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I know there are a lot of different contributing factors (different dynos, more aggressive tuning etc), but I cant imagine that headers will really make a 20hp+ increase on a T-bird. If that were true, I may say goodbye ported manifolds and get some kooks!
Long duration cams with a tight LSA (long overlap period) and stock exh manifolds do not mix. The reason is the that the overlap period allows for the exiting exhaust gasses to draw more a/f into the cylinder but this doesn't happen when the engines have the stock manifolds. The longtubes allow for scavenging while the stock manifolds (and shortys) do not.

Long tubes are the best option for heavy, autmatic transmissioned cars as they produce more midrange hp/tq than manifolds, shortys and mid lengths. Mid lengths would be the next best option and IMO stock manifolds and shorty headers are not a viable option in any way.

While we are on the subject of injectors would 42's or 60's be too much for my 4v? I want to experiment with E85 so I will be needing more injector, I think my dual 255 walbro's are up to the task and I'll be fabricating new filter to fuel rail lines and in tank lines / y-fitting.
I'll make this quick as not to contribute to any hijacking of the thread. 42s would be enough for a stock 4v on e85. A single 340lph pump or two 255s will work.
 

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Long tubes are the best option for heavy, autmatic transmissioned cars as they produce more midrange hp/tq than manifolds, shortys and mid lengths. Mid lengths would be the next best option and IMO stock manifolds and shorty headers are not a viable option in any way
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THANK YOU! That's what I've been trying to cram into the skull of certain boneheaded people but nooooo, they won't hear of it!
 

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Discussion Starter · #246 ·
One darned good explanation there on how cam overlap works with scavenging. You pickin' on my hard skull GM? :tongue:

I'll make do with what I've got, I more or less accomplished my goal to get a "fun street toy". It's more fun than last year for sure, but who knows - maybe it will be more fun next year than this year! :)

The tune needs work, no doubt, but I'm learning more as I go.
 

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Discussion Starter · #249 ·

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Lots of companies make 4.6L headers. The real questions is who makes them for the MN12?

The answer is:

KOOKS is the only company who makes them for the MN12. They only come in mid-length and you can only buy them through SuperCouper Performance as he as exclusive rights to them. It's my understanding that he paid KOOKS to develop them in exchange for exclusive rights to sell them. The only other option is to make your own or buy the KOOKS used.

You can get the KOOKS with 2.5" collectors or the bigger 3" collectors.

Some here have made their own by modifying other headers to fit the MN12.
 

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The answer is:

You can get the KOOKS with 2.5" collectors or the bigger 3" collectors.

Some here have made their own by modifying other headers to fit the MN12.
I've had many set of 4V and 2v headers but have never seen those for this body.

I would use the mids which I assume are 1 5/8" and lengten/step them with 1 3/4" tubing to 32-34" and use a collector no larger than 2 1/2". The amount if midrange power, at no loss of peak, would be substantial.

Has anyone tried the JBA mids made for the mustangs?
 

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Pipemax?

So far its me and one other guy who have modified/rewelded MAC longtubes for our 'chassis' using a 4.6
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I have a few "tools" as well. ;)
 

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IMHO - it needs a good set of headers. Stock MN12 manifolds start off 0.25" smaller inside than Mustang ones and the bends are horrendous. Cheap crappy Mustang long tubes are worth 18-20RWHP over Mustang manifolds so you can estimate about a 20-25RWHP gain from just a header swap in this chassis.

Then the auto sucks about 5-10RWHP over a stick, electric water pump is another 5-10, elbow/TB/inlet pipe is another 5-10. It all adds up but its a lot of small expensive stuff here and there. The 300ftlbs shows the potential, usually the HP limit is about 10 less than the torque peak with that intake on similar combos when maxed out.

The tighter LSA will make the torque peak higher, but will kill the power after the HP peak faster all else being equal. Retarding the cams with those exhaust manifolds will probably just cost power everywhere.
 

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Discussion Starter · #257 ·
IMHO - it needs a good set of headers. Stock MN12 manifolds start off 0.25" smaller inside than Mustang ones and the bends are horrendous. Cheap crappy Mustang long tubes are worth 18-20RWHP over Mustang manifolds so you can estimate about a 20-25RWHP gain from just a header swap in this chassis.

Then the auto sucks about 5-10RWHP over a stick, electric water pump is another 5-10, elbow/TB/inlet pipe is another 5-10. It all adds up but its a lot of small expensive stuff here and there. The 300ftlbs shows the potential, usually the HP limit is about 10 less than the torque peak with that intake on similar combos when maxed out.

The tighter LSA will make the torque peak higher, but will kill the power after the HP peak faster all else being equal. Retarding the cams with those exhaust manifolds will probably just cost power everywhere.
Thanks for the valuable input Nick. Headers are on my list of things to buy now that I better understand how cam profiles and scavenging complement one another, but I'm doubting they'll happen for at least 12-18 months. For the time being I'm focusing on cleaning up the rough edges in the tune and for the heck of it I'm putting a P&P'd plenum on it to go with the TB to see if it makes any noticeable difference in airflow.
 

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Increasing the airflow will do little if you don't als increase the ability of the exhaust system to get the larger air mass out. Also, electric water pumps are gret for racing and will free up some power, but I've never seen a 10rwhp gain from one, 3-5 is the standard. Auto tran's use roughly 5% more power than a manual; the more your engine makes the more power they eat.
 

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Something on the auto it sucks more power the higher the RPM and the heavier the converter. I remember a NMRA racer years back swapped from a 4R70 with a lightweight triple disc to a C4 with an unlocked converter and the HP curve matched up to about 4000, and above that the C4 was gaining more the higher the RPM. The C4 is a ton lighter rotationally.

On the plenum if you are going to polish up a stocker use the Crown Vic one, it is a good bit taller and fits under a stock MN12 hood. I have one on mine. You probably won't see any gain without also the exhaust swap, best I ever saw was 10RWHP from a combo of the Accufab and the JLT, and each seemed to be worth 5 by itself from all the other testers out there.

JL once mentioned to me the IRS ate a few HP (I don't know how much especially if the rear arm bushings are worn), and that his personal car never tested higher than 270RWHP.

The MAC headers GM has for sale would be nice or the Kooks I listed on Ebay. The Kooks are sweet at the head flange, best flange I have seen and equal to the Edelbrock Victor headers. The MAC need about an hour with the grinder in this spot, but with the MN12 conversion they have done that is a steal of a deal. Either one would be the best you could get IMHO, their just ain't any other choices I would spend money on.
 

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Discussion Starter · #260 ·
I am very interested in GM's set of longtubes, but I'm not sure how much I can justify spending right now (wedding in less than 2 months). It also seems like there's a lot of competition for those - and for yours too for that matter.

The right deal will come along, I just seem to have to sit by and watch this one drive by...
 
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