A- series standoff problem

[sir yun]

Hi David,

I have this a series engine i build and it is giving me a headache.

engines have been build pretty much from the same parts with good results ( the only difference is that i cannot fit the 1/2 inch spacer to the mini spares manifold as for some reason the engine is a bit more backward on the 73-78 model cars and then it won't fit.



It is a BL a series engine 1310cc
head is just a rather normal 35mmin. /29mm ex fully ported jobbie as per Yellow Book only minor changes. ports are very near stock
RC40 exhaust, maniflow freeflow/cooper header

CR is 10.5:1

cam is a 276 *0.290 lift symmetrical profile RE13

Checking height: 0.016" @ lobe

Timing: (Intake): 34.5/61.5 (Exhaust): 63.5/32.5

Nominal lobe lift: (Intake): 0.290" (Exhaust): 0.290"

Duration (Intake): 276 (Exhaust): 276

Lobe centre angle (Intake): 103.5 (Exhaust): 105.5

Lobe separation angle: 104.5

Lift on overlap: 0.085"

installed at 105 degrees ( triple checked but now i'm not quite shure..maybe i was just consistently wrong)

tappet clearances 0.5mm


carb is an SU HIF44 (constant vacuum) with a exponential donut ram''pipe'' and and foam dome filter. it is very effective in keeping spitback to a minimum (Blair has an interesting article about this..it works in practice)
Rockers are mini spares forged items which are quite a bit over 1.5 ..more like 1.56

ignition is a MegaJolt Lt jr with a crank trigger ( 29-31 degrees total advance all in by 3K)




the combination of parts is nothing special but it just does not want to play ball.

on the first chassis dyno session it was uncontrolably rich down low and uncontrolably lean up top.

Suspecting only fuel delivery problems (maybe draining the float bowl..modded the float valve) I spend ages fiddling and fitted pump/reg and such and had it running decently for just driving around. .

for some reason pulling the choke helps a lot but the amount of extra fuel is very small compared to the amount that should be delivered my the main jet..

could it be that pulling the choke has a venting effect on the float bowl (al the connections are fitted breather is open and venetd to air..

return to the rollers it turns out the problem is still there and still huge.

power was about 85 bhp, but it runs like a turd especialy on load


AFR goes to beyond 7 down low to the point it bogs down and leans out up top.

nothing will cure this as it is impossible to get a needle to do this

after taking the air filter of it showed a large amount of standoff/spitback

removing the bellmouth (exponential one) it went from bad to horrific with clouds of fuel drfiting from under the bonnet. (Blair was right about the exponential bellmouth being good for keeping sitback to a minimum). the huge fuel saturated cloud suspended in front of the carb mounth causes it to go wildly rich...


i know what i am seeing.

I sort of know what is going on
I have no clue what can cause it
i have even less of a clue on what to do about it.


how far would the cam timing have to be out to cause this much grief ?

induction noise is very LOUD ( as in not legal for track use .. let alone road) and as i suspected earlier there lot of energy there messing up the fueling.

i had a MG metro manifold fitted with larger and slightly longer ports and that seems to work a bit better, but stupid me replaced it with the one we used before.

the exhaust is not ideal for this cam but could it be such a major factor?


the dyno operator suggested to fit a weber (this case on a swanneck manifold as it was what was available) just too see if the differnt intake situation would cure the standoff .while it runs i wanted to check it it if firing on 4 cylinder so i pulled some plug leads..

turns out the engine idles fully on the center cylinders (and it even sounds like a four cylinder this way)..according to Mr Calver this is mostly the case but only with race cams and it should not be this pronounced.
on the outer two it will not run..

so the two outer cylinder are firing/burning (the mega jolt is quite effective according ot my neurons ) as the exhaust are hot . but whatever is happening is not happaning at the correct moment in relation to TDC (i guess).

there should be at least another 15 bhp hidden somewhere.

it seems it dislikes pulling with load.. on a wet street it produced rolling wheelspin in 3rd gear. on the rollers it bucks and hops.

will retime the cam on monday i hope. i hate working on engine in car.


ANY thoughts very very appreciated as this is seriously cooking my noodle

[rrrobert]

that cam lobe seperation angle seems v small sir yun ,are you sure of it ?
regards robert

[FlowSpecialist]

Do a compression test. Always start with the basics!!!!

Put a dial gauge and degree wheel on every lobe and check that the cam is correctly ground. You might have some sort of phasing cockup.

Cams usually prefer being run about 2 to 3 degrees advanced. Yours is a tad retarded although that isn't the main problem.

Does the carb have the appropriate spring in it, oil in it, a piston that isn't sticking, the right size main jet and one that's not worn? There's no such thing as an SU that's uncontrollably jetted. You can always get them as you want even if it means starting out with a very lean needle to get the bottom end right and polishing it down in the lathe to get the top end right. Just because there might not be an ideal needle off the shelf shouldn't be any hindrance to an operator who knows what he's doing.

Dave

[Sonett]

Once you have checked out the basics, as advised by FlowSpecialist and assuming everything is as it should be, the next difficult step is finding a dyno shop/operator that knows his way around SU carbs. Sometime ago i fitted twin SU carbs onto my Saab 8v to replace the awful twin Strombergs, i set them up as best i could and then took them to a dyno operator that really knows SU carbs, he ran the car on the dyno a few times and noted the AFR, he whipped out the needles and filed them by hand with a flat swiss file, my intial reaction was shock and i think he saw that by my face, as he assured me it would be OK, i took the car for a spin and it ran so much better than before, smooth and crisp is how i would describe it. Fortunately the dyno is only about an hours drive from my house, the operator new exactly where to remove material on the needle. Of course the downside is that these needles are now unique and if they wear or get damaged, i would have to go through the whole process again.
Hopefully my ramble will give you some reassurance about so-called impossible to get needles.

[FlowSpecialist]

FYI you're not actually far off the spec of my old Metro 20 years ago.

1380cc, 35mm/29mm head, 544/643 Leyland cam (Piper regrind), std rockers so not much valve lift, the stock HIF44 on an MG Metro manifold, cheapo LCB and the std 1275 Metro exhaust with the silencers chopped out and an MGB one welded in. Still had the original peashooter bit of tailpipe sticking out the back so it looked stock from behind. We didn't find the puny bore of the stock 50 bhp Metro exhaust restricted it at all.

85 bhp at the wheels with a couple of flash readings of 89 bhp, Best estimate about 108 bhp flywheel. Went like shit off a shovel and still gave 40 mpg. We did spend a lot of time on the flowbench getting the head right though.

DV do you remember trying to keep up with that Yank V8 that night in it when you, me and your daughter were heading out to the chinese restaurant to get a takeaway? I don't think we'd have got far if he'd been really trying but it did go well for a little A series.

Needle as I recall started out as a fairly weak one and had to be polished down a lot to get the top end right. It also ran a lot weaker on the road than it did when it was stinking hot on the dyno and we had to keep taking a bit more off the needle to get it right. When it looked right on the rollers it was actually so weak on the road I had to pull the choke out. Sounds a bit like your case.

If you get really stuck with it (and assuming you're in the UK) I can probably give you someone to go to who can set SU's up properly. Check the basics first though.

Dave

[sir yun]

hiya.

the lca is 104.5 according to Piper.

the guy setting up is very experienced (does loads and loads of SU's for midgets, Jags and such.. as well as Le Mans , European champions in formula fords.. the guy generally knows his stuff)

carb is rebuild and checked.

but i'll recheck the cam..

did not measure it prior to installation. .crap.

some of the Kent chain drives strecthed a lot during the first time maybe the timing is cocked up now.


Addition:

I checked the cam using the lift on overlap method.

i seems that quite a bit of chain stretch has occured (i estimate some 4 degrees retard that was not there when i put it in).

[DavidVizard-GFN]

Originally Posted by FlowSpecialist

-----estimate about 108 bhp flywheel. Went like s--t off a shovel and still gave 40 mpg. We did spend a lot of time on the flowbench getting the head right though.

DV - do you remember trying to keep up with that Yank V8 that night in it when you, me and your daughter were heading out to the chinese restaurant to get a takeaway? I don't think we'd have got far if he'd been really trying but it did go well for a little A series.

Needle, as I recall, started out as a fairly weak one and had to be polished down a lot to get the top end right. It also ran a lot weaker on the road than it did when it was stinking hot on the dyno and we had to keep taking a bit more off the needle to get it rig -------

Dave

Yes I remember the zooming off to go for dinner at what I recall was a great place for such. But as much as I rack my brain I can't remember getting into a race with any car - but there again I do have a bad memory and I tend to zoom about when I am going anywhere. That's one of the reasons why I find it hard to drive economically. Now if you were to ask about the chinese dinner I seem to remember Danielle and I had a feast. You know what the scary thing about this is - it looks like I am more interestied in food than racing - but that just can't be.

Now before I get into trouble for so-called street racing with a 4 year old in the car let me tell you folks out there that whatever it was would have been low key. I have found that racing on the street is somewhat tame compared to the real thing so it does not hold any great interest for me other than maybe a quick blast from a standing start to maybe 40-50 mph. My experience as a road course instructor is that most folk who think they are a hot shot on the street would still be short of competitive on a road course.

Now that Metro of yours Dave. So long as I am thinking of the right one (bear in mind I get to drive a lot of cars) what I remember was, apart from having a good deal of power, that it drove very well. You could slip it up into top gear and it still pulled strong even from low rpm.

When it comes to drivability and carbs it seems to me a good ol' SU is hard to beat! You just have to master that needle profile problem and there you go.

All this begs the question - what are you driving now and what's done too it?

DV

[FlowSpecialist]

Originally Posted by sir yun

Addition:

I checked the cam using the lift on overlap method.

i seems that quite a bit of chain stretch has occured (i estimate some 4 degrees retard that was not there when i put it in).

So instead of the 3 degrees advanced you ideally want to be you're over 4 degrees retarded. That's a hell of a long way out and could be costing 10% of the engine's power. I don't see it stopping two cylinders running properly at idle but that may be a red herring. A series have some weird charge robbing stuff going on between the inner and outer cylinders. As long as it runs ok at high rpm.

Checking the cam phasing isn't very onerous though. Just zero the degree wheel to full lift on any inlet lobe and check that the others are reaching full lift every 180 degrees from this. The actual timing doesn't matter at this stage. Then repeat for the exhausts. Then do your compression test.

If you don't have a duplex chain on a tuned Mini then I'd suggest it's cheap insurance and well worth fitting. Then set the cam to 101.5 ATDC full lift on no 1 inlet and see how you get on.

Dave

[FlowSpecialist]

Originally Posted by DavidVizard-GFN

All this begs the question - what are you driving now and what's done to it?

DV

A fairly boring but reliable 2001 2.0 ESP Ford Focus that's bog standard barring a Focus ST170 tubular exhaust manifold which is the biggest restriction on the standard engine and worth about 15 bhp. My days of crawling under cars to mod them are long gone and as long as it starts and runs when I need it to I'm fairly happy. I'd love to stick a turbo on it, or maybe a BV head and throttle bodies but it's too much work.

Having said that I love the Focus to bits. Best car I've ever owned. It goes round corners like a race car compared to anything I've had before and still floats over the bumps like a magic carpet. Modern OE suspension systems are so damn good compared to the live axle crap of 30 years ago.

Dave

[FlowSpecialist]

Originally Posted by DavidVizard-GFN

When it comes to drivability and carbs it seems to me a good ol' SU is hard to beat! You just have to master that needle profile problem and there you go.DV

Bloody brilliant carb IMO. I think the world has pissed away a fortune on catalytic converters and other expensive crap to solve emissions when the SU had most of it there to start with. OK maybe 6 bhp down on a 45 DCOE for race use but 50% more mpg most of the time and sod all in them to go wrong.

If we're concerned about oil reserves and oil consumption then surely mpg is more important than emissions. Cats and FI are of course good for emissions but the best mpg figures I've had in daily driving have actually come from SU carbed vehicles.

I've kept a log of the mpg for every tank for every car I've ever owned over the last 30 years and average mpg hasn't gone up a jot. In fact it's gone down. What modern FI engined cars gain in mpg from engine efficiency they lose from the weight that central locking, crash protection, air bags, electric everything add.

In the 80s the average hot hatch weighed 850 kg. The Mk1 Golf, Fiesta XR2 are examples. Now a hot hatch weighs 1250 kg. The Golf has bloated up by 50%. Every measure our lords and masters take to save fuel is cancelled by another they take to stop us killing ourselves.

My solution is simple. A sharp steel blade sticking out of the steering column that you'll impale yourself on if you crash into anything. No added weight for air bags, side impact protection or anything else. Simple light cars with SUs and Darwinian safety features which mean if you are stupid enough to crash you get out of the game.

Dave