Crappy Dyno Results on 3.4L Rebuild (Status Update)
 

I just came back from a dyno run on my 3.2 to 3.4 rebuild, which included 98mm Mahle pistons, GT2 cams, Bursch 1 5/8 ID headers, M & K muffler, Autothority MAF, Polished intakes, matched injectors, SW chip, aluminum pressure plate. Dyno gave me a very disappointing 196 rear wheel HP (SAE corrected). I was expecting about 40 HP higher. Of course the Fuel to Air Mixture was very high (about 15). My question is: Can all of this be corrected by getting a new chip to fix the fuel mixture? Or do I have bigger problems?

http://forums.pelicanparts.com/uploa...1395518898.jpg

I would contact Steve Wong. I understand that he can take direct data from a Dyno Jet when he is doing custom chips. It may be that your engine combination doesn't exactly suit one of his normal chips.

It is too lean. Get your chip adjusted or get your DME adjusted. Run premium gas; make sure yiur DME is set right; i think there is also a California smog wire you need to disconnect (use search, I can't remember the details); get your AFR into the 13 or 12.5 range at peak torque. You are way too lean. I think the DME may retard spark if it detects too much heat, too, so that could be a factor if you are so lean you are overheating the engine...not sure, it has been a few years since I had a Carrera.

You should get more out of that engine if you have everything set right.

Check plug gaps, too. And air filter, etc.

Good luck!

no results are bad, they tell you if you have a problem and help diagnose issues. you cannot compare results across dynos.

you are way too lean. did the dyno operator say anything? i wouldnt have kept doing any more runs and would not drive the car until you diagnose why you are soo lean. chech that other stuff emery said too. you want to ba about 12.7 - 13 under full load

who built the motor? sure the cam and ignition timing are right?

Maybe my math is wrong, but the relative increase in displacement is close to the relative increase in HP, so it seems to me (from what I know) that the change is reasonable, considering that no major change was made to the induction system, i.e. no ITBs. Grant it, you probably have some room left on the table in regards to tuning.

Is this cam optimal for plenum induction?

Agreed. That 15:1 would have me looking at a misfire perhaps. 13:1 is the target I use when tuning all motor air to fuel. When I look at your peak numbers vs. Rpm, I think you're leaving a lot on the table here. Generally when I see this and there is no misfire I think the fuel pressure regulator isn't matched to the chip/programming.

http://forums.pelicanparts.com/porsche-911-technical-forum/452853-motronic-tuning.html

The above thread has some detail about the CA wire and the DME settings you can make yourself. Be careful with changes - you do not want to introduce a scenario where you damage your engine, so take it slow.

You also should check your fuel delivery overall: plugged filter? Etc. For some reason you are lean.

It comes down to two dimensions: timing advance and fuel delivery in combination to get you where you want to be.

Thanks for all the advice.
Redcoupe: I sent an email to Steve. I’m starting to think that I have another problem, that once fixed will allow my chip to work fine. I found this thread very helpful in addition to the one Emery suggested:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/288564-dme-motronic-o2-sensor-questions.html?highlight=DME+O2

Emery: I checked for a vacuum leak using a can of carb cleaner and found none. I inspected the air filter and cleaned it. It did not appear clogged or damaged.

Overheating? I do not know what the cylinder head temp is reading (could be part of the problem), but the oil temp gauge is reading in the low normal range.

JohnJL: I did 3 runs--all with very similar results. Dyno Guy offered to do more runs, but I did not want to because (as you stated) fear of doing damage. I didn’t come prepared for tuning. If I did I would had put on the stock “flapper” mass flow sensor and seen if the Autothority MAF is the problem.

As for who built it? I’ll leave his name out of it for now. I do not want to give him bad press before he has a chance to fix it… but he is a very reputable builder, does lots of race cars, hill climb cars and has worked with people such as Alois Ruf. My plan is to take it back to him and ask some questions based on all of the Pelican’s advice.

AlfonsoR: Yes you are right the HP is not that bad. Assuming I was at 207 BHP when I started. The pistons should have brought me to 207 x 3.4/3.2 = 220 HP, then accounting for 15% drive train loss, it would bring me back to 187 RWHP, which is close to the 196 that I got. I just think with the cams, intake and headers, I would be closer to 220 RWHP. The guy did the run in 4th gear. Is that normal? So, to your point (and JohnJL “there is not bad dyno results”)… the problem is NOT the HP, but the mixture.

Lapkritis: Misfire? Would I hear it? It sounds great.

One other symptom, which might be related is that sometimes it will not idle and shifts to 2,000 RPMs (high idle?) and sometimes to 1,100 RPMs.

Bottom line: I’ll take it back and have them check the plugs, fuel pressure and cam/ignition timing.

Thanks for all your help. I’ll let you know what I figure out.
Tim

Problem with the chip tuning is that it's not the typical type of tuning done for the engine. This is because of the Autothority MAF system you have installed. I'd consider getting a baselined 3.4L chip from SW, and install the old standby barn door air flow meter. SW knows the deal with the Autothority MAF. But I suspect you'd be better off with the original system because he's done MUCH more development & tuning on cars with the original system.

Way too lean.
13:1 maybe down to 12-12.5:1 to get the most power.
I think you should be close to 220 rwhp.

Kevin,

I agree with what you are saying... I have never been impressed with that Autothority thing. I would have been horrified if I paid full price for it. One thing that makes me think it is OK: Before I did all the internal engine mods, I put in the chip, the intakes and the MAF. I passed emmisions testing... but of course that wasn't under Wide Open Throttle.

Tomorrow, the shop is going to look at it. If they can't find a fuel pressure or a timing issue, I'll go back to the flapper door sensor.

Tim

Tim,

What fuel were you running? Did it have any alcohol content? As the motor was super lean near PK TQ it is possible you ran it out of injector. Do you know what fuel pressure you have? Can you monitor it on the dyno? I would be checking spark plugs if you made 3 pulls at 15 to one. I would suggest you have the dyno operator NOT continue any pulls that go leaner than 14.2 at or around PK TQ.

Good luck. Please let us know what you find.

That is a good observation PFM (that max lean correlates to peak torque, thus injectors might be maxed out). Fuel had 10% Ethanol (yuk!).

I'm taking it back to the shop tomorrow and will have them check fuel pressure and pull the plugs. I'll get a pressure gauge to tap into fuel rails for MY next dyno. Should be a simple tool I can get from our Host?

SW informed me the chip was created from some air flow data he received via phone... so, although I probably have some other hardware issues (fuel pressure), eventually I'll need a new chip.

Stochiometric of E10 is richer than gasoline, around 14.1. So this exacerbates the lean issues more.

Its back at the builder, now. He thinks it is a fuel pressure problem. He is also going to swap out the chip since that chip was made for a special/unusual engine. When I go back to the dyno, I'll bring my stock flapper valve to swap it out if required. I'm also planning on using ethanol-free racing fuel. She should be on the dyno in a week.

Thanks for the help Pelicans,
I'll let you know how it turns out,
Tim

Tim,

I am glad the builder is looking at fuel pressure. I questioned the alcohol only because it takes even MORE injector to handle that. What injectors do you have? I maxed out my 3.6 injectors on a 3.1 at 5500 RPM before I moved to E85. You did increase the motor size and the required fuel.

Good luck.

Injectors? I pretty sure they are stock, but I'll check. Builder did say they were "matched." I didn't think that they could be the weakest link in my fuel delivery. What type of injectors do you recommend? I didn't see any any from our Host or a quick Google search, but I'll keep looking.

Tim

I would question the builder about cam timing, and ask for a recheck. Did you remove the O2 sensor and put the probe into the hole for the O2 sensor to check the AF ratio at wide open throttle? If the readings are at the tailpipe, and you have a CAT, then you are not "way too lean". Also, lean mixtures that do not misfire usually give more HP. Your curve seems pretty smooth to me, not indicating a way too lean condition. Note that at peak power, your AF ratio is about 13.5 which is pretty close to ideal. So, if the readings were at the tailpipe with the cat in place, you are probably rich.

Steve,

I do not have a cat. I have headers (with an O2 sensor) and M&K muffler. Air-to-Fuel readings were taken at the tailpipe. Builder is checking cam timing. Yes, at 6,000 RPMs the mixture is reasonable, but my first concerned about the 4 to 5,000 range where it is very high. I'm concerned about engine damage. However, you are correct--this will not effect the relatively low HP at 6,000 RPMs.

Thanks,
Tim

Jim,

Get your part number and check hereStan Weiss' - Electronic Fuel Injector (EFI) Flow Data Table to see what pound per hour and at what fuel pressure your injectors are rated. Porsche tends to push towards 95% duty cycle there is a column for HP per injector at rated pressure.

Just a guide but worth a look.

Before I discuss the limit of the fuel system, I should state that a new fuel pump was installed as part of the build and my injectors were inspected and cleaned.
PFM brought up a good question, what is the limit of the stock fuel system? Assuming my injectors are the stock Bosch 0-280-150-158 (I think that is the right model number?) and the fuel pressure is 36 psi (from the Bentley manual), then according to Stan Weiss’s website, they should output Fuel Flow = 21.8 lbs per hour per injector. To convert this to maximum rear wheel Horse Power:

RWHP_max = FF * BSFC * DutyCycle * (rwHP/BHP) * #Cylinders

Where FF is fuel flow in lbs/hr, BSFC is Brake Specific Fuel Consumption or the fuel flow required to produce one HP, in units (lbs/hr)/HP. Not sure what this value should be? The higher the BSFC, the LESS efficient the engine. Stan’s website suggests a “Modern Engine or Light Modified Engine” is 0.52 BSFC and a racing engine is 0.47—so I assume that my engine falls in the Light Modified Engine category (0.52 BSFC). Next, (rwHP/BHP) is the fraction of power that passes thru the drivetrain, which I assume is 85%. For Duty Cycle I assume 0.95. Does anyone know the maximum? Can they reach 100%? For these numbers, maximum Rear Wheel HP is only 203 HP (233 BHP), ...which is close to my max 196 rwHP.

I find this hard to believe because everyone doing moderate modifications would run into this limit. It would be a bigger problem at lower altitudes. If I use BSFC = 0.47 and 100% Duty Cycle, then my fuel system can support 237 rwHP and it isn’t a problem. Does anyone have better numbers for BSFC and Duty Cycle? Also, Could I increase the fuel pressure to 43.5 psi via the fuel pressure regulator? Then, I could support 213 rwHP, but can the fuel pump support this? If I put a pressure gauge on the fuel system, what should I see at high loads? Bentley provides 29 psi for “Engine running”, but I assume this is not under load. I guess I’ll start researching fuel system on Pelican and see what I can learn.

Tim

The 964 injectors are smaller than the 3.2, but operate at a higher preasure, 3.8 bar I think, and they support up to 300 FWHP.

I don't think the problem is your system's ability to flow enough fuel because your peak power fuel is fine, which is at the highest flow rate. The 4 to 5 K rev band is your problem area, which has a lower demand for fuel compared to peak. I wouldn't change the chip before you recheck after retiming the cams. Then do another dyno run. Be sure to get the fuel readings in table form for Steve W.

Steve,

Since the motor is normaly aspirated peak fuel usage normaly happens at or near peak TQ. So I do not agree. I would still be looking at fuel. An easy test is turn the pressure up a few pounds and see what the air fuel ratio does. I see Porsche commonly runs 90% plus duty cycle so a bit more cam a bit more displacement running out of fuel is no great shock.

OK, I have done some calculations of fuel flow. I found a graph of BSFC for a 911 SC from this link:

The BSFC chart thread (post 'em if you got 'em) - Page 20 - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

which I reproduce here here:

[IMG]<a href="http://s1349.photobucket.com/user/tpjung92ungspike/media/Fuel_Consumption_911_zps652b666f.jpg.html" target="_blank"><img src="http://i1349.photobucket.com/albums/p759/tpjung92ungspike/Fuel_Consumption_911_zps652b666f.jpg" border="0" alt=" photo Fuel_Consumption_911_zps652b666f.jpg"/></a>[/IMG]

I then converted the BSFC to lbs/hr/HP (Americans can think in metric units):

[IMG]<a href="http://s1349.photobucket.com/user/tpjung92ungspike/media/BSFC_zpsb33a0ca0.png.html" target="_blank"><img src="http://i1349.photobucket.com/albums/p759/tpjung92ungspike/BSFC_zpsb33a0ca0.png" border="0" alt=" photo BSFC_zpsb33a0ca0.png"/></a>[/IMG]

I do not know the quality of the data, but it is the only BSFC curve I could find for 911s, but all BSFC curves I saw for other vehicles had similar shapes. This graph confirms Stan Weiss's BSFC = 0.52 for a moderately modified engine. However, above 4,000 RPMs, since BSFC rises, the engine is getting less efficient (takes more fuel flow to produce 1 HP)--and is approx 0.60 at 7,000 RPMs. Now, to figure out the demand on each fuel injector, I multiply BSFC by HP and divide by six cylinders, which yields this graph:

[IMG]<a href="http://s1349.photobucket.com/user/tpjung92ungspike/media/Fuel_Flow_V2_zps8ff88a9a.png.html" target="_blank"><img src="http://i1349.photobucket.com/albums/p759/tpjung92ungspike/Fuel_Flow_V2_zps8ff88a9a.png" border="0" alt=" photo Fuel_Flow_V2_zps8ff88a9a.png"/></a>[/IMG]

So, the max fuel flow occurs at maximum RPM (not maximum torque and not max HP). I also used the BSFC plot to calculate the fuel flow for a theoretical stock 3.2L and a 3.4L with 240 BHP using the same BSFC curve. (Yes, the Carrera and SC have different fuel injection, but the BSFC shouldn't vary much). I also drew a horizontal line showing the limit of the fuel injectors (21.8 lbs/hr). Thus, a 240 HP 3.4L will probably start to lean-out above 6,300 RPMs. Does that check with 3.4L owners? but, back to my "crappy dyno run," since I was only producing approx 200 HP, my fuel injectors were probably not the problem.

Tim

I sit corrected... Teach me to reply from work without looking at my data....

The spec I used for my 2 liter was 225 g/hpH

That is 225 grams per horsepower per hour or .496 pounds
That is the old factory carburetor spec for best economy I think it is in the fwm

Status Update: Got a call from the builder today:

Spark plugs were very white, as expected. He found the fuel pressure 3 psi low. Cam timing was perfect. So, hopefully, the lean mixture was only caused by the fuel pressure and custom chip.

THE BAD NEWS: He heard a noise from the right bank--so some damage was done. He is going to drop the engine and take a look. He is going to fix it under warranty--thank goodness. Hopefully, it is something in the heads and not in the cylinders/rods. FYI, compression tests were good. Even though he is going to take care of it, I am still very nervous about what he will find.

So, no Drivers Ed for me, but I'll go autocross with my 16 year old son in his Impreza.

Some important questions before you can jump to conclusions
What deck hight are you running?
Do you know the compression ratio of the engine after the build?
Is it a single plug still or dual?
Also i would not be the least bit concerned about a compression test, because it dose not tell you Anything about what is happening inside the engine~ i would be asking for a leak down test so you can see whats really going on~ are all the valves sealing? did the rings seat properly? all that and more can be determined from a leak down.
If you can get the answers to those questions id have a better shot at helping you out.

The Mahle pistons were supposed to give 9.8:1 compression, but I do not think the actual ratio was ever measured. I don't know the deck height. It is single plugged.

Jim,

So do you have an update on this?

Thanks for asking. No significant updates. Builder said he was going to pull the engine and fix it at his cost. However, he said he is busy with the racing season, so I told him that he could get to it when he had time. Maybe I was too nice? Oh well.

I would ask him for the answers to the questions I asked you ;) and he is right it is race season and we are all slammed, in reality it takes much more time then any one ever gets charged on builds to finish well built, thought out engines that will be reliable and make good power. So you being to nice wouldn't be what I'd be concerned with :)
Remember the the old saying "you can't have all three cheep perfect fast, you have to pick two ;)
keep us posted

Not a good answer, you have to set a deadline, otherwise you'll get it back next year. I guess you wan't to use the car this summer.

Isn't this a little unusual?

Todd

You guys are right. I'll stop by the shop early next week.

Just let him know you want it for the season... not a back burner project.

Stopped by the builder today. He has my engine apart. The cylinders (which were bored and plated for the build) had some minor marks on them. Couldn't feel them by running a figure over them, but could see them with a flashlight. The marks are from high temperatures caused by the lean mixture causing binding-I almost ceased the engine! Luckily, nothing is out of spec. He still did not find the source of the engine noise, so he is going to remove the connecting rods and check the bearings. The exhaust port on #5 was black (not white as you would expect from lean). He thinks that the injector wasn't spraying right, so he is replacing that. No damage to the heads, valves, etc. So after checking the rod bearings, he will re-assemble and re-tune the Motronic with a flapper mass flow sensor.

Unfortunately, there is no such thing as "minor" marks on the cylinder. If the piston tried to seize due to an overheat and left a mark on the cylinder wall, rings are most likely toast. Also, if it got hot enough to partially seize it's very likely it was detonating which pounds the crap out of the rod bearing. Could end up being the source of the noise from the right bank.