Porting 4.5L Inlet Manifolds - Is it worth doing?

[A and K Cerbera]

While working on our Cerb 4.5L AJP V8 engine I had to take the throttle bodies off. In doing so, I took the opportunity to look more closely at them. In the top of the TBs, there is a step around the inside where the injectors are located.
Is there any benefit in porting and removing the step?





Also there is the end of a bolt sticking through the wall of the TBs. Should this be shortened so the end blends in with the inside of the TBs?
When looking into the bottom of the TBs there is a lump. Is there any reason why one should not remove that lump and make the aperture more round in shape?





Finally I measured the TB's and to my surprise the top aperture measured 46.5mm and the bottom aperture measured 40mm internal diameter and 39.5mm i.d. where the lump is. The inlet port in the cylinder head is a fraction less than 40mm i.d.



I'm impressed with the 4.5L AJP. These engines can produce over four hundred horsepower through such a small aperture.
I have a lot to learn. I would appreciate your thoughts.

[DaviesDJ]

As somebody planning a major 4.5 to 4.7 build I am very keen to get everybodies opinion on this who know the engines - my experience from other Marques is uniformity and blending may help - as would thinning the spindle - difficult to say ???

[pmessling]

I was looking into this subject for my MINI, only because I've got to take the head off. But found that a turbulent airflow can have its benefits too as compared to a smooth . But guess it's all down to the inlet design and path the air takes.

[Byker28i]

This was part of the work done on my 4.2 throttle bodies when I had mine sorted.

[ukkid35]

Perhaps I should do something about the crushed airbox ports on mine - LOL

Still managed 410 with a Joolz remap, despite the dished lifters, and corroded liners, and probably inaccurate cam timing.

[DaviesDJ]

Funny the variety in these engines isn't it!

[Jhonno]

A and K Cerbera said:

I'm impressed with the 4.5L AJP. These engines can produce over four hundred horsepower through such a small aperture.
I have a lot to learn. I would appreciate your thoughts.

Actually, the inlet ports are too big for a 4.5L engine..

[Byker28i]

So here's the original thread on some work that Jools did a few years ago, mapping and work ont he ports/throttle bodies
https://www.pistonheads.com/gassing/topic.asp?h=0&...

From this:
The 4.2 inlets have a few area which need addressing to improve flow, mainly centred around the butterfly spindles, the area just immediately after the butterflies and the waisted section at the manifold to head face. The inlets need stripping down off the car in order to do it and refitting/balancing when back on the car, plus one slip in the butterfly area and it's an expensive mistake so time/patience/care are the order of the day .. hence the cost is quite high.

[DaviesDJ]

46mm ITBs sound about right to me

[julian64]

I bought and machined a new butterfly spindle and turned the round spindle into flats, smoothed down the steps below the butterfly valve and though I was doing well only for a thread to come up on PH saying it was all a waste of time and that the big gains in a 4.5 were with the massive steps seen in the exhaust manifold to head connections that made all the steps in the inlet look like nothing in comparison.

[Jonbouy]

Julian what changes modifications did you make to the exhaust manifold?

[Luckyone]

I spotted those steps in the 4.5 body's a good few years ago so ground them smooth & welded some new metal into the other side of the step you can't see from above, then couldn't get it to idle after putting it back together. So took it to APM Andy who look after before I took to making a mess of it my self.

He said there was a whole batch machined like that. He got it running fine again but my work made no notable difference to the running of the engine!

[julian64]

Jonbouy said:

Julian what changes modifications did you make to the exhaust manifold?

At the place where the exhaust manifold mates to the heads exhaust ports its a bit of a disaster. I made a former out of wood that stuck in the head poking out of the exhaust port. An exact match. I then tried to offer up the exhaust manifold and the bolts were misaligned by about half a cm top and bottom

I therefore did some grinding on the exhaust and the head to try and get a better match

You can do the same just with an exhaust gasket but I'm a bit dense like that.

[Luckyone]

I used one of the single exhaust gaskets longbow had made that I did the second run of the GB on to port my exhaust manifold. The D shape port on the heads would be perfectly with the correct sized pipes on the manifold, to make a step to stop reverse pulses...

I spent ages port matching everything, but my power curve shows it wasn't worth it, yet anyway.

[ukkid35]

A and K Cerbera said:

I would appreciate your thoughts.

A cheap quick improvement you can make is to replace the (probably worn) throttle link ball joints with rose joints. You need both RH and LH thread, I think there is a place listed in the Alt Parts thread for the LH thread one you will need.

[pmessling]

or ask and i'll make you one.

[Byker28i]

ukkid35 said:

A cheap quick improvement you can make is to replace the (probably worn) throttle link ball joints with rose joints. You need both RH and LH thread, I think there is a place listed in the Alt Parts thread for the LH thread one you will need.

Yes that was a good investment. Gives a really good and positive adjustment

[A and K Cerbera]

I've got the exhaust manifolds off and can see the witness marks where the exhaust gases hit the flanges.





Based on your comments, it looks like we will be doing a standard spec rebuild with the addition of ACT exhaust manifolds and a short induction kit.

Thanks for your thoughts

[ukkid35]

The things I do like about TVR's AJP8 manifolds is that they are incredibly light, and far less absurd than what they employed in the Chims and Griffs - all that heat radiated in the front of the engine bay!

But I agree, they do not seem to be that well engineered.

Funny thing is there have been a number of cars that have tried to improve things, but the dyno charts never seem to bear it out.

[julian64]

I personally think you are on the right track.shortened induction pipes, a bit of lip removal but don't worry too much and a better flowing exhaust.

I kept with the slightly limiting standard exhaust manifold but added a set of linked exhaust pipe to try and improve the restrictive effect of the slightly compromised exhaust manifold, then bought the ACT back box as its a lot less restrictive without being too loud.

.
.
.
.

To go further there was a post many moons ago and I can't remember who did it but it was to take the head off and match the combustion chambers followed by sending the crankshaft off for decent balancing. This is where I would go next with either the 4.5 or 4.7 depending on what you want to do.