Small block Chev (classic) exhaust notes/tuning physics etc

[HowlerMonkey]

http://forums.hybridz.org/index.php/topic/70271-diy-180-degreesingle-planeflat-plane-v-8-crankshaft%e2%80%a6/

 

[faytmorgan]

I'm friends with Paul the guy who started that thread (braaap). We have both talked on this subject. I also have posted on that thread. I am part of that forum. That is far from new to me.

So what is the shorter vs longer primary going to do to the power curve? Anyone?

 

[HowlerMonkey]

That was covered in headers 101 during freshman year.

 

[faytmorgan]

That was covered in headers 101 during freshman year.

... what?

 

[mender]

Long works better for lower rpm, shorter is for higher rpm. A reasonable length for street is in the 36 to 42 inch range depending on the application.

A longer tube will respond to higher rpm as well because of "overtones"; the resonance is not as strong though.

 

[faytmorgan]

Will them being that short compared to the 34 inches have a particularly negative affect though? As in on the dyno power?

 

[HowlerMonkey]

"Shorty headers" are a compromise for ease of installation.

They fall somewhere between stock manifolds and proper equal length headers.

Since I've been a Z car specialist for 25 years, what is the goal of this project?

 

[faytmorgan]

weekend road racer/street/show car I did three years of research before I bought an engine block, 6 months of research before I bought my heads, another 6 months of looking at every engine builder in MN before I chose a guy to do the heads and block.

I am well acquainted with what I am doing with this car and why I am doing it. The biggest challenge is lack of tire, and finding parts to meet exactly what I want, as many other things as well of course. I have been asked by hundreds of people the purpose of the car and been told hundreds of opinions. I couldn't care any less about opinions than I already do, I want exact facts.

I am using the stock r200 3.545 gear set, 245/50r16 tires on 16x8.25 inch rims. I measured the width of the rim they are actually 240mm in width so 245mm would be perfect. They are 320aa rated firestones. I have a deal with bridgestone/firestone that give me buy two get two. These are the only W rated tire I could find in the width I needed in a 16. Which makes sense seeing that it is an 80's IROC size tire. 1978 280z 5 speed donor car. I will be working with carbon fiber to for body work as soon as the engine is in. I am keeping the glass, I don't want to mess around with not being able to see. I am using 280z stub axles as well as the half shafts with the premium grade u-joints until I get the arizona z suspension kit. I will be using the toyota pickup upgrade for front brakes. For the rear brakes I will be trying to locate a kit for the 240sx brake swap. M and M are a pita to get a hold of I've tried for 6 months now. They can go to hell as far as I am concerned. I may make a bracket myself and sell it for half the price to the z guys just to spite of them.

This is also a car I will be keeping for the rest of my days so there will always be more. Eventually I will be making my own custom efi itb setup from a e92 m3 intake and itbs. Lots of projects for this car ahead.

Did you have something else to add?

 

[faytmorgan]

Long works better for lower rpm, shorter is for higher rpm. A reasonable length for street is in the 36 to 42 inch range depending on the application.

A longer tube will respond to higher rpm as well because of "overtones"; the resonance is not as strong though.

Can you touch a little more on "resonance"?

 

[Highspeed]

Think of resonance as pushing someone on a swing. If your timing, resonance, is in tune with their speed you can add to their speed (or maintain it) by pushing fairly lightly each time. If your resonance is out of tune with theirs you will either impede their movement or have to push harder to affect it (imagine pushing when they are almost at their peak outward moment). The problem with exhaust is that it's not as simple as a siphoning effect from the exhaust passing the other pipes at the collector. In reality, a pressure wave bounces up and down the pipes, and if you did everything correctly, it creates a low pressure in the pipe at just the right time. The problem with that is, the wave moves so fast that the first wave is not the one you can use (at least not on a vehicle - this is where the 'overtones' mender was referring to come in). Through resonance, the waves work together to create the pressure wave at the right time and aid in exhaust scavenging; but that's only part of the story... Collector length affects tuning also, as well as diameter. But, the rest of the exhaust has it's own resonance too, which can sometimes cause some unexpected, and irritating, noise from the exhaust at specific engine speeds.

Header programs generally ignore the rest of the exhaust system and normally the dynos don't have the entire exhaust system in place. For racing that's fine, but for street it's misleading. The shorty headers have a resonance to them, but it's like someone pushing the swing more often, so the swing has to swing faster to match the resonance. And, just to make it worse, once you pass peak torque the whole collector (and exhaust) is just getting in the way anyhow. Exhaust (and intake as well) is a very dynamic area with more R&D than you would ever think is required.

 

[faytmorgan]

Well I suppose that is the exact reason why I am here asking questions.

Also I have been told to make as short an exhaust as I possibly can, for basically the reason you just gave. If I can get the headers from an x pipe immediately to a muffler that takes the exhaust out the side immediately that is what I am after.

That tone from the shorty headers (sound of the exhaust created) is something I am after btw I don't know if you saw the videos I posted.

 

[HowlerMonkey]

Did you have something else to add?

Sure, I'll bite.

Headers: If your piping diameter, length, and collector dimensions are not tuned for your desired rpm range, then all you have is headers that flow better than the stock setup.

Yes, your scavenging will increase with shorty headers over stock manifolding (not all) but the lack of tuning diminishes your returns.

The tipping point that made shorty headers popular is the ease of installation of shorties vs a much harder install for the true tuned long tube headers in the fox body mustang.

I would consider that the recipe of header length/diameter/collector...etc. for your desired rpm range has already been beat to death and is chronicled on many an internet site for sbc and that your issue will be either finding a vendor that has the product you need or building your own to fit your unibody.

If you want true 180 degree headers, I'm not sure where you would have room to pull this off and still be able to keep the length of the tubes optimum.

R200: I would recommend a 4 pinion carrier for it.

Engine: If you want 10.5 to 1 on pump gas, there had better be some quench in your setup or you will be compromising the power by having to pull too much timing.

I feel that the later iron vortec heads from the late LT1s, if found at a salvage yard, would be the best bang for the buck and would pick them even over the aluminum lt1 heads from the corvettes of the same year.

I saw 7 of them while contemplating the two Lincoln mk Viii 4 cam engines a couple of days ago.

If you've already cemented your engine, then continue on but beware high compression on older cylinder heads designed before what we know now because most lack the quench (read detonation resistence) you need to run that ratio.

Transmission: Hammering the tunnel or cutting material away will be needed for clearance of the transmision itself. You also might end up with having to relocate or modify the gas pedal linkage because it will also hit.

Distributor: You surely won't be getting optimum engine position with a Delco HEI distributor overhanging the transmission flange so that has to be considered...unless you run the horribly crappy optispark...which is a distributor mounted to the front of the engine...which fills with water or oil if you aren't on top of all leaks.

These are just a few things off the top of my head that you will have to address for success.

I would be glad to make you headers but my current backlog of aston martin header fab jobs dictates that I we would have to charge near 10k for them to put the aston stuff on the back burner.

 

[mender]

I can help you out with that: send a few of the Aston Martin guys up here and I'll fab headers for them!

 

[faytmorgan]

Where does one find said 4 pinion carrier? I have never seen them available for the r200.

The heads are aftermarket AFR nockoffs that are getting done up by Travis knowlton at Knowlton's thunderhead in bethel mn. So I am not worried a damn about quench. He think I can take it higher on compression but I am going to stay on the safe side of 10.5:1