What kind of FMU to buy?

2512 Views 18 Replies 7 Participants Last post by CRXType-R, Mar 6, 2002

Blaze

Discussion Starter · Mar 2, 2002

I have a 91 Rex, soon to have the B16 and
I plan on boost to around 12lbs.
Should I buy a Apexi Vafc or a Voretech FMU
or what? I really dont know. I would go
Hondata but I dont have an extra 1000
in the budget, Im thinkin around 400 and
down. Thanks for the help. Blaze

1 - 19 of 19 Posts

BoostedRex

· #2 · Mar 2, 2002

usually you need an fmu to go with an apexi safc. so i would first buy the fmu, and if you want better tuning, invest in a safc.

but just looking at your plans, i wouldn't set your goal boost that high. the b16 has fairly high compression and doesn't take high boost levels like that very well without great tuning with a hondata. so i would either suggest lowering your goal boost or getting a hondata.

Blaze

Discussion Starter · #3 · Mar 2, 2002

You can take that out with Mat3t4. He
said that high comp. engines are
better for turbo, though I can't really
tell you why, hey matt if ya look over
this post tell us again why its better
to have a high com engine. I doubt I'll
ever run 12psi. My axles will snap! But
Max psi is 8 @ the track and 5 around
town. Post matt post~!

b16ahybrid

· #4 · Mar 4, 2002

Blaze said:
You can take that out with Mat3t4. He
said that high comp. engines are
better for turbo, though I can't really
tell you why, hey matt if ya look over
this post tell us again why its better
to have a high com engine. I doubt I'll
ever run 12psi. My axles will snap! But
Max psi is 8 @ the track and 5 around
town. Post matt post~!

It's not a matter of which is better,they both have their strengths and weaknesses.On a low compression engine you are able to run more boost then you would if it was a high compression engine.Now let me explain that.Say you have a b16a with the stock 10.2:1 compression with decent tuning your limited to about 8-10psi of boost.Now the same b16a but with low compression (without factoring in the sronger forged pistons or rods) say 8.5:1 compression.You will be able to run about 12-14psi with the same tuning.A high compression engine is more prone to detonation when under boost.A high compression engine will spool a turbo faster then a low compression engine will so you will build boost sooner on a high compression engine then you would on one with lower compression.It really comes down to how much you have to spend and how good the tuning is.The higher compression engine will require more precise tuning to handle the same amount of boost as a low comporession engine.And as we all know tuning is the key to power and engine life.

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CRXType-R

· #5 · Mar 5, 2002

as for the FMU, you can get one on thepartstrader for like 90$. If you don`t know what kind of injectors you intend to use, then figure that out BEFORE buying a Vortech FMU as they are sold with 12:1 10:1 8:1 or 4:1 disc. U'll need to figure that out..ohh and not to mention the hi press fuel pump.

b16ahybrid

· #6 · Mar 5, 2002

I also have a few recalibration diaphrams that i would like to sell.

I have everything except for the 6:1 diaphram.

oneslwcivic

· #7 · Mar 5, 2002

The vortech one is nice.

robthegr8

· #8 · Mar 5, 2002

Get the vortech. Dont go any higher the 4:1. Its not needed.

UndaRated

· #9 · Mar 5, 2002

ABout compression and Turbo

if you have a completely stock b16 boosting 6 lbs with 10.2:1 compression, it's the same as boosting about 8lbs with a compression of lets say 8.5:1. Everyone thinks that low compression is better for turbo, even though it is, it's just a good safe-guard from poor tunning. High compression works with turbo well as long as you "tune" it right. Just one trip to the dyno and a knowledgeable tuner and you can run good with high compression with no problems whatsoever.

oneslwcivic

· #10 · Mar 5, 2002

Tuning is necessary with a high compression motor. They are easy to blow since they were not meant for a turbo from the factory. But if tuned right you will be taking out cars way out of your class.

b16ahybrid

· #11 · Mar 5, 2002

robthegr8 said:
Get the vortech. Dont go any higher the 4:1. Its not needed.

Thats kind of a vague statement.Sure 4:1 is all you need if your running 440's but with stock injectors your going to run lean.

CRXType-R

· #12 · Mar 5, 2002

b16ahybrid said:
Thats kind of a vague statement.Sure 4:1 is all you need if your running 440's but with stock injectors your going to run lean.

yeah if hes running stock injectors, he needs 12:1 !all depends

robthegr8

· #13 · Mar 5, 2002

If you plan on running any more then 7psi of boost, your easily going to be over 100+ fuel pressure with the 10:1 or hell the 12:1 Thats just to much in my mind. If your looking for that much HP, then you sure as hell better get soem injectors and lower the pressure.

CRXType-R

· #14 · Mar 5, 2002

robthegr8 said:
If you plan on running any more then 7psi of boost, your easily going to be over 100+ fuel pressure with the 10:1 or hell the 12:1 Thats just to much in my mind. If your looking for that much HP, then you sure as hell better get soem injectors and lower the pressure.

true true, but until I can get 440cc for my baby and a 8:1;4:1 disc, I will be running the 12:1 with my 255 walbro which kinda do the job for now..I only need to figure that injector problem. I was thinking about some turbo DSM injectors but the problem with those is that they are peak and hold and I don`t want to mess around the resistor box that much...Also that RC engineering arent cheap too. But hey! when you mess with a turbo be prepared..thats what Im telling myself. SO, if you guys have any suggestions like (*GET THE RC INJECTORS *) lemme kow..

b16ahybrid

· #15 · Mar 5, 2002

CRXType-R said:
true true, but until I can get 440cc for my baby and a 8:1;4:1 disc, I will be running the 12:1 with my 255 walbro which kinda do the job for now..I only need to figure that injector problem. I was thinking about some turbo DSM injectors but the problem with those is that they are peak and hold and I don`t want to mess around the resistor box that much...Also that RC engineering arent cheap too. But hey! when you mess with a turbo be prepared..thats what Im telling myself. SO, if you guys have any suggestions like (*GET THE RC INJECTORS *) lemme kow..

I you plan far enough ahead (what i should have done) get some 440's and a vafc.As soon as you install the injectors and vafc you will need to have it on a dyno because the stock ecu won't idle with injectors that large.If you go that route you could run a 4:1 (which might be to much) o reven a 1:1 and fine tune it with the v-afc.Get the RC's

.I have a set of 310's and a 6:1 fmu (which is still a bit much because my car runs pretty rich still) and i'm pretty happy with it,a lot more then with the stock injectors and 12:1.

CRXType-R

· #16 · Mar 5, 2002

Well, my system in kinda rich at idle but I`m runnin a hi pres fuel pump here, so thats why im good with it for the moment with 12:1...

robthegr8

· #17 · Mar 6, 2002

Whats your boost fuel pressure? Its gotta be over 100 with that, right? You really are pushing those injectors hard. You should seriously look into bigger injectors.

CRXType-R

· #18 · Mar 6, 2002

actually, fuel pressure is up sometimes at over 100psi...Yeah I know im watching my ass rest assured!!

Maybe next month a set of 320 and new vortech disc..money...its all about money!!

CRXType-R

· #19 · Mar 6, 2002

Whats your boost fuel pressure? Its gotta be over 100 with that, right? You really are pushing those injectors hard. You should seriously look into bigger injectors.

Here`s my theory :
http://www.turbogs.com/tech/star_turbo_install/star_turbo_install.htm

minor note, the B16 injectors are 240cc instead of the 235 mentionned. So far so good.

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