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  #16 (permalink)  
Old 01-07-2009, 02:27 PM
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my less than $.02:
the 5,000lb trailer is going to have you constantly/repeatedly in a very low Hg, crummy velocity, "rich mix" condition due to the load on the motor just driving normal....

to truly gain anything, you would need to custom engineer the whole exhaust system based on those conditions and your specific motor combo....

at only street rpms, 1500-3000, there aren't enough pulses in the pipes to make a big difference with which ever stock manifolds (or headers)....

your firing two cylinders on one head in succession so it's chaos anyway....

the cam and timing and rear gears ratio your using are going to account for the TQ available

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  #17 (permalink)  
Old 01-07-2009, 02:58 PM
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Well as long as we are dissing stock exhaust manifolds, let me add shorty 'headers' to the list of bad actors. They are nothing more than tubular stock manifolds and do NOTHING to add power. In fact, if I were a betting man, I would wager that Detroit spent more time designing their cast iron boat anchors for 'performance' than the shorty header guys do.
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  #18 (permalink)  
Old 01-07-2009, 08:13 PM
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Quote:
Originally Posted by willys36@aol.com
Well as long as we are dissing stock exhaust manifolds, let me add shorty 'headers' to the list of bad actors. They are nothing more than tubular stock manifolds and do NOTHING to add power. In fact, if I were a betting man, I would wager that Detroit spent more time designing their cast iron boat anchors for 'performance' than the shorty header guys do.
Amen brother, can I hear a hallelujah???
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  #19 (permalink)  
Old 01-07-2009, 08:30 PM
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Yes, long-tube headers are best for power, but in some applications they drag the ground so badly you can't get in and out of the driveway, much less negotiate some of the finer Louisiana railroad crossings. I had my fill of that business a long time ago.

As to the original question, the 350cid IROC-Z upswept manifolds had 2.25" outlets, and were only recently discontinued by GM. The aftermarket (Dorman, etc.) might be making reproductions, but I haven't checked.

Have you looked as Sanderson Headers? They're not cheap, but they make a bunch of different configurations and lengths of headers, and they also make a couple of different cast-iron manifolds for the SBC, one of which dumps downward just to the rear of center, and one that dumps farther to the rear. Check the buyer's guide at www.sandersonheaders.com
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Old 01-07-2009, 09:40 PM
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In fact one of my personal cars has factory cast.
Hooker Super Comps are $700+ and I don't feel that I need the extra power nor the $1000 expense to change out a system that is already working.

I build quite a few rods with cast iron manifolds for customers.

Sometimes the owner doesn't want the hassle of replacing gaskets
sometimes they don't want the expense of $1000 custom headers,
sometimes the ground clearance is a serious issue.

sometimes they don't really care about ultimate power. They just want a decent hassle free street rod/street machine that they can drive and enjoy.
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  #21 (permalink)  
Old 01-07-2009, 09:59 PM
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Here are the facts on headers vs. manifolds. Headers do increase power BUT - they do it at a specific RPM range at the expense of other RPM ranges, i.e., if they are designed for optimum performance @ 3500 rpm they will likely have less power @ 2000 or 5000 rpm. They do benefit from a little harmonic boost @ multiples of 2x rpm so the 3500 rpm ones would see a little bump @ 1750, & 7000 rpm. Further, that benefit only occurs if the headers are properly designed for that specific rpm. Unequal length, improper length, too large tubes, too small tubes all work against performance. Shorty headers violate all the rules - they are WAY too short, they are unequal length, exits are poorly designed - just not performance items. There are other considerations though - hot rods MUST have headers to look right, the look great under the hood of a stoplight bandit, etc.

Point being in 49willard's situation, looks don't really matter, he wants a good exhaust option so a cast iron manifold that fits will fit his needs perfectly.
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Old 01-07-2009, 10:47 PM
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Most headers are useless on a street driven vehicle.

The fact is that for the headers to be making more power ... the RPM range is above what a daily driven street vehicle runs most of the time. I ported the POO out of a set of manifolds for my 32 3W ... ( like I did for my 32 roadster ).

I may be giving up 15 to 20 HP over 3500 RPMS
The fact is ... I rarely have to turn my 32's that much. When I do ... I still have enough to do what I need it to do. Without all the header hassle . Headers also add a lot of under hood heat to the ambient under hood temperature ... which is not good. I like to run my spark plug wires down the rear of the block and up to the plugs.



I also like to use a set of Corvette ignition shielding to protect the spark plug wires from HEAT.

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  #23 (permalink)  
Old 01-08-2009, 12:33 PM
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here is a nice header versus manifold comparison article.

http://www.chevyhiperformance.com/te...ase/index.html
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  #24 (permalink)  
Old 01-08-2009, 12:43 PM
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shorty headers did better on this engine.

http://www.chevyhiperformance.com/te...out/index.html
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Old 01-08-2009, 02:00 PM
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Quote:
Originally Posted by ScoTFrenzel
Sometimes the owner doesn't want the hassle of replacing gaskets
sometimes they don't want the expense of $1000 custom headers,
sometimes the ground clearance is a serious issue.

sometimes they don't really care about ultimate power. They just want a decent hassle free street rod/street machine that they can drive and enjoy.

Exactly. Where is it written that performance always has to be about peak hp @ WOT?? Some of us like things like throttle response, reliability, bottom end power, street manners and fuel efficency.

Also, Id like to see a link that proves that equal length tubes is worth the bandwidth that it requires to write it.
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Old 01-11-2009, 09:51 PM
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That ZZ430 is giving up WAY MORE than 15-20hp over 3500 rpm.

Nice engine though, shame to not rev it over 3500rpm. Its such a great enegine when allowed to run to its potential.

peace
Hog
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  #27 (permalink)  
Old 01-11-2009, 10:14 PM
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Quote:
Originally Posted by Hogg
That ZZ430 is giving up WAY MORE than 15-20hp over 3500 rpm.
I do not know ... but I doubt if it is much more loss ... if any.
The manifolds are ported and then extrude ported.



As you can see from the GM chart ... horsepower is the best at just over 3800/4000 RPMS ... The roadster weighs just a tad over 2200 lbs and the coupe is just over 2600 lbs ... so they are rather " BRISK " at WOT. The 32 3W is actually the harder pulling and quicker of the two ... because it has a 700R4 ( 3.06 first gear ) ... and a 3.50 rear gear. The roadster was built before 700R4's became popular and has a Turbo 400 ( 2.48 first ) and a 3.00 gear in the gear ( now ) because of no overdrive.

With a 3.70 rear gear ratio ... the roadster has gone 11.70 in the 1/4 a few times. It would go quicker if I could put larger tires on it and work on the suspension for drag racing.

Have not been able to try the coupe at the track. They told me it needs a rollbar/cage Will not let me run the roadster anymore either. New track management ... and I guess it is best ... that way for safety.
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  #28 (permalink)  
Old 01-12-2009, 01:24 PM
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Quote:
Originally Posted by Deuce
As you can see from the GM chart ... horsepower is the best at just over 3800/4000 RPMS ...
That's torque. The horsepower curve is in solid blue, and reaches its peak a lot higher than that. Read the first paragraph in the page you scanned:

"This limited edition ZZ430 is GM Performance Part's most powerful small block crate engine. With 430 horsepower at 5800rpm and 430 foot pounds of torque at 4000rpm, the ZZ430 is the most powerful small block produced by GM."

Headers work. They provide a better orifice to dump the exhaust gases into, and the longer primary tubes shield the pulses of one cylinder from interference from others. That's one reason Brzezinski's modified manifolds, for circle track racers who have to use manifolds, work better than the merely ported or extrude honed. He welds in deflector plates to provide some of the same shielding. And even he can only get 65% of the same gains that you can from headers.

You're going to incur a penalty if you use manifolds instead of headers. If you've got competing priorities that rule out headers, that may well be an acceptable compromise. Does it really matter if that ZZ430 actually makes 430 peak hp or only 395, if it's pushing the car down the track as fast as you want to go?
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  #29 (permalink)  
Old 01-12-2009, 02:06 PM
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Remember the original request - desired result is good 'mid range' torque. That means good torque @ speeds below 2000rpm which is where the vast majority of us drive and where 49willard specifically intends to run his stump puller. Unfortunately all the advertised 'performance' products don't even start their power curves before 2000rpm. This is mostly because us hot rodders are most interested in the big HP the widgets make and that usually is @ 4000rpm and higher. Ignore the fact that you can probably count on one had the times your stop-light bandit will run up there. However, another reason is they don't want to show that their product will make a lot less torque and HP than a warm stocker at the low end of the RPM curve where most of us live.
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Old 01-13-2009, 08:57 AM
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Well, the original request had to do with what were the best manifolds to use since headers wouldn't fit. It then sort of morphed into a headers vs. manifolds threads.

You and I have a different definition of "mid-range." I don't consider 2k rpm and below mid-range on anything except my IHC Scout II with its 3600 rpm red line. But then that 392 was designed as a commercial truck engine. For non-commercial uses, even in a tow vehicle, more flexibility is required. Even that 330hp crate engine going into the '49 p/u that started this thread will probably have occasion to see more than 2k rpm. And the fact is, headers provide a useful increase in what I consider mid-range power. During its budget build of a GM Goodwrench engine a few years back, Chevy High Performance noted that the addition of headers alone provided a maximum increase of 53ft/lbs of torque on an otherwise stock 350 at 3400 rpms. Naturally, the engine saw increases above and below that engine speed, just not as large.

In addition to that, peak torque was actually achieved at a lower rpm than with stock manifolds. Manifolds weren't designed with to optimize anything other than durabilty, ease of installation, and price point. Certainly not performance at any engine speed.

They are adequate in what I consider the off-idle and low rpm range. But then, if you're only interested in performance at 2k rpm and below, you can't really justify a 4bbl carb let alone headers. At that engine speed a 350 only requires 200cfm of airflow.

Last edited by BinderDriver; 01-13-2009 at 09:08 AM. Reason: accuracy
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