Did someone throw a boat anchor behind my car at 4500?

[max71]

I already posted this in another thread but this is where it probably should go.....
______________________

After all these years -- PROGRESS!

So here's the story and I would love some racers and Malcolm's feedback.

I had #6 in the carbs as mentioned before with K&N filters in place of the stock air cleaners/cans. Car hits the wall at 4500RPM. Will not go further.

We ran the analyzer and it shows under load on runs when it blogged down the meter read high 17's to 18.

We richened it up which was too rich for the lower end but the top got a hair better.

We put in a pair of MME needles Sean Brown had sent me and dialed back the carbs to where they were before. Same issues but maybe a thou or two higher before complete bog down.

After the mandatory scratching heads then answering all the things I've tried, Stewart suggested its getting too much air at the top so have I ever tried putting the stock cleaners back on? I reluctantly put a pair on that Steve had in his garage thinking, "Pheh, tons of people run K&Ns. But its one thing I never did try".

Went for a run and it went to redline. I couldn't really get it to bog down.

After returning we put the A/F meter back on and went for a run. This time it stayed in the 12s during wind out. Once it bogged slightly and Steve said it spiked for a moment to 14 then recovered.

I still feel it doesn't pull like it used to (with old rebuild) and there could be fine tuning with different needles and I would get better top end although if the meter now says 12s I guess its where it should be.

What I don't understand is many people use the K&N's and never go above a #6 needles. Why does my car need such rich needles at the top end? It is a Huffaker head that was flowed quite well and Sean Brown redid the valves and flowed it a touch more but he's done that for many B owners. He had told me he's never had to suggest more than #6s.

I wasn't expecting anything but the same old mystery so I'm too stunned to actually find it was the K&Ns all this time... But Yippeee!

[malcolmr18zoy]

Hi Gary,
I'm glad that you've nailed down your problem finally. Now you have to make a proper repair instead of just masking the problem! The problem, it seems, is too much air at high revs, ibso facto, too little fuel at high revs. The whole point of better cams, and gas flowwing, is to get more charge into the cylinders. Your car obviously flows more charge than the stock air cleaners will allow. By restricting your air flow you're making the air flow match the allowable fuel flow. Looks like you need needles with a more pronounced taper, So you richen up as the revs increase, while still staying lean enough at low revs.
Malcolm

[max71]

Hi Malcolm!

SU needles are quite expensive. Is there one you think will do the job? Or is this a dyno thing with a box full of needles?

[malcolmr18zoy]

Hi Gary,
I'm not familiar enough with MGs to suggest a particular needle, but if you have access to a BL special tuning catalogue you should be able to find some clues there. If not, you may have to get some old needles and taper them youself. Do you have access to a small lathe? With a small lathe you can taper the needles a little at a time and experiment with the results.
Malcolm

[max71]

Malcolm,

Aren't all SU needles the same for all cars that used fixed needles? I don't have access to either and haven't working a lathe in so long getting both identical would be an extreme challenge.

[malcolmr18zoy]

Hi Gary,
What camshaft is in your car? If your cam is quite radical, you may have to suffer some over richness at low revs, which should disappear as you come onto the cam at higher revs.
All fixed needles are not the same. The stock needles for yor car are FX. #6 is a rich needle, and #5 is listed as stock. I'm not familiar with needles listed by number, so can't comment.
Malcolm

[max71]

Hey Malcolm

Its supposed to be a APT VP-11 cam. Not that radical. There was talk in the past that APT has some problem cams. I never mic'd it when I got it prior to installation.

I'm playing with a Needle chart but in all honesty I'm not sure what I'm looking for station by station other than a richer climb.
http://www.mintylamb.co.uk/suneedle/

BTW, I rode in Steve BGT with your rebuild and a lessor cam and it seemed to pull a lot stronger than my mill.

[grantour]

max71 -

ding dang, sounds like the mystery may be over ! hooray

[max71]

Thanks Grantour - now if I can resolve it as Malcolm is lobbying for it might be fun to drive again.

Malcolm and all. I played around with some needles. The AZ (green) looks interesting. There's the baseline #6 (although I have MME in right now which is in the graph also)

[max71]

Ok, while I thought I found the solution Malcolm has a good point. Before I go on, my biggest question is: Would I really be gaining any performance in resolving the issue with the K&Ns in place? Opposed to going back to the Coopers?

Here's what the brain trust between Jimmy Hilton carb rebuilder and Sean Brown head reworker. Neither has ever experienced anything like this or ever heard of anything like this. Sean redid the head and intake manifold and said he's never had a customers have these problems. These were evident before I sent the head to Sean to redo the valves and slight touch up.

The only thing they thought of is the piston springs are weak and the piston is raised all the way before it hits top RPMs. They suggested either new springs or stiffer springs.

Jimmy does the same stack mod on the K&Ns that I have and never had an issue. Jimmy's only other thought was to plug the PCV and open the front tappet to the air. I'm reticent to do this as I've read enough about the PCV valve to know its important.

Neither believes chasing richer needles is going to resolve it since the MME which are much, much richer than #6 had a minor benefit.

I'm baffled. Yet again.

[Steve Simmons]

I'll repeat what we talked about in person the other day just so it's in here... If your engine can suck in more air than the stock cleaners allow, then yes the K&Ns will offer a performance boost, once everything else is tuned to match (needles, valves, timing, etc). If the stock cleaners are not a restriction, then the K&Ns will not improve anything.

Since you have a super high flow head and air filters, you need to match the needles to whatever amount of air the engine is capable of taking in. I have no idea how air that amounts to on your engine nor do I have any worthwhile experience matching needles to performance modified engine components, so I can't help other than my own general observations.

[max71]

I fully comprehend all that. What I don't understand is my setup isn't so special. Yes, the head has a lot of work and Sean even put in bigger exhaust valves but nothing so radical that he hasn't seen before. Many people are running his heads in various states of porting and reworking even you. They also run these K&N's.

Therefore Sean should have some experience in the hundreds he's done. The carb rebuilder should have somehow heard of something like this. All agree and even Cutro that #6 is all you need and the MME is much richer than that. As Malcolm said I could turn my own needles and see. Finding the other needles that are richer are seemingly impossible to source.

It just doesn't make the sense to me its making to you. I don't believe my present setup is the first of its kind.

[Steve Simmons]

Many people are running his heads in various states of porting and reworking even you.

But mine is forced induction. Big difference. Besides, I thought your head was a Huffaker race head, not a Flowspeed head. That's definitely different than most people run on a street engine.

Overall I simply look at the situation differently than you do. Rather than strive to get the engine using the same parts as other people, I would just get a set of needles in there that offer the correct mixture for what you have. If it runs well then it doesn't matter what parts are in the thing, nor does it matter what the numbers are. I'm more of a seat of the pants tuner, which is why I still think you should just sand your needles down a bit. That's just what I'd do though.

[max71]

It is a Huffaker race head but since Sean saw it he was familiar with it. He said they did do some things he didn't.

What I'm saying is I'm not sure needles are the issue. At this point I'll have to get a hold of some old needles and play with them as Malcolm said. Otherwise the other two do not believe needles are the issue since the MME only had a very insignificant improvement.

[Steve Simmons]

I offered you my old needles and some emory cloth when you were here the other day!

[max71]

You did???

No you didn't

Did you really?

[Steve Simmons]

Yep.

Offered a complete set of HS4s to try, too. Can't remember what needles are in them though. The aforementioned spare needles were FX and came from my '67.

[max71]

Ok I remember the set of carbs. That was before we tried the Coopers

I'll take you up on the needles and borrow the springs to see if they make any difference. I must have been in shock that the Coopers worked and I THOUGHT I WAS DONE!!!

I'll have to come by. Tell Linda Nui ate the coffee cake! I only had a few bites....

[malcolmr18zoy]

Hi Gary,
You say that MME needles made an insignificant difference. Perhaps they are rich all the way, so you would have to be running really rich at low revs to be anywhere near at high revs. This is one of the downfalls of using a mixture of components some of which are raceworthy. Why don't you just fit the stock air cleaners, and be happy that your engine runs up to red line. If you make it run right with the K&Ns, you may be able to rev beyond the red line!
Malcolm

[max71]

Hi Malcolm,

Honestly I think I'm going back to the Coopers because I need a break from this. After more research I'm thinking chasing needles isn't the answer without some significant dyno time.

I'm also wondering to your point about the cam affecting this which I still believe is possible but again, without great expense I won't know if its degreed incorrectly or the cam itself is not ground correctly.

I've give Steve's springs a go and unless they do something I'll just pack it in and revert to the Coopers. Odd thing is with the Coopers and the Huffaker head/manifold/cam/carbs previously I could bury the tach.

It may be several things contributing to this.... Thanks for your help and advice.

[max71]

Just a reminder how whacked the power band is here's the dyno graphs.

[malcolmr18zoy]

Hi Gary,
If the air fuel ratio, wth the K&Ns is almost 18:1, there is absolutely no doubt that your car is running lean. The dyno graphs show this as well. You can mask this problem by fitting air cleaners that restrict the air flow, and if that works for you, fine. I think that your car has been the subject of too many differing opinions. The answer, only in my opinion, is to take everything back to stock. The manufacturers know how to make the car run at it's optimun for street use. If you're preparing the car for competition, that's another thing. Always know that whenever there's a gain, something has to be sacrificed.
Malcolm

[max71]

But - and I respect everything you say - why are so many MGB running with similar set ups without issue?

One of the biggest problems is my compression is too high. This was due to a shop error and previous mechanic. He wanted them to skim the block and they decked it to zero height.

So I would need to invest in a new block and a new head?

[Steve Simmons]

But - and I respect everything you say - why are so many MGB running with similar set ups without issue?

I still think your engine is anything but a normal setup. How many people could possibly be running around with 12:1 compression and a race-prepped cylinder head?

By the way, I thought you said your torque peaked before your HP? The charts show a perfectly normal curve in my opinion. Gobs of torque down low, which barely drops off as the revs climb, and max power in the higher revs. I'd be thrilled with those numbers.

[max71]

I might have oversold the race head. I sent it to Huffaker for street polish. The person I talked to later who did it said he was bored and went "overboard" but don't tell Joe.

Sean Brown who flowed it recently didn't think it was excessive.