Aluminum Heads with Cast Iron Exhaust Manifolds

Much appreciated, Jim! (and Tony)

 

I guess it all boils down to this: manifolds (even with an "X" pipe) will never perform as well as a full-length set of headers, particularly when the power levels increase.

Which brings us to the realization that it really just comes down to what power level you're seeking to achieve, and use whatever gets you there. There'll always be trade-offs.

Sure, headers could give substantially larger numbers across the entire powerband, but if those numbers exceed the goals sought, the question would be whether or not that extra power was desired, or could be accommodated by the rest of the car's drivetrain and suspension.

Then there's the other considerations: sound level, fitment, ground clearance, cost, appearance (stealth or stock look desired), longevity, preference, etc.

To remain a bit more on-track with the theme of the thread, manifolds would work fine on the aluminum heads, and a desired power goal could easily be achieved (as was previously mentioned), within reason.

Just tossin in my 2c.

Thanks to everyone.

 

Also keeping to the theme of the thread...the final results of the engine's output is more determined by the builder's plan to use such characteristics.
Even changing the valve job and basic bowl work helps to blow down the cylinder, changing the effectivity of overlap or if little used, the cam's phasing to balance reverse pumping at the bottom of the powerband with a strong step-up in response when awakened, or if the application requires a smoother tuning.

It's quite feasible to utilize manifolds with very high powered engines.
You just need a good plan.

 

Your generalizing.. which leads to pages of nonsense.

Limit your input to the BBB, and your experience with it.

I agree that if you spend $600+ porting stock exhaust manifolds, they will work fine on the average 12 second car.. That's a 450HP motor.. still gonna be 10-20HP shy of long tube headers, but alot of guys like manifolds.. which is fine.

Your talking about "very high power" engines. In my book, that is 700 plus.

So tell us about your very high power Buick 455 based engine, with iron exhaust manifolds.

It's apparent, you "have the plan.."


JW

 

I'm actually quite impressed by yours and Chris' manifolded combinations, and was thinking about results you've posted previously that show the biggest gains being in the lower end of the rpm range.
I think the combos you two show are extremely well suited to the demographics of the customers.

No intent to create 20 pages of havoc.
I'm generalizing because the values offered are very generalized.
Not all headers affect the same rpm range or power level, obviously.
As stated, Buicks have fairly nice manifolds...I think the OP's query is a fantastic one.

If my comment was out of place, feel free to delete with my apology.

 

No need for that.

Just understand that in this forum, we have a focus on the Buick V8, and in this category, the 400/430/455.

So when someone asks this question, what they are really asking is should I get TA or MT headers (Dougs to a lesser extent) or keep my manifolds.

So I use the headers they are going to use..certainly in primary size and length, as well as collector size.. most likely they are the exact ones that they will install.

We simply don't have the variety of primary sizes that you can get with a Chev or a Ford.. so discussions of headers specifics are not really required. They tend just to mush up the topic.

I think that everyone agrees that you can spend $500 to $700 on ported manifolds, and in the 400 to 500 HP range they won't be a huge hindrance. Under 400 HP their really is no need for them at all.

But above 500 HP, enough airflow exists that your really starting hinder the engine, and there is nothing your going to do with the manifolds, the engine parts or specs to change that to any great extent.

It's simply a cross sectional area issue.

JW

 

Does milling the divider and/or using a spacer move the peak hp rpm any?

 

No, no change in rpm band/peaks, just better numbers. Not enough of a difference to raise the torque peak, like a single plane intake does.
JW

 

In reply to your post #26;

I'm referring to how the length of the tubes affect the rpm band, ie. shorty headers and manifolds have more of an affect (if any) at a higher rpm, whereas the longer the tubes get, the lower the rpm range is...with a slight carry over beyond that.

My comments are meant to support what you are saying regarding cross sectional area and the common sense of a well put together package suited to what the market supports with complimentary components...I get it.

I also support that it's very difficult to use the same manner to test where and how said gains are at due to the limitations and protocols of the hot-rod type water brake dyno.
You just aren't going to see step-up response, get a stable enough pull down low, or be able to maintain a part throttle procedure across the board that shows the improvements to driveability or mileage because of the type of dyno.
That doesn't negate perceived benefits, only that it's tougher to test or prove.
I've seen the same things with every engine type I've tested or built, including Buick powered daily drivers.
I chose not to use that method for testing those things.
I'd really like to see Gary's creativity developed via vehicle testing, even though it may not be in the OP's thoughts for this thread.

So, the OP is asking a very general question, "does it make any sense to...?".
Of course it does, and even so...
A well matched combo as shown will 'likely' have low and midrange increases with long tube headers, but like anything else...relies on good tuning and matched components.
Likely only means that I haven't purchased or tested the actual engines shown here in the thread to quantify the results.
Full throttle power from the torque peak upwards would still be as predictable as it's always shown, with any type of engine, just as it's been shown here, noting that Buick manifolds are better than most.

 

If you want more power out of an engine with the stock manifolds...plumb them into a turbo. Problem solved. :laugh:

 

To be honest, I wouldn't really consider 10* of exhaust duration to be a 'manifold' type cam (especially on a BBB, which has stock cam specs in excess of 30* exhaust emphasis), no matter the power output (if my opinion holds any value).

We've seen camshafts used by Chris to have 20* of exhaust emphasis with extra lift on the intake, with very impressive results.

It's something that I have mentioned before seeing his cam specs, and I was delighted to see positive real world results. So now the big, heavy ball is a rollin'...

Knowing that it can't get in if it can't get out, increased airflow demands that more exhaust evacuation be facilitated in some way, usually headers, but the more these engines produce, the more difficult it becomes in trying to get manifolds to perform--even ported, showing very small gains for high dollars (perference/ruleset has no pricetag in some cases), but we also know that having the rest of the exhaust system pull harder on the manifolds will aid them in dynamic ways the manifolds themselves are not capable of; the trick here would then be to find out how much is feasible/possible.

I don't believe anyone here is trying to belittle or question the validity of anyone else's hard work and impressive results. Just offering up some ideas/suggestions in a generalized way which can be applied to these big blocks.

We could create another thread to discuss this if it is not deemed appropriate to do so here?

There is good reference here in this thread already though, so would be ideal to continue in this one.

 

You must be talking about advertised specs on the cam Gary, no factory or aftermarket cam has 30* more exhaust than intake duration @.050

I am talking about duration at .050.

Lots of crossed wires in this thread, previously someone thought I said headers were worth 100 HP, then someone else thought I said headers were only worth 8 HP more than manifolds on a 500 HP engine.

Camshafts with 19* more @.050 duration have been around since the mid 70's. The KB 118 and 113 cams specifically.

I have an entire line of cams designed for stock appearing engines that I use regularly. They are proprietary and have lots of split.

Those are iron head camshafts, totally different exhaust port than the alum heads. 10* split on an alum stage 1 head is plenty.

This is the problem with these discussions in generalities.. You need to specify exactly what your talking about, because as we all know, it's all about he combination of parts.

JW

 

I enjoy discussions of all types, because you just never know when you're going to learn something. Thankfully, I never stop learning, and it enriches me more and more every day.

I greatly appreciate you taking the time to reply and engage in this discussion, Jim.

I feel privileged. :bglasses:

Oh, and here's that cam with 30*+ duration I was referring to for the BBB.

I did mean @.050, since this OEM replica made by Federal Mogul shows 194*/225* @.050.

That rings in at 31* exhaust emphasis @.050 and a whopping 46* @.006!

Crazy, huh?

Those stock cams can be kinda weird though. Asymmetric lobes and all that.

 

I stand corrected...

I should have said "performance camshaft".

Something with 194* at .050 is not really worth looking at, with today's gas, your talking about an 8.5 or less compression engine to keep from rattling it to death.

I build performance engines, be they stock or beyond that.

JW

 

Jim, speaking of stock appearing cams with wide splits, what do you feel is the most overlap (@ 0.050" timing events) that doesn't hurt performance in an iron headed stock appearing engine?

 

Overlap.. the boogie man when it comes to stock appearing.... p

I like 7-10 degrees overlap in"well prepped" versions of these engines. Too much more than it seems to hurt output.

And that little overlap does make is sound more legit. :grin:

JW

 

Thanks Jim! I've run ~7 and it seemed reasonable but haven't tried more in pump gas engines.

 

I'm going to go out on a limb here and say that I suspect that at least part of the reason that JW recommends the use of Fel-Pro exhaust gaskets is to protect the cylinder head-to-exhaust manifold surface from galvanic (dissimilar metal) corrosion. Continuing along that line of thinking, I'm recommending the the exhaust manifold install fasteners be wet-installed with silicone sealant or exhaust header/manifold paint. By wetting the inside of the exhaust manifold holes in the cylinder heads, and the threads of the bolts with high-temperature silicone sealant or (VHT) high-temperature flameproof paint, and installing and torqueing the manifold/header bolts while still wet, the threaded aluminum holes will be protected against corrosion for many years.

 

I don't look at just the small number, but the relatively large number on the exhaust side and the relationship between the two, which was the point I was trying to make. Not trying to get off on a 'stock' tangent here, but touching on the subject a bit to make a relevant point about how exhaust emphasis exists in copious amounts, even for stock cams (when manifolds are expected to be used).

All engines are performance engines, it just depends on the degree of performance.

The asymmetric lobes on that particular cam I showed create an airflow dynamic that presents larger changes as RPMs increase, and a 91* IVC point (based on its retarded position 282* @.006 specs, not its advanced position 194* @.050 specs) puts it above and beyond most 'performance' camshaft profiles which would allow a high compression engine to run on very low octane at low load and lower RPMs, but cylinder fill and VE potential unfold exponentially as RPMs climb. IF one were to take the time to study the cam specs on that camshaft (as opposed to dismissing it based on glancing at its smallest number), one might be surprised at what one might learn on what non-quench, large combustion chamber detonation tolerances are expected to be from an engineering perspective given the target audience of intended usage. Also not to be dismissed are the specs @.006, especially when the ramp profile is much greater between it and .050.

That cam is capable of in excess of 400 hp and well over 500 ft. lbs. with very little done to the rest of the engine. I believe there is room for improvement, which is what I wanted to lead into here, but I know a roadblock when I see one.

I believe the ratio relationship between the intake and exhaust play more of a role in how much emphasis is needed, which is why the aluminum heads get away with needing less; however, when you're using the same exhaust manifolds that came with iron heads, more is needed/utilized despite how much the heads can flow since the manifolds are the restriction in this case. This would not be observed when using headers.

The point being that putting manifolds on an engine that makes much better use of headers would come as no surprise that the manifolds castrated it.

Thanks again for this dialog, Jim.

 

Your make some strong claims, and I look forward to reviewing your testing data.

JW