Custom Race Header Power Loss.

[jimmysxxl]

Hello Everyone i am new to this forum my name is Jimmy and i am from Greece. Lately i stumbled upon a strange issue and i would like to think what you experienced guys think about the issue. The engine is a Honda 1.8 litre , 12.7 CR. The Cam is 265@1mm for Both I/E , 12mm Lift Int. 11.5mm Lift exh. Exhaust opens at 55Degrees BBDC.

The Engine was built for track racing and last dyno figures where 230hp@9000rpm tuned at 12.5AFR. The Header on the dyno was a 4-1 1.77 diameter 34inches long with a 2.5inch Short Collector.
In the Pursuit of making it stick to the competition in the straights we built a new Header. 4-1 Rotational Firing Order 1.88 diameter 21.5 inches long with a 2.5inch Long Collector with a 2.25 inch chocke. The intended powerband was 6-9krpm.
The Result we got was Vast Loss of Power. Power Loss Occured only on High Cam. Low Cam everything was Smooth, AFR's where spot on, Throttle Response was Crisp.
When High Cam Engaged AFR Suddenly drop to 9:1 from 12.5:1 that was tuned with the previous Header and stayed around that value till the revlimiter.
I am trying to find out which aspect of the header could cause such behavior and why only on the High Cam ? Overlap Issue ?

Pics of the Said Headers

Old One


New One



Any Insight on the issue would be Really Helpful! And sorry for my mediocre English usage

[W. Tripp]

Pull the plugs and look closely at cylinders #1 and #4 with a magnifying glass or jeweler's loupe.

[CamKing]

Can you make it engage onlt the high lift intakes, and leave it on the low lift exhausts?

[CREngines]

My thought is the primary is to short. Probably need to be more like 28". Collector could be a bad length also. Somebody will pipemax it for you and give you a better idea. Id do it now but i need to get back to work. If nobody does it later ill run it for you. Beautiful job on the header though.

[jimmysxxl]

Unfortunatly no i can't do that without fabricating locking pins for the intake. Do you think it has too much Cam on the exhaust for that short primary lengths ? btw the Opening Value for the exhaust is measured @1mm

[CamKing]

Do you think it has too much Cam on the exhaust for that short primary lengths ?

That was my thought. If you had a shorter duration exhaust cam you could run, that would be the first thing I tried.

[german4inline]

Hello,

my estimation is that your primaries are much too big for your expected output of around 230 bhp. A primary dia. of 1,88 inches ( for us Europeans 47,7 mm) is big enough for about 300+ bhp. 15 years before, I did engines for the German STW ( similar to the british BBTC, 2,0 Liters , max. 8500 rpm ). Your exhaust dimensiones are definitly good enough ( just regarding the dia.) for 300 ++ bhp, thereby it doesn´t matter that your engine is just a 1,8 l. The required exhaust pipe dia. depends from the amount of gas flow created by the combusted charge, in turn depending of the power output. No matter which displacement the engine has ( we talking about 4 inlines basically)

I guess your previous header was not that bad, but still too big for your target. I would prefer a 4-2-1 style which creates a bit more torque in mid reange with almost no losses in peak power if the tuning is well done. Primaries dia. max. 42 mm, Lenght 75 cm, secundaries 15 cm, Main dia. 2,5 inches.

I know the disappointments with too big headers. The well-known british Rover K-engine , as well 1,8 liters, generates 240 bhp with 38 mm primaries, at least if you believe the rumours.
For 230 bhp, the peak rev with 9000 seems too much for me, if the engine is perfectly tuned, this kind of power has to be seen at 8200-8500. This is always a sign of too big header or probably too big porting with too low gas speed and maybe low rate of combustion. How much spark advance does your engine require with the big header for max. output?
If you choose a header too big, you will loose overall power, low, and midrange and probably peak. If you choose a bit too small, you will probably loose a bit of peak , but you will win low and midrange torque and races

Udo

[jimmysxxl]

Thanks a lot for your reply. Yes i know that the header diameter is too big compared to other engines out there but OTS 4-1 Aftermarket Honda Headers are usually around that primary Diameter so even if just diameter was the problem i dont think it would cause such a massive loss. As Camking mentioned earlier we have also reached the conclusion that exhaust Cam duration is too big for the Primary lengths. But i've crunched the numbers before fabricating and it's not that far off optimal at least on paper.
I had also simulated the header in EAP ( Engine Analyzer Pro) and the actual result was far off from the Simulation .

[CREngines]

this should be in the ball park. i got the inputs close but they are not exact. your length looks right but way to big on diameter. Anybody feel free to run it again i may have missed something.


--- Single Primary Pipe Specs --- for 109.378 CID from 7000 to 9500 RPM
Diameter= 1.492 to 1.617 Length= 20.3 to 23.5 inches long
--- 2-Step Primary Pipe Specs ---
1st Dia. inches= 1.492 Length= 10.2 to 11.8
2nd Dia. inches= 1.617 Length= 10.2 to 11.8
--- 3-Step Primary Pipe Specs ---
1st Dia. inches= 1.492 Length= 10.2 to 11.8
2nd Dia. inches= 1.617 Length= 5.1 to 5.9
3rd Dia. inches= 1.742 Length= 5.1 to 5.9

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 2.769 to 3.019 Tuned Lengths= 12.3 best and also 6.1 or 24.6

--- Header Collector Specs (Megaphone or Diffuser Cone Shape) ---
Diameter= 2.269 taper to 3.269 Megaphone/Diffuser Length= 12.3 inches

Best HP/TQ Tuned Collector Lengths= 12.3 , 24.6 , 49.1 , 98.3 inches long

Worst HP/TQ Loss Collector Lengths= 18.4 , 36.8 , 73.7 , 147.4 inches long

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 93.7 inches long ... typically never used
2nd Harmonic = 34.8 inches long ... longest recommended
3rd Harmonic = 20.3 inches long ... highly recommended , best Torque Curve
4th Harmonic = 13.8 inches long ... shortest recommended
5th Harmonic = 10.1 inches long ... typically never used
6th Harmonic = 7.7 inches long ... typically never used
7th Harmonic = 6.0 inches long ... typically never used
8th Harmonic = 4.8 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 98.3 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 49.1 inches long ... longest recommended with Mufflers
3rd Harmonic = 24.6 inches long ... more bottom-end Torque
4th Harmonic = 12.3 inches long ... highly recommended , best Torque Curve
5th Harmonic = 6.1 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 3.1 inches long ... reduced Torque , not recommended


************** Metric Units ******************

--- Single Primary Pipe Specs -- for 1.792 Liters from 7000 to 9500 RPM
Diameter MM= 37.897 to 41.072 Length= 516.8 to 597.9 MM long
--- 2-Step Primary Pipe Specs ---
1st Dia. MM= 37.897 Length= 258.4 to 299.0 MM
2nd Dia. MM= 41.072 Length= 258.4 to 299.0 MM
--- 3-Step Primary Pipe Specs ---
1st Dia. MM= 37.897 Length= 258.4 to 299.0 MM
2nd Dia. MM= 41.072 Length= 129.2 to 149.5 MM
3rd Dia. MM= 44.247 Length= 129.2 to 149.5 MM

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter MM= 70.344 to 76.694 Tuned Lengths= 312.0 best and 156.0 or 312.0

--- Header Collector Specs (Megaphone or Diffuser Cone Shape) ---
Diameter MM= 57.644 taper to 83.044 Megaphone/Diffuser Length= 312.0 MM

Best HP/TQ Tuned Collector Lengths= 312.0 , 624.0 , 1247.9 , 2495.9 MM long

Worst HP/TQ Loss Collector Lengths= 468.0 , 935.9 , 1871.9 , 3743.8 MM long

Note-> all Pipe Diameters are OD and based-off 1.588 MM Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 2381.2 MM long ... typically never used
2nd Harmonic = 883.9 MM long ... longest recommended
3rd Harmonic = 516.8 MM long ... highly recommended , best Torque Curve
4th Harmonic = 350.8 MM long ... shortest recommended
5th Harmonic = 256.3 MM long ... typically never used
6th Harmonic = 195.2 MM long ... typically never used
7th Harmonic = 152.5 MM long ... typically never used
8th Harmonic = 120.9 MM long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 2495.9 MM long ... longest with Mufflers and TailPipes
2nd Harmonic = 1247.9 MM long ... longest recommended with Mufflers
3rd Harmonic = 624.0 MM long ... more bottom-end Torque
4th Harmonic = 312.0 MM long ... highly recommended , best Torque Curve
5th Harmonic = 156.0 MM long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 78.0 MM long ... reduced Torque , not recommended

[Strange Magic]

Even if you where to double the HP (460) and double the liters (3.4), your new header would still have to large of a primary and way to short of length.

Just taking a stab at it, the header primary's should be around 1.687 and no more than 1.750 with a length of 28-31 inches and a 2.5 can that is 10 to 12 inches long.

[german4inline]

Even when Aftermarket headers from well reputated comp. are that big diameter, I wouldn´t trust those stuff. The companies make whatever customers are asking for, and most customers are thinking the bigger, the better. In Germany there are also headers offered which are way too big, they will be bought by guys which have never seen a dyno or rolling road. Definitely, the dia is too big, the calculation after my posting confirms the dimensiones, and the others experiences guys does it as well.

[jimmysxxl]

Thanks a lot for your Replys everyone. As CRengines mentioned the Length seems good on paper but in Practice it just fails miserably. As for Primary Diameter the area of the exhaust port face is 1271mm^2 in a 42.5mm ID pipe is 1418mm^2 and in the current 45.5mm ID is 1590mm^2 .
Is the Change THAT Big that would cause such a tremendous change in Engine Operation ?? I got zero empirical information on the matter so i am sorry for all the questions.

[CREngines]

How long is the collector portion?

[jimmysxxl]

Strict Collector Length is 7" the tailpipe is 15.5"

[Runit]

In the 70s Cosworth BDDs (1600 4valve) used either 1.875"x27"-2.25"x27 "or 2"x24"-2.5"x24". They made 215 or so and would run to 9600. A 1.75" system killed them.