engine upgrade options
11-25-2010, 01:27 PM
#16
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I have some interest in your adventure in that we are starting to buy used parts for a budget project. I am not sure my questions are on-song in that I have only a motorcycle roadracing background, where you can gear to the track with a quick change of sprockets.
Your mention of gearing brings up this question. If the gearing change options are in the gear box or tires (tires not being gears but changing the ratio to the ground), it appears you have to figure out which track you run the most and gear for that track. It sound like you can out drive the guys but in the straights, they are pulling you. Correct gearing for the straights may produce a drastic change. I geared so that I was maxed out of RPM in top gear right before the off gas/breaking point of the longest straight (approx- you get the idea). If you are geared too high you can not use the RPM to get you max HP. Not sure how you do that with a 911 but just thinkin.
Fuel air mix. This may be more than a dumb question, but will Webers give better jetting than FI? Air density is key to correct jetting. Altitude and air density go hand in hand. The higher the elevation of the track usually means less fuel in the ratio to air. Lower means more fuel. Temperature interplays and impacts that. Hotter is less air/oxygen, colder is more oxygen and more fuel and horsepower. Humidity is a factor that I never really got a handle on, except more water in the air meant less oxygen per bucket full of air. If you can jet for the condition you can get your max HP.
The question is do Webers still have all the various jet sizes to tune/jet to the ambient conditions of that track? Can Webers be tuned to be more effective than FI. Can you get closer to the optimum air/fuel ratio with jets in the carb thereby producing more horse power? My guess is that it will give a considerable advantage, but just guessin. Word of caution about carburetors and jetting. Setting up the jetting for practice on an overcast cool morning will give you jetting that will be rich if you get a sunny hotter afternoon. Good way to hole a piston if you set up on the hot part of the day and run on a chilly morning the day after. Also, if you do this, carry the best temperature, air density (a good one that is easily read with no conversions), and humidity reading devices.
Air resistance, air flow, and air drag are probably moot points.
Your mention of gearing brings up this question. If the gearing change options are in the gear box or tires (tires not being gears but changing the ratio to the ground), it appears you have to figure out which track you run the most and gear for that track. It sound like you can out drive the guys but in the straights, they are pulling you. Correct gearing for the straights may produce a drastic change. I geared so that I was maxed out of RPM in top gear right before the off gas/breaking point of the longest straight (approx- you get the idea). If you are geared too high you can not use the RPM to get you max HP. Not sure how you do that with a 911 but just thinkin.
Fuel air mix. This may be more than a dumb question, but will Webers give better jetting than FI? Air density is key to correct jetting. Altitude and air density go hand in hand. The higher the elevation of the track usually means less fuel in the ratio to air. Lower means more fuel. Temperature interplays and impacts that. Hotter is less air/oxygen, colder is more oxygen and more fuel and horsepower. Humidity is a factor that I never really got a handle on, except more water in the air meant less oxygen per bucket full of air. If you can jet for the condition you can get your max HP.
The question is do Webers still have all the various jet sizes to tune/jet to the ambient conditions of that track? Can Webers be tuned to be more effective than FI. Can you get closer to the optimum air/fuel ratio with jets in the carb thereby producing more horse power? My guess is that it will give a considerable advantage, but just guessin. Word of caution about carburetors and jetting. Setting up the jetting for practice on an overcast cool morning will give you jetting that will be rich if you get a sunny hotter afternoon. Good way to hole a piston if you set up on the hot part of the day and run on a chilly morning the day after. Also, if you do this, carry the best temperature, air density (a good one that is easily read with no conversions), and humidity reading devices.
Air resistance, air flow, and air drag are probably moot points.
11-25-2010, 03:21 PM
#17
RL Technical Advisor
Jakeflyer's point about gearing is spot-on as that makes ALL the difference in the world. A properly chosen set of close-ratio gears is like adding 50BHP to the performance of the car and naturally, carries no durability penalty.
Regarding AFR's, Webers & PMO's can be jetted to work VERY well provided one takes the time to do this properly. This can be every bit as time consuming as EFI so patience is required.
Jetting (or programming) any air-cooled engine to peak power (13.2:1 AFR) is a recipe for disaster so SOP is always toward the rich side of that value to prevent engine damage under a variety of conditions. Frankly, those last few HP will not make a difference for anyone but professional racers.
Regarding AFR's, Webers & PMO's can be jetted to work VERY well provided one takes the time to do this properly. This can be every bit as time consuming as EFI so patience is required.
Jetting (or programming) any air-cooled engine to peak power (13.2:1 AFR) is a recipe for disaster so SOP is always toward the rich side of that value to prevent engine damage under a variety of conditions. Frankly, those last few HP will not make a difference for anyone but professional racers.
11-25-2010, 03:59 PM
#18
Race Car
Here's my bargain-basement 3.6 path:
1) Sell your toasted old motor (for 2K, in my case)
2) Use that against the 6k price for a 1995 993 motor (patience -- or additional k's -- required)
3) Do the install in your own garage in a weekend (friends required)
4) Head to the dyno with your Steve Wong chip (Steve required)
It's a never-touched 1995 3.6 motor. 264 at the wheels. I also have close-ratio gearing and some other stuff.
1) Sell your toasted old motor (for 2K, in my case)
2) Use that against the 6k price for a 1995 993 motor (patience -- or additional k's -- required)
3) Do the install in your own garage in a weekend (friends required)
4) Head to the dyno with your Steve Wong chip (Steve required)
It's a never-touched 1995 3.6 motor. 264 at the wheels. I also have close-ratio gearing and some other stuff.
11-25-2010, 07:46 PM
#19
uninformed gas bag
(contemplating on whether gas bag is one or two words)
Rennlist Member
(contemplating on whether gas bag is one or two words)
Rennlist Member
Here's my bargain-basement 3.6 path:
1) Sell your toasted old motor (for 2K, in my case)
2) Use that against the 6k price for a 1995 993 motor (patience -- or additional k's -- required)
3) Do the install in your own garage in a weekend (friends required)
4) Head to the dyno with your Steve Wong chip (Steve required)
It's a never-touched 1995 3.6 motor. 264 at the wheels. I also have close-ratio gearing and some other stuff.
1) Sell your toasted old motor (for 2K, in my case)
2) Use that against the 6k price for a 1995 993 motor (patience -- or additional k's -- required)
3) Do the install in your own garage in a weekend (friends required)
4) Head to the dyno with your Steve Wong chip (Steve required)
It's a never-touched 1995 3.6 motor. 264 at the wheels. I also have close-ratio gearing and some other stuff.
11-26-2010, 07:53 PM
#21
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i went the other way with the wheels, putting C2 17's (7.5 front, 8 rear) the offset allows the stock turbo front hubs to fit and its easier to find the 17 inch DOT-R tires. Nitto NT01s - i really like grip and they talk to me. a good PCA mate runs 15 inch Hoosiers but i'm still a little shy of the "no warning" i've heard about them.
