Help, Grumpyvette!

[John Scott]

With all the variables with headers, could you give some idea as to the power differences on a 383 running a 1 5/8 shorty, 1 3/4 shorty, and full length 1 3/4? What effect would changing the collector on the full length from 3 to 2 1/2, for floor clearance, have on the engine? I assume few will ever run a dual 3" system anyway.

JS

[Guest Fast Frog]

Grumpyvette and/or others!!

 

John and I appear to be "tracking" together on this one! Both John and I are having the same engine builder(from Ft Collins, Colo)build our new engines. John, as noted, is having a 383 built. I just recently, finally, made the decision to have a 406 built to replace my 383. I think we both have a good handle on what performance application we're looking for with respect to street vs race and the engine components needed to make it work.

 

I've got a good feel for what I might need for heads, roller cam, compression, etc. And of course I'm keeping my Accel DFI sys and fuel inj intake manifold. But the big frustration is trying to sellect the proper exhaust components My application,(though a larger engine than John's) may be little milder than John's. My cam may not be quite as radical and my head work work may not be quite as intensive as John's. My goal is 450HP@5500rpm+ or -(at 4700 ft elev)and 450-475Ftlbs of torq@4000-4500rpm.

 

EXHAUSTwise I'm thinking that 1 3/4" headers dumping into dual 2 1/2" pipes with low resistance mufflers like the Dynamax Magnum(now called Welded)should do the job.

 

All expertise, suggestions, comments, etc will be welcome!! ALSO, from earlier posts(of a few months ago) regarding the applicability of Sanderson 1 3/4" headers, is there another 1 3/4" header out there that provides a better fit in the proverbial shrinking 280Z engine bay!!

 

Thanx,

 

Rick

[John Scott]

Grump mentioned a while back, the torque curve from a hugger 1 5/8 to full length 1 3/4 would move upwards about 500 rpm and 250 rpm wider, no mention of hp differences. I guess I'm throwing in too many variables.

From what I could gather, shorter tubes for high rpm motors, longer for low end. So much more to this, but looking for the best compromise.

Anyone, ANYONE else using a different 1 3/4 besides S&S full lenghth?

Fastfrog, as Rick Johnson suggested, maybe we need to see how much it would cost to have S&S build one to fit the Z chassis better. I would go for the 2.5 collectors, shorter overall by about 6" and somehow raise the passenger side where it should be. My starter is really small.

JS

[Guest Fast Frog]

John:

 

I'd be interested in checking into a set of custom made 1 3/4" block huggers that would that would both improve performance and fit better in the Z engine bay. Maybe have the driver's side header extend about 15 degrees rearward to better clear the steering linkage! Who/what is S&S? And do you have a phone # or email address? John, email me at home.

 

Rick

[John Scott]

Rick, I'll give you a call this weekend.

JS

[grumpyvette]

sorry guys I have not checked this forum lately;

look here,

Exhaust Valve

 

When the exhaust valve opens, a compression wave is sent downstream and reflects back as a rarefaction wave when an opening in the exhaust system is encountered. Experimentally it has been found that the optimum position of the piston when the wave returns is 120o. At this position the remaining exhaust gas can be scavenged from the combustion chamber. The required length of the exhaust pipe can then be determined.

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

Exhaust System Diameter and Engine Horsepower- A popular idea is to select/size the exhaust system components to the engine's horsepower output. This idea typically attributes a header diameter or an exhaust system diameter to a particular horsepower level. To resolve this, look at how an engine operates and consider one cylinder. The cylinder will move a volume of air based on its crankshaft geometry, rpm, and sealing capability. The amount of air that can enter the cylinder is dependant on the intake flow capability, crank geometry, rpm, and valve timing as a minimum consideration. Likewise, the amount of air that exits the cylinder is dependent on the same characteristics.

 

An engine's output is usually thought of in terms of horsepower. Actually, an engine produces torque, and the horsepower is calculated through a units conversion. The amount of torque an engine can produce is directly related to the amount of cylinder pressure generated. This is all affected by the same previous characteristics (intake and exhaust capability, crank geometry, rpm, valvetiming, etc). So basically an engine's power output is about air exchange capability. Using this line of thinking, look at the exhaust path again. The exhaust system is more reflective of the engine's ability to move air, as opposed to horsepower numbers. Engine output does not address the breathing aspects of the engine and is probably not a good rule to use for exhaust sizing.

 

There is a very good reason that tuners/engineers/specialist have attempted to assign exhaust to intake relationships around 70-80% for a typical natural aspirated set-up. In non-detailed terms, it is a range that offers a good balance for power capability. Other relationships, such as 1:1, are used and they work very well, but these methods have to be applied and tuned for very specific circumstances. This relationship does not stop on the flow bench, it goes all the way from the intake path opening to the exhaust system termination. In short, try to maintain exhaust sizes that are inline with the intake capability. Also, do not stop your analysis at the intake and exhaust paths. If the engine already has the camshaft, look at the valve events. If the specs favor a restricted exhaust (indicated by early and wider exhaust openings with wider lobe separation angles), then size it accordingly by using exhaust components with smaller cross-sections. If the valve timing specs favor the intake, then the engine needs some serious exhaust flow capability which is only possible with larger cross-sections.

 

This section was written with natural aspirated combinations in mind. However, by using the 'air exchange' rationale, it becomes apparent why forced induction engines typically benefit from increased exhaust flow capability. Also, look at the nitrous combinations. The intake system remains virtually unchanged, yet with the major increases in cylinder pressure it acts like a substantially larger engine on the exhaust side, requiring earlier exhaust openings and/or higher exhaust flow capability

 

first look here to get an idea of the pipe lengths necessary,

 

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

 

now the short answer is that the inside header dia. should be the same size or slightly larger than the exhaust port on your cylinder heads so as not to cause a restriction in the exhaust flow and a length determined by the engines displacement and rpm range but read these exerts from other articles.

 

 

 

http://www.burnsstainless.com/TechArticles/Theory/theory.html

ust flow capability.

 

How much hp can a 1 5/8 header support? When should you "graduate" to a 1 3/4? Are there other factors besides hp that determine primary tube size? Thanks here this will get you a ballpark idea on what size header to use,..as a general rule your going to make more hp and torque with a 1 3/4" header size in most cases if the engine flows more than 660 cfm useing this formula (displacement/2 x max rpm /1728)

example#1 (a hot 383 that spins 6500rpm racing)

383 /2=191.5 x 6500rpm=1244750/1728=720 so this engine would be better off with 1 3/4"

 

example#2 (a 350 tow engine that seldom if ever sees 6000rpm)

350/2=175 x 6000rpm=1050000/1728=607cfm so this engine would benefit more from 1 5/8" headers

[John Scott]

Thanks Grumpy, your advice always appreciated.

Do you ever take a break from our enquiring minds?

This guy needs a medal or something.

I'm starting to learn a little more here. After reading what would be ideal for a particuar application, sooner or later, due to time and money restrictions, we need to realize there's going to be a compromise when dealing with a tight frame and big engine. Try to shoot for the best bang for the buck. After reading the Headers by Ed site, someday I'd love to make my own set of headers.

JS

[danj]

Grumpy

 

Would you please view the comments under the topic 280ZX Conversion in this exhaust column and comment on fabrication design, which becomes a big issue on most sbc installs. Thanks,

 

DanH

[ZROSSA]

Howdy all,

 

I went throught the headers buy ed site about a year ago and ordered his tapes and cataloges and all the rest. When this came up the other day and i listened to his tape again. He is very particular about equal lengths and not over sizing the exhaust. I belive he sugested the best place to start with a small block chev was 36inchs long with a 1 5/8 d. and 2.5 inch collecter. Now The husband of one of the ladys that I used to work with is way into v8s, nascar and in exhuasts. He has done a lot of work for the local race guys and agreed with a lot of what Ed says. I can give him a call if you want. Last time i was yakking he wanted flow rates on the heads and cam timing to set up the headers. I didnt,and still dont have this inf. yet so i havent talked to him for a while but if you can get me some specific questions i give him a call.

 

Btw, Grumpy, whats your opinion on 180 degree headers or 180 degree cranks. I just love the sound but wonder if they are worth the effort.

 

Happy easter all.

 

Douglas

[grumpyvette]

180 deg headers are great but a hell of a lot of work because some of the cylinders on one side of the engine must feed the collector on the oposite bank of cylinders, 180 deg cranks are just not worth the extra expences involved in changeing the engine to run a 180 deg crank.

[Guest Rick Johnson]

Grumpy,

Excellent referal to the exhaust/intake length site. Intake air temp is easy to ball park. What about exhaust temperature?

 

What temp is the exhaust from a good running SBC at 5K RPM?? With this we can determine theoretical header length.

 

Further, would we size our header length to coinciden with max torque, max horsepower, or possibly for our max RPM (shift point)to provide less horse power drop before we shift??

 

Thanks, Rick Johnson

[grumpyvette]

1250F-1300F or 950K-978K for the site

 

try sizeing the headers for max hp but at 1000rpm lower than your engines red line rpm