost, but in the end, the old addage is true; no replacement for displacement. If money, time and effort were no issue, I'd drop in an aluminum roller big block with a blower and declare myself king! (lol) God bless, Sensei

 

[QUOTE=ajrothm]I mean, I love the tq and low rpms of a good big block, hell we own one.. To reiterate my question, WHY? THis is not a BB vs. SB debate, I KNOW a big block will make MUCH more power easier and cheaper then a SB, I just don't under stand why they don't make more power with traditional parts. I mean even the stock oval port, 119cc chamber LS5 heads have HUGE ports and valves, 10-1 comp and the ability to rev to 6k. Why don't they make more power?


By traditional parts, you mean the parts available in the early 70's when they stopped putting them in corvettes?
Seriously though, take a set of any of those stock heads and put them on a flow bench; I bet they would flow in the mid 250's at best. As I mentioned above, a good set of Sportsman Edelbrock (oval) heads flowed 282 cfm @ .600 on a flowbench.

Another interesting point that I have HEARD about is that if you take a small block vs. a big block (making same HP, same car, etc and you run them at the track), the big block will have about 5 more MPH in the trap speeds. Any validity to that??


B