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Discussion Starter #1
I upgraded the turbo on my 1996 900SE to a Viggen turbo that I found at a salvage yard. Made some improvements to it and installed the turbo yesterday. Great boost, as this picture shows.



I also made two short videos, one of the boost gauge and the other of a 25-60 mph run. To download them right click and Save Target As.
Boost Gauge
25 to 60 mph

More info and pictures at my website. Eric's Saab Site - Viggen Turbo Upgrade

Expectations for the upgrade was 30-40 hp and this feels about right. There is a noticeable increase in top end power and the boost pressure stays up longer, not falling off until 5000 rpm. Unexpected benefit is also quicker spool up. 20 psi is reached by 2600 rpm, where as the T25 took to 3000 rpm to hit 20 psi.

The only issue right now is fine tuning the boost control. The wastegate was shortened and the MBC has occasional trouble maintaining control. On one run the boost spiked to 31 psi
A resistor mod to the MAP sensor and a crushed fuel pressure regulator is what allows me to run such high boost. My goal is a nice solid 20 psi like the video shows, but it is not always consistent. Overall this was a great upgrade and the install went relatively smoothly.

Eric
 

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Nice! always love hearing new mods from you eric!! i like how you got that head unit to fit in there with the gauges..good work as always! nice touch with the videos!
 

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Nice, very...


Coincidentally I've been looking into trying to get an A/F and EGT gauge in my 9000. I'd be interested in knowing what sensors you used- esp for A/F (was it a wide band one?) and how you installed them.
 

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Very nice mod, Eric
.

You've taken some precautions so the fuel system can keep up with the increased airflow to the cylinders. I lack the technical skills and selfconfidence to do the crushed fuel pressure regulator mod, so I've been looking at a RRFPR on the Speedparts website. They list several different ratio's, which one would be the best option when I replace my turbo by a T25/28, T28 or TD04?

Some other upgraded turbo/fuel system questions
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At what point does it make sense to upgrade the fuel pump?

What's the max capacity of the stock fuel injectors?

If nothing is changed to the fuel system, would upgrading to a bigger turbo be safe? I reckon APC will interfere when the engine is running lean, but this way one may not get the full benefit from the bigger turbo. Does this make sense ?
 

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Eric, does the crushed regulator increase the pressure linearly (i.e. the same across the range of manifold pressure) or is the characteristic non-linear? Have you measured the fuel pressure since performing the mod? I've heard people talk about this mod, but haven't been able to find figures to say exactly what effect it has.
 

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Eric, in the 25-60 vid an orange light illuminates temporarily on the dash at around 5,500 rpm.

What does it indicate?

Thanks.
 

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Discussion Starter #10
Mark E The A/F ratio gauge is hooked up to my stock O2 sensor. It is neat to watch and is helpful for maintaining good gas mileage, but it is rather worthless for tuning. The exhaust gas temperature gauge is a lot more valuable. I noticed a 100 degree F drop in max temp when I crushed my fuel pressure regulator.

Maarten (900 Hirsch) I picked up an extra fuel pressure regulator when I purchased an entire intake manifold from Ebay, so I wouldn’t be stuck if I messed up. As for technical skills, it requires non to crush the regulator, just a vise, a socket and an accurate ruler. There is good info and how to here, How to crush the fuel pressure regulator

I ended up crushing the regulator 0.1192 inches. I used a caliper to get very accurate measurements. As it turns out though, the regulator cannot be crushed much more than this because the boost/vacuum nipple would be damaged. Here is a picture to help.


That nipple also means that it is a rising rate fuel pressure regulator. No need to upgrade to one because these Saabs are already equipped. The GM900 has 352cc +/- 28cc (per minute) injectors. I do not know the max flow rate of the stock fuel pump. But I just changed my fuel filter and ported and smoothed out the banjo bolts.

One of the reasons I went with the Viggen turbo was so that I did not need to change my fuel injectors. If I had upgraded to the 9000 Aero Td04 I would have needed larger injectors. Things have worked out well with the Viggen turbo and crushed regulator. I have measured a decrease in maximum temperature since the upgrade.

BillJ Crushing the fuel pressure regulator does not change it’s characteristic response. It simple increases the spring force, so the reaction is still linear.

Eric
 

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Thanks for that, Eric. That web site mentions 10psi for 1/8" "crush". Is this similar for the Saab FPR? If so, you've added about 9.5psi, which seems a lot.

Have you measured it yet?

I'm interested in a small increase in fuel pressure to enrich my mixture a bit more at maximum power. According to the figures I got from the last Power Engineering dyno day I was at, I probably need about 17% extra flow at maximum power. I don't want to go for bigger injectors yet, as I intend to do a few other things when I do that, including an ECU remap. I just want to give my engine an easier time.

Anyone know enough about fluids to describe the relationship (if there is a constant relationship) between pressure and flow, given a constant viscosity and cross-sectional area? Is it directly proportional, as I think it might be, analogous to Ohm's law? If so, 10psi extra is indeed what I need (3.7 bar).

I understood that a RRFPR differed from the Saab FPR in that the pressure above manifold pressure changes as manifold pressure changes. For example, the standard Saab regulator might always maintain fuel pressure at 3 bar above manifold pressure (e.g. 3.5 bar at 0.5 bar boost and 4.0 bar at 1.0 bar boost), while a RRFPR gives a rising fuel pressure above manifold pressure (e.g. 3.5 bar at 0.5 bar boost but 4.5 bar at 1.0 bar boost). Did I get that wrong?

I understood that FPRs generally worked the same way as the Saab regulator, even on non-turbo cars, because you need to maintain a pressure difference between the fuel on one side of the injector and the manifold pressure on the other, rather than maintaining a constant fuel pressure regardless of manifold pressure.
 

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Try this site

www.rceng.com for spreadsheets to calculate fuel flows, though there calculation for BSFC at 0.7 for a turbo car is very pessimistic. Try closer to 0.45 to 0.5.

Basically the fuel flow changes to the ratio of the square roots of the pressures. ie changing from 2bar to 4bar base pressure would increase the fuel flow by 1.4x .
 

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I tried this today. From Alex's information, I needed a pressure increase of around 1.1 bar. I was going to try doing it in small increments (say 1mm) and measure the pressure each time, but the plumbing for my pressure gauge is so dodgy that I decided just to go for it and measure the pressure afterwards. If I went too far, I could always get another used regulator.

I crushed mine by 3mm (yours translates to 3.02mm, Eric, so they're about the same), also measuring with a caliper for accuracy. When I put it back on the car and fired it up with the manifold pipe disconnected, a quick reading showed the pressure was 4.2 bar. Just over my target. I'd expect yours to be almost the same (my gauge wouldn't be precise enough to tell the difference between them).

No apparent running problems so far and on a test drive I was getting respectable boost for such a warm evening. I'll take it somewhere soon to have the A/F ratio checked out again.
 

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Originally posted by ERP:
[qb]One of the reasons I went with the Viggen turbo was so that I did not need to change my fuel injectors. If I had upgraded to the 9000 Aero Td04 I would have needed larger injectors. [/qb][/b]
Eric,

I'm a little confused by this... I don't see why the spec of the turbo should make any difference to the fuel flow required for a given desired hp output. It's still going to require the same boost pressure and volume of air. OK if you're out of the optimum compressor efficiency range, there may be a slight intake temp increase, but your basic fuelling requirement is still going to be governed by the amount of air being induced...
 

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I thought the only difference between the Aero and Viggen turbos was the size of the turbine nozzle area, the Aero having 6cm2 and the Viggen 5cm2, the compressors being the same. This difference would only limit the power at the limits as the Viggen turbo would put more backpressure into the system.
 

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Originally posted by BillJ:
[qb]I tried this today. From Alex's information, I needed a pressure increase of around 1.1 bar. I was going to try doing it in small increments (say 1mm) and measure the pressure each time, but the plumbing for my pressure gauge is so dodgy that I decided just to go for it and measure the pressure afterwards. If I went too far, I could always get another used regulator.

I crushed mine by 3mm (yours translates to 3.02mm, Eric, so they're about the same), also measuring with a caliper for accuracy. When I put it back on the car and fired it up with the manifold pipe disconnected, a quick reading showed the pressure was 4.2 bar. Just over my target. I'd expect yours to be almost the same (my gauge wouldn't be precise enough to tell the difference between them).
[/qb][/b]
There is also a another fairly cheap way to mod the original FPR into an adjustable one. Here is a link to a Finnish site that showes the basics.
http://www.amworks.com/fin/irtokannet.htm

Basically you need to rip off the original cover from the FPR and replace it with the new one.
After the mod the FPR will work identical to stock one, but you have the option of changing the pressure.

Following tool are neede for the work:
lahte or grinder
basic hand tools
 

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Discussion Starter #18
Thanks Bill for measuring the upgraded pressure of the crushed regulator. I wanted to measure my new pressure but didn’t have and good gauge to use. I’m not surprised that the information on the webpage detailing how to crush the fuel pressure regulator does not match your results. Our regulators are different than the one on the website.

Mark E – My reasoning is based on a conservative analysis of the fuel system on my GM900. Most tuning companies offering a turbo upgrade of 300 hp or more also include larger injectors. The Aero turbo with it’s larger housing is capable of maintaining high boost to redline where as the Viggen turbo gets chocked above 5000 rpm and will fall off to 15 psi. I am not sure if the stock injectors, even with a crushed fuel pressure regulator, could handle high boost near redline. This is why I feel that if the Aero turbo is going to be used that the fuel injectors should also be upgraded. I could be wrong but I am trying to error on the side of caution. If I could afford some serious dyno tuning time I would be able to give a definitive answer.

Eric
 

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Originally posted by ERP:
[qb]I am not sure if the stock injectors, even with a crushed fuel pressure regulator, could handle high boost near redline.[/qb][/b]
What I can tell you is that the air/fuel ratio measured on the dyno on my 305hp run showed that I was running approximately 14:1 which although stoichiometric, was not ideal at that sort of power output. The guys at Power Engineering reckoned they'd rather see 12:1. So I needed about 17% more fuel at peak power and according to Alex, that meant 4.1 bar instead of the standard 3.0 bar. With my modification, I now have 4.2 bar which is pretty close. So I'm running 300-odd hp, standard injectors and a FPR crushed just about as far as is safe, and I'm supplying a safe amount of fuel with some to spare but not much.

My 9000 Aero does, of course, have the Aero turbo. The Maptun ECU tapers off the boost at higher RPM. - the beauty of digital control. It would likely be a different story with a manual boost controller and in that case a less-capable turbo will provide the taper for you. I can't think offhand of another way to taper the boost mechanically to a particular specification, i.e. to limit maximum airflow.

I really must get some new plumbing for my fuel pressure gauge (or fit a test point to the Aero). It was rather disconcerting to see the fuel spraying all over the engine as if I had fitted an external 5th injector
 
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