Phoenix 6:3:1 Manifold

[Richard H]

Dear All

I've finally fitted my complete Phoenix twin box system with manifold as above but now have a mis fire around the 3000rpm mark, perhaps a little higher.

Have tried the following:

Cleaned injectors with airline

Cleaned spark plugs.

fitted new K&N Cone air filter to end of fexible tube.

 

Car did not stutter prior to fitting new system and pulled well thro the rev range.

Starts and revs fine, just under load at around 3k rpm, she seems to struggle.

Car is standard 150bhp injection, 1972.

 

Could this be a timing issue due to the new manifold?

Unfortunately, I'm no expert and do not have the strobe etc and know - how to adjust.

Going to book in for MOT so may ask the garage to have a look.

 

Any thoughts would be most welcome. I've searched the archive but got disheartened after 4pages, am I lazy???

cheers

Richard

[mikew]

Richard,

 

There is some considered opinion that the 3 unequal length sets of primaries in a Pheonix exhaust can cause bumps in the torque curve, which may be what you are feeling, or perhaps the mixture is now out, have you tried running it in the "misfire - stutter" region for a while and then pulling the plugs to see what colour they are - black to rich - white too lean - perhaps worth putting the standard air filter back and seeing what happens - the K+N offers less flow resistance so maybe it makes the mixture too lean

 

mike

[Richard H]

Richard,

 

There is some considered opinion that the 3 unequal length sets of primaries in a Pheonix exhaust can cause bumps in the torque curve, which may be what you are feeling, or perhaps the mixture is now out, have you tried running it in the "misfire - stutter" region for a while and then pulling the plugs to see what colour they are - black to rich - white too lean - perhaps worth putting the standard air filter back and seeing what happens - the K+N offers less flow resistance so maybe it makes the mixture too lean

 

mike

 

Thanks Mike,

I'll put the original air filter on and see what happens.

cheers

Richard

[JohnC]

While it's always a good bet that the last thing you changed caused the problem, it's very hard to see how a different manifold design would cause stuttering. I've done many rolling road sessions on my car to test out exhaust designs (among other things), and while they do have a noticeable impact on the torque curve I have never seen the mixture change to anything which would cause a misfire. In fairness I haven't got a Phoenix 6:3:1 to try, but I can tell you that even the 'nasty' TT1200 6:2 with a peaky torque curve doesn't do it. Makes the car feel like it's towing a caravan at low revs, but no misfire.

 

Is it possible you disturbed something else when switching manifolds?

 

Does the misfire continue above ~3000rpm, or is it only in a narrow band? Does a tiny amount of choke fix it? I know you blew out the injectors, but did you check the spray pattern afterwards?

 

Keep us posted on your progress. It won't be long before Richard C sorts you out

 

Cheers,

John

[stephen cooper]

Why is it hard to see that a different manifold design would cause the stuttering? Fitting a 6-3-1 even the inferior phoenix manifold is an improvement over the standard item, pulse effect and all that + better flowing is going to demand an increase in fuel & air. Of course with a 6-2 toilet tune one you won't see any difference - the standard item is better! I could tell you where to get a recalibrated MU but i'd probably get lynched.

[cord]

Hi All....So I get the idea here that the Phoenix 6-3-1 is not the best pulse type extractor on the market, any comments on what is???

[JohnC]

Why is it hard to see that a different manifold design would cause the stuttering? Fitting a 6-3-1 even the inferior phoenix manifold is an improvement over the standard item, pulse effect and all that + better flowing is going to demand an increase in fuel & air. Of course with a 6-2 toilet tune one you won't see any difference - the standard item is better! I could tell you where to get a recalibrated MU but i'd probably get lynched.

 

Simply telling you my experience. In the dozen or so dyno tests I've done, misfiring (under power) has only started at an AFR of around 14:1+. Unless you're running EFI, target AFR under power should be 12.6ish (obviously leaner is OK on over-run). So if the engine was correctly set up before the manifold swap, the manifold needs to increase airflow by over 11% vs the standard item in order to induce misfiring. Maybe the Phoenix manifold (or system - I expect you need to do the whole thing to get full benefit) does this, in which case I stand corrected, and you can add 14bhp to the flywheel power output by a simple manifold swap (assuming you recalibrate the PI). I see why the Phoenix manifold is so highly regarded.

 

Incidentally, the 6:2 manifold is worse than the standard one on the road - again in my personal view. But I'd be talking to those who used them on the track in the 70s before making a sweeping statement that "the standard item is better". My engine develops slightly more top end power with the TT1200 (and I don't exceed 5500rpm on the dyno), but at the expense of an unacceptable loss of mid-range torque (both vs the standard manifold). If I were on the track that top-end power might outweigh the mid-range loss. Now I understand that there are manifolds better suited to racing than the TT1200, so it's neither fish nor fowl, but it's not worse than the standard one in all situations. I think it has probably been unfairly maligned because some large parts suppliers sold it as a road manifold which would liberate noticeable amounts of power at little cost. Which is tosh.

 

Anyway Richard, it would be easy to check if you do have a lean mixture - just put the car on a dyno. I don't know how things work in the UK, but here in Sydney my local tuning shop is happy to put my car on their dyno for $88/hr (about £40?). They're quite amused that somebody is bothering to get dyno data on a car that has no turbointersuperchargerisor, can't be tuned using a PC, and barely makes enough power to turn the wheels. Not to mention that it's nearly twice as old as any one of the guys in the workshop. "Hey guys, it's got points!" In any case, you can do quite a bit of diagnosis in an hour, and even a little mixture adjustment in the idle/mid-load areas, although tweaking the max fuel and datum track would probably take a bit longer. Incidentally, I am not suggesting you allow anyone to "tune" the PI unless they're a recognised expert on our engines. I do suggest you get a graph of AFR vs rpm at full throttle, and even some part-throttle readings. Any dyno should be able to do that, and they can tell you how your electrics are functioning at the same time. Besides, it's fun.

 

As always YMMV (and probably will).

Cheers,

John

[jean]

I hope you carefully checked the matching of the manifold with the outlets in the head, this including the gasket. Must say never saw a direct, proper fit in this area. From what you state there could be a serious airleak around the inlet/outlets.

Before fitting any manifold inlet or outlet it's a good practice to put it on a thick flat surface, glass is the best, to verify that the mating surfaces are perfectly flat

[Alec Pringle]

Hi John,

 

Nothing adrift with your logic.

 

However, if the mu is such that this car was tending towards the lean previously, the manifold might just have tipped it over the edge ? The timing too might just have been sufficiently out to now need a tweak ? In combination, that could explain the scenario ?

 

As for exhaust manifold design, I had a hand in developing and testing some of the TR variants back in the 70s. You can't have the cake and eat it, a given manifold isn't going to be 'the best' in all situations. There are quite a few desirable attributes involved, and you're always going to have to compromise one against another.

 

And your suspicions are largely correct . . . in my limited experience, what works well on the road - in the mid-range where you need it - won't show up so well pushed at high revs on the track. Vice-versa also applies, of course. In any case, there's a lot more to an exhaust system design than just the manifold and downpipe/s.

 

As a real-world illustration, running Pinto-engined single seaters back then we had 3 basic exhaust systems in order to make the best of very different circuits. What worked best on a flat-out power circuit with long straights would be sadly lacking on a tight hilly track, and the other way round.

 

At the risk of stating the obvious, any manufacturer and his distributor ought to be able to give at least some specific guidance in respect of the influence of a particular manifold, for example - as applied to standard engines, and to engines utilising the generally favoured tuning upgrades. If that info isn't available, then presumably the 'design and development' process might have been rather less comprehensive than one would wish.

 

Cheers,

 

Alec

[Andy Moltu]

Given that you've just changed the exhaust manifold you will in the process have disturbed the inlet manifolds.

 

Probably the most likely explainationfor your cars ill running is goint to be out of balance inlets.

In 20 years of owning a 6 it still amazes me how rough they run unless the throttles are properly adjusted.

[Richard H]

Dear All

Many thanks to your valuable suggestions.

I think ultimately, the work is beyond the scope of my expertise.

Have been meaning to get the car to Rob Forster in Hucknall so I think this is my next route.

Due to change of jobs, my TR will be my new company car so it needs to be right!

cheers All

regards

Richard

[Richard H]

Dear All

Many thanks to your valuable suggestions.

I think ultimately, the work is beyond the scope of my expertise.

Have been meaning to get the car to Rob Forster in Hucknall so I think this is my next route.

Due to change of jobs, my TR will be my new company car so it needs to be right!

cheers All

regards

Richard

 

Just a quick update from tinkering yesterday.

Following passing the MOT on Thursday, I was able to legally go for a good run.

Car was running rough through the complete rev range but felt like it wanted to go, but couldn't.

I worked through the injectors again, started a number 3 and worked to the back.

I got to number 1 injector last to find it completely dry. I knocked it with a spanner, still nothing.

Realising that this could be the problem, I pinched the needle and pulled it out.

After wiping the fuel from my eyes and face, I realised you should not look directly at the injector when performing this task!

Good move I thought but was pleased to get a face full as this meant the injector was probably blocked and now clear.

I put the bits back together and went for a run. She went like the stuff flying from the shovel! The responsiveness of the throttle was tremendous and was still pulling when I had to ease off at 90!

Delighted with the performance now and have since put the K&N cone filter back on, attached to the bracket along side the rad so it sticks as far forward as possible.

So in conclusion, it seems that even after blowing out all the injectors, there was still something blocking it. This may mean that the diaphram in the metering unit is on its way out??

Thanks again for the advice and pleased to report that the Phoenix manifold and twin box system sounds great.

cheers

Richard

[Andy Moltu]

So in conclusion, it seems that even after blowing out all the injectors, there was still something blocking it. This may mean that the diaphram in the metering unit is on its way out??

 

Unlikely - if the diaphragm fails you tend to run very rich (the diaphragm doesn't directly contact the fuel)

Usually debris in the injectors comes from the seals. Some injectors can be stubborn to bleed.