RV8 4.6 - 4CUIX vs Thor

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garrycol
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RV8 4.6 - 4CUIX vs Thor

Post by garrycol »

My RV8 4.6 is basically built - only changes are a towing cam, 4.0 pistons to raise comp ratio a bit and the inlet/exhaust ports have been cleaned up - so not a race engine. The injection/ignition system will be controlled my MS3.

I will run the engine in using the old 3.5 carbs I have then turn to the issue of putting the injection on.

I have a complete Thor manifold and injectors and also a complete 4CUIX manifold and injectors from a 3.9 RV8.

The Thor as original equipment will run the engine but is a bit quirky with things like its thermostat etc. The 4CUIX is simpler but of course is set up for a 3.9 not a 4.6.

If I did go the 4CUIX route will the air flow meter size, air inlet size, trumpet size and injectors be OK to allow a 4.6 to reach its full potential. If not, are simple mods needed such as different injectors or will simply programming the MS3 to deliver more fuel to meet the larger engine requirements.

Thanks

Garry



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Ian Anderson
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Post by Ian Anderson »

Ok for a comparison
I have a seriously tuned JE engine 3.9 that will poll to 6800 with ease

It is running a Hotwire 4CUX

I believe after about 5000 the injectors are at 100% open
So higher than that and it will lean out, but at the same time the air flow meter starts restricting flow so overall not too bad

Oh no cats and a straight through exhaust too!

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Post by DaveEFI »

You'd not normally use an AFM with MegaSquirt. It calculates fuelling from the TPS position, RPM and engine vacuum.

There are calculators to give you the injector flow rates needed for a given output.

This site it pretty useful:-

http://users.erols.com/srweiss/tableifc.htm

It is worth making sure the injectors are correct. Too 'small' and obviously you'll not get maximum power. Too large and you can have idle problems.

The Thor manifold will give the best bottom/mid range. The older hotwire manifold, a better top end.
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garrycol
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Post by garrycol »

I now have my 4.6 in the vehicle currently with carbs.

As I have two sets of Thor manifolds I was intending to use them when I go MS3 but now that I have the engine in it is clear the Thor Plenum is too wide at the air intake so I need to look at different options.

If the 4.6 Gems manifold and plenum is the same width as a 4CUIX Plenum then I know it will fit. The issue is sourcing a Gems manifold and plenum.

The Thor Plenum comes in two basic pieces - the banana plenum itself which is not all that wide and the air intake at the front that hangs out over the left hand side of the engine causing an obstruction. In theory I could unbolt this section and cut the top air inlet and throttle body off it and turn it back 90 degrees so it now intakes air over the center of the plenum but that seems like a lot of work and maybe just as cheap as

Image

Image

So anyone who is familiar with the Thor plenum know of an alternative air intake section that bolts up to the standard plenum so that the actual air intake/throttle body is in a different spot.

Also the fuel rail on the Thor does not have a fuel return - does the Gems fuel rail require a fuel return to the tank and what pressure does the fuel rail run at. I have a a fuel regulator and new CUIX fuel pump (that I bought from V8 Maegasquirt) that I was going to use on the Thor fuel rail and am hoping I can use it with the GEMS system.

Thanks

Garry

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Post by garrycol »

I guess there are no Thor people on here.

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Post by DaveEFI »

Thing is the Thor was optimised for a luxury auto 4x4 - so perhaps not the natural choice for other uses. It also has Motronic injection which an after market ECU like MS is unlikely to better.

As regards the fuel rail, either return or single ended can be made to work with any injection. Return is probably simpler, though. Single ended requires a more sophisticated pump and electronic control of it to set the pressure.

BTW, I'm not really sure there is much difference between any of the injection manifolds etc before Thor as regards performance. More just detail differences to the plumbing and so on.
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Post by Eliot »

Thor manifold will give you more low end torque - given you said you fitted a towing cam, i assume you are 4x4 ? Which would suit this manifold.

I believe you can fit the hotwire fuel rail to the thor manifold - or simply modify the existing thor rail and plumb in a 3bar FPR on the dead end and convert it into a returned fuel rail.
Keep the OEM thor injectors - they flow more than the 14cux ones IIRC.
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Post by garrycol »

Thanks Eliot - not going to use a 4CUIX manifold as it is too small for the 4.6 - the plenum air inlet is quite a bit smaller that either the Thor or Gems 4.6 manifold. Just interested if the GEMS plenum etc is the same physical size (height) as the 4CUIX as I will get a Gems if the Thor will not fit my engine bay.

A question for the V8 experts.

What I can do is remove the throttle body (top pic - top left) and put on a vertical 180 degree bend and bolt the throttle body to that so it sits directly above the actual inlet but pointing towards the centre of the bannanas. This will lengthen the distance from the throttle body to the plenum by about 6".

So what impact (if any) does lengthening the distance from the throttle body to the plenum have on the engine?

Thanks

Garry

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Post by Eliot »

I happen to have Gems and Hotwire plenums at the moment (I sell bored out 72mm plenums) - they are the same height, but the gems is more square.
Here's a photo of them side by side:


The manifold base is the same. The hotwire plenum will work on engines up to 300bhp, ideally with a 72mm plenum. You would need a ported manifold from a griff 500.


Not following you thought pattern re. adding a 180' VERTICAL elbow?

I assume you have seen the photo's of people removing the front part of the plenum and attaching throttle bodies to the two side plenums?
Image
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Post by garrycol »

Eliot wrote:Not following you thought pattern re. adding a 180' VERTICAL elbow?

I assume you have seen the photo's of people removing the front part of the plenum and attaching throttle bodies to the two side plenums?
Image
Thanks for the input.

This is what I was thinking re the 180 degree bend -

Image


I would bolt the throttle body on the new inlet position. I do not have room beside the engine but I do have room at the top above the bananas for the throttle body and other inlet plumbing from the air filter.

No I haven't seen alternatives to the standard intake and while I would np0t use twin throttle bodies this has prompted me to expand my thinking - may be just join the two two plenum intakes with a Tig welded pipe arrangement and sit the throttle body on top.

I would prefer to stay with the Thor as I have a cople of inlet manifolds and plenums and have the MS3 items that go with the Thor system so want to keep expenses as low as possible.

Cheers

Garry

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Post by garrycol »

Been thinking about the issue of no room at the front left hand engine bay area (passenger side) where the Thor manifold throttle body is and the air inlet.

I do have lots of access at the rear of the engine on the right hand side (drivers side) so this got me thinking if I could turn the Thor plenum around on the manifold so what is now the front becomes the back. I have noticed that the inlets on the manifold vs the plenum are all symmetrical as are all the bolt holes so when the plenum is reversed everything still lines up - the only issue seems to be the dowls which will mean some bolt holes enlarged to fit.

So when I go to fit things up I might have a look at this option.

Garry

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Post by ChrisJC »

The coil packs will need a bit of thought, but it's an interesting idea to flip it 180degrees. Let us know what you discover!

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Post by unstable load »

What about lopping the 2 ends of the intake off and simply swapping them side to side?
Cheers,
John

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Post by garrycol »

Hi Chris and John,

Coil packs will not be an issue - if all else fails I will leave them mounted where I have them now (engine currently on carbs) on the front of the engine just in front of the Plenum.

Ok checked my idea more throughly and while the bolt holes at then ends line up perfectly - the ones that bolt the plenum to the manifold in the centre are out so kills my idea a bit.

John - I have already thought of your idea - cut the back ends of the side tubes on the plenum off and tig on a mounting plate to each and bolt on the air intake throttle body onto this - and block of the intakes at the front.

Lots of options that I would not have thought of without posting here - the comments have made me think out of the box.

I needed to run with carbs to run the cam in and take the vehicle to get a LPG MOT (annual check) by 10 May which I have done so now have the time to sort the installation of the Thor stuff and MS3X. I will now take the carb manifold off and bolt up the Thor manifold, fuel rail and injectors - then sort the manifold with everything in place on the engine.

Thanks for the input - as I said it has made me think things through a bit more.

Cheers

Garry

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Post by unstable load »

garrycol wrote:John - I have already thought of your idea - cut the back ends of the side tubes on the plenum off and tig on a mounting plate to each and bolt on the air intake throttle body onto this - and block of the intakes at the front.
Garry, what I was thinking is easier (I think)... Looking at the picture you posted of the manifold with the fitting you cannibalised from Madame's kitchen sink:lol:,..... a vertical cut to cut the ends off the horizontal section that the throttle body bolts onto and holds the barbed fitting on the other end and swap those pieces left to right.
I am crap at posting pictures and I don't have a photobucket account, but if you look at the manifold end-on, the cut would be just outboard of the outer end of the vertical part where the tracts go down to each side's chamber area.
That way, the inlet is on the left, looking at the manifold, and the barbed fitting on the right.
Cheers,
John

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