Freeflow pipe diameter on a 4.5

Engines and Engine Systems
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Freeflow pipe diameter on a 4.5

Post by Zantus » 24 Nov 2012 05:33

My Patrol has 270K on the clock and it still has the factory exhaust and catalytic converter.

It' time to do a freeflow system and let her breath properly, but the question is, what diameter pipe should it be and why?

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Re: Freeflow pipe diameter on a 4.5

Post by Tinus lotz » 24 Nov 2012 07:14

I do belief that cats on patrols came out. Only on some s.x models but I might be wrong if you have a cat and you remove it you have to make a plan to con the lamda censor to keep every thing happy I will keep manifold and put 50 or 63 to the back
It works well with 2 big boxes
Keep in mind the under bonnet temps when u remove mainifolds

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Re: Freeflow pipe diameter on a 4.5

Post by Peter Connan » 24 Nov 2012 08:21

Zantus, do you truly have a Cat on your Patrol? I have looked at several much newer cars (up to 2003/2004 4.8's) that did not have cats?

Anyway, to answer your question, I believe that the experts say that the pipe needs to be smaller for the first section, then open taward the back. There is an old post here somewhere with a more complete explanation, but as a shortcut send Frans Fourie (Tour de Frans) a PM.
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Re: Freeflow pipe diameter on a 4.5

Post by marakasmalan » 24 Nov 2012 10:23


Yes, Peter, the pipe needs to be smaller closer to the manifold as a certain level of "backpressure" is required for the engine. Towards the rear it can open up to provide less resistance to flow. I personally do not like to tamper too much with the factory set-up, as they take a lot of factors into account when doing these specifications, and when you alter this you alter the pressures and flow rates in the combustion process. Hence it is possible to create more power, by enabling it to combust more fuel and placing the whole process outside the design specifications - which can be detrimental to the engine in the long run.

As for the cat, if there is a cat, you need to replace the lambda sensor with a resistor. messure the amperes and meassure the voltage as well as the voltage drop over the sensor on this circuit when the engine is hot and running smoothly. Get the clever guys to calculate the resistor value. Ideal would be to set it up so that these values can be monitored in the vehicle so you can monitor the effect under different conditions. It is trail and error to a certain degree so try to obtain information from somebidy who did this already.

Back in 2006 we hacked the ECU code for a OM 501 LA-541 engine and we were quite surprised to see where the lamba value was parsed to. Though we did not bother too much about this, it affected or was fed to the inlet/turbo pressures, the fuel management (mixture adjustment, and injection pressure managment) routine and the retarder routines also aquired this value. What exactly it did we did not know, but it was not a value that was simply monitored, these units actually used it as input, with lots of other values, to create output.

This was in Europe and a Euro-5 complaint engine, so emissions were critical.


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Re: Freeflow pipe diameter on a 4.5

Post by Kagiso II » 24 Nov 2012 17:21

Hond se maaaaamie -- julle kan hirri nuwe frgggn tegnologie maar HOU -- Lam daar, lam hier, e-gee-tee, en dan alles on sensuur ook nog, alewag gesensor met noggge sensor om elke hoek en draai, en boonop hoor ik nou van katte wat nesmaak inni exhozzt .. se mur - Gee my 'n ou-skool V8 .. klaar gelag.
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Re: Freeflow pipe diameter on a 4.5

Post by SJC » 18 Apr 2016 07:49

What would be the ideal freeflow setup for a 4.5? wrt,pipe diameter, number of boxes?

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Re: Freeflow pipe diameter on a 4.5

Post by Michael » 18 Apr 2016 14:25

I dont belive in the back preasure thing and belive that there is only one engine that requires back preasure......and thats a 2 stroke engine.

Any other engine performs better the fater you cab get the old air out and the fresh air in. More back preasure means less wxhaust gas will actually get out of the combustion chamber which in return will give you less oxygen when air needs to enter the engine.

Motor manufacturers focus allot on emmissions so they will gladly secrifice performance to get better emmission readings.

One thing is sure, when you install a freeflow exhaust the engine will run more on the lean side, so its best to dyno it asap as a Patrol engine running lean can lead to burnt valves. :mytwocents:
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Re: Freeflow pipe diameter on a 4.5

Post by jonathan » 18 Apr 2016 15:13

Fanus hieronder is raad wat ek by Frans gekry het 'n paar jaar terug vir my 4.5. Ek het die kompleel stelsel opsie gedoen en ek was baie happy! Selfs my swaer wat 'n cruiser man is het opgemerk hoe baie torque op lae revs die patrol gehad het :lol:

" 'n Kompleet stelsel. Gaan vir 63mm. met 2 silencers. Maak die front pipe 50mm tot by eerste box, die box maak jy 63mm. Voltooi die sisteem met 63mm.
n Halwe freeflow. Gooi die agterbox uit en sit n 400mm lank 63mm box in, voltooi die res met 63mm.
Indien jou kar 63mm op het, werk net die boxse. Dit alles natuurlik as die pypwerk nog in n goeie toestand is.
Die 50mm pyp voor die eerste box gee meer torque op lae rpm, en boet geen krag in op hoe rpm nie.
As jy hou van n crisp klank, maak al die boxe "centre to centre" MAW jy moet regdeur die box kan kyk."

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Re: Freeflow pipe diameter on a 4.5

Post by David M » 18 Apr 2016 15:27

Remember that on the 4.5 if you go the branch manifold route with the freeflow you must ceramic coat the branch or your under bonnet temperatures go through the roof.

A couple of the guys here including myself have been very happy with Abel from Viper's branch and freeflow.
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Re: Freeflow pipe diameter on a 4.5

Post by BulDog » 22 Apr 2016 11:56

How's it guys
I read this post quick and I'd just like to add my 2cents. I might be wrong but I seriously remember reading some where once that on a petrol car the exhaust is the other way round. With that I mean that the exhaust starts out wider/bigger and then slightly narrows towards the end. The reasoning behind this was that as the exhaust gasses leave the manifold they are hot and heat has a high expansion value ie more volume. Then as it goes down the pipe it cools slightly and contracts taking up a lesser volume/space in the pipe.
What this means is that it causes a type of vacuum and by so doing helps suck the gas out the pipe and engine faster.
Ill try look it up where I saw it.

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