where are the horses?
 

My engine was dyno'd after it was professionally rebuilt, and it had 199 RWHP. This is what I expected, and was about 3 years ago.

This is a 1981 911 SC Euro, stock, other than headers and muffler.

Since then, I added Buckley Racing Headers, to replace the rusted European Racing headers it had. I was hoping for 205 to 210hp after the header swap.

I raced for a season (2013) with the new headers, but at the first race this season I could tell something wasn't right power wise.

In preparation for digging into this problem, I did a valve adjustment. Almost all were too tight for the feeler gauge which is somewhat interesting, I visually inspected the spark plugs, cap and rotor, and replaced the air filter.

I also did a leak down. Each cylinder has between 2% and 5% with the engine cold.

The timing was at 33 deg total advance after the rebuild. I use super unleaded (91 or 93 octane in these parts) so I set the timing down to 31 degrees BTDC at full advance. There are no vacuum hoses connected to the distributor or WUR.

Now for the amazing (SAE corrected) dyno numbers. My best run was 184 RWHP.

The air/fuel ratio was in the 14s and 15s at idle, was in the 13's until mid RPM range, then went down to the mid 12's for the last 2000 rpm. Each side of the exhaust showed the same A/F.

I tried several other timing settings - 33, 28 and back to 31. None improved the situation.

All of this looks to be as expected, other then the power. And, I don't have an idea as to what the problem could be.

A few other details. The dyno pulls resulted in 184, 175, 170 and 170 rwhp, in order, with timing of 31, 33, 28 and back to 31 BTDC. It seems like it got worse as we went and it seemed timing adjustments didn't make the changes we expected.

Any ideas as to what I might check next?

could be anything or nothing. Probrobly that it was a different dyno and that you had it done after a fresh rebuild.

Tell us about your air intake system and exhaust in addition to the new headers.

I was at a friend's dyno session and he found swapping the exhaust changed the HPs and even going back to OEM airbox.

Sounds like the last dyno was prob correct.
Getting 199 rwhp from a factory 204 hp unit is a bit unusual and slightly impossible.

As mentioned above... Different dyno.

Did you check....
 

the cylinder compression? When the engine was "brand new" the compression was probably a bit higher than it is now after some hours of track time. The valves being tight indicates to me that the valves and valve seats are wearing. This will cause your valve clearances to tighten up.

George's headers:
https://www.gt-racing.com/products-page/911-exhaust-systems/headers-for-911-2-7-3-2-liter-motors-with-street-adaptor/

Buckley Racing:
Buckley Racing - 911 Racing Headers
The only thing I can figure is the step to a larger diameter in the Buckley's (about mid-way?) slows the travel rate of the exhaust on stock/lower powered engines.

Buckley Racing - 911 Racing Headers
http://forums.pelicanparts.com/uploa...1401540968.jpg

Bigger pipes are not better, often you will lose low and mid band torque (from what I've read).

The Buckley's seem to be longer than the George's, typically meaning more low/mid torque for the longer Buckley headers. However, they may be slowing the gasses down with that step, which is great for 400 hp engines requiring that mass flow of volume, not so great for 200 hp engines which cannot push so much exhaust.

http://www.buckley-racing.com/911racingheaders.html
http://www.buckley-racing.com/images/parts/BHPleft1.jpg

EDIT:
I could not find the diameter of the George's street adapter which is after the 3:1 collector, but it's an apple & oranges thing as they are two different header designs.

1 3/4" is way too large for a 3ltr or even a 3.2. The correct size is 1 5/8" and anything larger like Kach says, you will lose tons of low and mid range hp and torque. You need at least a 3.6 to run those large headers, so if the new headers are the larger size this is undoubtedly the problem.

Exactly what I was leading to, my friend was hoping for HP gain with bigger pipes but was dismayed when he lost HPs, went back to his original aftermarket a more restrictive set up and HPs came back.

I am also concerned about the tight valves gaps, not good, sorry to write.

And there you go. :)

Frankly, 1.5" headers are the right size for a stock SC engine like yours. We get 255+ BHP from such engines using 1.5" ones so I'd be using George's Headers for your application.

Lastly, mufflers make a noticeable difference and I can tell you without reservations that they are NOT all the same, performance-wise. Choose wisely here, otherwise you wind up with less power than stock.

We routinely see 10-20% difference between the dyno we use the most (Mustand, maybe???) and other dynos.

fussy little things these engines are. I assume your using the stock CIS system and have to for rules?

Its the same dyno. And, we have to assume dynos are accurate or else there is no reason for us to use them.

The intake system is stock, and has not changed since the first dyno runs.

Buckley sells, I believe, more than one size of header. I have the one sized for the 3.0L motor, the original one.

Plenty of people have 3.0L euro motors (9.8:1 compression) and make over 200 RWHP.

I have not checked compression, but did a leak down as reported above.

The CIS is all there and all stock components. The only changes I can think of are adjusting the timing and removing the vac lines to the WUR and distributor.

Does it seem logical that this has to be an airflow issue (either intake or exhaust) since the A/F ratio looks good? My mailman suggested to check the throttle to make sure its opening all the way which I'll do next.

Maybe the A/F ratio needs to be altered outside of the typical normal band to resolve the issues. Maybe it needs to run much richer or leaner to suit this situation................more of a question or guess on my part.

Some reading on the topic I've done lately suggests that you are on the right track in attempting to tune the intake to match the exhaust cycle.

Exhaust System Theory 101
Exhaust System Theory 101
I would ask Buckley for help on this issue, they must have run into this before themselves during product development.

In the end; this just might be too much header for this engine.

You could exchange the headers for smaller diameter ones or get more hp out of your engine to fill out the power capacity of these headers.

Plenty of people have 3.0L euro motors (9.8:1 compression) and make over 200 RWHP.

I have a 930-10 and they are rated at 204 at the flywheel...I have SSI's and a 2 in 1 out muffler so it may make 215-220 max.
Drive trains take about 20% of hp.
You have about the same but are only losing 10% or less...what's your secret?

I have verified my throttle linkage is working. That was my best guess.

Here is a dyno chart for a PCA legal (ie stock other than exhaust) SC euro making 210 RWHP.
Buckley Racing - 911 Racing Headers

I made over 190 RWHP with the Euro headers, was expecting over 200 with the Buckley headers.

Are you running mufflers now off the Buckley headers? I've never heard of anyone doing that before?

The "mufflers" I have are the tail pipes that came with the headers... same as in the picture.

Anyone else use that Dyno recently that thinks it was reading low?

We recently dynoed a couple cars that made ~8% less HP then expected. Didn't trust the numbers as one of the engines was a fresh build that we had engine dyno data for so towed the cars over to another Dynojet on the other side of town, and they made the HP expected. Long story short, the first Dynojet had fallen out of adjustment and the brake was dragging a little bit.

If the car feels strong and all the correction factors are the same as the last Dyno, I'd try and find another Dyno. Something strange could be happening but those Buckley headers are supposed to be very good and I have first hand experience with the HRG branded stepped headers of similar concept to the Buckley's (the HRG's utilize a second step, and anti reversion chamber combine with a very trick custom collector instead of the ubiquitous Burns but the design principles are similar as would seem the results) and they have been good for 10-15whp over any other headed we have tested so your not wrong expecting more power if the engine is indeed still healthy.

A mechanic friend suggested to do a compression test next. I'd like to have other ideas.