turbo suggestions for 91 DOHC OBD1

[GTP091]

I've been researching a turbo application for my car on and off for quite some time now and I was wondering if you guys could clear up a few things I can't find answers to after reading and searching countless threads. I understand that the smaller the ar on the exhaust side the faster the turbo will spool and start making boost (read that one) but it will have lower torque to spin the blower side of the turbo (implied but not directly stated in a thread). Is that correct?? So a t3/t4 t04e with a .63 exhaust and .50 blower will spool quick but wont make much boost?? What does AR stand for (air ratio) and what does the pitch of the wheel do in relationship to the AR?

If I was to pick a turbo right now it would be a t3/t4 to4e but I have a feeling it's to small. or a T4 t04b but it may spool to slowly. If that's right about these two is there a happy medium?? Im looking to keep my car as a weekend toy not a track car so making 400 hp isn't the goal more like 280-320. I would like to get it up to 7-10 psi. any suggestions?? Most likely I would have to use a FMU and get some ALDL gear from moates... I've seen RRFPR around is that the same as a FMU but with a gauge??

[RedZMonte]

sounds exactly like what im making on that ammount of boost. on my T04E. I live 5000+ft elevation so it does spool a little slow.. at lower elevation it will not be a problem. i think D.O.H.C. has a T3/T4 on his and he is in florida... might wanna ask him what he is using and how fast it spools. A large T3/T4 should be sufficent.

[timg]

For conventional turbos, T04E 60 trim or 60-1 works well on a compressor side. The turbine side should either be a stage 5 T3 wheel or a P-trim T4 wheel. Small turbines kill efficiency. The standard 4 cylinder T3/T4 hybrids may work, but you should be very careful. They tend to have very small turbines compared with their compressors.

Tim

[GTP091]

Any opinions on FMU's. I see RRFFPR here and there and they seem to be the same thing but maybe not. looks like a FMU of 12:1 is standard for a DOHC using it. The ratio is for?? I had thought the fuel pressure should rise at the same rate as the boost 1:1. definitely not 12:1?

[RedZMonte]

I ran a 12:1 on mine with a walbro 225. i have the Vortec FMU disc kit to change the ratios if your interested.

[GTP091]

I ran a 12:1 on mine with a walbro 225. i have the Vortec FMU disc kit to change the ratios if your interested.

walbro 225 is the fuel pump I assume; good to know. Can rising rate fuel pressure regulator replace the FMU?? and what the hell is the 12:1 ratio all about??

[RedZMonte]

I assume the RRFPR would work.. Esencially a FMU is just that.

dunno, everyone i know has allways ran a 12:1... sound a bit extreme but thats what they use.. you can prob. run something less but thats just what i ran..

Yes the Walbro 255lph is the fuel pump.

S

[GTP091]

An even bigger question to is what bin do you guys use. Looks like a few thought about using the TGP bin ( $8F?? ) but it was diificult to change all the spark tables over. From searches I've done the bin of choice is the original bin but with 2 bar map changed. Have the bins you've used for your turbo DOHC's been put in the download section??

[robertisaar]

do you have a 5 speed or the auto?

if you have the auto, TGP code(alone) won't work for you because it won't control the tranny, something your DF code PCM does now.

if its a manual, i don't see any problem

you could also consider code59...

[GTP091]

It's an auto now but I would like to do a manual swap at the same time when the car is down for awhile. I'm a complete newb when it comes to ecm tuning ( I have tunerpro but right now all the fields are mostly gibberish ) so I would need something that is closer to done. code 59 seems like a huge learning curve and some guys think it's not necessary. I wouldn't try it if I have to start from scratch.

[robertisaar]

both TGP code or 59 will work great, but 59 is much more detailed, and if i had to chose, that would be my choice, but whatever, your call.

[RedZMonte]

An even bigger question to is what bin do you guys use. Looks like a few thought about using the TGP bin ( $8F?? ) but it was diificult to change all the spark tables over. From searches I've done the bin of choice is the original bin but with 2 bar map changed. Have the bins you've used for your turbo DOHC's been put in the download section??

I have a OBDII conversion.. and tuned with DHP. on mine the MAP maxes out (stock 1 bar) and the MAF (mines a 1995) reads the boost. the FMU should do the trick for low boost but any higher then ~5psi you would wanna 2 Bar map and a tune.

S

[WrathOfSocrus]

I assume the RRFPR would work.. Esencially a FMU is just that.

Please correct me if I am wrong since I don't have a turbo nor see one in my near future . . . but from what I have read a rising rate fuel pressure regulator (rrfpr) increases fuel pressure by one psi for every psi read from the manifold.

If you have your injectors shooting 55 PSI into a 0PSI manifold (55 - 0 = 0) then the resulting fuel pressure the manifold receives is 55 PSI. Add 10 PSI of boost and you get ( 55 - 10 = 45) only 45 PSI of fuel entering the manifold. The rrfpr adds an equal amount of fuel pressure to counteract the effect of boost on the manifold ( so according to the hypothetical above would be 65 -10 = 55).

Using the FMU without the rrfpr means for every pound of boost you add, the fuel pressure the manifold sees is the fpr PSI + FMU added PSI - PSI boost added to the manifold. Lower boost levels wouldn't be affected drastically but higher boost would be getting less fuel per pound of boost than a lower amount of boost would. Adding in the rrfpr would mean for every pound of boost the FMU would add its ratio of fuel pressure increase and that is it. It would give a linear amount of fuel per pound of boost whether at 3 PSI or 30 PSI.

While boost is cost prohibitive to me at the moment, it is very interesting to learn about. I have read some conflicting information about a few things and the rrfpr has been explained in several confusing ways. I read up about it and what I wrote above is my understanding of it at the moment. If anyone knows anything to confirm or deny the statements above I would appreciate the input!

[GTP091]

As I understand it now a FMU has a changeable diaphragm to adjust the fuel curve 12:1 is 12 per pound of boost added. so 2 PSI boost is 24 psi to the rail. A RRRFR is the same thing but has an adjustable ratio? You don't use both it's one or the other.

[WrathOfSocrus]

Yes that's how the FMU's work. Some of them have interchangeable diaphragms for different ratios such as 10:1 8:1 and so on.

As far as I know the rrfpr's are not adjustable. You can adjust the static fuel pressure by adjusting how much fuel goes back through the return line, but I just searched through over 20 rrfpr's on summit and they all do 1:1 ratio.

Like I stated earlier, there is conflicting information regarding rrfpr's on this website and I would like to clear up the confusion for myself and others. I will have to hunt down exactly where I had read about the rrfpr's role in counteracting the manifold pressure to maintain constant fuel delivery.

EDIT - Apparently the rest of the web has a bunch of confusion as well. After hours of searching I have found a few small insights. By definition I guess all FMU's are rrfpr's because they increase fuel pressure based on a boost reference. There are rrfpr's out there that are adjustable and even ones that don't begin to add fuel pressure until a certain predetermined boost pressure has been achieved. These rrfpr's go downstream from the main fpr on the fuel return working exactly like a FMU.

This is in contrast to the typical rrfpr's that I have come across on such websites as Summit and ebay. All of these are FPR's designed to replace the stock FPR and most are adjustable FPR's with a non adjustable boost reference of 1:1. After an extensive search I did see one reference to the 1:1 ratio being solely used to counteract the manifold pressure under boost from working against the injectors. The page was so long and dry and hard to read from the colors that I wont even bother to post the link.

So I guess that technical difference between an FMU, an adjustable rrfpr, and the FPR's with a 1:1 boost reference that is referred to as a rrfpr is the source of the confusion. It seems if you intend on adjusting your base fuel pressure (and tuning for it of course) and have boost then the boost referenced FPR's are better than the ones without the boost reference to keep the fuel pressures constant for tuning purposes. When your injectors are maxed out and using a larger injector is impractical due to idle fueling issues or any other issues for that matter (money for one), then a FMU or rrfpr that goes on the fuel return line will be needed to keep the engine fueled and avoid running lean.