Bonnet jiggling
Discussion
Don't be so quick to jump in and buy new rollers.
Have you had a look at the slots they run in?
My rollers are in decent nick, its the GRP which has a slight groove worn in it where the rollers naturally sit, and this allows the rollers to lift with the air pressure at speed, making it look like its flapping about.
If you google GRIFFITH SPLITTER you will find loads of discussions on it.
here is one to get you started
http://www.pistonheads.com/GASSING/topic.asp?h=0&a...
Have you had a look at the slots they run in?
My rollers are in decent nick, its the GRP which has a slight groove worn in it where the rollers naturally sit, and this allows the rollers to lift with the air pressure at speed, making it look like its flapping about.
If you google GRIFFITH SPLITTER you will find loads of discussions on it.
here is one to get you started
http://www.pistonheads.com/GASSING/topic.asp?h=0&a...
Edited by Barreti on Thursday 18th December 17:16
Backseatdriver said:
My bonnet is jiggling around and lifting slightly at the front when at driving at speed. Is there a simple fix for this?
The previous owner put Velcro tape on the GRP guide/runner, that has been quite effective and is easily replaced. Having said that, at speed the bonnet does a bit of jiggling, mainly because the whole fixing is very imprecise.As for the splitter, I can't comment whether that will help but I have two knocking about, which you are welcome to take a copy from. They are only bent aluminium plate. Both my Griffs have the splitter removed. Pete
It would probably take an aerodynamisist to explain the actual working/action of the air-dam, but the way I see it, is that the dam creates a pressure ahead of it, forcing air thru the rad, which gets expelled via the bonnet gap/outlet, which in turn creates a slight underpressure in the engine bay keeping it cool(ish) and holding the bonnet down ?
Backseatdriver said:
Thanks for that, what do you mean by a splitter, also can new rollers be purchased from anywhere.
Hi Backseatdriver, PM me, I have some spare splitters from a batch I had made last year when I supplied our local TVRCC group (Griff & Chim). My design, works really well on my Griff, also improved my cooling! Regards, Petebluezeeland said:
It would probably take an aerodynamisist to explain the actual working/action of the air-dam, but the way I see it, is that the dam creates a pressure ahead of it, forcing air thru the rad, which gets expelled via the bonnet gap/outlet, which in turn creates a slight underpressure in the engine bay keeping it cool(ish) and holding the bonnet down ?
Actually it's the opposite. It creates an area of negative air pressure in the area behind the radiator and as a result draws air through the radiator, which is expelled both over and under the bonnet. Cooling was the primary function of the splitter but the negative air pressure has the added benefit of pulling the bonnet down.It works as I've driven many miles both with and without the splitter and when it's missing the bonnet flutters at motorway speeds and doesn't when its fitted.
V8 GRF said:
bluezeeland said:
It would probably take an aerodynamisist to explain the actual working/action of the air-dam, but the way I see it, is that the dam creates a pressure ahead of it, forcing air thru the rad, which gets expelled via the bonnet gap/outlet, which in turn creates a slight underpressure in the engine bay keeping it cool(ish) and holding the bonnet down ?
Actually it's the opposite. It creates an area of negative air pressure in the area behind the radiator and as a result draws air through the radiator, which is expelled both over and under the bonnet. Cooling was the primary function of the splitter but the negative air pressure has the added benefit of pulling the bonnet down.It works as I've driven many miles both with and without the splitter and when it's missing the bonnet flutters at motorway speeds and doesn't when its fitted.
ah, I see !
For some reason I've always found aerodynamics fascinating...
What you're saying is more or less the same principle applies as with a rear spoiler, creating down-force or an ailleron on a plane creating uplift ?
When I was on the hunt for a Griff, one of them had this bonnet vents (a la Chim) but aren't they then negating the effect of the splitter ?
Would it be possible to vent the warm air from the engine bay, for instance thru a double venturi under the car ?
Frank
(@OP, sorry for the partial hyjack...)
bluezeeland said:
What you're saying is more or less the same principle applies as with a rear spoiler, creating down-force or an ailleron on a plane creating uplift ?
When I was on the hunt for a Griff, one of them had this bonnet vents (a la Chim) but aren't they then negating the effect of the splitter ?
Would it be possible to vent the warm air from the engine bay, for instance thru a double venturi under the car ?
Yes I guess it's an upside down 'Gurney flap' in effect. I've never liked calling it a splitter as it doesn't perform the same function which obviously is to 'split' airflow.When I was on the hunt for a Griff, one of them had this bonnet vents (a la Chim) but aren't they then negating the effect of the splitter ?
Would it be possible to vent the warm air from the engine bay, for instance thru a double venturi under the car ?
I believe the area created is actually quite small and localised so I'm not sure the effect is spoilt by the bonnet vents. I think you'd need to complex panels to duct the air away and as the exhausts are in the way I think you'd struggle to do anything worthwhile and it's probably not a good idea to introduce extra air under the car at the front as that can lead to instability.
From personal experience the bonnet vents and splitter work extremely well together and made a dramatic improvement to the cooling on my precat, it’s very noticeable that my cooling fans now run a lot less. I wouldn’t of thought the improvements would be so noticeable on a 500 with the opened up front end but I do now consider them essential on a precat.
V8 GRF said:
Yes I guess it's an upside down 'Gurney flap' in effect.
That sounds worrying as an upside down 'Gurney flap' would create lift that can cause instability so I’m pleased to hear you go on to say its V8 GRF said:
I believe the area created is actually quite small and localised
Therefore I would suggest an aluminium splitter so you can bend it up to limit its effect and also suit your local speed ramps, I can also confirm the vents and splitter together didn’t cause any “Bonnet jiggling”.stevesprint said:
V8 GRF said:
Yes I guess it's an upside down 'Gurney flap' in effect.
That sounds worrying as an upside down 'Gurney flap' would create lift that can cause instability so I’m pleased to hear you go on to say its V8 GRF said:
I believe the area created is actually quite small and localised
Therefore I would suggest an aluminium splitter so you can bend it up to limit its effect and also suit your local speed ramps, I can also confirm the vents and splitter together didn’t cause any “Bonnet jiggling”.The fact that the one as fitted by the factory is also aluminium and has a quite shallow angle would bear out your last comment.
stevesprint said:
From personal experience the bonnet vents and splitter work extremely well together and made a dramatic improvement to the cooling on my precat, it’s very noticeable that my cooling fans now run a lot less. I wouldn’t of thought the improvements would be so noticeable on a 500 with the opened up front end but I do now consider them essential on a precat.
Thanks for sharing that ! Will consider installing one then..Gassing Station | Griffith | Top of Page | What's New | My Stuff