Manifold trickery

[petervr6 0]

hmmmm ive just got my self a polished 2.9 manifold for 50 quid

[petervr6 0]

thinking it not worth it now if you lost low down power.

[dstyrrell 0]

I used to have loads of these types of plans until i spoke to my friend thats a motorsport engineer(very clever guy, the type that designs F1 cars) and he made me realise that there is alot more to it and also i'm afraid to say that alot of the things that are on the market for tuning are basically cr*p, and alot of the things that are supposed to work actually dont.

Basically the 2.9 manifold works with a 2.9 engine because its tuned to, someone has calculated the optimum intake manifold size that'll maintain a good air delivery pressure throughout the rev range based on the cylinder displacement of the 2.9 engine , without forced induction putting a bigger air intake on will actually have an adverse effect.

Analogy

Imaging using a suction pump to take water from a well, with a smaller hose(normal manifold) the water is easy to get from the well to the pump and out the other side at a good pressure using that size pump, but with a larger diametre hose(large manifold) getting the water to the same sized pump is alot harder work and it comes with less pressure(poor bottom end) ,and too keep it flowing with reasonable pressure at a good rate you must keep the speed of the pump higher(top end gain). The only ways the large pipe will work economically throughout is

1. Larger pump (bigger cylinder=more suction)

which is why the 2.9 has bigger manifold.

or

2. Push more water into the sucking pump (Forced induction)

This would deliver the larger quantity at a good pressure throughout, which we know works.

More air is great but it needs to be compact so the pressure of delivery is important.

This is my view on the situation anyway, i think it makes sense.

Dave

[clarkie 1]

finaly got it finished. just need 2 start sanding and polishing now

[gav_113 0]

get polishing stu, and after that i'll drop mine rnd!! ha ha

[bigdong101 0]

Cool, fair play on getting a bit done on the manifold, see you've plugged the top sides of spark plug holes but not removed the actual holes and undersides. Was it a bit of an after-thought or something??

I'll make a start on my 2.9 clone manifold once it's passed an MoT and the stereo's sorted! Ciao

[Bazmcc 0]

I managed to snipe a 2.9 manifold on ebay for under £60.

I'm in the process of polishing it at the minute and i'm seriously considering making a polishing attachment for the drill and doing the insides of the runners. Has anyone tried an inside and out poilsh?? What about getting it completely chromed smooth? It's bound to increase airflow.

Baz

Baz

[dstyrrell 0]

PUTTING A LARGER INTAKE MANIFOLD ON YOUR CAR WILL LOOSE YOU BOTTOM END AND POLISHED SURFACES WILL REDUCE AIRFLOW!!!, I CAN SEE WHY YOU WOULD THINK THESE THINGS WILL HELP BUT THEY DON'T, YOU ARE WASTING YOUR TIME AND MONEY.

AS FAR AS THE WHOLE MIRROR POLISHED INLETS TOPIC GOES, THINK ABOUT A GOLF BALL, WONDER WHY IT HAS DIMPLES ON IT??? ITS BECAUSE THEY MAKE IT TRAVEL THROUGH THE AIR BETTER...SAME GOES FOR SURFACE AERODYNAMICS THE AIR WILL TRAVEL OVER A ROUGH SURFACE BETTER THAN A SMOOTH BECAUSE AIR GETS TRAPPED IN THE ROUGH CREATING A SURFACE OF AIR WHICH OFFERS LESS RESISTANCE. DON'T BELIEVE ME, HIT A SMOOTH GOLF BALL THEN A DIMPLED GOLFBALL SEE WHICH TRAVELS BETTER.

READ THE SCIENTIFICAL FACTS ON HERE, http://en.wikipedia.org/wiki/Cylinder_head_porting#The_.22Porting_and_Polishing.22_Myth

I'M SORRY IF I COME ACCROSS AS BEING NEGATIVE BUT I'M TRYING TO PREVENT PEOPLE WASTING THERE TIME AND MONEY, I WOULD SAY THAT YOU WOULD POSSIBLY GAIN FROM LARGER INTAKE IF FORCE INDUCTION IS IN PLACE. iF YOU READ THE ARTICLE IT EVEN SAYS THAT 'SOMETIMES REDUCING INTAKE SIZES MAKES IMPROVEMENTS'.

JUST TRYING TO HELP GUYS.

DAVE

[clarkie 1]

depends what engine you have. mine is a 2.9 so it will be better for mine.

[gav_113 0]

dave why are u shouting! lol

[dstyrrell 0]

Gav sorry to shout mate, i felt like this required 'caps lock'.lol.

Clarkie obviously if you have a 2.9 engine you would have a 2.9 manifold, this would obviously work better because the manifold is designed for that engine with that cylinder displacement. My point is that putting a larger manifold on will hinder low down torque you might gain top end bhp but it will take you longer to get there. This is different if you have forced inducion.

I was just trying to be friendly and stop people wasting time and money.

Dave

[Bazmcc 0]

Cheers Dave - I know what you mean about the aerofoil and turbulance properties. My intention is at some stage to go to 2.9 but for now I'll just have a nice polished 2.9 manifold (only on the outside for looks though). When I do my engine rebuild I'll just be honing the cylinders unless there's any problems or major wear. If there is, i'll be going to 2.9 to kill 2 birds with one stone. I think I can even get a 2.9 block complete so that might even save some cash. The guy who will be doing my remap is VERY good as well and he'll be sorting out a nice smooth power curve and combined with my other mods and a well lightened car, I think that the loss of low end torgue might not be as noticable. Then there's always the option of a SC but i'll stick with all motor for a while first. A lot of the guys on vortex have dynoed the 2.9 mani mod and found if gives them a little boost in the hp numbers. And if that's the case then so be it and I'm happy enough to accept the loss in torque for the time being. It'd be nice if we all had short runner intakes but we have VR6s so our pockets aren't exactly overflowing.

Baz

[Steve @ 1]

Got a spare 2.9 Corrado manifold if anyones interested?

[dstyrrell 0]

Cheers Dave - I know what you mean about the aerofoil and turbulance properties. My intention is at some stage to go to 2.9 but for now I'll just have a nice polished 2.9 manifold (only on the outside for looks though). When I do my engine rebuild I'll just be honing the cylinders unless there's any problems or major wear. If there is' date=' i'll be going to 2.9 to kill 2 birds with one stone. I think I can even get a 2.9 block complete so that might even save some cash. The guy who will be doing my remap is VERY good as well and he'll be sorting out a nice smooth power curve and combined with my other mods and a well lightened car, I think that the loss of low end torgue might not be as noticable. Then there's always the option of a SC but i'll stick with all motor for a while first. A lot of the guys on vortex have dynoed the 2.9 mani mod and found if gives them a little boost in the hp numbers. And if that's the case then so be it and I'm happy enough to accept the loss in torque for the time being. It'd be nice if we all had short runner intakes but we have VR6s so our pockets aren't exactly overflowing.

Baz

[/quote']

Baz,

If you get you get a 2.9 block and use a 2.9 manifold you will basically have a 2.9 VR6 which will work fine, i can't understand why you would sacrifice low end torque(which is what makes your VR push you in your seat and fun) for top end bhp? If anything i find my VR a little sluggish below 3grand anyway the last thing i'd want to do is make it worse and have to rev the shit out of it constantly.

Just my opinion anyway.

Good luck mate

Dave

[gavinvr6 0]

i agree with dstyrrell on that, i also think that my vr is sluggish from idle to 3 grand but once you hit 3200 rpm all hell breaks loose right up to the red line, surely it would be better to improve that bottom end section and get that torque all the way from idle, but playing devils advocate i do dis-agree with the rough surface airflow thingy, i can see how it makes perfect sense and yes a dimpled ball does go better but if that were the case why have people been smoothing out the ports for years and all saying it works? and why do car manufacturers try to produce smooth flowing lines?

[dstyrrell 0]

i agree with dstyrrell on that, i also think that my vr is sluggish from idle to 3 grand but once you hit 3200 rpm all hell breaks loose right up to the red line, surely it would be better to improve that bottom end section and get that torque all the way from idle, but playing devils advocate i do dis-agree with the rough surface airflow thingy, i can see how it makes perfect sense and yes a dimpled ball does go better but if that were the case why have people been smoothing out the ports for years and all saying it works? and why do car manufacturers try to produce smooth flowing lines?

They all say it works because someone has told them it does,probably the person thats getting paid to do the work, If you don't know about something in depth its easy to be convinced, anyone would logically think that a completely smooth surface would offer less resistance but in reality the air almost sticks to it, as i said before the reason a ruffed surface is better is because air traps in the surface producing a surface of air, what better surface for air to travel over than air?. This is obviously with reference to engine internals, having golf ball dimples all over the outside of car would probably help airflow but wouldn't look that good and be a pain to clean. LOL.

[FishWick 21]

Interesting thread!

OBD2 has the smallest bore throttle plate and body of all VR engines.

OBD1 Golf and Corrado share the same size throttle plate, but the Corrado body deletes the ramp that the Golf body has in it, and is instead replaced with a 2 stage linkage.

The reason the Corrado got these changes was for high rev gas flow. They wanted it to be the flagship VW in terms of top speed, so they made if flow more air at the top end and raised the rev limit.

The 2.9 capacity means practically nothing in real terms over the 2.8, it's barely noticable, but was enough in combination with the aforementioned mods to get the Corrado up to 146mph (book speed), which is all VW were interested in. The 2.9 does pull a little harder from 4000rpm but not so much as to pull out a massive lead over a 2.8.

Personally, I think the 2.8 OBD2 engine is the best of the lot. It's the torquiest and certainly matches the 2.9 on power.

In reality though, no standard Corrado gets close to hitting the rev limit in 5th, so it's all a bit of a wasted effort on VW's part imo. Just gives you a little more revs to play with through the gears.

I wonder if that's why 2.9s wear out faster? The extended rev limit.....

[RIX 0]

Interesting thread!

OBD2 has the smallest bore throttle plate and body of all VR engines.

OBD1 Golf and Corrado share the same size throttle plate' date=' but the Corrado body deletes the ramp that the Golf body has in it, and is instead replaced with a 2 stage linkage.

[/quote']

i have had my hands on a 97 trottlebody(golf vr6 2.8)

and it´s 72mm

from what iknow the obd1 body is 64mm,so are you british cars strange ore what

i have now found out that what i thort i knew was not true in regards to all obd2 cars have the big manifold that nots true,but they du have 72mm trottle body at least in dk and germany.

also the last comment is not thrue the 2 stage linkage is not on a 2.9 body nore as you said the lip

Best Regards

RIX

[petervr6 0]

So i think what the thread is about is it work fitting the 2.9 manifold to a 2.8 golf please reply

YES

or

NO

Cheers pete.

[FishWick 21]

NO it isn't worth it.

Rix, the 2.9 body DOES have a 2 stage linkage. Want me to take a picture of it and prove it to you?

In my garage I have OBD1 Golf, OBD1 Corrado and OBD2 throttles, so I know what I'm talking about.

Obviously things are different over there but I am speaking in the context of UK cars.

[dstyrrell 0]

So i think what the thread is about is it work fitting the 2.9 manifold to a 2.8 golf please reply

YES

or

NO

Cheers pete.

I think that you'll all know my answer

NO

[RIX 0]

i keep for getting that sorry,my syncro golf dosn´t have that stupid link thing