Dynojet Fun!
 

Well today I took my car to the chassis dyno. I've gotten the car to really drive well but my cheapo A/F meter was telling me that the mains where too lean, it couldn't have been more right. Brief rundown on the car, 1966 912 chassis with a 911 ('70-71) trans, 7:31 R&P, '81 3.0SC motor, early exhaust with a custom 2.5" X-pipe exhaust/muffler system, Zenith carbs with 36mm venturis. I started out with 0.65 idles and 1.6 mains. The best run was with .68 idles and 1.70 mains but I could fatten if up a little more. I also found a clogged fuel filter that was only noticeable at full throttle on the dyno and my fuel pressure of 2.5psi was too low to feed the carbs. I bypassed the filter and upped the pressure to 5psi, no problems with flooding etc.

The first pull was WAY lean so I cut the car off at 5400, it only made 134 hp. After making the changes with a few runs in between the car made 174.43 hp and 180.27 ft/lbs. Has to be the best $85 I ever spent! The first graph is the HP/Tq comparison of runs 1 and 4 the second is the A/F graph of run 4, notice how much smoother the HP/Tq graph is with the 1.70 mains, bypassed filter and higher pressure. I think I can go a little fatter on the mains, maybe 1.75-1.80 and get those numbers a little higher. It's clear I need a bigger cam to go much farther though.

http://forums.pelicanparts.com/uploa...1151778617.jpg

http://forums.pelicanparts.com/uploa...1151778637.jpg

My next trip to the dyno will involve larger mains and well as playing with timing a bit.

Something occured to me from my holley/drag racing days. On holley carbs if the floats are too low the car will surge a bit at cruise which my car does slightly and they will need a larger jet because it's harder to pull the fuel up to the booster. The other thing is that I just might not have enough fuel pump for this engine as it always seems to get leaner towards the end of the run when fuel demand is the highest. The pump in there now was installed by the PO and looks like a Facet pump. I've got a nice Mallory with a regulator that I might install just to see what happens. For now I need to dig out my float gauge which I can't seem to find. When I rebuilt the carbs I just put the needle valves in with the same shims it had before since I'd misplaced the float gauge.

Shouldn't this configuration be making more like 180-185 at the wheels? Notice the A/F graph looks like a roller coaster.

Hmm, no one loves me...:(

Ok so in my boredom tonight I've been looking at BA's performance handbook and low and behold he lists a 3.0SC with Webers and early exhaust at 210 HP @ 6000 and 200 lb/ft @ 4500. Adding 15% (divide by 0.85) driveline loss to today's dyno numbers I get 205 HP @ 5750 and 212 lb/ft at 4600. Stock '81 SC is listed as 180 HP @ 5500 and 175 lb/ft @ 4200 so I'm not doing too bad. He also recommends 0.65 idles and 1.60 mains as a starting point richening especially the idles for good drivability with no popping or surging. 34mm venturis are also indicated. Digging further into the book reveals that my engine has 34mm ports on the intake side, I wonder if the signal at the boosters is week due to 36mm venturis and 34mm ports?

Anyone else have a carbed 3.0 with early exhaust that's been on a dyno?

Edit: corrected conversion math

Wow, picked up 30 hp and similar torque...money well spent I'd say.

congrats

Carbs and a backdated exhaust should be good for 10-15hp on an SC engine. My old motor was a '78 Euro with SSIs and CIS. It put out 215hp according to the performance meter and drag slips. Your numbers seem about right but as you stated there are a few more horses in the barn to be let out with a better fuel pump and jetting. The old 2.4L I had with Webbers really responded well to fine tuning.

By the way, I haven't forgotten about your cross bar. On Friday I received a slew of great info on linkage setups. If you e-mail me your address and a pricing total I'll shoot you out a check.

Vizard says at 6k you need 33.9 vents, Bosch says 34.6. I don't your cam specs but it should be less than 6k?

Vizard says best atomization is close to 80% of butterfly size. Best working range is 72-80%.
40 x 80% = 32
40 x 90% = 36
"this formula is unlikely to be off a mm or two."

wtf.. try the 34s

Upon further research I found this info on the net: "Facet Fuel Pump:
This is one of those little square pumps with the transistor mounted on top that make a ticking noise all the time. These pumps are TERRIBLE. No volume and High Pressure. These pumps have been sold for many years with Weber and Mikuni conversions and have cause many people alot of tuning problems. They are a pulse type pump that delivers almost no volume (usually less than the stock mechanical pump did) and usually at High Pressure. This cause flooding at idle and lean out conditions under high load. Do not use them...."
Found here: http://www.racetep.com/webfuelspark.html

The PO did put a Facet pump in it and one of those dial-adjust Purolator regulators. From a spec sheet I found online the pump is only good for 25 gph and 150bhp. The above page recommends a Carter pump which is fine for me as I've had experience with one on a big block work truck I used to have, dead reliable. I think I'll need some sort of cabin pressure gauge though as high rpm WOT heavy load is the last place I want to see a car going lean. The HP and Torque graph s with the smoothing off and you can see the jaggedness of the curves, much better on run 4 with a less restricted fuel system. I had a long talk with someone much more knowledgeable than I this morning and the concensus was that the wavy A/F line is likely due to unstable float levels, the lower the float level the harder it is for the engine to pull fuel up through the emulsion tubes to the boosters thus making the A/F erratic (unfortunately the A/G graph has smoothing turn on) and therefore HP and Torque less than optimal.

Ron, I think I will try the 34's at least with these cams. Eventually I'll install at least a Webcam 20/21 or 964 cams as a minimum of I'll go all out and install early SC heads and JE pistons so I can run S cams.

All in all I'm pretty happy with the baseline numbers, I've got 25 more HP and 37 more lb/ft than a stock SC (per BA's book) with only an exhaust backdate and a carb install. I've also moved the curves up the rpm scale by 3-400 rpm. I figure I'll get 210-215 with a better pump and some fine tuning as I haven't even touched ignition timing from my baseline settings. I need to pull the pulley off the motor and put it on my rotary table for my mill and scribe some real degree markings in it.

Brian if the crossbar will work that's great I'll shoot you and email later today. Thanks guys. :)

Cool Christian! Where is Akron Horsepower? I'm rebuilding calipers today and one piston in each of my front's are stuck:(

Pete,

Akron Horsepower is down near the Goodyear blimp hangar on Massillon road off Rt 224. They specialize in Mustangs which is only practical due to popularity but they told me they've had everything from a Ford GT to some guy's WIFE's Carrera GT! They could remember what he said he drove but it was even more exotic than the Carrera. The most powerful car they ever tested was a stroked bib block Mustang with nitrous, something like 1200HP at the wheels on the juice. Really nice guys they sell 3 runs for $85 with A/F or rent the dyno by the hour for $150.

A couple of thoughts. Solid engine mounts (if you're using them) can cause lots of float bowl 'frothiness' and mess with AFRs. I thought 5 psi was high for Webers but my experience is more with sidedraft DCOEs. Having a proper pressure regulator that has a bleed port is much better than the dial-a-pressure inline variety. I'm not sure if any of this applies to your situation.

Larger main jets look to be in the cards to pick up a couple more HP.

Thanks Matt,

Actually I have quite a bit of experience with high performance fuel pumps and regulators. I've got a pump and regulator here but it might be too big, SX race pump and regulator with -10AN lines, not sure where I'd run 5/8" fuel lines on a 911 LOL :D. Anyway I'll probably go with a Carter or Mallory pump and a Mallory regulator, I've had bad luck with the Holley pumps. Ideal would be return style but my 912 original tank and chassis doesn't have a return line and I don't feel like running one. I'll definately go with return style when the engine gets moved to the '73 chassis. Probably -6AN feed and -4AN return.

No solid mounts on the motor. I've been told that the Zenith's have a better split float design over the Webers and that PMO actually used this type setup for their carbs. I would havve figured setting the regulator at 5 psi would flood the carbs, turns out the whimpy little Facet pump only puts out 4psi max and 24gph max. It's also a pulsating flow being a diaphragm type as opposed to the smooth flow of rotary vane pumps. In any event I'm going to install a cockpit fuel pressure gauge from the carb side of the regulator so I can actually see what's going on.

Still I have to be happy with it, especially the carbs. Properly tuned they are a joy to drive and the throttle response is incredible, can't beat the HP increase for a stock cammed engine with only carbs and early exhaust. It was a whole lot simpler than trying to splice in the CIS system into a car that originally had a carbed 4cyl.

Hmm, I've got a perfectly good (well as good as they can be) Holley pump and regulator sitting here in a box that I dug out of my drag racing parts pile. I'm thinking clean it up and use it for now then put a Mallory in it later, thoughts?

Well I went for it and installed the pump and regulator. I even used some -4AN braided line and fittings from the regulator to the carbs which I machined fuel rails for. I got the regulator and fuel lines hooked up before I put the pump is so I decided to check the pressure on the POS Facet pump. Set the pressure to 3 psi and just with free revving the motor the pressure would drop to about 2 psi then back up to 3 psi. Looks like that pump is about worthless for my application. After a thorough search on the forum I found several threads where guys had installed the Holley pump in the smuggler's box so I did the same but man is it loud

BELL! I need your help! This damn pump is louder than the engine at idle and you've heard my mufflers. Dynomat? Help before it drives me crazy LOL :D

The good news, this pump is rock steady. I still need to run a line in the tunnel for a cockpit fuel pressure gauge so I can monitor it on the dyno as well as when driving but it's late and I'm tired. Kinda difficult to drill mounting holes in the smuggler's box without an angle drill.

The base of the pump is about 4" above the base of the fuel tank, Holley recommends the pump be below the tank but that's not practical in a 911. I did test the pump with a gallon of toluene 12" below the pump and it had no trouble pulling so I figure it'll be fine the way it is.

Anyone else running a Holley have any suggestions on quieting it down? Personally I don't like Holley pumps but I had this one lying around so I figure what the heck.

Then you directly mounted the pump to the smugglers box wall and created a speaker from the tin. It should be called sympatheic harmonics, i forgot?

I'd probably isolate the mounting by seperating the pump. Maybe set up thru bolts in as small as necessary piece of wood. Mount the wood using a seperator of a sheet or three of Dynamat or thick rubber. Mount the pump to the wood using a seperator. I'd use thick fiber wood like 1/2 teak instead of oak or walnut. The more the wood absorbes the harmonics the better. If you don't seperate the pump bolting from the tin the bolts will carry the harmonics to the newly created speaker. Then line the smugglers box with soundproofing. If the smugglers box has open holes like mine leave them open to the ground and steering rack.

Christian,

Are you going to go back up and get it dyno'd again? I am going to get my car up there in the next week or two, I didn't have too much time the other day.

Oscar,

76' 2.7 Turbo EFI

Ron,

Good idea, how about a piece of tire thread?. Smuggler's box lid, any reason not to remove it? Soundproofing, that's where I get ahold of bell as it's his area of expertise.

Oscar,

I'm ordering a new float level gauge from Pelican since I can't seem to find my old one. I'm going to double check the floats and the fine tune the accel pumps. I'm also gonna get a set of 34mm venturis, which should increase the signal at the boosters and smooth out the A/F curve. I figure not this weekend but the following weekend I'll go back on the dyno.

I'd love to see your car run on the Dynojet, PM or email me for my phone number and I'll come watch.

Late response...but I have a carburetted 3.0 which was recently dyno'd.

1979 3.0L
40 IDA
Webcam 120/104 cams (equivalent)
JE 9.5:1 pistons
SSI
Dansk Sporto muffler

The dynomometer was not a dynojet, but it was calibrated to give number similar to a dynojet. (much debate blah blah blah, some stock cars that ran that day gave higher than expected numbers, some gave lower than expected)

Anyway - 223 hp peak at the rear wheels at 7000 rpm. torque was an unbelievably flat 200 ft-lbs from 3000 or so to 7000 .

A/F meter installed during the run showed slightly lean. I forget the numbers now and the data is at my office. I've been running 94 octane pump gas since the upgrade and so far so good.

Unlike you though I run this motor in a LONG wheelbase car. Unlike you I am not crazy.

SmileWavy

LOL, Over the winter it's going into my '73 tub street/track car. I can clearly see the benefit of the early heads on your car as well as those cams. Certainly gives me something to shoot for, I'm planning the same pistons and porting the heads out to at least 78-79 specs. I haven't decided on cams though. 50 or so extra RWHP seems worth the money I'll spend. I've got a few things to do before I go back on the dyno, hoping to pick up 5-10HP with the new pump and some more tuning, at that point I figure I'll be at the limit of the heads and cams.

Think I'm crazy in this car? I used to run a Mustang with a 650HP stroked 351W (410") with a spool in back, 3:73's and a top-loader 4spd on the street. I could light the rear tires in high gear at 55mph! Couldn't turn worth a damn but I was young as stupid then. Now I'm just old and stupid. :D