The missing LINKage to more power?
Discussion
Daydreaming the other day about the difficulties our Griffiths have in breathing, I thought back to one of the most basic checks that you can do with an internal combustion engine. Does the pedal actually deliver full throttle? By that, I mean, does the butterfly within the throttlebody sit completely flat allowing maximum flow when the pedal is fully depressed?
With the help of a colleague on the pedal, and the plenum elbow removed, to my surprise, it didn't. In actual fact it had about another 5-10mm of travel, before it became flat and hit the stopper.
Trying to understand how to rectify this was a little baffling at first, as I had assumed it was almost certainly the cable slack adjustment, but on closer inspection, I found play in the main arm of the linkage that strikes the butterfly arm (beneath the vaccuum pipe in the pic).
All that was needed to be done was to adjust the 8mm nut on the end of the throttle return spring closest to the butterfly, (to the right of the vac pipe, above the main axle in the pic) to remove the free play.
Difference...?
Sure is!
In the two years i've been tinkering with/upgrading my griff, this was the one change that made the most difference, not only was it noticably faster, but it actually sounded different at full (now actual full!) throttle. Not only that but the pedal feel got much better with a distict snap open feel!
Seriously guys, every griff and chim deserves a link inspection, your car could be hiding a lot more power!
With the help of a colleague on the pedal, and the plenum elbow removed, to my surprise, it didn't. In actual fact it had about another 5-10mm of travel, before it became flat and hit the stopper.
Trying to understand how to rectify this was a little baffling at first, as I had assumed it was almost certainly the cable slack adjustment, but on closer inspection, I found play in the main arm of the linkage that strikes the butterfly arm (beneath the vaccuum pipe in the pic).
All that was needed to be done was to adjust the 8mm nut on the end of the throttle return spring closest to the butterfly, (to the right of the vac pipe, above the main axle in the pic) to remove the free play.
Difference...?
Sure is!
In the two years i've been tinkering with/upgrading my griff, this was the one change that made the most difference, not only was it noticably faster, but it actually sounded different at full (now actual full!) throttle. Not only that but the pedal feel got much better with a distict snap open feel!
Seriously guys, every griff and chim deserves a link inspection, your car could be hiding a lot more power!
Clearly if the butterfly is not opening fully it will have a detrimental effect on power returns 
Good Post
ETA I see your point but i have had a situation in the past that meant my butterfly was not fully opening so it is also worth taking off the 45 deg hose and checking when the pedal is down that the butterfly is fully open.
Good Post
ETA I see your point but i have had a situation in the past that meant my butterfly was not fully opening so it is also worth taking off the 45 deg hose and checking when the pedal is down that the butterfly is fully open.
Edited by Pasco on Tuesday 2nd September 14:02
Agreed, good post, I would raise a couple of other pointers for peeps though . . Along with the 8mm there are a couple of points to try . . .
1 - Cables do stretch and this restricts the available butterfly aperture . . Hence the adjuster.
2 - On the pedal box there is an adjustable throttle stop, this can also be incorrectly adjusted and also restricst butterfly aperture.
3 - The cables supplied currently that I have been able to get are already a little too long and I've had to wind the throttle stop to it's maximum to make sure the butterfly is competely horizontal at full throttle which it hadn't been when it was last mapped, having recently changed throttle cables. I probably need to do some further adjustment of the throttle spring as yourself to get it spot on otherwise as soon as it stretches I'll have an issue again.
HTH
1 - Cables do stretch and this restricts the available butterfly aperture . . Hence the adjuster.
2 - On the pedal box there is an adjustable throttle stop, this can also be incorrectly adjusted and also restricst butterfly aperture.
3 - The cables supplied currently that I have been able to get are already a little too long and I've had to wind the throttle stop to it's maximum to make sure the butterfly is competely horizontal at full throttle which it hadn't been when it was last mapped, having recently changed throttle cables. I probably need to do some further adjustment of the throttle spring as yourself to get it spot on otherwise as soon as it stretches I'll have an issue again.
HTH
Pasco, my description was a bit waffly as usual but removing the plenum elbow/ 45 degree hose was exactly how I discovered the issue!
V8s I completely agree, after adjusting I recommend a friend opens the throttle fully via pedal, as you examine the linkage and butterfly for stress and flexing.
V8s I completely agree, after adjusting I recommend a friend opens the throttle fully via pedal, as you examine the linkage and butterfly for stress and flexing.
Edited by Hamburglar on Wednesday 3rd September 09:18
HRG said:
just a thought, would this affect the throttle pot setting? (I haven't actually been out to the garage to look yet!)
Shouldn't; that's keyed to the butterfly spindle. The pot voltage is set up from a closed throttle position. Whenever I'm about to go on the rollers I always check for backlash and make sure the throttle stop is contacted when the pedal is burried (Jenvy).
HRG said:
just a thought, would this affect the throttle pot setting? (I haven't actually been out to the garage to look yet!)
Not on a standard set up as Bruce has highlighted it is set from full stop.However, you can move the full stop as it is adjustable and if you set the throttle cable wrongly.
If you're using an aftermarket such as Emerald then you do need ot reset this in the map every time you change the throttle fixed position so that the variable positions correspond to the load sites programmed.
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