Turbo question.

[Ziegelsteinfaust]

How does a engines instant torque response effect turbo spool up? Reason is I bought a 4.6 sohc for my project truck, and they are not known for strong na power. Although they hold up very well for turbo power, and I have been wanting something to turbo.

I got the 4.6 since they are stupid cheap, plenty of swap parts cheaper, decent dress up items, they litter pick a part, available aluminum block if you look, and I paid $600 for a 80K mile running car that was mildly wrecked.

So if my goal is 450+ HP to make the truck interesting to drive, and before I start to tank regular mpg when I go for drives. This is going to be my personal driver when done. I have a company van so please do not mention getting a car I do not want.

Technically from what I understand I can get there with my non PI motor, but I would be at roughly 14 psi.

If I use a PI headed engine it takes less psi, but since the heads a quite a bit bigger. How does or does it effect initial spool up?

This truck may end up being my only truck so I will need to tow a bit with it plus torque makes a vehicle fun on the streets.

[BR3W CITY]

When I think of a "larger" head I think of the chamber. Having a larger chamber on an unchanged bottom end will lower the compression ratio, but holds a larger volume of air.

If it lowers the compression lets say .5, you make less power on motor, but leave more room before detonation on boost. I think those NPI motors are like 9.2:1 and the PI heads have a 8ish cc smaller combustion chamber, which would increase your compression. It would make more power, but would be at greater risk for detonation.

Again, I don't know ford-specific stuff other than what I've seen and seen written. There are way more combos of 2v and 4v heads etc so the math I did might not even be close to what your actually working with.

[Ziegelsteinfaust]

Originally Posted by BR3W CITY

When I think of a "larger" head I think of the chamber. Having a larger chamber on an unchanged bottom end will lower the compression ratio, but holds a larger volume of air.

If it lowers the compression lets say .5, you make less power on motor, but leave more room before detonation on boost. I think those NPI motors are like 9.2:1 and the PI heads have a 8ish cc smaller combustion chamber, which would increase your compression. It would make more power, but would be at greater risk for detonation.

Again, I don't know ford-specific stuff other than what I've seen and seen written. There are way more combos of 2v and 4v heads etc so the math I did might not even be close to what your actually working with.

I was referring to the port of the head.

So when I get the time to turbo the engine I will likely build a engine to perform its best at my power level desired rather then take a chance. Mod motors rods a bit weak especially the ones my motor has, and fixing it requires a rebuild.

My thought is 9-1 compression, tweaked PI heads, but mostly a stronger bottom end.

[BigDan3131]

The turbo forums will have all the answers your looking for, they have engine make sections.

[BR3W CITY]

But I guess thats what I'm trying to figure out. With a 4.6 and PI heads (with the #'s I have), your compression would be high 9's, 10's if you milled the head. If you wanted to go any lower (stock 9.2 or below) You'd need to have a dished piston, or run a really thick head gasket to get enough chamber size to lower your compression for boost.

With those internals, and too much compression, you'll have to have a REALLY solid tune (and/or methanol) to avoid knock...which is what destroys those.

Again, not a mustang guy, just going off the #'s

[Ziegelsteinfaust]

LS guys run more boost and timing. So if the build up to full boost is steady, and with quality gas. It will be a pretty solid combo.

Just need to do a ton of research on street combos.

[BR3W CITY]

Originally Posted by Ziegelsteinfaust

LS guys run more boost and timing. So if the build up to full boost is steady, and with quality gas. It will be a pretty solid combo.

Just need to do a ton of research on street combos.

wait your still talking about your ford setup right? Cuz ya, if we're talking an LS turbo build then its a different story.

[Ziegelsteinfaust]

Yes it for my Ford as the engine is going into a F100.

The engines are not that different in many key ways that are important to my build. So LS engines can get away with it. I will get similar results provided I take my time with tuning, and run it a bit fat under boost.

The engines share similar bore stroke ratios, and head chamber design. The head chamber is the mechanical reason the engines are capable of boost, and higher compression. I am not sure if the bore stroke ratio affects compression tolerance. The big reason LS engines run so hard compared to the 4.6 sohc is port volume, and the 4.6 can't compete in the aftermarket front. The 4.6 is more rpm tolerant due the ohc design.

The 4V heads are to much for my blood, and won't give me the HP/TQ a simple turbo build will. Plus I can turbo at my convenience, and enjoy the truck before hand. Where the 4V is all up front, and with the money I could swing all I could likely build would be a Navigator 5.4 4V. Which by the time I rebuild it, and get one in my truck would be a few grand more then a built turbo'd 4.6 pushing 100+ more HP/TQ. Yes if turbo'd will smash a sohc, but cost several thousand more.