Bigger Headers, Slower Car

[padam]

I switched out my old Hooker headers with 1.75" primaries and 3" collectors for a set of Dougs headers with 2" primary 3.5" collectors.
Neither of these have collector extensions.

I got out to the track Friday night, and found that the car slowed quite a bit
60' 1/8 1/4
Before 1.621, 7.623 90.20, 11.985 112.30
After 1.685, 7.687 89.70, 12.089 111.06

I think it bogged a little of the line, so matbe torque is down.
Later I removed the air cleaner/filter, and it seemed to slow a little more.
From this I am thinking it may be running lean with the new headers.

Can anyone recomend a move to get back the lost power?

 

[kiwigtx]

Need more back-pressure.

Sometimes less is more.

 

[ruffcut]

Looks like headers are too big for your combo without knowing the facts of the build. Just my thoughts.

 

[Cranky]

Need more back-pressure.

Sometimes less is more.

Boooo LOL. Like ruffcut said, need a LOT more info. Would also be good to take a read on the plugs. @padam do you have an O2 sensor on the car? I know larger tubes isn't always going to increase flow when maybe the smaller tubes were already doing the job. Usually leaner mixture means faster but at a cost of possible burning things up....also depends on the weather. What was the weather like with your last faster passes? I used to run my junk rich so the weather didn't have much effect on what my car was running. Actually slowed the car down to make it more consistent. Anyways, backpressure is usually what ya don't want! Sorry Roger lol

 

[WileERobby]

AS stated, the engine config is unknown. So, the pedestrian response would be to check AFR first.

Need more back-pressure.

Sometimes less is more.

Boooo LOL. Like ruffcut said, need a LOT more info. Would also be good to take a read on the plugs. @padam do you have an O2 sensor on the car? I know larger tubes isn't always going to increase flow when maybe the smaller tubes were already doing the job. Usually leaner mixture means faster but at a cost of possible burning things up....also depends on the weather. What was the weather like with your last faster passes? I used to run my junk rich so the weather didn't have much effect on what my car was running. Actually slowed the car down to make it more consistent. Anyways, backpressure is usually what ya don't want! Sorry Roger lol

Perhaps "backpressure" is not the applicable term here. Moreso, the "scavenging" effect of the headers and exhaust system, where the resonance is not optimum.

 

[padam]

1964 413 Block .030 over

906 Heads, milled .100, stock size valves.
Gasket matched intake ports and bowl area ported to the DC templates.

Compression ratio is roughly 11:1

Lunati Hydraulic Cam Part# 10230906
In Ex
.509 .534 Valve Lift
235 245 Duration at .050
Rhoads Hydraulic Lifters
Lunati 73815 Single Valve Spring W/ Damper

Edelbrock Torker intake.
Quick Fuel 850 race carb (OOTB tune).

Ignition system is an MSD 6AL-2

 

[padam]

The weather was a little worse (DA) but honestly the weather doesn’t seem to affect it a lot.

 

[Cranky]

1964 413 Block .030 over

906 Heads, milled .100, stock size valves.
Gasket matched intake ports and bowl area ported to the DC templates.

Compression ratio is roughly 11:1

Lunati Hydraulic Cam Part# 10230906
In Ex
.509 .534 Valve Lift
235 245 Duration at .050
Rhoads Hydraulic Lifters
Lunati 73815 Single Valve Spring W/ Damper

Edelbrock Torker intake.
Quick Fuel 850 race carb (OOTB tune).

Ignition system is an MSD 6AL-2

First thing I would do is to do a plug check. Seems like having an O2 sensor in the car makes things a lot easier to make sure your AFR is right.....I know adding headers for sure will change that but not real sure what going to bigger tubes will do but imo, you need to jet up. Do you know if the plugs were running clean before? If so, you're probably too lean now. Btw, I took a set of 906 heads and turned them into closed chamber heads years ago. Wasn't too crazy about how thin some areas looked though.

 

[Curiousyellow71]

Try collector extensions.

 

[padam]

First thing I would do is to do a plug check. Seems like having an O2 sensor in the car makes things a lot easier to make sure your AFR is right.....I know adding headers for sure will change that but now real sure what going to bigger tubes will do but imo, you need to jet up. Do you know if the plugs were running clean before? If so, you're probably too lean now. Btw, I took a set of 906 heads and turned them into closed chamber heads years ago. Wasn't too crazy about how thin some areas looked though.

I don’t have an AFR gauge.
The plugs looked good when I did the header swap but I haven’t pulled them since.
From what I understand you must check the plugs at the end of the run to really get good reading, and I really don’t want to go through all that.

 

[RemCharger]

Try collector extensions.

^^^^ might see 2 tenths. Go straight to 24".
At least that's what I'm trying and expecting.

 

[Photon440]

I don’t have an AFR gauge.
The plugs looked good when I did the header swap but I haven’t pulled them since.
From what I understand you must check the plugs at the end of the run to really get good reading, and I really don’t want to go through all that.

If it's too much hassle, at least pull one plug on each side. I'm betting that going up a couple of jet sizes will show an improvement.

I bought a 455 Pontiac once that ran terrible, the headers were rusted out and full of holes. With no other changes than new headers and exhaust it eliminated the stumbles and pops and ran strong.

 

[padam]

I had a couple of cracked tubes and plenty of backfires and popping.

But I’ll pull a couple of plugs.

Im not sure the whole back pressure thing isn’t a wives tale.

My plan is to upsize the jets and see what happens.

 

[ruffcut]

Forget the back pressure. Thats the reason for going to open headers in an all out race application, to eliminate any back pressure. Yes, it would have been good to read the plugs right after the run to get an idea if too lean.

 

[PRHeads]

I’m also in the collector extension camp.
But there is likely a loss of TQ in the launch rpm/shift recovery region that may just be gone with the bigger tubes on that combo.

Don’t take this the wrong way, but that engine combo isn’t “hot” enough to make proper use of 2 x 3.5 headers.

But some extensions should perk it up.

 

[Cranky]

I had a couple of cracked tubes and plenty of backfires and popping.

But I’ll pull a couple of plugs.

Im not sure the whole back pressure thing isn’t a wives tale.

My plan is to upsize the jets and see what happens.

A buddy of mine started over after burning a hole in a piston because of being lean but that's the way he rolls.....always looking for that extra bit of ET. I ran brackets so being consistent was what I was after and found that being on the rich side (along with a few other changes) made it that way. And I'm with Mr. Porter above about 2" tubes are on the large side with your combo but if you plan on going faster sometime in the future, you already have them. If your engine is built well, can ya take your shift points a bit higher? If you can, you might see an improvement in your ET.

 

[33 IMP]

Try collector extensions.

THAT is EXACTLY what I would suggest! No extensions gives up a bucket-load of midrange torque. Especially with a possibly too-big collector. I run 2" hookers on an iron head 440, and built a 3.5 exhaust system to simulate 3.5 collector extensions while running with mufflers. I wouldn't be surprised if my car is slower, uncorked,with no extensions.
Edit: hadn't read the whole thread before I opened my mouth. Looks like several people smarter than me already covered the collector extensions.
Engine masters did a show on collector extensions, lengths and size. Naked headers, no collector extensions, gave up something like 40 foot-pounds in the mid-range on a 500hp engine.
(You could try a 3.5 to 3 reducer, and a 3"extension after that)

 

[PRHeads]

The “just right” Goldilocks size for a combo like that are probably 1-7/8 x 3, like the Hooker Competition headers.
And even those would likely only be marginally better than the 1-3/4 x 3.

 

[Rusty knuckles]

I don't think a need for back pressure is the issue. I think your tune has changed with the bigger header. Specifically your air fuel ratio. I'm not at all a believer in back pressure being a good thing.

 

[Cranky]

I don't think a need for back pressure is the issue. I think your tune has changed with the bigger header. Specifically your air fuel ratio. I'm not at all a believer in back pressure being a good thing.

BP is NOT what ya want in any high performance engine......or any engine imo.