I heard on the internet, they can. does anyone have any proof?

 

Both with the same size valves?

edit: I'm going into nit-picking mode.

The same power can be made with both if the target is a specific value, say 300 horsepower. Just use different components other than the heads.

Now if you meant to ask if you can make the same maximum horsepower with the only difference being the heads, that is a totally different question.

 

I haven't seen any dyno numbers of stock Js vs stock Cs. I've read numerous times on our site that the Cs are more desirable and the Js are just restrictive smog heads.

That being said, I don't think J heads should be discounted simply because they were used during smog years. If you have the desire, means or money to measure the difference with a dyno chances are you'll just have them modified anyways.

 

Why don’t you do it?

 

stock..the J’s only came with 2”. So, let’s compare both big and small valve C’s because there is very little flow difference between the two C’s

 

Im here to learn. there must be someone who’s done the test.

 

We dyno tested our engine with stock J heads, W/Z manifolds, cast iron intake, W30 manual cam, etc. It made in the mid 370's for HP, which was more than the C heads made. It also made significantly more torque than the C heads. With headers and intake we made in the low 390's. So they aren't junk. These were stock, with rotators and the spring load was pretty low but the valves didn't float. In my opinion you can make 400 HP with them, not sure about how much more you can make. It's in part 2 or 3 of the write up.

jerry

 

Something, something, port velocity?

 

I would love to spend a week playing with various heads and the velocity tubes on the flow bench at Livernois. But this Dyno project has had a LOT of scope creep and while we are 675 pulls, I bet we will end up north of 800. So I just don’t see having the time to do this. If someone wanted to come and do it, we can discuss that….

jerry

 

Has anyone done flow testing with the valves in motion, like on a Spintron?

 

I don’t know if that’s possible. About 25 years ago I ran the valvetwain on my race Olds engine on the Spintron at Roush. But there wasn’t really any way to attach that to a flow bench. Not saying it can’t be done, but it would take some work.

jerry

 

My point is that you're measuring static flow with no account for reversion created by the motion of the valves. Seems futile to me. In speaker enclosures, parallel surfaces can create standing waves which cancel each other out. I would imagine the same can occur in a port.

 

I agree. Anyone that uses just cylinder head flow alone is a not making an informed decision. I'd love to find a way to add some kind of velocity component into all the head flow testing that we've done, to give people a better picture. I have flow data, that will get published, of every big block Olds head except H's. But the E's are clearly better, on a stock type W-30 engine than C's. The J's were a little better than the C's. We did make 439HP with C's and I don't think, but don't have proof, that we could make the same power with the same parts. I still have or have access to every head that we've flowed. I would just need time to figure it all out and then add that. All this dyno testing has certainly take me down a few rabbit holes...

jerry

 

I am beyond shocked by this statement, beyond............

 

x2

 

What about variations in castings? During the golden era of stock, racers would flow many sets of heads looking for CFM variations in head castings. To have a head to head comparison between stock heads would not the heads have to have the same valve and seat angles, same valves and the valves be set at the same depth in to the head/seat?

 

The 455 Olds is undervalved, and crossectional area is far from optimal. The fastest class an Olds 455 runs in is D/SA, they do not run J heads. I can't speak for Jerry, but I do believe if I tested the J head back to back with a C head, both stock I believe the C head would prevail. The bigger intake valve combined with more cross section would allow the engine to make more power @ a higher RPM. My last 455 build the customer wanted a stroker, I advised against it, my argument was: A Edelbrock head can't support a 455 much less 500 inches. My question to this forum:

Which is quicker down a Dragstrip

Engine 1. 500 HP @ 7000 RPM 490 TQ

Engine 2. 500 HP @ 5400 RPM 550 TQ

 

Engine 2

 

OK-anyone else...........................................

 

Engine 1

 

I'm not saying the J head is better than a C head. In a "stock like" 1970 W-30 configuration the J heads make slightly more power than the C's and a decent amount more torque. I have made in the mid 450's with stock C heads prepped for adjustable valvetrain. I don't think we'd get to that point with a J head. But J is NOT junk by any means. Sure the flow numbers are far from stellar, but there is more to a head than flow, and the J's do well in a stock engine trim. The dyno data proved it. Hell, the E heads made significantly more power than a C head in a stock form engine. But based on flow numbers you would pick C.

In the end there is no correct answer, it depends on what you want to do and there are parts to this that are not understood, at least by me. If you want a 400 HP engine, a J head will do just fine in stock form.

jerry

 

Not enough data. It depends on gearing and what the power curve looks like, what transmission. A heavy car with a powerglide would benefit from engine 1 if the power curve was flatter and not as peaky, as the RPM's wouldn't put you too far out of the power band of the engine. It's a question that can't be answered in it's current form.

jerry

 

JerryW correct answer not enough data. He has thrown this "bait" out before. Differential ratios can skew the answer either way.

 

Of course Bernhard is correct!

 

There's only one way to run a car down a Dragstrip in my opinion, full utilization of the power available. A question to you Jerry: In NHRA Stock Eliminator trim which 455 makes more power:

1. 455 Olds
2. 455 Pontiac
3. 455 Buick

And why does one particular 455 brand make more power? We won't include any of the BBC combinations because we all know they all make more power than any of the above. I would also add a power glide has no business behind any NA 455 engine period.

 

I'm just thinking out loud here....

When I flow cylinder heads, using the SF600 and the port analyzer software hooked to the flow bench, when you are flowing the head the flow moves up and down probably 2-3% peak to peak. This is why the software takes 5 samples about 3/4 to 1 second apart and then gives you that average as the head flow. But if I flow the same port 3 times (because I have done that) you will a variation of like 5ish CFM from the same port flowing it multiple times. I have not flowed a lot of the same heads, in fact probably only 1 of each head, but to try to find 3-5 more CFM, while not impossible, certainly is an art and not a science. The engineer in me struggles with "arts" as the world should be black and white.

Next time I flow a cylinder head I'll record a video so you can see the variation. I'm not saying that the stock guys didn't find power years ago, but I feel like it would be tough with the equipment I have access to.

jerry

 

Engine 1. You can put more gear behind it, which then puts more power to the tires.

 

By "quicker", what's the definition, a hundredth, a tenth, etc? Is cost a consideration? What's the difference between an orange?

 

Buick 455 will make more power due to its large bore 4.3125 and shorter stoke 3.90. It will move more air and rpm is your friend in stock class racing.

 

I will put it to you this way, its probably safe to say/post my NA 350 fuelie headed long bed shop truck is quicker than your Olds, more converter, more gear, more RPM.....................................

 

Exactly..................

 

I always find myself agreeing with you

 

Do to the age of the heads is it not hard to get a direct comparison in stock form? Would not any valve & seat work that has been done or not done to the heads over the life of the heads not effect the data? My question is not a knock on the testing! It would seem that once the heads have been ported or had valve seat work performed, that it would be a more direct comparison of skill, knowledge and potential of any given cylinder head.

 

I’m not a machinist, cylinder head porter, or an expert engine builder. With that in mind, it would seem that with enough money and flowbench time, you could get the worst head close to what a good head is capable. In the case of the J head, from what I understand it’s the most restrictive, smallest ports, and small valves. It seems to me if you had lots of time to experiment, you could port the heads to come close to what a performance engine really needs. You can make a port bigger, kinda hard to make it smaller.

Which brings up another question that’s been on my mind: I have seen numerous engine builder say there isn’t a big difference in flow numbers (with the exception of the j head) between all the castings. So why did Oldsmobile make so many similar heads?

 

matt69olds wrote:
Which brings up another question that’s been on my mind: I have seen numerous engine builder say there isn’t a big difference in flow numbers (with the exception of the j head) between all the castings. So why did Oldsmobile make so many similar heads?[/QUOTE]


That is a great question why did they have so many heads so similar?

 

Lots of reasons for different heads. First off when they added rotators they had to change the spring pocket depth. The F and D heads had one of the center exhaust ports NOT tied to the cross over. While I haven't published the data, the F heads seem to have something done to the ports to change their flow compared to the E head. But I bet most of the head changes are for cooling. Meaning there are directors cast inside the head to direct coolant flow where the designers want it to flow. My OEM background had a lot of changes to the heads for cooling and not for air flow. This is a bigger deal than most people realize.

jerry

 

Honestly you'd be surprised how little the valve size has to do with flow. Our port matched SpeedMasters have 2.07" valves and flow within a few percent of the Edelbrocks with 2.15" valves. The Batten heads that flow mid 320's have 2.105" intake valves and 1.605 exhaust valves (and that is the best flowing exhaust port I've tested). I am told that the main thing in the valve size is the ability to do a better blending from the valve seats into the bowls. Certainly the valve job and seat angle/s can have an impact on flow. I'm not trying to put together a perfect list of head flow. I have the cylinder head guy at Livernois cut the valves and seats to the production angles for that head. Newer heads had different angles than the older heads. This is about all I can do to make the testing as accurate as possible. If someone wants to being a "bunch" of the same heads to Livernois I'd flow them all to see the variability, but I doubt that's worth the effort.

Did I answer your question, I'm not sure.

jerry

 

Don't sell J heads short. You can make 400 HP with a set of stock J heads. That's pretty decent. If all you want is 400HP then they work just fine with no work to them.

jerry

 

Here is a dyno run comparison of C heads to J heads, with everything else being the same. Below 3000 RPM on the C head run I didn't have the throttle to WOT, so ignore that part. But the poor flowing J heads do pretty well.

jerry

 

Here is a graph of C to J heads with headers and an O4B intake. You can see at this point, once you start to modify the engine, the C heads perform better.

jerry