Putting My 3.0 MFI Motor Back Together
 

I'm starting to reassemble my motor after my little hiccup (see my "expensive lesson in MFI tuning" thread). I figured I run this past you guys as a sanity check before I button her back up.

To recap, the pistons I was supplied provided a whole point more compression than what I had actually ordered. On top of that, I was running a great deal more ignition timing than I should have been, especially in light of the higher compression (33 degrees total). Finally, an exhaust change leaned it out and, well the rest is history. One blown CE ring and the commensurate head and cylinder damage. I think I've learned something from all of that, so here is the plan:

I'm keeping the 10.5:1's and actually lowering the deck height. I had it at 1.4 mm with two .25 mm base gaskets. I'm going to one gasket to lower deck height to 1.15 mm. Steve Weiner and Grady Clay both explained the concept of detonation caused by excessive deck height in their replies on my other thread. Essentially, if the squish band isn't "squishing" as designed, and forcing the charge towards the center of the combustion chamber and creating turbulence, they tell me a ring of very high compression is formed over the squish band. So, what I'm thinking is that I'll get a more effective "squish", and even though I'm raising compression just a wee bit, I'm actually decreasing the likelihood of detonation. Make sense, or am I off base?

I'll be reducing total advance to somewhere in the neighborhood of 24 degrees. I'm a little worried about combustion efficiency on a single plug at that timing. Thoughts?

When at the track for my DE days, I'll be running it on race gas as an added safety measure. We have three different octane ratings available at Pacific Raceways. I can't remember offhand what they are, but I'm sure I'll have no trouble getting suitable gas. The big question is with regards to my street driving. We have 92 and 93 octane available around here. Now I won't be running it anywhere near as hard on the street, so will I be able to get away with that low octane?

I'm thinking the MFI may be an advantage in that department. I can run it richer than carbs and still maintain decent combustion because of its much better atomization. I think that will provide the safety margin I need. Not rich enough to cause cylinder washing or anything like that; I'm thinking 11.5 to 12:1 A/F. As a side note, it did make it's best mid range power at 11.5:1 on the dyno. Kinda stinky, though...

I was clearly right on the edge prior to the damage. I had over 6,000 street miles on the motor before the fateful track day. That's kind of what has me thinking that with some minor tweaks on the tuning, I will have a safe, viable combination. The other choice is to switch to the 9.5:1 pistons; it's still not too late for me to do that. I really don't want to, but if I'm all wet on this stuff, I will. What would you guys do?

Hi Jeff: I've been reading with great interest, your lessons learned on playing with the MFI adjustments...thanks! Regarding your question, I think the planned change in deck height is a good one. I've had no experience with running motors with as high a CR as yours with no twin plug. Have you calc'd the new CR after lowering the deck height? I think dropping the total advance will help and even cure the detonation. Actual required total advance will however vary with the gas you use. You have to find the right advance by trial and error and correct exhaust gas monitoring and of course listening for pinging. If you optimize the total advance for pump gas, you'll be leaving some HP on the table when you go to race gas. If you run an electronic ignition system, you could program it to run on street gas (less total advance) and race gas (higher total advance).

Jeff,

Some thoughts,......

1) I would strongly recommend having the lower plug holes machined in the heads while its apart. We call that "planning",....:)

2) 10.5:1, single-ignition, and today's pump gasolines are simply not compatible,.......they are mutually exclusive, especially in hot weather. Rich fuel mixtures help, but they are not a panacea for the correct configuration.

3) 24 degrees of total timing will help the engine live with the combination, but thats REALLY retarded and that makes for very high cylinder head and EGT's.


Bottom line,.....you truly need twin-ignition to run pump gas at 10.5:1 with these larger bore engines.

Thanks for the input, guys. Steve, thanks for confirming what I should have already known. It's nice to hear it from some one with your experience, as opposed to hearing it from that nagging little voice in the back of my head. At this point, it will be very little more work to machine the second plug hole. I think I'll have Monty go ahead and do that. Time to start saving my allowance for something to light that second plug with...

Well, the second spark plug holes are going in as we speak. Now it's time to decide how to light them.

I see our host carries the JB Racing twin plug distributor and the Electromotive setup. I'm leaning towards the JB Racing distributor. Comments? Pros and cons of the two different systems? Help me decide...

3.0 MFI engine in a '72T? No question - twin plug dizzy. Steve sells one, too.

Indeed, I do,...:) :)

Jeff,

I agree with the Most Erudite Guru from The Pacific Northwest, Dr. Ing. Steve Weiner-- maybe not with regard to everything (like which wine to serve with fish)- but where matters of Engine Rebuilding are concerned, I'm in his corner. So let me echo that reducing deck height IS a good idea AND that twin-plugging is required in order to cope with the Reformulated Panther Pee (with 10% Ethanol, maybe they get the Panther drunk) that is passed off on an unsuspecting public as Gasoline.

Also, I wish to publicly throw down the gauntlet on the observation that you made best midrange power at 11.5:1 AFR. Are you absolutely certain, was the AFR equipment recently calibrated? Chemistry would suggest that something in the low thirteens is more likely. If you ARE absolutely certain, that raises other issues, such as what was going on to require SO much fuel that the power peaked there instead of leaner. That would send me in the direction of checking AFR from bank-to-bank, or if the dyno is equipped with the instrumentation, on an individual cylinder basis. NOT trying to be controversial, just thought I would raise the question and maybe have a fun discussion about it.

We know that too-rich mixtures can CAUSE detonation-- this is one of the observations of George Braly and the GAMI crew-- so I would shoot for tuning for best power in the low 13 range under load. From a chemistry standpoint the extra fuel at 11 AFR is just being wasted, so there must be a PHYSICAL thing going on, charge cooling from the excess fuel or something, or different flow rates among injectors, that is responsible for that observation.


Finally. . . heretic that I might be. . . despite the aesthetic RIGHTNESS of a 12-plug cap in your longhood. . . I have to say that crank triggered ignition IS more accurate and coil saturation a thing of the past. . . I would look at what Pelican offers and also surf on over to the Clewett engineering catalog, he makes some cool stuff. If I ever get around to building a GT motor I'm going to look hard at coil-on-plug, once you commit to direct ignition it makes sense to eliminate plug wires.

Good luck!

If I may add a few thoughts to Professor Von Cramer's treatise above,........

Max HP is around 13.1-13.2:1. This is THE target in a water-cooled engine but too lean for extended running in an air-cooled one. 11.5:1 is close for a turbocharged motor, but FAR too rich for a N/A one and all that does is wash down cylinder walls and dilute the oil (read: rod bearing issues). Shoot for 12.6-12.8:1 at full load, WOT.

Crank-triggered ignitions are not all the same, despite what they may look like. Some work OK on race engines that never idle and are operated above 6K all the time. Some cannot keep the plugs clean for street use and one struggles with all the associated problems with that. Some run OK when the AFR's are perfect,..........

You get what you pay for and I'd strongly encourage anyone considering such systems to do their due diligence and homework by talking to people with extensive experience with all these components. Coil-on-plug, used with good Engine Management, is the way to go, but don't overlook a good distributor/MSD setup when using carbs or MFI. If the distributor is in excellent condition, the timing signal is VERY steady as these are driven directly off the crank (which is very stiff), unlike other engines where they are driven from cam or other auxiliary drives.

JMHO, so YMMV,

John, the A/F was measured at the muffler outlet by the dyno shop's instrumentation and by my LM1 that was laying in the front seat at the time (connected to the bung on the left hand SSI). They agreed within about .10 of a point or so.

My only thoughts concerning this relate to the high compression and advanced ignition. I'm thinking that with the spark lighting so early on a correct mixture, it may have been seeing peak cylinder pressure occuring too soon. In effect, "pushing back" on the compression stroke. The overly rich mix may have been slowing combustion enough to reduce or eliminate that affect. That's my purely wild ass guess, anyway. I would love to hear from some one who knows what he's talking about with this.

I'm with you on the ignition. I just picked up a twin plug Electromotive setup from a local R Gruppe buddy who had been running it on his 2.8 short stroke. As an aside, I just can't say enough about the camaraderie within the club - another member, who had first dibs on the Electromotive, alerted me to its availability and graciously stepped aside and let me have it. Big, big thanks to Brooke for giving me a great deal on it, and Kenik for letting me know about it. These guys saved the day (and a great deal of money) for me.

Anyway, so I've now got the Electromotive. Anyone have any suggestions on low speed, mid range, and high speed advance settings? 3.0 liter, MFI, 10.5:1 compression running on our locally available 93 octane Reformulated Cougar Pee (we call 'em "cougars" in this neck o' the woods...).

Can't wait to see her run! The sad clown face you've been showing around lately was getting old. ;)

Well, I can't do anything about the clown face, but I'm working on the sad...

jeff

What kind of HP did you get before the fateful incident? Just got my heads off the other day. Now to remove and send my pistons/cylinders to EBS while I disassemble the heads.

Sorry John, but that should read:

Herr Prof. Ing. Steve Weiner

:)

I got about 198-199 at the rear wheels, Kent. I was hoping for a bit more. In retrospect (funny how much clearer things get under 20/20 hindsight) that may have been due to the undetected detonation, too advanced timing, or whatever. I'm scheduled to run it again on the 14th. I'll report back after that.

What's that translate to at the crank roughly? My 911/83 spec 2.7 MFI is supposed to be rated at 210 hp 188 lb-ft like the RS. You have more displacement, so you must have more power or maybe it is tuned for torque?

The conversion factor I see used most often is +15% for crank horsepower. So, somewhere just shy of 230 at the crank. I'm hoping for better with the twin plugs.

I have read. A 2.7RS w sport muffler put closer to 230fwhp.

A 2.8 twin plug w mod S cams, Webber 40's. and sport muff is 260FWHP. (Old porsche artical on a 914 build.)

I would hope for about 280 FWHP on a 3.0 twin plug MFI depending on cams, fuel ...

That is about 238 rwhp.

Compression and twin-plugging both add HP. I think the Twin Plugging adds about 3% on its own.

I am far from an expert. I did have a 2.8 twin plug once w specs as above except w RS MFI, but never dynoed it.

However, in a striped 72 911T body w LSD and 23" tall sticky 225/50/15 R1's's, it was wicked fast. 992TT's did not seem as fast to freeway speeds.

How we doin' Higgy? We gonna see the blue car tomorrow night? :)

Nope, not tomorrow. There were some problems in finding a good replacement head that delayed things a bit. The first one had been modified for a 98 mm bore (which I didn't notice) so I couldn't use it. I finally got a good one to Jeff so he could drill it up for the second plug, but that wasn't until Thursday evening. I'm hoping if all goes well that I might get everything back this week. If so, it might make an appearance on Saturday. We'll see.

Thanks Jeff
I'm looking for a 10:1 pwr/weight. Since my car weights 2200lbs I was hoping for that number of 220-230hp at the crank. I think I'll get the same cam from John as well.

My current 2.7 makes about 195hp so that will be a nice 15% increase.

Well, it's finally back together and running. I picked up the heads late Friday afternoon and had it up and running Sunday morning. Some observations:

I can't believe the difference in overall temperment the twin plugging made. Steve, your advice and observations on the merits of twin plugging are spot on. It idles better, is smoother overall, and any part throttle gurgling and whatnot it displayed before is all gone. It's as even tempered as my wife's Subaru.

It runs about 15-20 degrees cooler. Where the previous incarnation ran at about 195-200 degrees on a day like yesterday (75-80 degrees) it ran "on the thermostat", or right on 180 degrees all day. This is with an Elephant Racing "Wide Mouth" cooler and finned lines.

It has noticably more power (according to the old "butt dyno") than the first build. I'm anxious to get it on the dyno and quantify that. Hopefully I'll be able to get it in later this week and get some hard numbers on it. I'll report back when I do.

That is fantastic news! I assume when you go in for the dyno run, you will be tweaking the ignition curves, as well? Given the infinite variability of your Electromotive set up, I'd bet there is some optimization to be had.

Jeff,
Great news - way to bounce back from your setback with the best attitude.

Jeff,

Glad you're back on the road.

I am curious as to what thoughts pushed you to run the Electromotive crankfire vs. standard twin plug dizzy?

Congrats on getting it back together. I know that is a huge undertaking to do it twice.

I would be interested to know what settings you use for your advance curve. I am about to embark on a similar build.

Joe, it was very much a matter of cost and availability. A local friend had been running the Electromotive on his hot rod 2.8 short stroke, and he gave me a very good deal on it. He actually switched to a twin plug dizzy, so the Electromotive was looking for a new home. If I were looking to buy new, with costs being roughly similar, I would be really torn. I think in the end the Electromotive would have been the choice anyway. I like the individual coils, the elimination of the (expensive) cap and rotor, and the tunability.

I understand that Electromotive may have a hard time in the relatively "dirty" environment of MFI, and can be prone to foul plugs. I'll just have to see. It won't tolerate the wide plug gaps that an MSD box will, and that is supposed to be a part of the problem. All I can do is try it and find out.

Jamie, I simply started out with the advance curve programmed into it for the 2.8. The idle is at five degrees advanced, and the top end is at 24 degrees. I can't remember off hand the mid range. The top end is the total of the idle, plus the mid range, plus the top end, as the settings are cumulative. I'll check the mid range and report back.

it was cheap, available and I didn't needit... :)

One of the things that really impresses me about the Porsche community is guys like Kenik. He actually had dibs on the Electromotive (looking to run his 2.5 on it, me thinks), but when he saw my dilema, he alerted me to the fact that our mutual friend Brooke had it and graciously offered it to me. It's selfless moves like this, and the eagerness to help one another, that makes our little community a great one to be a part of.

Jeff,

I've been planning an upgrade to my 3.0 and reading posts here. If I remember correctly, you built up your 3.0 with a special ground cam from Camgrinder. I currently have an Electromotive HPX single plug unit and have had no issues in 10,000 miles of country road driving. Steve Weiner mentions in this post that crankfires have issues which might not make them the most suitable for street use. I don't know why. I have read that EM units like to eat plug wires every few years but I havn't changed mine in 3 years of owning the car. I am experiencing an off idle stumble that I think is more related to fuel than it is to electrical, so maybe I'll pull these plugs and take a read on them.

BTW, I'm curious to see a dyno on your car once it's fully done. My plans for this winters rebuild are for a 10.5:1 bump, DR40 Cam & twin plug.

Nicely done, Mister Higgins,...:)

All of those benefits result from using twin-ignition and the much-reduced advance values needed for best performance.

The only downside is the initial cost, but the overall behavior makes it all worthwhile in the long run, especially when using the sperm whale piss called pump gas. :)

Well, I ran it on the dyno today. I'm very pleased with the results. It picked up significant horsepower and torque over the earlier, single plug iteration.


http://forums.pelicanparts.com/uploa...1213752571.jpg

Very nice torque curve. Looks to make at least 180 ft/lbs from 3500 all the way to 6500. I can see why your butt dyno feels a big difference in your light weight.

How different are the raw numbers?

Joe, it picked up 16 horsepower and 23 ft lbs of torque over the first build.

It's now pretty much everything I was shooting for. It's a very torquey street motor that I don't have to rev the bejeebers out of to make good power. It looks like I can set the rev limiter at somewhere around 6,600-6,700 and have a nice over-rev past the hp peak that will keep it in the meaty part of the power band when I upshift.

So, the small port ('83 vintage) 3.0, relatively small (for a 3.0, anyway) 36mm "S" throttle bodies and stacks, high compression, and custom high lift / short duration cams look to be a success, at least for what I wanted. Granted, 3.0's can make a good deal more power if you want to rev them higher. The cost, however, goes up considerably. Much larger throttle bodies (or big PMO's), performance valve springs, head porting, and so forth. The induction actually becomes one of the major expenses when going bigger than what was available stock; reworking 36mm throttle bodies and stacks to 40-44mm or buying high butterflies, or buying big PMO's, is very expensive.

Anyway, I'm finally happy. I got what I was after. Good, cheap (relatively, in Porsche terms), and now hopefully reliable and long lived power for my street car that sees a good bit of track time. And what I have learned about 911 motors has been invaluable. They are far different than anything I have ever worked on; much more demanding, interesting, and fun than big American V-8's where I cut my teeth. I've had a lot of fun. Hopefully my trials and tribulations are over, and have contributed to the body of knowledge, so I can spare some one else the "fun" I have had learning.

Remind me, was that RWHP or corrected for driveline loss?

RWHP. Corrected for drivetrain loss (+15%) it's about 245 horsepower and 230 ft lbs of torque.

Interesting that torque went up more than HP. I guess retarding the timing really built up the low end more than high end.

I too have a small intake 3.0 and want to preserve some of its low end response. With PMO 40s, SC cams, SSI & M+K, the dyno pull measured 186 ft lbs and only 178 HP. This works well in a car w/8.3:1 Crwp and stock tires, but with my 911 trans and 50 series tires, I run out of revs quickly. I'd like to move my peak up to low 6000s and be able to shift just under 7k. From what I've read, stock springs should be ok to that range.

The way I figure, If I port my small intakes to get more breath up top, I can restore some of the static compression lost by this and S cams by bumping the squeeze to 10.5:1 and twin plug. I've got an EM HPX now so a splitter and another 3 coil unit will get me the 12 sparks I need. I know that this configuration won't have as strong a bottom end as your setup and I suppose that's partially my concern. Since I run a 901 trans, It can handle only so much torque. This is why I discounted building up a 3.2 SS. At 230 ft lbs, I think your configuration would push the envelope as well. I'm just not sure how much. :confused: Maybe someone with actual experience can chime in.

See I spend my time on the street and autoX. I need to launch hard in 1rst gear, the achilles heel of a 901. So I need to have a responsive low rpm to get me through 1rst quickly plus give me good power out of the tight tuns in 2nd gear without torturing the crown ring pinion. From what I've been researching on the gear charts, I"ll be running approx 500 rpms higher with a 23.1 diameter tire than with stock tires. This should keep me in the power band to get me the results I'm looking for. Any thoughts?

I too cut my teeth on V8s. Mopars to be exact. I built up a 440 once and put a long runner single plane intake on it. Not a good combo for 3.23 gears and 3 speed automatic. Much better with the 3.91s but really not good for street & highway. So I changed in an M1 dual plane and 3.55s. That was the ticket.

I'm trying to only do this build once. As we both know, domestics are a wee bit less costly to build than these Porsches ;)

Ah, another old MOPAR man. I went through a succesion of them in the late '70's to mid '80's. Several 383's and 440's passed through my garage in those days.

Anyway, I'm hardly one to give advice on cam selection, but I obviously shied away from the "S" cams. Their aura of being a "wild" cam was generated in the little 2.0 liter motors. If you pour over the basic numbers on the cam charts, and compare it to other commonly used 3.0 cams, it becomes obvious that they really don't offer much in that big of a motor. They only offer .005" more lift on both intake and exhaust than stock SC cams. They pick up a great deal more duration, but that is not what you want in a "torque motor". Duration drives the power band higher up into the rpm range. Narrow lobe centers (lots of what us old hot rodders called "overlap") drives the power band up as well. They do this at the expense of bottom end and mid range power; they effectively "fool" the motor into having less dynamic compression at lower rpm's and more dynamic compression at higher rpm's.

The long duration / high overlap scheme takes advantage of intake and exhaust charge momentum to do this. It works great at higher rpm's, where the momentum of the escaping exhaust charge actually draws some intake charge beyond the combustion chamber and out the exhaust port. Both valves have to be open at the same time to do this, so their opening periods "overlap". At higher rpm's, the exhaust charge (in a carefully designed port and correct length primary header pipe) will reverberate a bit, actully "bouncing back" that overdrawn intake charge back into the chamber. It's almost a mild form of "super charging" when it works right. Problem is, at low rpm's, you don't get this reverberation and the portion of the intake charge that made it past the exhaust valve simply follows the exhaust charge out. In extreme cases, it actually draws some more intake charge out of the cylinder, effectively underfilling it. Back when drag racers still ran high overlap cams, we could smell the unburnt fuel coming out of the exhaust at idle, it was so bad.

This affect is what gives "S" cammed 2.0's-2.4's such a dead bottom end, and such a satisfying "hit" on top when them come up "on cam". That's not what you want. That's not what I wanted, so "S" cams were out.

There is, however, what appears to me to be a dearth of suitable cams for hot street 3.0's on carbs or MFI. The normal run of cams used as bolt-ins on CIS motors (964, 20/21, etc) don't have enough duration and the lobe centers are too wide. They have to be "CIS friendly", which precludes any overlap at all. CIS gets confused if there is any reverberation into the airbox. The other end of the cam spectrum includes the RSR Sprint and DC/GE 60 and 80 series (I skipped right past the 40 series, or "mod S" cams as having insufficient lift). These cams provide what I feel is enough lift to wake up a 3.0, however, they have even more duration than the "S" cams. Their power bands are too high, at least for me. They also require performance valve springs, adding to the expense. I was stuck.

That's where our very own Camgrinder, John Dougherty, came to the rescue. We discussed my needs and my thoughts on meeting those needs, pouring over his cam charts over the phone. He suggested that his GT2 cams had the lift, short duration, and gentle ramp angles (to allow stock springs) I was looking for, but the lobe centers were too wide. No problem; his computerized grinding equipment could be easily reprogrammed to narrow the lobe centers to whatever we wanted. John suggested 102 degrees, so that's what we went with. He can cut these anytime, at no more expense than any "standard" grind. I sure like them; they did exactly what we thought they would. I think they would work well in your application.

did a nights sleep resolve the ignition cut out issue you were having yesterday?

or is that the next topic of discussion to see in this thread?;)

What are the symptoms?