Technical Big Bob

[allanhelen]

Oldschool has seen this thread, and I was waiting for him to chip in, but I suppose I had better fill you in.

He sees no restriction with the current 899 bob design. If I recall right, the bob inlet is fine because the throttle butterfly and associated gubbins brings down the overall cross sectional area. Also the air flows fastest in the middle and this is where the butterfly and associated gubbins is, so therefore the current bob inlet should flow just fine. That was the general consensus. Whether this would still apply with a 40mm TB I don't know.

I seem to remember a post from Tricker a while ago something along the lines that that in normalish trim the normal GSR kit (ie bob) was fine but at 40mm plus at higher revs there was some question about airflow.

I have a GSR and and well pleased with the result and i am not questioning the the reseach behind it, as I respect the the work that oldschool does but if there is more available above this then i want it and if it isn't there then i don't mind helping to get it

 

[Fivehundred]

Has anyone ever tested a Novitec air box against a GSR against some of the other solutions that are out there on the same car on a rolling road?

The novitec solution keep the Sporting airbox which sits on top of the throttle body, and then just replaces the front part of it. There's a photo of it in my "productive day" thread.

 

[arc]

He sees no restriction with the current 899 bob design. If I recall right, the bob inlet is fine because the throttle butterfly and associated gubbins brings down the overall cross sectional area. Also the air flows fastest in the middle and this is where the butterfly and associated gubbins is, so therefore the current bob inlet should flow just fine. That was the general consensus. Whether this would still apply with a 40mm TB I don't know.

or 43mm, as that is what my car will be running when i put the bloody thing back together!

 

[arc]

also, if john couldn't get more than 70bhp using the 899 bob - but changing just that allowed for more power, it's a fair assumption that the bob was causing the problem.

 

[sei tan]

Tricker, your points are appreciated, no offence taken.
Allen, i think all of your points are achievable apart from the last one
as the parts and labour would be too much to achieve everything else.
i'm still unsure though which would be better, a smooth 90 degree bend on the top or a side entry?

 

[Fivehundred]

also, if john couldn't get more than 70bhp using the 899 bob - but changing just that allowed for more power, it's a fair assumption that the bob was causing the problem.

But he took it off completely whilst mapping the car. Now that's fine, it tells us there is a restriction but in the real world there is a bonnet sitting just above the throttle body. Somehow whatever you use has to turn the air through 90 degrees, fit in the available space and draw air from a reasonably cool space.

I've only seen two fundamentally different approaches, the GSR approach which removes the whole assembly and the Novitec approach which retains half the original airbox which I think was also tried by Hormann.

There are umpteen different ways of doing the first one, people are using the 899 bob a la GSR, silicone hose corners directly onto the throttle body, bits of domestic plumbing or you can build a bespoke bob. It seems to me that it would be interesting to see if there is some actual data available before charging off in a particular direction.

 

[Italian Coke Can]

My mate (main mechanic) has banned me from buying a GSR kit. He wants to base my new airbox on the Novitec design, but some mods at the back of the airbox to smooth out the flow.

I’m tempted to do the best I can with a home grown kit, then run them back to back on a dyno (if they don’t charge me the earth).

 

[bad_boy_cinq]

I’m tempted to do the best I can with a home grown kit, then run them back to back on a dyno (if they don’t charge me the earth).

Thats the main problem the cost of the dyno runs, ill hopefully be putting mine on the dyno again soon to see if there is any difference between the 899 bob and the one that i have got on now. I found a different bob at the scrap yard yesterday (i think it was off a bravo) its bigger and slightly taller and the intake pipe is around 45mm. It needs minor adjustment to fit as its fitted the other way round on the bravo. Ill get some pics up later but so far there seems to be a difference.

 

[T.E.D. Jordan]

was up at matts earlier, he seems to have found a decent (fiat ) solution, as his Bob only needs minor modifications to fit the 40mm TB, it has the same ID as the seating base of the TB so it seats well and tight and only needs the original bolt hles moothed over and the new two added, perfect for someone wanting a cheap solution from the scrappies, has at least a 45mm inlet too so would be perfect for the select few running 43mm TB's looks quite good too!

Jordan

 

[rallycinq]

Until they go on the rollers its only supposition, but it can't be worse, I don't think.

Cheers

D

 

[bad_boy_cinq]

Until they go on the rollers its only supposition, but it can't be worse, I don't think.

Cheers

D

Thats true, ill hopefully run my car on the dyno soon, perhaps myself and jordan can book a joint session and get his base reading from that.

 

[bad_boy_cinq]

Well jordan and i went down to the Dyno centre today, ran my car with the larger "bob" and it had no effect it lost around 5 BHP and the torque was also down. Im not to sure if its now to large and causing vortexes in the air flow.

 

[arc]

did you do back to back dyno runs with the big bob and the other one?

 

[T.E.D. Jordan]

yeh think we did (i was sortign out my car at that time so only caught the second run he did) but i think he ran it with standard bob first time and with the new one the new time

Jordan

 

[nitrane.co.uk]

But he took it off completely whilst mapping the car. Now that's fine, it tells us there is a restriction but in the real world there is a bonnet sitting just above the throttle body. Somehow whatever you use has to turn the air through 90 degrees, fit in the available space and draw air from a reasonably cool space.

Indeed the bonnet is there, but there is approximately 90mm usable height to get a new airbox in (much more than the 899 bob allows), and that's on my car which has MPi so the TB sits a lot higher than a SPi TB.

There are 2 issues with the 899 bob. First it has a 38mm inlet - my TB is 43mm. QED. Secondly the top of the bob sits in close proximity to the top of the TB, creating the possibility of resonance in the inlet manifold.

Best solution is a stable volumous source of air into the TB. Watch this space...

John

 

[nitrane.co.uk]

He sees no restriction with the current 899 bob design. If I recall right, the bob inlet is fine because the throttle butterfly and associated gubbins brings down the overall cross sectional area. Also the air flows fastest in the middle and this is where the butterfly and associated gubbins is, so therefore the current bob inlet should flow just fine. That was the general consensus. Whether this would still apply with a 40mm TB I don't know.

I don't want to get tedious about this, but my RR experience is that the 899 bob in my application restricted the power to around 70bhp. So its use is fine in std tune engines where you want to sort out the inadequacies of the std air box design. Go beyond that and it really strangles the engine above 4000rpm - remember my working rev range is 5-7000rpm.

On another point, the butterfly does not reduce the flow by the 300mm2 difference that the Tricker TB is worth.

John

 

[Fivehundred]

If the MPI throttle body is higher than the SPI 1242 throttle body you won't get a Novitec airbox in the space, I struggled to do it on a 1242 SPI with a Punto throttle body.

I accept your findings, if the car makes more power without the bob, than with, then there are improvements to be found. It just strikes me that the solution should be looked at as a whole. With the induction kit design there is a large hose with a bend in it, another potential flow restrictor.
When creating a new solution from scratch it may therefore be worth to also look at a redesigned version the original design with a fairly large chamber sitting on top of the throttle body drawing in air from the front of the car. There is room to considerably increase the opening size by going that route.

Indeed the bonnet is there, but there is approximately 90mm usable height to get a new airbox in (much more than the 899 bob allows), and that's on my car which has MPi so the TB sits a lot higher than a SPi TB.

There are 2 issues with the 899 bob. First it has a 38mm inlet - my TB is 43mm. QED. Secondly the top of the bob sits in close proximity to the top of the TB, creating the possibility of resonance in the inlet manifold.

Best solution is a stable volumous source of air into the TB. Watch this space...

John

 

[nitrane.co.uk]

I accept your findings, if the car makes more power without the bob, than with, then there are improvements to be found. It just strikes me that the solution should be looked at as a whole. With the induction kit design there is a large hose with a bend in it, another potential flow restrictor.
When creating a new solution from scratch it may therefore be worth to also look at a redesigned version the original design with a fairly large chamber sitting on top of the throttle body drawing in air from the front of the car. There is room to considerably increase the opening size by going that route.

I agree about finding an ideal solution to the problem, however there's no sense in throwing the baby out with the bath water. Yes the GSR hose has a 90deg bend in it, but it has a 70mm ID and a fairly open bend. It is a also connected to a massively oversized filter (I know of a 500bhp Sierra Cosworth that uses something similar).

So designing something to match on to a cut down GSR hose is a good technical solution, as well as being an affordable one for those that have already spent £100 on an induction kit.

Not forgetting that although the GSR kit is a compromise (to make it affordable) it is perfectly acceptable for modest power gains - its just not good enough for serious tuning.

John

 

[Fivehundred]

Absolutely, again I wasn't bashing the GSR, it does what it does perfectly well, and is as you say, it was designed as an initial upgrade to an essentially standard car. It does that at a price that is affordable to many and that should be applauded.

I'll be interested to learn how you get on with this, best of luck with it.

Peter