Tlambert

Should I upgrade my exhaust?

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My 72 had the engine rebuilt 7k ago, before I owned it. E12 head, 9.5-1, 90mm piston, 284* cam. 38/38 Weber.Still has the stock exhaust. Will I gain much by installing a header, larger dia. tubing?
Thanks, Tom
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10 minutes ago, Tlambert said:

Will I gain much by installing a header

 

Not much, the 72 exhaust manifold didn't have the restrictive thermal reactor found on the later cars.  Somewhere in the archives, someone compared the flow rates between the Tii manifold, and other manifold options and I remember there not being a huge difference between them.

 

Most of the fun owning these cars is working on them and upgrading them.  It's always nice having new parts under the hood and the pride of doing it yourself and knowing it is better, even though you can't feel the difference between stock.  Some upgrades pay huge dividends, others don't.  This one is the latter.  If you do change it out, use the gasket from a BMW 320i with the heat shield and update your exhaust nuts with copper.

 

IMHO,

 

 

Mark92131

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Remove old exhaust manifold and heat shield .

Install Stahl Header Ceramic coated

use exhaudt header gasket/ heat shield

combo

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3 hours ago, Mark92131 said:

Some upgrades pay huge dividends, others don't.  This one is the latter. 

 

 

I disagree.  A nice ceramic-coated header drops underhood temps by a noticeable amount and a nice header/exhaust does add a some power.

 

Case in point, here's a 8whp and 9ft.lbs. of torque difference between a "tii" system and an aftermarket.  When we're dealing with 105whp that's roughly an %8 power gain.

 

https://www.bmw2002faq.com/forums/topic/156299-any-experience-with-ies-shorty-header-for-2002/?do=findComment&comment=995319

Edited by AceAndrew

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Andrew, thank you so much for the science/ data proof on the performance  improvement with a good header.  The Tii manifold is so good I wondered how much hp you could get better. It's nice to have a objective confirmation , It helps me justify my header habit.

 

Thanks again, best regards Peter

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I have a header habit as well.

 

But let me add...

 

y do u want to consider a new set up?

 

hp?

sound?

looks?

sexiness?

 

 

I looooove aftermarket or custom exhausts. 

 

Many set ups wont do much....and can even hurt power

 

Andrews post is a great one...and he knows

 

I enjoy driving  car more w/ a custom exhaust sound...some prefer oe noise. My experience is that a well chosen set up always gave me more than oe......sound, less bulk, and  more at upper end of rev range..above 4k.

Edited by jrkoupe

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I have a header habit as well.
 
But let me add...
 
y do u want to consider a new set up?
 
hp?
sound?
looks?
sexiness?
 
 
I looooove aftermarket or custom exhausts. 
 
Many set ups wont do much....and can even hurt power
 
Andrews post is a great one...and he knows
 
I enjoy driving  car more w/ a custom exhaust sound...some prefer oe noise. My experience is that a well chosen set up always gave me more than oe......sound, less bulk, and  more at upper end of rev range..above 4k.

Just info for down the road a bit, you know just putting my fingerprints on the car. New suspension goes in soon, nothing crazy- I.E. stage one, with Billy hd's, Rot R20' s soon after that. Eventually a 245, that's pretty much it. When I was young I had an 02 "race car" with a license plate, don't need that again!


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With what you've done to the top end, yeah, I'm with Andrew- something a bit 'bigger' will help.

 

MY take on it is that if you did a collector- back pipe, you'd probably see the best bang- for- buck:

the stock system's about perfect for a stock engine turning 3500, but at 5500 with better carb and cam,

that pipe's small.  If you keep the stock tri-y, it'll not hurt torque as much as a header "might".

 

The stinker with all of this, of course, is that the only real way to test it is to dyno, put on the new parts, and re- dyno.

 

So most of us do what makes us feel fastest (red underwear, etc) and say "It added at least 15bhp at the wheels".

Because science is hard, and at the end of the day, if the driver's happy, it's a good day.

 

t

 

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I will give a seat of the pants perspective on this. My Porsche 911 would barely pull redline at the oldest, most famous Hill Climb in the USA, Giants Despair. Giants Despair was won by Roger Penske in 1959 in a Porsche RSK, Carroll Shelby, and other people race there in the 50s and 60s.

On the final straightaway which has a higher/steeper slope ratio than pikes Peak, my 911 would pull all the way to eight grand after I put on a set of larger headers, the difference in top end power (6000 RPM through 8500 rpm) was huge, when running flat out. The headers brought me within one /2 seconds of the historic class record at that time, which was held by a Penske  Trans Am Camaro.

TLambert, with your pistons, cam and carburetion you may pick up a good 10 hp with a large header, and a free-flowing muffler, such as magna flow. There is always a balance between creature comfort And performance. I will say as I've gotten older I prefer exhaust systems that don't drone, or wear on me on a long trip. I say go for it, I think I would use an Ireland Shorty header, with 2 inch through pipe and low flow muffler such as a magna flow at the back of the car to keep sound down.

Best regards, keep on oversteering, Peter911.JPG

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Good  story, but what is the relevance of the exhaust of a 911 to a 2002 M10  ? Have you ever seen the exhaust manifold of a 911 OMG   Maybe I missed something in the post.    Beautiful  911  BTY   No disrespect I've had several 

Anyway regarding BMW 2002's 

I've looked at a number of posts  with dynos etc. on the Tii exhaust compared to a header and it seems that a Tii exhaust  produces greater HP in the mid range rpms  And  you don't want to go over  1 3/8  tube size if you have a car that will be driven on the street.   Look at some old Sthal  dyno  info on Goggle

I was going to buy a header ( 1 1/2  tube size)  which seems common , and a stainless steel exhaust from IE for my current rebuild  9.5 compression 292  cam Weber 38/38 carb  etc. , but after considering the increased mid range power of a Tii manifold and more free flowing exhaust , the expense  doesn't seem worth it considering  less mid range power on a car that will be street driven

 I've come to the conclusion that these motors are more drivable on the street with a little restriction on the exhaust . Be careful about big porting and big exhaust unless you have a race car.

Now if you are driving on the track and want flat out top end power , then go big !

My evolving theory for a street car,  is to port the intake manifold to mate with the heads and polish the exhaust ports of the head to meet a Tii manifold for  best  all-around performance on the street 

Comments and experience are most welcome

Thank you my friends

 

Rob

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Rob, 

 

You have looked at outdated data.  A proper header does not lose midrange in comparison to a Tii header.  You want a 1.5" primary on a street car (especially if we are talking about a mild street cam).  I've said and proven this over the course of the past several years.

 

On the exhaust side, try to keep your porting to a gasket match so as to keep a mild step between the header primary and the head itself.  You do not want a smooth transition at that point (especially on a street car).

 

Hope that helps, good luck with you project.


-Andrew

Edited by AceAndrew

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Thanks Andrew, 

Coming from you I will take this as Gospel  I'm sure you have seen more recent dyno runs to confirm this

 I may just buy the IE header and the stainless exhaust which was my original plan. I know you have noted that the header and exhaust system should be part of a 150 hp build

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Rob, my point is that the increased primary tube diameter is just as relevant on a BMW 2002 or a Porsche 911 when you are looking at flow, dynamic  waves, and back pressure. An engine is essentially a pump, and optimal tuning of the intake and exhaust track significantly affects flow, based largely on things like the classic formula for flow, being one over r  cubed. It's not just the car, it's physics.  I added the story because it was a very real seat of the pants difference. Before I would be in third gear and watch the tach very slowly crawl from 6500 rpm's upward. After adding larger diameter primary headers, the car would continue to make power so much that I took the Rev limiter out and would let it slowly wind to 8000 + rpm's, which it reached just at the finish line. This was at a track with the absolute most fantastic power requirements of all due to the incredible slope and fight against gravity. My BMW M10 motor also ran better after installing a header, however, the difference was not so dramatic.

 

Best regards, Peter

DSCN8584.JPG

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Thank you Peter for clarifying  I was just speed reading and didn't follow you  My Bad  Your post and  those of others have convinced me of the importance of a header

My first M10 car felt very anemic compared to my 911SC as it should.  I'm now on a mission to produce 150 hp in the second car to get the 2002 up to the same power to weight ratio of the 911

Guess I'll have to break down and pop for a header and exhaust system

 

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