Topic: 91 Toyota 22re Valve Question

[Gnarly4X]

Would I be better off putting a stock exhaust manifold back on the truck for low end grunt?

Hey Grimmjow...

Swapping back to the factory exhaust manifold will most likely increase low end torque from 1000 to 2600 RPMs.  Will you notice a difference?... probably – if your engine in well tuned.

The Hedman header is a 4 in 1, and that design is known to help with the higher RPM range.  The Doug Thorley Tri-Y is known for keeping lower RPM torque.  I think 2.25” exhaust with a header for stock 22RE may be a tad too large… I’m sure there are those who will argue that.

Since you don’t like your glass pack, you might try installing a new cat and stock style muffler before swapping back to the factory exhaust manifold.  If it is easier to swap in the factory manifold, try that.

The other thing you could do to get “a little” more low end torque is simply make sure your valve adjustment is to factory spec .008/.012”.  If you tighten the valve lash, it will usually increase high RPM HP, but lowers the lower RPM torque numbers.

[Gnarly4X]

Incidentally, it is useful to avoid confusing backpressure with scavenging. Scavenging is good and backpressure is bad, but the two are often confused.

https://vpexhaust.com/exhaust-back-pressure-a-myth/
https://youtu.be/jjPeP_Nn2B4

This is fact, not opinion. It may be incredibly useful

Getting into the deep weeds on engine exhaust science is probably beyond you and me.

You can call it whatever you want, but in my experience on my stock 22RE an opened exhaust that reduced the backpressure too much in the exhaust system definitely decreased the low-end torque.  During my face-to-face conversation with a Doug Thorley engineer for about 1 hour, he used the word "backpressure" at least a dozen times and he was specifically referring to the DT Tri-Y design.  He also referred to scavenging, pulse waves, velocity, and exhaust gas temperature and density.

So perhaps it is just conceptual semantics, and a common word used when discussing exhaust systems, albeit by the lesser educated?.

The "pressure" part of backpressure logically refers to and perhaps describes affect of the exhaust gas density.  More dense (cooler), the slower it moves... less flow... less power.

Gnarls.... of course I could be full of backpressure!

[Snowtoy]

Incidentally, it is useful to avoid confusing backpressure with scavenging. Scavenging is good and backpressure is bad, but the two are often confused.

Yes, I know, but using the term backpressure is the simplest way of communicating the idea, as that is what everyone hears you benefit from by reducing it by going with a better flowing larger exhaust.  The industry really needs to stop talking about reducing exhaust backpressure, and use increasing the velocity of exhaust gas flow.  The best system would be an active exhaust system that automatically increases decreases exhaust velocity due the the throttle input, something like a butterfly valve linked to the throttle position sensor.

[Snowtoy]

You can call it whatever you want, but in my experience on my stock 22RE an opened exhaust that reduced the backpressure too much in the exhaust system definitely decreased the low-end torque.  During my face-to-face conversation with a Doug Thorley engineer for about 1 hour, he used the word "backpressure" at least a dozen times and he was specifically referring to the DT Tri-Y design.  He also referred to scavenging, pulse waves, velocity, and exhaust gas temperature and density.

Same issue when I went with headers and a high flow cat and muffler(at the right angle you could see through it) on my 3.0.  It was great for aggressive driving and pushing top speed in each gear significantly at the same shift points , but sucked for normal around town driving, cruising down the highway, and on the trail.  After speaking with a custom exhaust shop, the guy told me that I opened it up too much for normal driving, and said that I could try what the do on race cars, and that was reduce down the exhaust tip, or run a different muffler.  I didn't care for the drone of the muffler, so I swapped it out.

[Grimmjow [OP]]

I have decided to buy a new header that comes with the 2" down pipe. The header now doesnt fit well, it actually runs against the torsion bar mount pedestal. It also has some small leaks in it I found the other day. The small air ports on the bottom are cracked. I think I will just go back with a 2" turbo muffler and call it  day. These engines wouldn't need a huge exhaust pipe as they do not produce much power I would think.

[Gnarly4X]

I have decided to buy a new header that comes with the 2" down pipe.

What manufacturer?  Who makes a 2" collector?

Gnarls.