VR4 upgrade with little difference...again!:(

[Dirk Diggler]

Well, I think I may have made a mistake. I purchased a vr4 last year and would only get 8psi with my 6 rib setup. I sold my VR4, purchased a nitrous kit and I was happy. My sn2000 got 8.5 psi and a 50 shot, i was good to go. I got greedy and sold my nitrous kit, purchased the vr4. I also purchased a 4 inch intake tube and filter, a 7.5 8 rib crank and 3.75 supercharger pulley. My old system was a 6 rib, 6.5 crank and 3.25 s/c pulley. Now, I can get 10psi of boost out of my vr4 but my problem now is that once I hit 5000 rpms =10psi, my car falls flat on it's face. SOLVED by gaping the plugs @ .028. My old setup with 8-9psi ran great but my Power difference with the VR4 is hardly noticable between my sn2000 and vr4:( :freaks:

Any suggestions?
I increased my inch/lbs from 45-56 on the VR4 and the boost is more consistant now, but once I get to 10, that's it?? At 45inch/lbs, the boost would build up to 8ish and fall back down during the rpm range, so I added a little more torque on teh ball dirve and now it' holds ten psi, nothing more:( :blob:

[speedytang]

What rpm are you seeing 10psi. List your car information and setup of engine in your signature and that will help myself and others to remember your car information. If you also move your PSI gauge to your supercharger fitting we can also see how much boost your loosing from the supercharger to the pistons. I want to see if you might have a bad case of blowby. Thanks

[Dirk Diggler]

speedytang,

My setup is as follows;
chevy 350 with 9.5/1 compression, AFR 190 heads, tes headers with a dual 3inch cat back system, crane hi6s ingition, ported plentum and slp runners, VR4 blower. I see boost building fast to 5psi, then it slows way down and slowly creeps up to 10psi @ aprox 5000rmps. My belt system is an 8 rib 7.5 crank, 3.75s/c pulley. I spoke with louis and he thinks i am having belt slippiage issues.?

[speedytang]

It probably is slip, your belt needs to be really tight. Look at your supercharger belt and blip the throttle and watch the belt, if it has twist vibration shake then it is not tight enough. 10psi at 5000rpm is good for a 350ci engine with good flowing heads. If your VR4 has the port at the rear plate move your gauge to that port and drive the car and see what the VR4 is really puttin out. You need a dyno or a track run to see what your really making in power.

[Dirk Diggler]

Yea, I figure I will get some dyno time next year. I"m jsut starting school and time is of the essence for the next year. After talking to louis, I think I may go with a 4.25 blower pulley for more grip. NOw, my Z is petering out about 4800rpms and above. I pulled my plugs and gaped them from .035 to .028 and it seemed to help for about 1/2 the day. But now, it's back to loosing power in that rpm range again? I got some new plugs and plan to gap them at .025 and go from there. Any suggestions?

[Dirk Diggler]

I have a 91Z with a paxton sn2000 mod impeller. I was getting 8.5psi and pretty good power. I purchased the VR4 impeller kit and was told I would be getting up towards 12 and possibly more boost with this new impeller. Well, I'm only gettin ten psi due to belt slippage, I can see the boost climb up to 5-6 fast, then, it struggles the higher the boost becomes closer to ten. The new impeller pushes 1400 or more cfm in cotrast with the old impeller @ 850. I can tell some difference in the power, but my car just looses power above 4800rpms. With the old impeller, my car easily climbs to 6K. At first, my car would fall flat on it's face @ 5K with the new impeller. I pulled my plugs and gaped them from .035 to .028. My car then seemed to run fine for a coupple runs. But now, the car starts to struggle @ 4800rpms, it does not fall flat on it's face, but it is really fighting to get power above 4800 rpms with the new VR4 impeller. It's lilke it wants to go beyond the 4800rpm's but it's surging and struggling to get past that rpm? With the old impeller, it would easily climb to 6K. I forgot to add, when I do get to the 4800-5K mark and I keep my foot on the gas, sometimes I will get a small back fire out the exhaust. Not excessive, just one pop?

mods include; ported intake base and plentum with slp runners, AFR 190 heads, Crane hi6s ignition, tes headers, 3in flowmaster cat back. Also, Ford SVO 24lb injectors, vortech FMU, and LPE 213 cam.

My thoughts are to change my fmu ratio from an 8/1 to a 4/1. I"m not getting any, or very very few kock counts(i've set my timingin the chip to 20 @ WOT from 3800 and above).

Any other thoughts greatly appriciated

[speedytang]

You are running lean, really lean, for you to get a lean pop when at wot you should have some melted plugs by now. You can try a different disc but you really need either 42lb injectors or adjustable Super FMU. Without the blower I would have setup your car with 30lb injectors and you probably would have been just safe at 6000 rpm. Speed Density is a pain to get the fuel map since what is programmed in the computer is nothing like the demand your putting on your fuel system and I hope your running a large fuel pump because the FMU is going to need a lot of fuel to keep up.

[Dirk Diggler]

Yea, I have the vortech fmu with the disks to make it a 12.1 ratio if need be. I have a 255lph pump in tank and an additional 155lph pump in line which comes on during boost. I have programed a chip to dump more fuel in on hte upper rpm's where she's dying.

[Dirk Diggler]

OK, here are my results. I ran the 4/1 fmu and the rpm surge was still @ 4800. I put a 12/1 fmu disk in, increased my fuel in the chip and it ran a little better. Speedytang, I think your right, I have ford svo24lb injectors. I think I need to upgrade to the 30lb injectors as louis has done.

[Dirk Diggler]

Well,

I took her out for a spin and here's whut's up. I ran the 4-1fmu and no change in how the car ran. I put the 12-1 fmu disk in, added more fuel to the chip in the upper rpm range. The car ran better. It still popped out the exhaust, but ran better than when the car had the 4-1 fmu disk in. I have ford svo 24lb injectors and it's time to upgrade to the 30svo's or even 36lbs. I have added as much fuel as the tables will allow me to do with the 24's and I'm beyond their range i'm sure of that. more money..................................:(

[Dirk Diggler]

Well,

I took her out for a spin and here's whut's up. I ran the 4-1fmu and no change in how the car ran. I put the 12-1 fmu disk in, added more fuel to the chip in the upper rpm range. The car ran better. It still popped out the exhaust, but ran better than when the car had the 4-1 fmu disk in. I have ford svo 24lb injectors and it's time to upgrade to the 30svo's or even 36lbs. I have added as much fuel as the tables will allow me to do with the 24's and I'm beyond their range i'm sure of that. more money..................................:(

[speedytang]

Now you have another problem but it is a easy fix. You can't run a smaller pump in line with a larger pump in the tank. You just made your 255lph a 155lph which is to small. You can run a 155lph in the tank and the 255lph after. Remove the 155lph if it is inline and you will notice a improvement in fuel flow. It does not matter what disc you put in the FMU if you have that small pump inline.

[Dirk Diggler]

I can easily disable the 155lph pump by the removal of a fuse. I had that pump to help my stock pump under boost conditions only. I grouned it to the hobbs swithc so it would turn on during boost. Anyway, It's disabled. TY for the info!!!

[speedytang]

The Walbro fuel pumps are a vane design and with it still inline even off will restrict flow just like you taking the belt off your supercharger, your car will still run but will have a restriction in the upper range the same goes for that pump in the way.

[pavement pounde]

I had about the same thing with an extra inline fuelpump.
Ditch the inline fuelpump.
The Walbro 255 is big enough.