110 replies to this topic

[I'm a Red Motor fiend]

Pistons wouldn't open fully with 12oz springs so we chopped them down and achieved full lift.
I really think there is enough fuel supply now and that the metering needle profile just isn't right for top end power.
We are way off of HP goal so far only 263HP (we were thinking 300) because as said, over 5000rpm it leans out badly and the curve just dies in the arse.

[rodomo]

Pistons wouldn't open fully with 12oz springs so we chopped them down and achieved full lift.

Love it! My kind of technical engineering!

[warrenm]

I use no oil in the dampers, Grose needle & seats 5.5/6 psi fuel pressure, no flooding issues & 270 something(I can't remember) hp at the treads & modified AAA needles.

[I'm a Red Motor fiend]

So I have finally got the donk in the car and up and running.
Felt so bloody good to drive a Torana for the first time in nearly two years.
Took a lot of time to set up the new linkages for the HD8's. Had to fabricate mounts and spring mounts. Chop chop, weld weld, grind grind.
Had to reset the float levels as on the dyno the carbs were perfectly horizontal, in the car they are not.
Put my chopped down 12oz damper springs on the scale, they are now around 10oz.
Running the UL needles still.
Idle AFR is around 13, cruise 14-15, light throttle 13ish. Mash the go peddle and when the cam comes on I'm seeing farkin 10's!!!!
WTF? On the dyno we couldn't achieve max power as it was leaning out, now same setup in car is pig, pig rich.
Can't win.
Put my 5oz damper springs in and it was way too lean so am sticking with my chopped down 10oz ones.
Next will try my UU needles as they have the same curve as the UL's down low but are leaner up top.
If these are still too rich I will go back to UM's which are leaner all the way through.

[claysummers]

Just chuck them pommy carbs in the bin. Just trying to be helpful.

Seriously though, they should be good once you get them right. Set and forget? Get out there and blow the doors off a few fat lazy v8s.

I’m in a cheeky mood this morning.


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[I'm a Red Motor fiend]

Yeah, once they are dialled in they will be awesome. Set and forget.
I will persist till they're right.

[LC-GTR-1969]

So I have finally got the donk in the car and up and running.
Felt so bloody good to drive a Torana for the first time in nearly two years.
Took a lot of time to set up the new linkages for the HD8's. Had to fabricate mounts and spring mounts. Chop chop, weld weld, grind grind.
Had to reset the float levels as on the dyno the carbs were perfectly horizontal, in the car they are not.
Put my chopped down 12oz damper springs on the scale, they are now around 10oz.
Running the UL needles still.
Idle AFR is around 13, cruise 14-15, light throttle 13ish. Mash the go peddle and when the cam comes on I'm seeing farkin 10's!!!!
WTF? On the dyno we couldn't achieve max power as it was leaning out, now same setup in car is pig, pig rich.
Can't win.
Put my 5oz damper springs in and it was way too lean so am sticking with my chopped down 10oz ones.
Next will try my UU needles as they have the same curve as the UL's down low but are leaner up top.
If these are still too rich I will go back to UM's which are leaner all the way through.

 

I had a similar issue which was my GROSE needle and seats were vibrating/shaking and unseating, allowing over fuelling. At least that was a problem I had. I suspected over fuelling so put some old VITON tips in there and it stopped it. 

 

May not be your issue but worth a thought. 

[I'm a Red Motor fiend]

I had a similar issue which was my GROSE needle and seats were vibrating/shaking and unseating, allowing over fuelling. At least that was a problem I had. I suspected over fuelling so put some old VITON tips in there and it stopped it.

May not be your issue but worth a thought.

Yeah, ta mate.
If I don't see a change up top with the UU's or UM's will definitely visit this.

[I'm a Red Motor fiend]

Ok so I said I'll stick it out till I dial these carbs in and I will but man my patience is being tested.
I went back to leaner up top UU needles and viton tipped needle and seats.
Mash the throttle and still seeing 10 AFR WOT.
Thought maybe heavier springs were not enabling full piston lift now the motor is in car thus enriching the mixture.
I put my light springs back in and adjusted jet tubes.
Idle high 13's
Cruise high 14's
Half to 3/4 throttle 13 - nice power
WOT I saw a 9!!!
Far out.
I am starting to clutch at straws.
My next train of thought is that it is over fuelling due to the elec. Pump set at 5 p.s.i.
I have run these same carbs on my old engine with a very similar cam with light springs, UM needles and a mechanical pump and AFR's were good.
I am now going to put the UM needles, light springs and wind pressure back to 3 PSI.
If this does not see a big change up top, I don't know. I may go back to a mechanical pump and see.
I know there are a few SU guys on here so if your reading this and have any more ideas jump in please!

[caterham2]

5 PSI is way too high for SU carbs 

[I'm a Red Motor fiend]

5 PSI is way too high for SU carbs

Yes and no. If you bothered to read the thread you would have seen that on the dyno at 5 PSI it was leaning out.

[u1 71]

Adam why did you use an open chamber head ? same deal with the rockers 1.5 on exhaust

[warrenm]

When you say you see "9 at WOT" is that flashing on your O2 sensor screen or is that in a Log? Are you using oil in the dampers? If so what grade? 

[I'm a Red Motor fiend]

Adam why did you use an open chamber head ? same deal with the rockers 1.5 on exhaust

The open chamber is not ideal but was what I started with years ago and have put big dollars into it now. It's a very good 9 port.

1.5 exhaust because I don't need anymore lift there based on the way the head flows.

[I'm a Red Motor fiend]

When you say you see "9 at WOT" is that flashing on your O2 sensor screen or is that in a Log? Are you using oil in the dampers? If so what grade?

Warren, dropped to 9 on the screen when it really starting choking up at WOT.
ATF in the dampers.

[I'm a Red Motor fiend]

Tried SU oil and straight 30 but ATF seemed better.
Give it a run without oil do you think?

[jd lj]

Warren, dropped to 9 on the screen when it really starting choking up at WOT.
ATF in the dampers.

I've found that it's best to do your tuning using the data recorded in the log/traceline as it can be difficult to read a gauge whilst at WOT. By the time you back off even slightly an sneak a glance at the gauge the AFR has changed. Sometimes when the throttles are snapped shut after WOT a momentary rich spije can be seen.

Are your rich AFR's whilst still accelerating?

[I'm a Red Motor fiend]

James, I've only got a basic unit at the moment so gauge only no data log.
With the pedal pinned i can glance at it the whole time and it progressively chokes up 12, 11, 10 and down to nine if i keep it pinned.
Just can't understand the radical turn around from the dyno sessions.
I think I'm pinning my hopes now on over fuelling from high fuel PSI and the violent movement of the engine under acceleration, vibration and gear change.

[I'm a Red Motor fiend]

Warren, you run HD8's don't you?
How far down the jet tube are you setting your float level?

[u1 71]

The original owner of my car replaced the original head with a yt stage 4 low comp one and he said he lost power and went backwards I'd be using 1.6 ratio on the exhaust.did you radius the bottom of your lifters ?

[I'm a Red Motor fiend]

You can still make power with an open chamber head. Power loss between a closed and open chamber head of the same CC capacity would be marginal I would say.
As said, 1.6 on the exhaust is not necessary. The flow figures determined this.

My last Cam was a Clive 191A and he did radius the lifters.
This cam is a custom grind from comp. And to be honest I didn't think of asking whether they radius their lifters or not.
All 12 of them spin so I guess they're fine.

[warrenm]

Warren, you run HD8's don't you?
How far down the jet tube are you setting your float level?

Yes, I do run HD8. I'll have to check my notes, I can't remember at the moment, "Great Northern" virus.

I don't use oil in the dampers of 2'' SU's, always use it with 1 3/4", but ATF(10 weight) when I did.

[LC-GTR-1969]

You can still make power with an open chamber head. Power loss between a closed and open chamber head of the same CC capacity would be marginal I would say.
As said, 1.6 on the exhaust is not necessary. The flow figures determined this.

My last Cam was a Clive 191A and he did radius the lifters.
This cam is a custom grind from comp. And to be honest I didn't think of asking whether they radius their lifters or not.
All 12 of them spin so I guess they're fine.

Nothing wrong with an open chamber head. My last 9 port was open chamber, made 200rwhp with small valves.

I wouldn't be running SUs with 5 psi fuel pressure- might be ok on a dyno but with engine movement, vibration, g forces etc of a driving car, i'd be worried about blowing the needle and seat. I ran a bit under 4psi from memory. With my webers I run 3.5psi.

What float level are you running?

It was a while ago when I ran 2 inch SUs but from memory, I had the float level set about 4mm from the bridge. Think about the placement of your floats as well- g-force can change the level in your floats a little, just something to take note of.

When you say you are seeing rich dips, where on the rpm range is this- is it on the cam or coming onto the cam- what rpm range? Can you feel the engine being pig rich at this time or is it just something you are reading flash up on your wideband?

I found no oil in dashpots was best performance with my 2 inch SUs/ SETON manifold.

When it was on the dyno did you run with your full exhaust? Just trying to think what could be different from dyno to car..

Also, you said when it was on the dyno it went lean up top- did it run like sh*t when lean or did it still run clean... Just wondering here, long shot, but if it was merging to pig rich, an ignition misfire can and does read as a lean condition (unburnt fuel/oxygen, O2 sensor reads the extra oxygen and flashes a lean mix). I doubt this is your issue but keeping an open mind, it may be possible.

Edited by LC-GTR-1969, 28 April 2020 - 07:38 AM.

[I'm a Red Motor fiend]

^^^ thanks mate was hoping you would jump in too.

Im definitely thinking now over fueling from the pressure.
I set my floats the same as you, 4mm down the tube.
Definitely feel the loss of power as it chokes up cam really starts to wake up closer to 5000, and from then on with it pinned just gets progressively richer.

Was just out the pipes on the dyno.

When it was leaning out on the dyno the curve was real messy and was nose diving.

I'm going to go back to 3.5 PSI, run no oil in the dampers and see what she does next.

[warrenm]

With Grose needles & seats set at 5.5/6 psi & Methanol, mine runs fine. With petrol & conventional needles & seats 3 psi is what I use.

Float levels are about 3 to 4mm down the tube, with the tube set .065" down from the bridge.

What plug gaps are you using?

Edited by warrenm, 29 April 2020 - 12:07 AM.