Exhaust Sizing

htibaja

New Member
So putting a 1uz into a 95 Toyota pickup for offroad racing application. Just getting to the exhaust fabrication portion. I have the ebay tundra headers that i am altering at the collector to run dual exhaust through two high flow obdII cats and into muffler dumped just behind the cab. So my main question is on the tubing sizing. I was thinking 2.5 but am worried about back pressure on the motor etc. If some one could give me some advise on tubing size it would be appreciated.
 

stevechumo

Active Member
Dual 2.5" pipes are pretty big. You don't want to go bigger than that, because you'll loose low end power if the pipes are too large. The stock pipe's inner diameter is only 1.75". To have low end power while still have high end power, anything between 2"-25" would be good. I'd do 2.25" to compromise for the power range.
 

htibaja

New Member
Thanks i am going with 2.5 straight back dumped was much cheaper for some reason to find tubing and v band connections for 2.5 tubing. Hoping since my application is for desert racing and usually at higher rpms 2.5 should work good
 

spf_lexus

New Member
2.5" dual is way too big for virtually any N/A application. A well made 2.25" can flow over 400hp on a UZ. a dual 2.5" can support 500+hp. Even with headers you'll be trading response, low and some mid hp/tq for a marginal gain up top. Since your installing this in an off road application, you might want to consider 2 sections of flex pipe to keep the system from cracking. If it comes down to price I found the dual 2.25" was cheaper. I ordered a PTB pre bent mandrel bend kit and bought some straight lengths and had an entire system built w/ x pipe for about $250. Another $225 to have the system put together. I got them off amazon.com You'll get much more low emd torque and plenty of top end gain w/ a 2.25" system. BTW, stock cats are very efficient.
 

jen3ss

New Member
Most people I have talked to reccomend using a single 3" system.
Does anyone have any thoughts/experience with this?
 
lol the "you need back pressure" myth that sells many a smaller, cheaper, easier and more profitable exhaust system!

after the headers you can have a 4 inch system it wont make any differences besides noise!

I have 2x 2.5 mandrel bent on my stock 09/96 soarer I got good numbers from it for a stock 1UZ conversely a mate ran 2x 2.5 on his turbo supra and put down 410rwkw...

 

htibaja

New Member
I already ordered all the parts for a 2.5 system so i think i am gonna go with it. If i feel like it reduces too much low end then ill downgrade it to a 2.25 do you guys feel that an x pipe system severly increases performance. It is hard to run them on a long travel system as the rear drive shaft swings substantially
 

gloverman

Well-Known Member
I have dynoed these N/a motors with single 2.25, single 2.5 and single 3inch and twin 2.5 with stock ECU and aftermarket ECU. The end power figures where similar with the 2.25 being slightly lower the others three where all in the ballpark of each other. The one which was the nicest to drive was the single 2.5 system. There where 2 double cab utes both with headers and aftermarket ECU. The 2.5 ute made more torque and bottom end response was far better than the ute with the 3inch system. Both had standard cams. The vehicle with the 2.25 system was amazing down low but then it was a stripped out race car. My own vehicle was a three inch single system and flows 300rwkw with 15psi up it. I prefer to ran 2.5 systems on most of my series one and two motors. Still working in the VVti motors to work out what gives the best result. Cheers
 

stevechumo

Active Member
lol the "you need back pressure" myth that sells many a smaller, cheaper, easier and more profitable exhaust system!

after the headers you can have a 4 inch system it wont make any differences besides noise!

I have 2x 2.5 mandrel bent on my stock 09/96 soarer I got good numbers from it for a stock 1UZ conversely a mate ran 2x 2.5 on his turbo supra and put down 410rwkw...

In my area, the smaller pipes are cheaper than the larger pipes. The dyno number looks good, but if you notice, its low end power suffers for a little before reaching its peak power at 5600 RPM. Proper pipe sizes are good for low end and high end as well. Bigger sizes are typically used for track racing, which doesn't need low end power.
 
In my area, the smaller pipes are cheaper than the larger pipes. The dyno number looks good, but if you notice, its low end power suffers for a little before reaching its peak power at 5600 RPM. Proper pipe sizes are good for low end and high end as well. Bigger sizes are typically used for track racing, which doesn't need low end power.
How did you come to the conclusion that its down on "low end power" ?
 

JBrady

Moderator
I have dynoed these N/a motors with single 2.25, single 2.5 and single 3inch and twin 2.5 with stock ECU and aftermarket ECU. The end power figures where similar with the 2.25 being slightly lower the others three where all in the ballpark of each other. The one which was the nicest to drive was the single 2.5 system. There where 2 double cab utes both with headers and aftermarket ECU. The 2.5 ute made more torque and bottom end response was far better than the ute with the 3inch system. Both had standard cams. The vehicle with the 2.25 system was amazing down low but then it was a stripped out race car. My own vehicle was a three inch single system and flows 300rwkw with 15psi up it. I prefer to ran 2.5 systems on most of my series one and two motors. Still working in the VVti motors to work out what gives the best result. Cheers
What pipe size are you running from the manifolds to the Y pipe?

For NA relatively stock engines (up to 350hp flywheel) I recommend 2.0" or (hard to find 2.125") tubes from each manifold/header outlet to a single 2.5" center tube with a GOOD (factory is very good) merge. The Tundra aftermarket headers have a 2.5" outlet which is TOO big and should be smaller. To run with 2.0" pipes requires a SMOOTH transition for best performance. The REAL magic is in the Y pipe.

Two 2.0" tubes with .065" wall thickness have a TOTAL cross section area 20% greater than the single 2.5" tube so the 2.0" pipes are not restricting flow (although poor transitions can and usually do).

Another component are the catalysts which in factory form bolt to the manifolds and actually work like one way check valves to assist low end response. Removing them can reduce low end response.

Of course the above is assuming mandrel bending of the pipes.
Crush bending reduces cross section flow area and adds areas of increasing and decreasing pressure and every change removes energy and creates restriction to flow. Now, if too large of tube is selected crush bending will actually HELP performance!!!

TURBO motors are a different animal because the turbo itself is a one way check valve.
Turbo exhaust should be much larger than NA because the low end is not compromised as much if too large and top end NEEDs the larger capacity.
Remember a turbo engine running 15psi is effectively TWICE as large (efficiency based statement)
 
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spf_lexus

New Member
the "you need back pressure" myth that sells many a smaller, cheaper, easier and more profitable exhaust system!
A dual 2.25" wont increase or "preserve" any back pressure over a 2.5". The area of concern is exhaust velocity and how quickly each pulse can exit the system. Jumping to a 2.5" dual will open up a lot more CFM but the downside is that each exhaust pulse will "slow down" as it expands within the larger pipe. Neil Griffiths from AU runs a dual 2.25" mandrel on his supercharged silvia which puts out double that of a stock UZ and still manages low 10sec passes.
 

8pack

New Member
the "you need back pressure" myth that sells many a smaller, cheaper, easier and more profitable exhaust system!
A dual 2.25" wont increase or "preserve" any back pressure over a 2.5". The area of concern is exhaust velocity and how quickly each pulse can exit the system. Jumping to a 2.5" dual will open up a lot more CFM but the downside is that each exhaust pulse will "slow down" as it expands within the larger pipe. Neil Griffiths from AU runs a dual 2.25" mandrel on his supercharged silvia which puts out double that of a stock UZ and still manages low 10sec passes.
Correct. The least back pressure possible, whilst still maintaining a high flow rate is the goal. 2.25 inch seems to be a good choice.
 

JBrady

Moderator
It is more than just SIZE. A single 2.00" pipe without restriction can easily support 200hp. So, dual 2.00" pipes can easily support 400hp.

It is when the pipes have transitions that things start getting fuzzy.
In the stock Y pipe the area the single center pipe is only 74% of the area of twin pipes that feed it.
On first glance this seems to be a problem... WHY would anyone want to "restrict" the flow like this???

The SIMPLE truth (this can actually get VERY complex) is that the single pipe has enough flow capacity for the power made. If you increase the power at some point the center pipe will be too small for the required flow.

BUT... remember the two pipes that feed it are LARGER. Therefore they have more flow potential and would support more flow. So, what happens if you install a center pipe that has the same flow capacity as the two pipes that feed it? Answer, you loose the efficiency of the Y pipe.

So, what is the Y pipe doing?

It accelerated the gas flow thereby REDUCING reversion flow back towards the exhaust ports. Reversion flow towards the exhaust ports RAISES the pressure in the ports making it harder for the engine to breath out.

Now, most of us power junkies look at those small pipes and BELIEVE that they are costing a bunch of power. The truth is the stock Y pipe is WELL engineered for a full range of power from low RPM to high. While it is possible to build a better pipe for high RPM power it will almost always be at a cost of lost low RPM power and response. It is MORE likely that changing the pipe will loose low RPM power and response and NOT give more top end power for a loss in overall power.

Some think well I will ONLY increase the stock pipes to 2.25". But 2.25" pipes are 33% larger than the stock 1.97" pipes and that causes a substantial reduction in velocity. Remember the stock 1.97" pipes flow more than the stock center 2.36" single pipe alrea.

A single 2.50" pipe is onlyl 62% of dual 2.25s. You want some change but only 62% is too restrictive. The stock 74% is a good target.

BEFORE increasing to dual 2.25" pipes I would instead upgrade the single center pipe from 2.36" stock to 2.50". A 2.50" is 83% of the stock dual 1.97" pipes. This will loose a slight amount of Y pipe action but increases total capacity by 13% and is INEXPENSIVE. If you upgrade to 2.25" pipes your center pipe needs to be 2.75" giving a 76% ratio... but make sure you need that much flow or you will be hurting the drivability and the fun. Why spend money to have less? Also 2.75" mufflers and resonators are very rare where 2.50" are very easy to find.
 
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gloverman

Well-Known Member
doing more at the moment. Went do a vehicle there isnt the budget to swap several different exhausts onto them and dyno each time so it takes a while. We seem to be going smaller on the early motors eg sometimes twin primary 2inch and single 2.5 single after the merge. VVti seem to be twin 2 1/4 into single 2.5 as well. We also have to cater to peoples perceptions so its not always what will work best but what looks good under the vehicle. Guys dont want their mates looking at their underbody and saying "man thats a small one" Cheers
 

fastegg

Member
Mr Brady

An interesting read about pipes on the '99 VVTi. I'm just about to change the system on my '98 VVTi. I think i'll toss the duel system and go a single 2.5" from where the pipe splits into 2 or would i go 2.5" from resinator back ? Have you any surgestions about what mufflers to use ? I'm looking for a nice almost quite 'purr', no drone, a bit of excitement when i floor it, looking for torque not HP as it almost never gets reved hard....
Did i read somewhere that the SC400 has a slightly larger resinator size ?
If so should i look for one and an SC400 Y pipe ? or just leave my stock Y pipe and resinator.... Any advice on mufflers in particular would be most appreciated. .. ...
 

JBrady

Moderator
An interesting read about pipes on the '99 VVTi. I'm just about to change the system on my '98 VVTi. I think i'll toss the duel system and go a single 2.5" from where the pipe splits into 2 or would i go 2.5" from resinator back ? Have you any surgestions about what mufflers to use ? I'm looking for a nice almost quite 'purr', no drone, a bit of excitement when i floor it, looking for torque not HP as it almost never gets reved hard....
Did i read somewhere that the SC400 has a slightly larger resinator size ?
If so should i look for one and an SC400 Y pipe ? or just leave my stock Y pipe and resinator.... Any advice on mufflers in particular would be most appreciated. .. ...
I am uncertain of your goals. It sounds like the stock system is OK and you maybe want more "sound"...

I would not recommend changing the stock duals to a single. The dual pipes allow much more muffling area.

Have you tried the muffler delete? Simply remove the rear two mufflers and drive the car. I will be louder but not loud. If you like this you can simply have straight 2" or 2.25" pipes installed instead of those two mufflers. This will slightly quiet the already minor sound change. Alternately keep the final two mufflers and replace the middle two mufflers with straight 2" pipe. A third option is replace the middle two mufflers with straight through round resonators in 2" with straight 2" pipes from there to the back bumper. If that is too loud for your tastes you can simply add straight through or turbo style mufflers back where the final two mufflers were.
 

Mat Grant

Member
Hi all,

I've got a 1uz I'm fitting to a Lotus eclat. I'm at the stage where I need to get an exhaust system made, I can't do exhaust fabrication myself so need to use an exhaust specialist to do it. So I need to tell them what I need. If anyone on here can help by suggesting design and sizes etc that would be great, otherwise I'l have to make my best guess and their advice.

The engine is stock with stock ECU 1uz from a 1992 soarer. Stock soarer manifolds, cut and rewelded at the bottom to clear the chassis in the car I'm fitting it to. approx same length manifolds.

One day I'd like to supercharge with a centrifugal supercharger and fish bracket etc but this is a long way off. So I would like it to work with a supercharged engine if poss.

I'm looking for as much power as possible without hurting the "drivability"

The car has space for two exhaust mufflers, the original car is a 4 cylinder, and has a 4 into two into one, a centre silencer, then back out to two pipes and two tail silencers.

The car is old and therefore not as strict on the sound levels to get through the MOT (UK version of inspection). Idon't want it stupidly loud, but it doesn't have to be realy quiet.

From reading/discussion etc I've heard that the X pipe design is a good one, so provisionaly in my head I've got- two pipes from manifolds Y into 1 pipe, tuned length of single pipe, back out to two pipes and two silencers.

However it could be two into 1 and just have one silencer(?)

If anyone can suggest a design type, sizes and lengths for x pipe or Y pipe bits or just general suggestions as to which way to go with this I'd greatly apreciate it. :)

Cheers, Mat.
 
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