Custom race Tri-Y headers going lean

[rj4004]

I originally put these on a nhra FE powered Stock Elimator National Record holding car. It left the line very lazy, but still ran decent mph, 60's and 330's were soft, but seemed to run decent up high, the air conditions were not very good as it was at the MotorPlex near Ennis. I was blaming my new cam for the soft performance, but decided to go to the dyno the next week and try some different cams, headers and collectors and compare the graphs. Once at the dyno I made a pull with the aforementioned "weak" camshaft, but instead of the Tri-Y's I but my 4-1 headers on. Then I installed the Tri-Y's and made a couple of pulls. When the graphs were overlaid you could see the issue. Around 3600 rpm the tri-y graph drops off 15 ft lbs Torque . At 4100 rpms Tri-y's are 20 ft lbs of torque down, at 4400 rpm's its 25 fts lbs low and at 5300 rpm"s its only off 2 or 3 ft lbs. Not much different on the HP side stayed 4-6 hp low all the way.

I took the Tri-Y's off and ran the 4-1 with the merge collector after that, now I want to try the TriY's again.
I thought at the time it was going lean because of the TriY's pulling hard on the carb signal, now i'm not so sure.
Any body have any experience or feedback they would like to share?
Thanks
RJ

[mag2555]

its hard to say!
The first thing I would want to do is see which cylinders might have a big change in EGT's in that rpm spread.

On the dyno where your BSFC numbers changing and going low in that rpm spread, and then climbing back up?

[rj4004]

Sorry but no O2’ sensors.

Appreciate your response, was hoping someone might have had same experience but worked through problem. I’m an old guy and down on my “get up and go” and looking at easy way to figure it out LOL.

Thanks
RJ

[mag2555]

Well another thing that comes to mind about running used Exh parts that are not in great shape, or ciramic coated on the inside is rust scale.
I have whitnessed test where the motor lost close to 45 hp up at 7400 rpm due to the added restriction created by internal rust scale in a set of Headers that no one noticed at first, and other folks have even reported bigger losses!

[rj4004]

Should of explained it better, motor had 20 or so passes on it with the 4-1 headers, Tri-y’s were given to me by REF unlimited (Greg) to try and give feedback.
Both sets of headers were coated inside and out. This was a fast combo before installing the NEW Tri-Y’s, nothing was changed in tune before install.

Hopes this helps.

Thanks
RJ

[Tuner]

Sorry but no O2’ sensors.

Appreciate your response, was hoping someone might have had same experience but worked through problem. I’m an old guy and down on my “get up and go” and looking at easy way to figure it out LOL.

Thanks
RJ

O2 sensors are the easiest way to figure this out. Any change of headers requires double checking jetting, whether different diameter pipe or length of 4-tube and is particularly so from 4-tube to tri-y.

Once upon about 35 years ago a 427 BBC in a '69 Camaro a header change from 1-7/8" to 2-1/8" headers that were otherwise almost identical (I recall both sets were Hooker) inside the frame unequal length pipes from ports to collector, most direct route so pipes progressed longer from rear to front cylinders, the engine ran so bad with the new headers I thought we broke the distributor cap when lifting the engine to do the header change. A well sorted out carb that ran sweet and got good mileage needed a total recalibration. Main jet went down several sizes and the PVCR went up to bring the WOT back to where it should be and the idle jet and air bleed both needed to move toward a significantly leaner calibration.

[motormonkey]

To get any true answers, we need more info to even start helping.
What did the plugs look like? Did you try jetting? Do any timing changes? Did mph fall off? Do you have the dyno sheet of the comparisons?
Changing headers means changing the tune for sure.

[Abbottracingheads]

If the motor went lean it means the new headers are not pulling on the carb as hard, therefore less signal.

[hoffman900]

If the motor went lean it means the new headers are not pulling on the carb as hard, therefore less signal.

Or they killed reversion and you’re not getting the double fueling effect in those rpm ranges, which you would expect properly built tri-y’s to do.

[Tuner]

Or, they are improving scavenging and pulling fuel through the cylinder out the exhaust port, in which case (actually any case - same with jetting) playing with collector extension length to find the ideal is an important consideration.

[hoffman900]

Or, they are improving scavenging and pulling fuel through the cylinder out the exhaust port, in which case (actually any case - same with jetting) playing with collector extension length to find the ideal is an important consideration.

That too.

Really hard to say without more information.

[Tuner]

BSFE numbers from the dyno would help.

[j-c-c]

Or, they are improving scavenging and pulling fuel through the cylinder out the exhaust port, in which case (actually any case - same with jetting) playing with collector extension length to find the ideal is an important consideration.

I would have thought this was a very favorable sign, and jetting and/or cam rethinking in order, just thinking out loud with no real expertise.

[bob460]

What's the size of each header?

[gr9082]

How long are the secondary tube and what size. Is the firing order right on the header tube