What will happen if you turbo a 10:1 motor?
 

Hi i have a jeep with a built 4.0. It has forged pistions and eagle rods and a comp cam. The compression ratio is 10:1. I'm only thinking of doing 6 to 8 psi. The jeep red lines at 5200 so not a lot of rpms. I was thinking of getting a fat head gasket to get the compression ratio down to like 8 or 9. Or Can I just leave it at 10:1 What do you guys think? Thanks for the input.

if you keep that boost down around the 6/7psi youll be fine.

Thanks for the info mstngsrule68. I called Aem and they side that it can't be done. That was a let down I have my kit done and was going to start the Turbo Manifold this weak.
What do you all think the target afr is on a 10:1 motor. Is it 14.5? I'm going with a 12:1 fmu with a mbc to get my afr right also have the Msd Btm for timing and a walbro 255. Will this work?
Thanks for the help.

Can be done easy with a GOOD tune, definatly would not run an FMU in your case.

it can be done. my stock 2.2 gm ecotec engine is 10:1 compression running 10 psi boost.
stay away from the thicker head gasket and the shitty fmu.
have it tuned and run 93 octane and you should be fine. if your setup doesnt include an intercooler then dont boost it past 6 psi.

Ive been trying to figure out what all these manufacturers are calling a fmu. Its basically a fuel booster pump with a pressure regulator spliced in and routed back behind the fuel booster pump, is it not???

Yes I do have a intercooler in my setup. So the the fmu with a mbc to get the afr right won't work? I'm not trying to race it. just need some more get up. 35" tires take it out of a 4.0 jeep. Thanks for the in put.

an fmu is not a tune. its a mechanical fuel enrichment unit that exponentially adds fuel pressure to your fuel rail. dont use it, dont waste your money and time. it will cost you in the long run. you will need a custom flashed tune. this will give you the most reliability and power.
a manual boost controller only controls the amount of boost. it has nothing to do with a tune.
if tuning is not at option on your vehicle then you may have to go with an extra injector controller which will add fuel to your intake system based on tps and boost pressure. this is the way i went as my car doesnt have many tuning support.

an fmu (fuel management unit) is a generic term for rising rate fuel pressure regulator. they were popular in the 90's when there wasnt any other way to enrich a n/a vehicle converted to turbo. it mounts after your stock fuel pressure regulator or on some higher priced fmu's, it replaces your stock fuel pressure regulator. all it does is mechanically restricts fuel going back to the fuel tank depending on how much boost it receives. fmu's create dangerous high fuel pressure, damage to injectors, cylinder wash out, and poor economy and power. they cannot adjust afr's dependent on engine load and rpm because they are mechanical and therefore they are not considered a tune.

I have a 98 jeep tj 4.0. Dont know if you have the same mpfi system. If so you have probably already done some timing/ mapping adjusting for the mods. If not im supprised your check engine light isnt burnt out. You mention the msd boost timing controll, what about the mapping, split second psc1-001? anything? Larger injectors and higher fuel pressure is the only way to get more fuel without burning out your stock injectors and you must bypass the stock map sensor cause it does NOT read boost. This is where a split second map adjuster would be used, or similar. Also where is your fuel pressure regulator, by the intake or above the fuel tank or on top of the fuel sending unit on the gas tank?

The way that I was told that you can tune the fmu is with a mbc. You just put it on the boost line to the fmu. Then watch the afr. Have any of you heard of doing it this way? I know it's not the right way but will it work? Thanks for the input.

Yes I have a fuel cut defender for the map. And I'm running a return line to the tank with a 94 fuel rail. It has the return line.

I think the only reason you want to run a fmu is so you dont burnout your stock fuel pump or starve the injectors. I agree with busa4 its a shotty way to get more fuel to the motor, your just basically forcing more fuel in the rail at higher pressures under boost. It will work but read what busa4 said. A better way is to use a map control module like the split sec psc-001 or something programmable that reads boost and larger injectors. It will do the same but safely. Your already using a walbro255 so fuel delivery shouldnt be an issue.

the split sec psc-001 dose that tap in to the map or ecu? Dose any one know what injectors I can get form the junk yard? The jeep comes with 19p injectors form jeep. Thanks for all of you helping me.

the mbc will only change the ratio of fuel pressure to boost. how it works is the mbc will vent a specific amount of boost to the fmu changing its ratio.

example: if the mbc is opened up most of the way then the fmu will have little rising rate such as 2:1(every psi boost fuel pressure will raise 2 psi)

if the mbc is closed most of the way then the fmu will have a larger rising rate such as 10:1 (every psi boost fuel pressure will raise 10 psi).

the rising ratio cannot be adjusted to different ratios at different rpms or boost so it will cause lean spots and rich spots in different rpm ranges so an fmu is not recommended.

please get the fmu idea out of your head. im trying to save you the trouble and your engine.

they have two types.
the psc-001 taps into the map signal

the psc-003 tamps into the maf signal

these units modifiy sensor signals sent to the ecm. i personally dont like these types of controllers as they are limited in adjustment.

these two extra injector controllers i would recommend. they allow you to use your stock fuel system and stock ecm tune
http://www.autopartsdealer.com/sard_..._content=rank1


Underdog Racing Development

I like the face. If I go with that I do not have to do any mods to the stock fuel set up? Just add the injectors and use the face to get the afr right. Can I use any injectors? How do you get fuel to them?
What about timing? Can I use the Msd Btm?
Thanks for the help.

the one with the adjustments on the face is for use with low impedence injectors. the controller mounts in your cab and you adjust the parameters from there.

the one for sale by underdog uses high impedence injectors. this one requires a laptop to program with the supplied software. it uses a 3d map based on tps, rpm and boost pressure. it can control up to 6 high impedence injectors. this is the one i am using.


these are just the controllers so you will need to purchase injectors, fuel rail and line to finish. these do not control timing. there should be no timing adjustment needed for 10psi boost or less. these are great because you use your stock fuel system, injectors, and stock tune so there are no issues with driveability and emissions.

injector size selection is based on how much hp over stock you are looking for. you should have a shrader valve on your stock fuel rail you can tap off of.

Were do I get the injector rail at or do I make one? What is high and low impedence injectors?

busa4 thank you for your in put. Do you have part numbers form your face kit?

injector rail can be purchased by the foot anywhere. search google and you find many options.

high impedence injectors are what stock engines use. there available anywhere and are cheap.

low impedence injectors are more responsive but there are more expensive and require a resistor box to use them to replace stock high impedence injectors.

part numbers? i used the underdog controller(the one without the control buttons on the face of the unit)

I went to the link you gave me and this is the part number I got xa58201. Is that the one you have? If so I can just go to the junk yard and get 2 jeep injectors and that's it or do I need a 3 bar map to? I just want to get it right this time. I wasted money and time with the fmu and mad Btm and fcd. That I have new at the house. Thank you for your time.

that part number is for the first link. i dont have that one. click the second link that says underdog racing development. thats the controller i have.

the map sensors are built into the units. you will run a boost line to them when you install them.

Ok I'll give them a call and see what up. Thank you.