edpurplett

I get right of first refusal :-).... PLEEZ! Have fun!! .. tell me to shut up if u want.. the injectors(possibly w/ another XX HP) and compressor wheels are probably close to their limits thought with the rising rate fuel reg I think those injectors can go mid 600's... but at 2500-2600 lbs the power to weight is silly fun.... ;_0 even with no mods.... :-)

and the turbo's ?I think ??they're S60's w/ .62 AR wheels... forgot...

Geoffrey

I think you are about right on with the HP level. The 44lb 993tt injectors are maxed at about 475fwhp at stock fuel pressure of 3.8bar. Upgrading to 5bar gets you to 500-510fwhp in my experience based on my chassis dyno work.

Open diff....nice...

edpurplett

Geoffrey... I know you'll shudder :-), but I think the rising rate goes to 6.X bar .... BTW did you ever run a 2wd on a chassis dyno?? with the 44's? and 5 bar?

ed

Geoffrey

Not really, the closest was a modified 3.4l with cams, EFI, etc and the shop installed 44lb injectors @ 3.8bar and they went to 100% duyt cycle at about 410rwhp.

Is it an adjustable rate rising rate FPR? I have a real distaste for them...

Jean

Ed, the car is yours, anytime you want it

Re. the injectors, they are 44lbs, and as a general rule of thumb these cars will be at about 0.5 BSFC, so, upside down, you get 1/0.5=2 HP/lb/minute
Now take the injectors, which flow at 44lb per cylinder, that makes the calculation 44 X6 X 2(hp/lb/min) = 528 HP at 3 Bar...
Convert now to 3.8 Bar and you get another 12% HP, up to 594HP.. Since they are usually run at 5 BAr fuel pressure, you will see another 15% HP, taking you to 683HP or so.. Voila!!

Injectors are not the limiting factor, and I am sure that if you put this car on a Mustang or dynojet etc.. and increase the boost, you will see 620HP or more.

It is amazing how much HP you can make with stock injectors! This HP is at the crank and based on this BSFC (Brake Specific Fuel Consumption).. In a MAF based car, you would be limited by the MAF, but since this car is Pressure sensing, you can go up to that HP if everything else is there (cooling etc..)..

Ed, these turbos can flow up to 35 lbs/min ( a bit more than a K26), therefore you can see around 595FWHP with them at 8.5 BSAC, which would be reasonable with good mapping. The N/A 3.2 engine is much more efficient than the turbo.

Geoffrey

Jean, I think some of your calculations are off. The BSFC of a 911 turbo engine is much higher than .5, especially when it is run at 11.8-12.0:1 afr and 1-1.2bar of boost. I can tell you that they run to 100% duty cycle as reported by engine management systems at 410rwhp and 3.8bar at the above mentioned afrs. There is no way it will see 620fwhp with those injectors. not a chance. Even Bosch 55lb/hr injectors were maxed at 600-620hp and 3.8bar.

**EDIT**
After looking at some engine dyno data I have from a 3.8 N/A engine and MoTeC, the BSFC as reported by a DTS engine dyno is .48 at peak power at an AFR 13.2:1 and that was with a highly optimized cylinder head, piston design and tightly controled squish and quench area.

Jean

Geoffrey,

A good efficiency number for an engine like this would be 0.5 BSFC, anything higher would be dropping efficiency. I am sure these numbers can vary up and down of course. I can see different numbers on my engine dyno datalogs, but directionally they should not be too far off.

Concerning the data that you mentioned, if you saw a BSFC of 0.48, then that means that you will be flowing 2.08HP/lb/min then if you take the 44 X 6 X 2.08= 549FWHP.. This was at 3 Bar I presume? So our numbers are not far off?

This car that I got is running 3.8 Bar therefore will be limited somewhat, but based on a similar setup (guess whose )and the engine datalogs that I have of it, I am sure it can run up to 640FWHP with this 3.8 Bar pressure regulator at 1 Bar and 100% duty cycle. I can check with Todd if you would like but I am pretty convinced of this.

Geoffrey

The engine that that data came from was 3.8N/A engine and I can't recall the injector size at the moment, but I'm going to guess it was the Bosch 803 37lb/hr injector and produces 396hp on an engine dyno.

While Bosch injectors are robust and I've run them to 92% duty cycle, as a general rule, I won't run any injector past about 85-88% duty cycle. Running a larger injector also provides a wider window for injection timing in a sequential injecton strategy which has added benefit of improved fuel economy and slight throttle response.

It has been awhile since I have had a 911 Turbo on an engine dyno, but I recall the BSFC in the .68 range, but again it has been awhile. Perhaps things are different for you, but for me, it is as I posted above and pretty consistent among the many 911 Turbo engines I've done.

Jean

Geoffrey,

0.68 is a very high number but can be there for sure, it however means that the engine is running very very rich, which is ok of course. My 3.8 is on the rich side for heat protection as well, and it sees higher BSFC that the norm, you will be limiting HP however as I am sure you agree.

In any case, thanks for the debate, I miss those from time to time, great insight! We'll see what this baby does.

edpurplett

This is fun! Thanks both.... !!

Geoffrey

That is the issue with the 911 air cooled engine. It has a very inefficient cylinder head design, the turbo piston has terrible squish area, the thermodynamics loses efficency, and the fact that in a turbo engine you need to be in the 11.8-12.2:1 when running .8-1.2bar or so just to keep the engine from self destructing. If this were a Honda engine with a turbo, the BSFC could be in the .5 range due to the highly efficient design of the engine. I run the engines as lean as I think I can get away with and still keep the engine together.

Jean, Oh yea, I wired my 964 RSR for a twin turbo engine, so at 2000lbs dry a turbo engine could make this car silly.

purplehaze.

Jean,

Congratulations! I think you will have a blast. It doesn't matter what you call it, or what forum you list it under - it's a beast.

I'm not wading into the BSFC debate yet, which is way over my head.

I have and love Ed's previous ride, Purple Guy, another of Todd's 3.3 creations. I'm sure you know more about her than I. It's been to Lime Rock and is gearing up for Watkins Glen in 3 weeks. Can't wait to stretch her legs a bit!

I'm sure you will get the wheels and interior to your liking shortly. I have the same Speedlines for street, and 9 and 12" -18" CCW's for track.

Mine started with front torsion, rear coils as well. Thanks to the cut rear torsion tube for the G50/50. Changed over to matching Bilstein coil overs (lowered spindles), 450/650 springs, revavled Bilsteins, bump steer kit, and Smart Racing ARB's. Street is sweet, and track will be seen shortly. Big reds as well.

Geoffrey tried mine with the 5-speed at Lime Rock. You only shift once into 4th for the straight away. The rest is just torque and boost in 3rd gear. He showed me how to keep the turbos spinning for easier aceess to boost - so now I have something else to practice. We were at the lower boost setting with only ~430 rwhp. Can't wait to try with ~500 rwhp at the Glen soon.

I'm just adding a front oil cooler this weekend.

Again, congratulations! Hope to see you both at the tracks.

Glenn

Geoffrey

Glenn,

I'll be at the Zone event which will be the first outing with my new car and I can't wait. I'll be a floating instructor for advanced drivers...

purplehaze.

Geoffrey -

Congratulations on the first track event in your new car!

I wish I could be there on Saturday to watch you take that thing out. Hate to see it get bugs, tar, tires, etc but that's what you built it for. It must sound incredible with that minimal exhaust.

I'll be driving up Sunday and hope to see you mid-day-ish. Don't know if I can get my car in the event, but who knows. Maybe you can still take it out and test the new springs. That is, if you're bored with yours by then ....

Can't wait to see you give Scotto a run for his money. I mean, SOMEONE has to or else it's likely to go to his head .... DOH

Glenn

Geoffrey

Glenn,

I'll add you to my guest list so you can get into the track on Sunday.