Q about turboing 4.0 OHV

[the1991mazdaguy]

1991 Mazda Navajo 4.0 4WD. i have a 7 PSI IHI RHB5 turbocharger that i would like to retrofit onto my Navajo. i was wondering if this engine could handle this tiny turbo with no problems, or if i would need to modify internals/gaskets/fuel system parts.

 

[FIND]

1991 Mazda Navajo 4.0 4WD. i have a 7 PSI IHI RHB5 turbocharger that i would like to retrofit onto my Navajo. i was wondering if this engine could handle this tiny turbo with no problems, or if i would need to modify internals/gaskets/fuel system parts.

a 7psi IHI RHB5 turbo?

I think you have a lot of reading to do before you consider putting a turbo on a vehicle.

RHB5 is the frame size (a really small one at that), not the type of turbo you have. You need to know what size compressor and impeller you have, and the trim and yadda yadda. What is it off of?

Actually, scratch that.

Quick lesson in forced induction, it isn't the PSI that is important, it is the CFM. An RHB5 is a small frame, they use it for small turbos like VJ11s, VJ20s, and a bunch of other small VJ, VF, and VI turbos, and they are usually used on engines under 1.8 liters of displacement, or in a twin setup for engines up to around 3 liters. You need something much larger to push enough air for a big V6 like a 4.0, even considering how low of RPMs these things run.

7 psi? I don't know where you got that number from, unless the wastegate is set up at 7psi, which is probably true, since that is what they are usually set around for OEM or light boost applications.

To answer your question though.... Assuming you had a bigger turbo that would flow enough to keep a 4.0 from choking out of air, to put 7psi to the engine, you would need a bit more fuel, so new injectors, and a higher pressure FPR. Internals, I can't tell you, but an OHV 4.0 is pretty stout, so I would be surprised if it were a problem. BUT. No one in their right mind would put forced induction to an engine with these pathetically flowing heads.... Well, maybe someone would, but, your turbo would be doing a lot of work and not getting much out of it. Your EGTs would be pretty high. I guess if you had a pair of VJ20s and some decent flowing heads, you could be somewhat OK, but it would be no powerhouse and might choke a bit at high RPMs.

 

[the1991mazdaguy]

a 7psi IHI RHB5 turbo?

I think you have a lot of reading to do before you consider putting a turbo on a vehicle.

RHB5 is the frame size (a really small one at that), not the type of turbo you have. You need to know what size compressor and impeller you have, and the trim and yadda yadda. What is it off of?

Actually, scratch that.

Quick lesson in forced induction, it isn't the PSI that is important, it is the CFM. An RHB5 is a small frame, they use it for small turbos like VJ11s, VJ20s, and a bunch of other small VJ, VF, and VI turbos, and they are usually used on engines under 1.8 liters of displacement, or in a twin setup for engines up to around 3 liters. You need something much larger to push enough air for a big V6 like a 4.0, even considering how low of RPMs these things run.

7 psi? I don't know where you got that number from, unless the wastegate is set up at 7psi, which is probably true, since that is what they are usually set around for OEM or light boost applications.

To answer your question though.... Assuming you had a bigger turbo that would flow enough to keep a 4.0 from choking out of air, to put 7psi to the engine, you would need a bit more fuel, so new injectors, and a higher pressure FPR. Internals, I can't tell you, but an OHV 4.0 is pretty stout, so I would be surprised if it were a problem. BUT. No one in their right mind would put forced induction to an engine with these pathetically flowing heads.... Well, maybe someone would, but, your turbo would be doing a lot of work and not getting much out of it. Your EGTs would be pretty high. I guess if you had a pair of VJ20s and some decent flowing heads, you could be somewhat OK, but it would be no powerhouse and might choke a bit at high RPMs.

holy **** dude! that awesome of you. the turbo is from a EA82 from a Subaru GL-10. Thats funny, the Subaru i had has head problems with forced induction xD I have heard the internals are very strong on the 4 liter, but you informing me about the heads is a trouble saver; i haven't really heard anything about the heads till now. also, I'm not worried about high RPM's, not really worried about anything over 4k, so i guess maybe i should i do torque build, which would be successful without a turbo. Well, thanks for info; i guess thats the end for my idea.

you must keep tabs on me or something. you always manage to fly in and be the first one to successfully answer my questions.

 

[tweakedlogic]

No one in their right mind would put forced induction to an engine with these pathetically flowing heads.... Well, maybe someone would, but, your turbo would be doing a lot of work and not getting much out of it. Your EGTs would be pretty high. I guess if you had a pair of VJ20s and some decent flowing heads, you could be somewhat OK, but it would be no powerhouse and might choke a bit at high RPMs.

Actually, the forced induction in a poor flowing system is an easy fix that even the OEMs use. It's an easy/cheap way to compensate for the losses in poor design.
take my Rx7 for instance. The TII has a horrible flowing intake manifold. the n/a has a better flowing mani, but you can't put it on the TII cause the turbo is in the way. Even the 3rd gen 7s have poor flowing ports. the intake is better, the ports suck. Only the cosmo motor has both good flowing ports and intake runners. And those were never brought to the states, and they only made a few hundred thousand Cosmos. very rare motors.

For decades people have taken poorly designed heads and intakes and tossed on a forced induction system to over come the losses. It works. As long as you don't over boost and set up the supporting mods right, you can see some decent gains. Usually the gains are better than high end all out build of an n/a.

I'm not saying this is the best approach, but it is an option for those that can't/won't tear into a motor.

 

[FIND]

yeah, I know, but I hat the idea of someone going through the work to weld up a manifold and downpipe, throw all that piping in, then tune, only to be blowing air into a head with 90 degree turns and big humps inside the intake ports. If a person was gonna go FI, they might as well get their heads ported and change cams. Would be a lot easier on a person when they want to tune it.

you must keep tabs on me or something. you always manage to fly in and be the first one to successfully answer my questions.

IDK, I guess you just ask a lot of questions I can answer. Plus, I get bored during the day. Just a coincidence honestly.

 

[tweakedlogic]

yeah, I know, but I hat the idea of someone going through the work to weld up a manifold and downpipe, throw all that piping in, then tune, only to be blowing air into a head with 90 degree turns and big humps inside the intake ports. If a person was gonna go FI, they might as well get their heads ported and change cams. Would be a lot easier on a person when they want to tune it..

I completely agree. I was only stating there are gains to be had with FI. I hear it's easier to tune at low boost (3-5 psi). One might not even need bigger squirts at that level. but I don't think it can be done with the stock computer. It would have to be a mega-squirt or other.

A super charger on the other hand can use the stock computer. It will cost as much or even more than going turbo, and you have the power in the bottom end. You will also have smaller gains with a SC. Good luck finding one. You will pretty much have to fab all the fit parts.

I've always wanted to try one (or 2) of those electric super chargers. Have you seen them. Just high speed ducted fans, but they have enough force to lift it's self. Never could justify the $400 each. I guess no one could and that's why they are no more.