I agree, bad move going from EFI to carb... This issue is NOT the FI system unless there is some defective part. Any decent tuner who is familiar with the Infinity should be able to get your car running exceptionally well in a couple days. You will lose the engine protection strategies available on the Infinity as well.

A friend of mine built a tool to help tune with the platform and it really makes short work of getting the VE table tuned in. You can read more about it here:

http://forums.pelicanparts.com/porsche-911-technical-forum/941314-tuning-aem-infinity-check-out-helpful-tool.html

Best of luck regardless,

David

Yeah stick with EFI. Far better with full sequential setup. Just tune it right and you’re done. Carbs are always going to be a compromise with setup as they are a blunt instrument by comparison.

OK, I am going to give my opinion here once again, the purpose of this thread is to help Nippy get his car running properly and we all are trying to help him.

The carb vs EFI both have there advantages and both work properly when the tuner is doing there part correctly. I wrote a small article on how carbs work and I will give a brief explanation.

Carbs work at the speed of sound and have the closest working relationship to the combustion engine of anything to my knowledge. By the way 6 1 barrel carbs on a 6 cylinder are actually sequential injection, each barrel sees vacuum or reversion, carbs work off the actual vaccum of the motor. This is why you can run a big cam on carbs because the 6 butterfly stops the reversion that will cause a single butterfly motor with a plenum to screw with every sensor information with the exception of a few like TPS sensor.

The first EFI production Porsche to use 6 butterfly EFI was the 1993 RS and RSR, I have a factory 1993 RSR 6 butterfly 3.8 motor, and yes it is slightly better on midrange on and off throttle on torque numbers than a 6 butterfly carb motor but there is a severe cost difference... Again if you carbs on a CIS or stock cam fuel injection motor with some low duration camshaft and wide lobe center your not going to like it. The problem is you need a certain amount of duration in the camshaft to stabilize the vacuum curve in the carb, this can be gained by increased displacement or enough duration in the camshaft.

I have motors out there today with carbs on them going strong for over 20 years. I may have cleaned them out every few years for the client that drive there cars 5 days a week. The view that EFI is better is an opinion that I agree with in some applications but I can easily draw a case that carbs are better.. I actually like both but there is no way to outpower the carbs with any EFI system for the same money. If it is a 6 butterfly factory injection, and old school 6 butterfly mechanical injection or 6 butterfly carbs there main advantage is always having 1 atmosphere of pressure over the butterfly and easily handling a performance camshaft. DP now builds a new Porsche RSR replica for a few hundred thousand dollars and it has PMO carbs on it. This talk of wearing out a carb is like saying I wore out a hammer it can be done but it is over decades.. The PMO carbs have replaceable bearings on the shafts..

Now to upset a few here I have never seen a PMO throttle body injection make equivalent power to a PMO carburetor size being equal on a Preformance camshaft. I sell a 6 butterfly plenum injection, but in my opinion it is a copy of a 1993 RS/RSR factory injection. (even the linkage is interchangeable..... Richard Parr wants to put my article on his website but I need to rework it a little first, but here is something to think about. If I take a 3 liter motor with a midrange carb camshaft lets say 255 deg @ .50 and .450 lift ( if I put a huge cam in it like 280 degrees duration and .500 lift cam do I have to reject it ? Or if I increase it to 3.8 liters do I have to reject it... ?

Answer for you to think about is this..... forget about the motor and think about a carb, if the jetting is correct on the carb lets say a (46 webber with 42 mm chokes and 170 main jets and 55 idle jets on a s liter with mod S cams and the air fuel ratio under a load driving is 12.5:1...... If I install a larger cam or increase displacement it only changes the volume drawn through the carb, It does not change the mixture only the quantity of air fuel being pulled through. more duration raises the peak torque number in the RPM range and makes more HP.. This is only simple math because HP is cumulative, (TQ)(RPM) devided by 5250 equals HP.

Hope this helps some understand carbs a little better, Mike Burns is very capable of dialing the carbs in in about 20 minutes. EFI is not so easy even with data logging... William Knight

That’s great Mr Knight, thank you for your perspective. I have found there to be a breaking point with size of cam when carbs will not run the car well on the street due to there being less vacuum at idle essentially stumbling the carb until it obtains more of a signal from the intake. EFI or MFI do not have that problem. I’ve seen a streetable dc80 efi engine which I know a carb could not handle. Lastly, carb chokes limit CFM coming into the engine thus bhp. A 46mm carb with 40mm choke isn’t flowing more than a 40mm throttle body let alone a 46mm throttle body. There is a definite trade in ease of tune but airflow-wise there can be no mistake in that a throttle body minus a choke flows more air. Ferrari saw this issue in the P3 and P3/4 series when the went Lucas mechanical injection and picked up significant power, same engine just different fuel intake configuration.

It should be a fun motor....GT3 crank, 930 oil pump,custom pauter rods, mod S cams, custom JE pistons, open up the heads, twin plug, 50MM PMOS. Different ratios in the tranny. I wont speak for Mike Bruns as his work speaks for itself. It will be a 3.6 and should absolutely eat a 964 and 993 stock 3.6 for lunch. Not to mention its going in a sub 2400lb car.

Anybody need my crank? Rods and Pistons? EFI? All for sale.

Finally the car will have the power it deserves!


Just dropped the EFI price, 4500 shipped.

Nippy, PLEASE reach out to me by email before you change the gears....... you really only need to change 5th you won't be able to shift it fast enough.. One of my clients with a 3.5 I built made 371 hp, we choked it down with 43mm chokes and he had another shop remove the engine and dyne it to see what it is making and it made 355 at flywheel... I have some lower ratio gears for sale but you won't like them with that much power.... Paul Ivie has a 3.4 in Huston they call the silver bullet with Mod S cams I built and he at the drag strip ran 11's in the quarter mile.. second is the only gear that is a little tall and 5th needs to be changed. my email is knightrace@mac.com. Thanks, William

I like an 8.21 5th gear ratio if you drive it on interstate. William

Mike is doing 5th and 4th and 3rd I believe.

Mike knows what he is doing, I just don't think you need to change 3rd or 4th but need a taller 5th. the big motors need to be around 3200 @ 80 mph for freeway use. The stock 5th on an SC is like .89 and with a 26" tire your 3600 rpm to do 80 mph.. The car will blow through stock 3rd and 4th, 5th to me is for interstate 90 mph crusing around 3400 rpm. I am glad you put your motor in good hands, Mike helped me out last week on some parts I needed and I may give him a call. I built a 3.6 on a 3.2 case about a year ago with 50mm PMO carbs and the mod S cam didn't seem big enough, it had quit pulling at 7K and felt under like an undersized cam. That carb motor on the dyno made 285 LB of torque @ 2850 rpm.. Maybe I could have changed the cam timing some and helped, not sure.

5th is 28:23 (0.82) in the '78 and '79 SC 915 and the '80 to '83 915 is 38:30 (0.79)

William builds some screaming engines. Geneman here on the forums has worked with William on a few of his car builds and the engine is always a mean one.

Which cam would you have used if you could go back?

EASY ANSWER ON CAM CHOICE, I have had great results with webcam however on the carb motors and rothsport injection motors every motor seems to like what I call the singer cam. It is not a singer product but there asking $2400 a pair list but I can sell them around $1400, there is not an advertised spec sheet on lobe separation but it has an advertised duration of 314/296 and that means very little. But I time the cams at 5mm, close to a 120/104 or mod S webcam but the fuel curve on the dyno tracks much better with carbs and it seems to make power to 8400 rpm on a 3.8.. It is made by Dema Elgin.. I have had some motors in my shop the past few years that have run terrible and was very difficult for me to figure out. I will not slander companies products but someone has the old GE or Garretson Enterprise masters making cams and the work is ok but the masters must be worn out or missing one of 4 necessary to complete the set. I have experienced as much as 17 degrees difference in valve opening between the left bank and right bank with the cams timed correctly. Car was sent to me for 3rd rebuild and it had a good leak down. took me a long time to figure out problem. I would go bigger than the Mod S cam or go Elgin custom. If you shorten the gears the mod S is not a good choice at all, last 3 motors I have done have it and it is a great cam up to 3.2 liters, I use the mod S on 4 speeds because it makes great torque everywhere but on the 3.6 motors it is almost flat by 6000 rpm, 1 3/4" headers and 50mm PMO's with 45 chokes and 3.2 heads with larger valves in it so I have to think it is the camshaft. If your going to shorten the gears go bigger than 120/104 Webcam has other great choices. I can sell you the custom ones and I am 90% sure that is what Mike runs in his motors also. William
If you look on youtube I didn't make the video or upload it but you can here what I call the Singer grind, look for ( Porsche 3.8 sound ) by William Knight

This motor is going to be amazing... Talked with Mike today, I look forward to the dyno numbers posted here on this thread.

Hey William, FINALLY looking to get the cams you mention above and supplied mapped on my car. Would you believe I still don’t have the car back (now in the 15th month), but hopefully next week.

GT3 crank, your ‘Singer’ cams, 98mm Mahle, AT Power ITBs, 993 plastic intake - with SSIs so a sub-optimal setup, for now.

http://forums.pelicanparts.com/uploa...1525382137.jpg

Looks very nice, I still have not been able to find anything better, I talked with Mike today and he has one set on his shelf, they run them in there race car and it works great, makes 430 hp.. My only concern on your motor is the SSI is small but maybe it will be enough to meet your needs. Cheers and update me at knightrace@mac.com William Knight

Sounds like a gigantic super angry, hungry tiger. I pity the people that are behind that car on the track!

A guy who worked for me posted that on youtube. Terrible video but that was just a 3.8 with 50 mm carbs and a full size clutch with steel flywheel.. I made the distributer from a 964. Blockhed, Thanks for uploading it, that motor was only 10.8:1 compression and the big Singer cam, Most people who rode in it or drove it refused to believe it had carbs on the motor.. I often had to go raise the engine cover and show them.. William Knight

I spent a lot of time on Datsun 240Z's with triple side draft Webers and would reinforce Knightrace's view, they can take a while to set up, but they do make excellent power and were good to live with. Us old farts who have been doing performance work before the EFI era remember some pretty good experiences with carburetors (and some awful ones with side draft SU's).

Only criticism I have of carbs was that it was pretty hard to get really, really good power and good fuel economy, generally seemed you had to make a compromise on those two areas with carbs...EFI it seems like you can have your cake and eat it as well in that regard

Dennis

Ok guys, I'm moving the engine progress and pics over to my build thread. If interested you can find it here, just go to the last page for the latest update.

http://forums.pelicanparts.com/porsche-911-technical-forum/895325-my-new-build-last-long-but-very-fun-journey-27.html#post10026436