Shimmed wastegate
01-22-2002, 09:47 PM
#1
Addict
Rennlist Member
Rennlist Member
Thread Starter
Join Date: May 2001
Location: A suburb of Silicon Valley, CA
Posts: 2,099
Likes: 0
Received 7 Likes
on
3 Posts
Shimmed wastegate
Ok guys will I risk damaging the engine if I shim the stock wastegate with no other modifications?
Currently my engine is completely stock, with 68k miles.
Currently my engine is completely stock, with 68k miles.
01-23-2002, 01:04 PM
#2
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
Yes. Your car currently has no means of supplying more fuel for the higher boost levels attainable by shimming the wastegate.
Also, as I found out, the computer will shut the fuel off if you exceed about 13.5 psi (1.85-1.9 bar on the stock boost gauge).
Good Luck,
Russ
Also, as I found out, the computer will shut the fuel off if you exceed about 13.5 psi (1.85-1.9 bar on the stock boost gauge).
Good Luck,
Russ
01-23-2002, 02:17 PM
#3
Addict
Rennlist Member
Rennlist Member
Thread Starter
Join Date: May 2001
Location: A suburb of Silicon Valley, CA
Posts: 2,099
Likes: 0
Received 7 Likes
on
3 Posts
Russ,
Thanks for your input!
That is what I suspected. I was hoping that I could sneak in a little easy HP. I guess I will need to hold off with the shims until I can get a means of additional fuel management.
I plan to not go the chip route. I believe that removing the stock ems/klr and replacing them with a SDS or Tech II unit is the superior path to HP heaven.
I guess its back to saving my milk money and waiting.
Thanks for your input!
That is what I suspected. I was hoping that I could sneak in a little easy HP. I guess I will need to hold off with the shims until I can get a means of additional fuel management.
I plan to not go the chip route. I believe that removing the stock ems/klr and replacing them with a SDS or Tech II unit is the superior path to HP heaven.
I guess its back to saving my milk money and waiting.
01-23-2002, 08:45 PM
#4
Race Director
Piece of cake! Shimming the wastegate will typically add about 2psi to your boost (about 18%), bringing it up from 11psi to just under the 13.5psi where the stock overboost-protection kicks in. But I've heard of A LOT of people not getting fuel-cutoff even at 15-17psi.
The extra boost will not cause you air-fuel ratio problems if you're not at full-throttle/high-RPM since the computer will still use O2-sensor feedback to adjust injector duty-cycle to match the air flow.
When it does go into open-loop mode, it uses a fixed duty-cycle to RPM look-up table. To make ensure correct air-fuel ratio in open-loop mode, increase the fuel-pressure. Get a 3-bar fuel-pressure regulator from Jason @ Paragon ($38). This coincidentally is 20% higher pressure than stock, roughly matching the 18% higher boost you'll have from shimming the wastegate.
I would initially shim the wastegate by just 2mm and watch the boost-gauge carefully. You want to shim it just enough to bring max-boost from 1.7 to 1.9bar. Do several runs with increasing throttle, watch the boost gauge and listen for knock.
Increase the shim-stack until you get 1.9bar on the gauge. About to 3-4mm, no more than 5mm due to coil-bind in the wastegate spring. If you get some pinging, you can retard the ignition by 3 degrees using the fuel-quality switch in the DME.
This was actually the first engine-mod I did on my car before I got a manual boost-controller and APE chips for full 15-17psi of boost. Which didn't give me as much of a performance boost as the simple wastegate-shim/3-bar FPR mod I initially did. I attribute this to the excessive amounts of ignition retard dialed into the APE Stg.2 chips and excessive mid-range richness. My guess is that APE did this to cover their a** and also to allow people to run 20psi of boost.
The extra boost will not cause you air-fuel ratio problems if you're not at full-throttle/high-RPM since the computer will still use O2-sensor feedback to adjust injector duty-cycle to match the air flow.
When it does go into open-loop mode, it uses a fixed duty-cycle to RPM look-up table. To make ensure correct air-fuel ratio in open-loop mode, increase the fuel-pressure. Get a 3-bar fuel-pressure regulator from Jason @ Paragon ($38). This coincidentally is 20% higher pressure than stock, roughly matching the 18% higher boost you'll have from shimming the wastegate.
I would initially shim the wastegate by just 2mm and watch the boost-gauge carefully. You want to shim it just enough to bring max-boost from 1.7 to 1.9bar. Do several runs with increasing throttle, watch the boost gauge and listen for knock.
Increase the shim-stack until you get 1.9bar on the gauge. About to 3-4mm, no more than 5mm due to coil-bind in the wastegate spring. If you get some pinging, you can retard the ignition by 3 degrees using the fuel-quality switch in the DME.
This was actually the first engine-mod I did on my car before I got a manual boost-controller and APE chips for full 15-17psi of boost. Which didn't give me as much of a performance boost as the simple wastegate-shim/3-bar FPR mod I initially did. I attribute this to the excessive amounts of ignition retard dialed into the APE Stg.2 chips and excessive mid-range richness. My guess is that APE did this to cover their a** and also to allow people to run 20psi of boost.
01-24-2002, 12:01 AM
#5
Addict
Rennlist Member
Rennlist Member
Thread Starter
Join Date: May 2001
Location: A suburb of Silicon Valley, CA
Posts: 2,099
Likes: 0
Received 7 Likes
on
3 Posts
Danno,
Its a MIRACLE, I can SEE hoursepower!
Once again you've led me out of the dark into the light.
AMEN Brother!
I got some stainless steel washers from Home Depot. Three of them put the thickness at 3.5 mm. I think I'll start there and remove instead of add. The FPR from paragon is on order.
That won't break the bank, good call. My lattitude with the bank (wife) has gotten very narrow after my recent purchases, $1,045 Centerforce clutch, $130 lighten/balance flywheel, $298 motor mounts, $390 misc seals/gaskets/bolts.
By the way Danno, I have been thinking lately that you should write a guide to hot rodding the 951. With all the knowledge that you have, it would save a lot of posts for a lot of people. You could work with guys like SFR (who routinely help rennlisters) in return for recomending their services and products (I WILL buy my stuff from them when it is time). Maybe other rennlisters would help out (there is a lot of quality brain matter on this board). Like 86944turbo, Rage2, etc, etc, etc.....
What do you think? I would buy one. Anyone else?
Its a MIRACLE, I can SEE hoursepower!
Once again you've led me out of the dark into the light.
AMEN Brother!
I got some stainless steel washers from Home Depot. Three of them put the thickness at 3.5 mm. I think I'll start there and remove instead of add. The FPR from paragon is on order.
That won't break the bank, good call. My lattitude with the bank (wife) has gotten very narrow after my recent purchases, $1,045 Centerforce clutch, $130 lighten/balance flywheel, $298 motor mounts, $390 misc seals/gaskets/bolts.
By the way Danno, I have been thinking lately that you should write a guide to hot rodding the 951. With all the knowledge that you have, it would save a lot of posts for a lot of people. You could work with guys like SFR (who routinely help rennlisters) in return for recomending their services and products (I WILL buy my stuff from them when it is time). Maybe other rennlisters would help out (there is a lot of quality brain matter on this board). Like 86944turbo, Rage2, etc, etc, etc.....
What do you think? I would buy one. Anyone else?
01-24-2002, 01:45 PM
#6
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
Posted prev. by Danno:
Now go easy on me, but wouldn't raising the fuel pressure by 20% only increase fuel flow by approx. 5%? To double the fuel flow you'd have to quadruple the pressure. Again I'm only regurgitating info gleaned elswhere, so maybe somebody could check my work.
Get a 3-bar fuel-pressure regulator from Jason @ Paragon ($38). This coincidentally is 20% higher pressure than stock, roughly matching the 18% higher boost you'll have from shimming the wastegate.
01-25-2002, 12:33 AM
#7
Addict
Rennlist Member
Rennlist Member
Thread Starter
Join Date: May 2001
Location: A suburb of Silicon Valley, CA
Posts: 2,099
Likes: 0
Received 7 Likes
on
3 Posts
wouldn't raising the fuel pressure by 20% only increase fuel flow by approx. 5%? To double the fuel flow you'd have to quadruple the pressure.
Trending Topics
01-25-2002, 01:58 AM
#8
Race Car
Hmm, I see the logic, but the fuel pumps are efficient enough to compenstate for the requlator increase, also, all four injectors are not driven at once, so the equation would not be devided by four.....
As long as the pump can keep the FPR supplied with sufficient fuel, Danno's figures should be correct..
As long as the pump can keep the FPR supplied with sufficient fuel, Danno's figures should be correct..
01-25-2002, 12:14 PM
#9
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
the fuel pumps are efficient enough to compenstate for the requlator increase, also, all four injectors are not driven at once, so the equation would not be devided by four.....
how much more fuel flows through the fixed dimension orifice at the end of the injector at a given duty cycle and a fixed fuel pressure (2.6 bar at full boost). Dividing by 4 has nothing to do with four injectors, but with relationship between pressure and volume of a liquid moving through a fixed aperture.
Unfortunately I don't know the precise formula, but it has something to do with the flow varying with the square of the pressure.
Somebody out there must remember their fluid dymamics or hydaulics!
01-25-2002, 12:39 PM
#10
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
the fuel pumps are efficient enough to compenstate for the requlator increase, also, all four injectors are not driven at once, so the equation would not be devided by four.....
how much more fuel flows through the fixed dimension orifice at the end of the injector at a given duty cycle and a fixed fuel pressure (2.6 bar at full boost). Dividing by 4 has nothing to do with four injectors, but with relationship between pressure and volume of a liquid moving through a fixed aperture.
Unfortunately I don't know the precise formula, but it has something to do with the flow varying with the square of the pressure.
Somebody out there must remember their fluid dymamics or hydaulics!
01-25-2002, 08:47 PM
#11
Nordschleife Master
What's involved in shimming the waste gate? I don't even know where it is...
So far I've been gettin all my work done at a local Porsche specialist, but I wouldn't mind getting my hands dirty, especially while my car's laid up over the salt season.
So far I've been gettin all my work done at a local Porsche specialist, but I wouldn't mind getting my hands dirty, especially while my car's laid up over the salt season.
01-28-2002, 08:53 AM
#12
Pro
Join Date: Jan 2002
Location: Toronto
Posts: 523
Likes: 0
Received 0 Likes
on
0 Posts
The question was raised as to how much a 3 bar fuel pressure regulator will increase fuel flow through the injectors. I believe the regular pressure regulator is 2.7 bar, and thus the 3 bar regulator will increase the fuel pressure by 3 divided by 2.7, or about 10%. By Bernoulli's equation for incompressible fluid flow (gasoline qualifies), the flow rate will increase by the square root of the increase in fuel pressure, or by about 5%. I use my car mostly for the track, and I need top end, so I've gone to a simple K26/8 with the Jon Milledge system, which produces about 285 flywheel horsepower. For this, the stock fuel pressure regulator works fine.
01-28-2002, 01:58 PM
#15
Pro
Join Date: Jan 2002
Location: Toronto
Posts: 523
Likes: 0
Received 0 Likes
on
0 Posts
[quote]Originally posted by Danno:
<strong>The stock 951 regulator is 2.5 bar.</strong><hr></blockquote>Sorry, didn't know the rating on the standard regulator. The 3 bar regulator would increase pressure by 20%, and the flow rate at the injector by about 9.5%, which is significant.
<strong>The stock 951 regulator is 2.5 bar.</strong><hr></blockquote>Sorry, didn't know the rating on the standard regulator. The 3 bar regulator would increase pressure by 20%, and the flow rate at the injector by about 9.5%, which is significant.