[BigRed-L72]

We need some advice on what to do with the smallish collector that is on a set of Hedman headers that we`ve been using.

Head pipes are 2.0" but the collector is only 3.0"
The exhaust pipe diameter that`s on the car is 4.0" including X pipe and turn downs.
Currently using a transition conector to step up to the larger pipe.

We`re thinking of a slip on merge collector with 2.0" tubes and a 4.0" collector.

Motor is a 555" that goes 7K rpm MAX.

Ideas ??

 

[marks412]

I have done all the dyno testing on this. The Hooker Merged Colectors worked the best. Funny thig is, thay are the least expensive.

http://www.summitracing.com/parts/HOK-14752HKR/

Only problem with your set up is thay have a 3 1/2" exit, not the 4" you need.

I used the 2 1/4" to 4" on my 582. 6800rpm.

Hope this helps

 

[BigRed-L72]

Thanks Mark. Schoenfeld has a merge collector that slips over 2.0" tubes and has a 4.0" exit. $41.00 ea.
That might be the one we need.

 

[540Hotrod]

It would be fun to do some testing on the small collector vs the larger one with the pipes attached. Depending on the 3" collector configuration you've essentially made sort of a venturi.

From Burns' site:

The construction of a merge collector is such that the change in area at the primary tube to collector transition point is minimized. This gradual transition allows the exhaust gas to maintain as much velocity as possible. Maintaining gas velocity is the key to allowing the exhaust system to reach its efficiency potential.

JIM

 

[1989GTA]

"Maintaining gas velocity is the key to allowing the exhaust system to reach its efficiency potential"

That potential is to create a greater "pull" during the overlap period to get the intake charge moving. Gots to fill those cylinders.

 

[Jesse 496]

I think the burns merge collectors are designed for open headers?

I'm using a 4 inch dr gas x pipe and its only about a 3 x 1 7/8 hole in the cross over so I think we got the venturi effect going on there lol.

I read somewhere for every 1/2inch you go up on the collector diameter it raises peak torque by 500 rpms ?
If this is true maybe it would help me get some consistent 60s.By softening up the bottom a bit.?

I have a small cam and heads for a 555 and a beastly 8 inch ptc converter with 9inch tires. Out of 30 are so runs 20 have been aborted due to traction issues.

It sucks to drive the car 70 miles pay the track and for gas only to get horrible 60 foots and abort most of my runs.

I hope they don't leak? when done.

 

[GRN69CHV]

I think the burns merge collectors are designed for open headers?

I'm using a 4 inch dr gas x pipe and its only about a 3 x 1 7/8 hole in the cross over so I think we got the venturi effect going on there lol.

I read somewhere for every 1/2inch you go up on the collector diameter it raises peak torque by 500 rpms ?
If this is true maybe it would help me get some consistent 60s.By softening up the bottom a bit.?

I have a small cam and heads for a 555 and a beastly 8 inch ptc converter with 9inch tires. Out of 30 are so runs 20 have been aborted due to traction issues.

It sucks to drive the car 70 miles pay the track and for gas only to get horrible 60 foots and abort most of my runs.

I hope they don't leak? when done.

Wow, does this sound familiar, except I only have to drive 45 miles. Just curioius, are these trips to the track on sanctioned event days or something like Friday night street nights? JMHO, I kinda doubt any change in header collector size is going to effect the torque curve enough to drastically change the ability of the car to hook on anything but the best track conditions without a true dedicated drag tire (here come the arguments). I fought this with a 469"/rec port/3000 stall combo. Never knew if the car was going to leap when I nailed it or it was going to be an on/off throttle deal at the light. Frustrating to say the least.

Can't comment on the collector size, you may even see a nice increase in top end just going to a 3.5" collector over the 3", then out to the 4" pipes as opposed to 4" all the way. Those Hedmans are typically a nice fitting header, but the 3" collector does choke it down some coming off of 2" primaries. IIRC, those are not equal length primaries?

This may get off topic, not meant to be. Closest I've ever come to getting the car to launch on the Friday Nights was when running a vac sec carb with a high rate black secondary spring, but, the car was always down 1.5-2.0 mph over a DP, which we just assumed was due to the carb not opening all the way. Holley used to make a HP1000 in a vac sec, was popular with the Mopar guys. Saw one on RJ last year that I almost bought to try. Prior to going belly up, BG had expanded their line of HP style carbs to include vac secs all the way to their 1000 cfm carb, were marketed just for this situation.

That 8" PTC converter is probably not helping things either. I went with TSI 10" extra low stall N2O converter (2700-2900) behind the 540" in an attempt to get the car moving well below where the torque curve gets real fat. Tall order considering how these motors build huge torque right off idle.