Z-11 vs BBC

jim_ss409

Well Known Member
Supporting Member 5
#1
I thought I'd put this in the Z-11 section because that was the final, and most powerful version of the W motor.
It seems to be an accepted fact that the BBC was a much better design than the W motor but I've often wondered just how much better it really was.

The 427 ci Z-11 was rated at 430 hp but most sources state that it actually made somewhere between 475 and 500 hp. That's in the ballpark of engines like the ZL1 and LS6, they were also underrated at 430 &450 hp But I gather their actual output was in the 500 hp range or maybe a little more.
The Z-11 did have two 4 barrel carbs but it was really hampered by a terrible intake manifold with harsh 90 degree bends. The BBC's on the other hand had very nice intake manifolds. I think the ZL1 had an 850 cfm Holley carb and the LS6 had a 780 Holley.

Here's a picture of a rare single quad Z-11 intake...
Z-11_zpsb1846629.jpg
Here's a L88/Zl1 intake. It has nice sweeping bends...
$_57.jpg

I'm no expert but I think a better manifold like this might have pulled the Z-11's horsepower up about 20 horsepower or more.

Another well accepted fact is that the BBC had a much better combustion chamber. Well if that's true why did they often need as much as 42 degrees of ignition timing where a W motor seldom needs more than 36 degrees? :scratch
I know some of the modern BBC heads out there have much improved combustion chambers but the factory stuff just wasn't that great. I could also add that the W motor is also less detonation prone.
Check out the size of the dome needed on this ZL1 piston, this doesn't make for good flame travel.

IMG_3193.jpg

Another legitimate knock on the W motor is that the pistons are heavy but if you look at the BBC piston above you can see it's no lightweight either.

It's also true that the W motor's pistons get more and more lopsided when you start to raise the compression but there was an easy fix for that, much easier than designing an entire new engine.
Take a look at the pistons in this 348 engine cross section picture. They aren't lopsided at all, they're gabled like a roof.
122.jpg

The pistons only get really lopsided when you try to raise the compression ratio.
Here's an extreme example of a high compression piston.

untitled.png

The original design of the W motor didn't have a lopsided piston at all, it only got that way once they started pushing up the compression.
This may sound like blasphemy but when they changed over from the 348 to the 409 they probably should have changed the deck angle. Yes, it would have required changes to the machining process but it would have been a lot easier than building an entirely new engine.

I would concede that overall the BBC is probably an improvement over the W motor but I don't think the difference is nearly as big as most people think, especially if you compare the Z-11. :deal

I'd love to hear some opinions on the whole BBC versus W Motor debate.
 
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jim_ss409

Well Known Member
Supporting Member 5
#2
I'd like to add a little more about the performance potential of the Z-11 engine.
A good example is an engine that Lamar Walden built using factory Z-11 heads. (ported)
I think it's 427 ci but it may be more because of the overbore. :scratch
It made 745 hp and 546 ft/lbs

I think that compares pretty well with any 427 ci BBC built with factory iron heads. :dunno

It's true that there are plenty of BBC's making a lot more power but most will be using highly evolved aftermarket heads.
The original BBC heads had a 26 degree intake valve angle but these days most of the aftermarket heads are 24 degrees or less.
It seems like they keep flattening the valve angle and I gather the really racy stuff is down to about ten or twelve degrees.
They've also raised the ports and shrunk the combustion chamber.
You could argue that the modern state of the art BBC heads are starting to look a lot like Z-11 heads. :scratch
Here's a regular BBC High Perf head and a modern Big Chief style head. There's quite a bit of difference.
When you hear about someone making 1200 hp with a BBC you can be sure they aren't using the #990 factory heads.
SA190_7-3.jpg

brodixbbcpb1800info2.jpg
 

Ishiftem

Well Known Member
Supporting Member 2
#3
750 hp is doable with the factory oval port bbc heads. Given that, I would think 850 would be attainable with the rectangular ports. Given the rest of the W architecture, the z-11 heads were no slouch, that's for sure.
 
#4
I LIKE it, Jim
:cheers

This NHRA / IHRA Stock Eliminator stuff that I do ( when I can ), is a pretty good test of what's possible with the factory specifications.... IE, stock cubic inch, stock compression ratio, stock lift cam, factory castings.
My car, at the moment, IS the fastset Stock 409. The engine is 422 CID, makes 488 ft lb torque, 530 HP... spinning to maybe 7300 RPM max.
A large port 396, prepared the same way, coming in at ( ironically ) 409 CID , for NHRA Stock Eliminator, will make 575 HP, and routinely go through the traps at 7600+ RPM.

I dunno ? What would my engine do, if I had a decent intake manifold:rub;):p

I agree, the angle of approach of the intake ports in the heads, is a terrible barrier ( I'm sure a Z11 head looks after much of that )... but I think there is an advantage to the simple combustion chamber configuration, and piston dome shape.
 

Blk61409

Well Known Member
Supporting Member 8
#5
Just my .02 worth.

I have had the pleasure of racing lots of different cars and engines and being on a Chev dealership racing team running both small blocks and 427's(69 ZL1). I ran the 409's in 64 & 65. Since I owned it and raced it on the weekends, I also had to drive it to work on Monday so I was not as hard on it as I could have been. I did have to learn all the tricks to get the ET needed. As I moved from the 13's into the 12's I did so with considerable effort of learning about jetting, timing, reading spark plugs, fuel cooling, tire pressures, etc. With only being able to run 7" slicks I had to ease off the line until the slicks caught hold and then hit it hard. I lightened anything that moved, aluminum flywheel, valves, retainers, etc. I do remember shifting at 7500 which totally baffled the small block guys. In addition, remember, technology in 64-65 was really only something we all stumbled onto and certainly did not call it technology, but rather tricks.

Now, forward to when we picked up the 69 ZL1 Camaro, it dropped into the 10's immediately!!!

What??? I had to have a better look.

What I discovered was the entire intake fuel flow and exhaust flow had been improved such that it was a straighter shot into the combustion chamber with a much less less bend in the intake. I also discovered we could lightened the pistons easier, shorten the skirts and made for a much lighter reciprocating mass. Today we can do the same with our '09's.
I do remember the Z-11's and the Mystery Motors used the 409 based lower end. Chevy had faith in that bottom end until they were proved wrong, needed cross bolted mains, webbing, etc.

Reading about how Chevy designed the 348 we must keep in mind they were chasing costs and torque so the design was not optimal. I agree that with a wedge combustion chamber we can still make lots of HP. I have one that puts out 755HP on a Dyno with original 1963 Z-11 Heads!!! Yes it can be done, but my belief is since Chevy was under tremendous costs control pressure in 1955 they were not thinking about racing at all.

Years ago I had the very good fortune to visit with Smokey Yunick. I engaged him in a discussion about the Mystery Motor. He shared with me the key was completely the design of the valve train, getting fuel in and out.

That's all of my .02 worth for now. Thanks, Pat
 

jim_ss409

Well Known Member
Supporting Member 5
#6
750 hp is doable with the factory oval port bbc heads. Given that, I would think 850 would be attainable with the rectangular ports. Given the rest of the W architecture, the z-11 heads were no slouch, that's for sure.
Yeah, I wonder what's the most anybody's made with factory BBC castings like the 990's :scratch
It wouldn't surprise me if somebody has made 850 but that would still be a heck of an achievement.

Here's a Quote from Pat's post...
I have one that puts out 755HP on a Dyno with original 1963 Z-11 Heads!!!

I think that's outstanding, and I also wouldn't argue that you could make more power with a BBC but not a lot more. And again, I'm comparing BBC's to W motors that have Z-11 heads.
 

jim_ss409

Well Known Member
Supporting Member 5
#7
Excuse the poor pictures but check out these state of the art cylinder heads...

Here's Chevy's SB2 Nascar Head...
sb2.png

Here's Chevy's even newer R07 Nascar head...
R07.png

Mopar P7 Nascar head...
nascar mopar p7.jpg

Mopar Pro Stock...
mopar pro stock.jpg

Ford "Yates" Nascar head...
0-yatesd3-cylhdvtrain3lr.jpg
All of these heads have very low valve angles, compact combustion chambers and raised ports.
They also have staggered valves, not in line like a Smallblock Chevy. In fact the Mopar Pro Stock head actually has a "W" pattern.
But that can't be right??? :scratch Everybody knows for a fact that the Hemi head is far superior to anything you'd find on dump truck engine???
I wonder why both Mopar's Nascar and Pro Stock heads look more like a Z-11 head???
To be fair, it might be a rule thing but either way, it looks like this style of head is pretty popular in high end racing classes.
 
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jim_ss409

Well Known Member
Supporting Member 5
#8
This NHRA / IHRA Stock Eliminator stuff that I do ( when I can ), is a pretty good test of what's possible with the factory specifications.... IE, stock cubic inch, stock compression ratio, stock lift cam, factory castings.
My car, at the moment, IS the fastset Stock 409. The engine is 422 CID, makes 488 ft lb torque, 530 HP... spinning to maybe 7300 RPM max.
A large port 396, prepared the same way, coming in at ( ironically ) 409 CID , for NHRA Stock Eliminator, will make 575 HP, and routinely go through the traps at 7600+ RPM.

I dunno ? What would my engine do, if I had a decent intake manifold:rub;):p
Yeah, and some cam lift. I think you're making fantastic power for a 62 409 but what if it was a 63 Z-11.
I think the Z-11 heads along with the much needed cam lift would get you up in the 600 hp range for sure. :deal
 

Ishiftem

Well Known Member
Supporting Member 2
#9
It has been said that an efficient combustion chamber needs less spark advance. My engine only wants 34 degrees with c-12 which is probably a little more octane than I need. That would say to me the "W" chamber is very efficient.
 

BubbletopMan

Well Known Member
#10
I guess I'll chime in on this as well. When I was working with Lamar Walden, he used to say that the 409 style combustion chamber was the most efficient design he had ever worked with, simply because the flat head and angled piston top allowed for much better flame travel across the chamber. He would say "I can't get enough air and fuel in the thing! With a big block, you have to jack the timing up to fire over the dome. These engines don't need near the timing as the Big Block's do." The port design and manifolds that were available up until recently have always been the greater limiting factors of this design. Jeremy
 

1961BelAir427

Well Known Member
Supporting Member 3
#11
My 433" rat motor made about 680 with mostly stock #026 heads. Those are pretty much the same as #990 castings, just earlier models. Mine are dated '71. The #026, #188, & #990 are all open chamber rectangle port castings and are generally considered the best of the iron heads. The heads were decked around .035" if I remember correctly to a 113cc chamber size and the bowls had a "throat cut" done which was blended in by hand. Stock sized Manley SS valves. The ports and chambers were otherwise stock other than casting flash removal. Compression was 13.6:1 and I had a solid roller with the specs of 278*/282* @ .050" and .714"/.680" lift (before lash). Not a small cam but certainly not the best grind for the most hp possible. Pistons were heavy TRW forgings (second design L88/ZL1 style domes) and Childs & Albert aluminum rods in the stock 6.135" length. Induction was an unported Weiand Team G 4150 series with a 1" spacer & Holley HP950 carb. (It made the same power - according to track MPH - with a 4500 series and an 1150 dominator.....just had much worse cold start manners.)

I think that the same general displacement & heads with no more work than mine, max'd compression and around .800" cam lift could make in the low to mid 700's. I don't think that would be easy, but attainable. Add a tunnel ram and fully ported to that and I'm sure that well over 800 could be made with factory iron bbc heads.

I'm sure that has been done before, but these days who would spend the money to build around those?
As far as comparing stock iron bbc heads to the Z11.......it sounds like a pretty even field to me. From looking at pictures of the Z11's I'd bet they flow better than the rat heads. If I remember correctly mine were around 325 cfm intake on the good ports and 220 cfm exhaust (with a 2" pipe).
 

jim_ss409

Well Known Member
Supporting Member 5
#12
My 433" rat motor made about 680 with mostly stock #026 heads.
That sounds like a nice combo. I think a W motor with Z-11 heads would be in the same ballpark if it was built the same way. It might not make quite as much power as the BBC but it would be very close.

What prompted me to start this thread in the fist place was something I read in the Chevrolet Big Block Muscle Cars book, and over the years I've read the same thing over and over,,, The truck based W motor doesn't breathe well,,, bad combustion chamber,,, can't win Daytona.
I think the breathing part and the "can't win at Daytona" are fair enough criticisms for the regular 348's and 409's but the Z-11 might have been a contender.

According to this book and other sources the W motor got replaced just so that Chevrolet could win at Daytona. I'm not sure how well that plan worked out, I looked it up and sure enough, a Chevrolet did indeed win at Daytona,,, but not until 1975 and I'm not sure but I think it may have been a smallblock by then.
By the way, Junior Johnson did win at Daytona with a 348 but apparently it was good driving rather than horsepower that got him there.

The winning at Daytona story is plausible because why else would they want to design a completely new engine? The W motor was certainly working well in trucks, and the high performance 409 was already testing the limits of the passenger car drivetrain.

It seems to me that they could have got a lot more bang for their buck by doing a bit of r&d and refining the already good Z-11 engine.
All the things that were done to make the BBC more durable, like four bolt mains, bigger crank and rods etc. could have been done to the W motor. A decent intake manifold would have been nice too. (although you've gotta like the way they raised the runners off of the valley cover)
They also could have raised the center exhaust ports and built even better exhaust manifolds, and if they wanted to take it a step further they could have changed the deck angle from 74 degrees to about 82 degrees to eliminate any problems with the high compression pistons.

It seems like anything they did with the BBC in the mid sixties could have been done with an improved Z-11 :scratch
 

1961BelAir427

Well Known Member
Supporting Member 3
#13
I agree with all of that. If they'd just beefed up the bottom end with 4 bolt caps and good rods. The Z11 heads already flow well enough to support big HP. I agree about the change in deck angle too. If they had went to something like you mentioned.....they could have kept the design of the W with the chamber in the block......only it would have been a much smaller chamber. That would allow smaller domes / less lop-sidedness of the pistons....which coupled with the longer rods would have given less piston weight and high compression. It would also have improved breathing by moving the valves away from the cylinder walls. Even more breathing improvement from the different deck angle would come from the intake ports being laid back.....giving a wider intake manifold which allows for better intake manifold runner length and shape.

I mentioned angle milling a block several months back and was told it's a bad idea due to valvetrain geometry issues that it would complicate. If GM had went to more of a deck angle like the 82* example you gave, then they could have also made a revision to the lifter bore angles to compensate for that I'd think. ???

Just think if they had stayed with the W instead of going to the Mark IV. I too have always wondered why the LS6,LS7, ZL1, etc. were such a big deal for making the numbers they did in 1969-1970 when the Z11 had already done it 6 years prior. You already mentioned it, but I've also always wondered why they never used the 2 piece intake on sbc & bbc......at least on the "Special High Performance" models. Whatever added cost it seems like that would have been outweighed by the benefits.
 

61 Bubble

Well Known Member
#14
Ok I have a bit to say on this!

Jim, funny we HAVE run or ARE running all those heads you have picture BUT for the P7 Mopars, and my own RO7's are collecting dust. I'm also currently running a set of Pontiac Pro Stock "427" heads, and a set of 1971 GM "074's". I can send you a picture of the NEW trick piston for the OEM BBc heads later this week.

No I have made a lot of power with OEM heads. I have to look for exact part numbers, but my 396 made right at 620Hp and my 433 oval port is right about that with the 215 head.

We have done another 433 with 074 heads and 198 intake that went over 770Hp and is racing in France. My own ZL-1 should be in the 850/870Hp range with 074 heads and OEM dual plane intake.

As for flow numbers, a "really good" steel head like LS-6 is about 355 cfm. My 074 flow OVER 380 cfm.

Now here is what I'm thinking:
ZL-1 block, 496 inch with Z11 heads and modified intake! Roll the heads over with OEM block and use a dish piston and a good intake with good roller and pump gas???? Figure 800Hp can be had"
 

oil4kids

Well Known Member
#15
I think I said this in a different thread but before Bill Jenkins passed away, he told me face to face his 63 Z11 made 540hp as delivered from Chevrolet, he pulled the motor from the 63 and had it on the dyno, then added some tricks

however he said he never broke the center driveshaft hanger, which was a little hard to believe, since I went thru 3 or 4 with my 63
 

chevymusclecars

Well Known Member
Supporting Member 5
#16
I think I said this in a different thread but before Bill Jenkins passed away, he told me face to face his 63 Z11 made 540hp as delivered from Chevrolet, he pulled the motor from the 63 and had it on the dyno, then added some tricks

however he said he never broke the center driveshaft hanger, which was a little hard to believe, since I went thru 3 or 4 with my 63
The company I worked for made the water pump seals and we tested every engine on a dyno to see what we were working with. I saw the test data on a 427 425HP engine and it made 525HP right out of the crate.

Bill
 

Blk61409

Well Known Member
Supporting Member 8
#17
Not sure where I posted it before, but I have an aluminum block with original 63 CFD Z-11 heads and it dynoed 755 HP with 618 ft lbs torque. Has Lamar's intake and a pair of Demons as well as a stock Z-11 intake and a pair of Demons on it as well. HP on the stock Z-11 intake is less by about 60HP.
This might be a little bit better proof of how well the old Z-11 heads flow.


quote="61 Bubble, post: 226731, member: 6375"]Ok I have a bit to say on this!

Jim, funny we HAVE run or ARE running all those heads you have picture BUT for the P7 Mopars, and my own RO7's are collecting dust. I'm also currently running a set of Pontiac Pro Stock "427" heads, and a set of 1971 GM "074's". I can send you a picture of the NEW trick piston for the OEM BBc heads later this week.

No I have made a lot of power with OEM heads. I have to look for exact part numbers, but my 396 made right at 620Hp and my 433 oval port is right about that with the 215 head.

We have done another 433 with 074 heads and 198 intake that went over 770Hp and is racing in France. My own ZL-1 should be in the 850/870Hp range with 074 heads and OEM dual plane intake.

As for flow numbers, a "really good" steel head like LS-6 is about 355 cfm. My 074 flow OVER 380 cfm.

Now here is what I'm thinking:
ZL-1 block, 496 inch with Z11 heads and modified intake! Roll the heads over with OEM block and use a dish piston and a good intake with good roller and pump gas???? Figure 800Hp can be had"[/quote]
 
#18
Has Lamar's intake and a pair of Demons as well as a stock Z-11 intake and a pair of Demons on it as well. HP on the stock Z-11 intake is less by about 60HP.
This might be a little bit better proof of how well the old Z-11 heads flow.
That, and just an indication of how much of a piece of sch!tt the stock intake is !

EXCELLENT information.
What's the cubic inch of that engine ?
 
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