4.2 inlets on a 4.5

[N4 FTW]

Hello all

As some of you know, my 4.2 has died and I have sourced a 4.5 to fit in its place.

I know it is popular to fit the 4.2 inlets to the 4.5, has anyone produced a guide for this?

Is it just a case of removing the airboxes, silicon hoses then unbolting the throttle bodies?

I assume you also swap the fuel rails, do you reuse the 4.5 injectors (I assume they are larger than the 4.2's)?

Cheers!

[Gazzab]

You need to machine the 4.2 inlets to the right width afaik. I cant remember the size off hand...

[julian64]

Not sure you can machine the 4.2's to any sensible degree.

You can certainly get rid of the lips, but I doubt you can do anything to the actual tubes.

The best would be to pass a flexible cylinder hone down one, but its likely you will do no more than thin the outside of the bend badly while actually making the curve less ...well...curvy.

There is no point in honing the inlet or exit of the 4.2s as the actual restriction is the curve you can't get to.

The best you have is to play about around the butterflies while being aware that you aren't actully touching the bit that matters.

The thing about the 4.2 inlets is either than they will flow enough or they won't. There very little effect I think you'll have on them.

I considered as the only option cutting them down each tube to thin them down and then reweld, but the amount of effort involved makes little sense when you have the 4.5 inlets that are easily machinable, plus put the power higher up the rev range where its most used.


The 4.2 are undoubtedly the better bit of kit but if you have an engine that actually requires a higher flow unfortunately I think you throw them in the bin and either get 4.5's or go bespoke.

Considering most 4.7's seem to be indicating that the 4.2 inlets are only just becoming a limiting factor, I think its a tough decision.

[N4 FTW]

Thanks chaps.

I actually meant just bolting the 4.2 inlets on instead of the silicon hoses and lower throttles that the 4.5 has.

Is this worth doing bearing in mind I have the 4.2 inlets sitting on the old engine?

[Gray_101]

You can just remove the 4.5 induction, and bolt the 4.2 induction in it's place.

The main thing to consider is putting the 4.5 injectors into the 4.2 manifolds, this is because the 4.2 injectors only flow for 400 bhp after that there not up to the job.

Don't be put off that the 4.5 injectors are shorter, it makes no odds.

I would also get a re map after the 4.5 has been fitted, better to be safe than sorry


I'm having a set of 4.2 manifolds boarded out to take 48mm butterfly's ( some extra bits welded on has been required ) and I'm having standard 4.5 injectors fitted in them

Edited by Gray_101 on Monday 15th August 18:36

Edited by Gray_101 on Tuesday 16th August 07:23

[N4 FTW]

Excellent, thanks for the information. I had a feeling that the 4.5 injectors flowed more, thanks for confirming.

[HarryW]

2nd it'll need a remap, I think you'd be extremely lucky if it doesn't.

[julian64]

Gray_101 said:

You can just remove the 4.5 induction, and bolt the 4.2 induction in it's place.

The main thing to consider is putting the 4.5 injectors into the 4.2 manifolds, this is because the 4.2 injectors only flow for 400 bhp after that there not up to the job.

Don't be put off that the 4.5 injectors are shorter, it makes no odds.

I would also get a re map after the 4.5 has been fitted, better to be safe than sorry


I'm having a set of 4.2 manifolds boarded out to take 48mm butterfly's ( some extra bits welded on has been required ) and I'm having standard 4.5 injectors fitted in them

Edited by Gray_101 on Monday 15th August 18:36

Edited by Gray_101 on Tuesday 16th August 07:23

Out of interest, why?

If you bore out the butterflies you will presumably lower the flow rate at the butterflies and increase the pressure/density at that point. You won't increase the overall flow rate because of the restriction at the bend. Hence the air over the butterflies will have to slow up.

If I am right all you'll do is decrease the flow rate at the point the injectors fire and slow the flow rate over the butterflies which will possibly make the throttle feel more sluggish to respond.

I'd be very interested in your experiences and how the expected benefits of this were explained.

[Gray_101]

It's all a bit experimental at the moment Julian, and you make a good point about the flow rate but the manifolds and not going on a 4.2, there going to be fitted to a 4.8

I hope the extra cc will compensate for the flow rate loss ( but I'm no expert in engineering and I'm the first to admit it ) but if it doesn't work I ll use 4.5 induction instead.

I really prefer the look of the 4.2 induction over the 4.5 rubber hoses and that's the main reason I've gone down this road, I just hope it works ?

Your thoughts on this would be greatfully recived Julian

[julian64]

Gray_101 said:

It's all a bit experimental at the moment Julian, and you make a good point about the flow rate but the manifolds and not going on a 4.2, there going to be fitted to a 4.8

I hope the extra cc will compensate for the flow rate loss ( but I'm no expert in engineering and I'm the first to admit it ) but if it doesn't work I ll use 4.5 induction instead.

I really prefer the look of the 4.2 induction over the 4.5 rubber hoses and that's the main reason I've gone down this road, I just hope it works ?

Your thoughts on this would be greatfully recived Julian

I totally agree with you about the look of the 4.2. I bought a set for my 4.7 (Still in pieces), as I really really wanted to use them.

Andy at APM (who is pretty much a fountain of all knowledge here abouts gives the impression the 4.2's flow enough not to be a restriction.

I am certainly no expert, just inquisitive. I would be really interested (for obvious reasons of my own build) how you get on, and what engine management /injectors you are planning on.

[Gray_101]

The engine is in it's final stages of assembly after having 2 dry builds and is yet to run. Ive not built the engine I've left that to the experts.

It will start off on standard 4.5 injectors and MBE ecu with a safe map. As its going in a road car and not a race car

I will start it's own thread once I've got the engine as I am going to fit it myself

Edited by Gray_101 on Tuesday 16th August 14:43

[Rufus Roughcut]

Gray_101 said:

................. once I've got the engine as I am going to fit it myself

Edited by Gray_101 on Tuesday 16th August 14:43

Gray, If you need a hand ? I've got a long reach engine hoist/adjustable ramps/sturdy trailer with tie downs for fetching and carrying etc, I'd be more than willing to help/learn.

[APMAUTO]

Gray_101 said:

The engine is in it's final stages of assembly after having 2 dry builds and is yet to run. Ive not built the engine I've left that to the experts.

It will start off on standard 4.5 injectors and MBE ecu with a safe map. As its going in a road car and not a race car

I will start it's own thread once I've got the engine as I am going to fit it myself

you should fit bigger injectors for over 4.5

Edited by Gray_101 on Tuesday 16th August 14:43

[Gray_101]

Thanks Rufus, I will be in touch closer to the time, I'm planning on pulling the engine, bell housing, gear box and exhaust manifolds out all in one go. So an extra pair of hands will be very welcome

Andy, why would you go for bigger injectors ? as the 4.5 ones will flow for 500 bhp

[Gazzab]

Andy has built many 4.7s and so has practical experience of fuelling.