Polishing for airflow - myth or not?

Post by **GeorgeHurst** » Tue Dec 08, 2009 12:18 am

Hello,

I recently bought a 'Flowtech' inlet manifold from eBay (metro type alloy inlet) to go with my 940 head.

The manifold is quite light in weight and has a very evidently uneven surface inside, as if it has been carved out with a small lino cutter. My father, who used to have a kit car company and who I consequently respect for mechanical advice, said that it should be polished inside. However Vizard states 'polishing ports does little or nothing to improve flow' (p 174, 3rd edition).

I'm wondering if I have bought a duff manifold - I can find nothing about 'flowtech' online and wonder if is trying to be 'psuedo Tourquemaster' with a racey name.

Any thoughts?

George

Also, just quickly, do I need anything other than the 4 studs and the thick spacer to connect a HIF carb to one of these manifolds? Are there any gaskets involved? Cheers

Post by **bmcecosse** » Tue Dec 08, 2009 12:27 am

Yes there are gaskets - and you should 'smooth' the manifold as best you can - but Vizard's point is - no need to 'polish' it! In other words - take away any rough marks/casting irregularities and ease the curves where you can - but don't aim for a chrome finish! He also has a neat trick involving cutting into the thick spacer and the manifold - to ease the junction between carb face and inlet runners. But - unless going for a full race 1300 engine (in which case use 2 X HIF44!!) I doubt you will notice any difference - that carb will give all the airflow you need.

Post by **GeorgeHurst** » Tue Dec 08, 2009 12:35 am

Cheers BM, will look into Vizards trick out of interest, but if effects are neglible may not go for it, certainly not building a 1300 race engine (if only!

).

I now understand what Vizard is saying, thanks, the inside of my manifold is seriously rough, it literally looks like a lino cut, and smoothing it out even to a 'cast' finish would be more effort than it's worth IMO. Have been offered a PECO inlet for a reasonable price, so will take that instead I think.

Cheers

Post by **MikeNash** » Tue Dec 08, 2009 7:29 am

George,
See PM, MikeN.

Post by **Peetee** » Tue Dec 08, 2009 8:31 am

My understanding of the water heated inlets were that they produced and 'copied' by many manufacturers and were sized for either 1.5 or 1.75 carbs. If your was the former it may have been bored out for the latter.

Post by **GeorgeHurst** » Tue Dec 08, 2009 11:32 am

Hi Mike,
I can't see a pm I'm afraid, can you send again?

Peetee, the inlet bore is 1.75" so you may well be right on that...

Cheers
George

Post by **bmcecosse** » Tue Dec 08, 2009 12:14 pm

There's no harm in the larger bore - even if using the smaller HIF38 carb. Any chance of a picture of the 'Flowtech' item ?

Post by **MikeNash** » Tue Dec 08, 2009 8:53 pm

George,
Sent another PM (twice) but not sure if the system is functioning properly. Anyway, if you've now got a spare intake I'm interested in buying your old one! MikeN.

Post by **GeorgeHurst** » Wed Dec 09, 2009 6:48 pm

Hi Mike, I'm afraid I still don't have the message. Another member has messaged me about purchasing it, but you got there just before him, so I think it fair to offer you first refusal. PM should be with you soon!

Roy, the inlet is at my parents house at the moment, so I won't be able to get a picture until next week, but will upload a couple if you are interested when I get back down there.

Post by **bmcecosse** » Thu Dec 10, 2009 12:31 am

Thanks - just for general interest to see how it looks!

Post by **GeorgeHurst** » Thu Dec 17, 2009 10:08 pm

For those that are interested here are some photos and dimensions of the Flowtech inlet manifold...

Carb facing bore: 44mm
Head facing bores: 31mm
Distance from carb face to head face (from 'above'): ~80mm
Distance from carb face to head face (from 'below'): ~105mm

Photos to follow...

Post by **GeorgeHurst** » Thu Dec 17, 2009 10:09 pm

For those that are interested here are some photos and dimensions of the Flowtech inlet manifold...

Carb facing bore: 44mm
Head facing bores: 31mm
Distance from carb face to head face (from 'above'): ~80mm
Distance from carb face to head face (from 'below'): ~105mm

Photos to follow...

Post by **GeorgeHurst** » Thu Dec 17, 2009 10:09 pm

Post by **GeorgeHurst** » Thu Dec 17, 2009 10:10 pm

From 'below'...

Post by **GeorgeHurst** » Thu Dec 17, 2009 10:10 pm

View of interior surface, from carb face...

Post by **bmcecosse** » Thu Dec 17, 2009 10:33 pm

Thanks for the pics! Pretty much like the MG Metro - it could certainly take some grinding to smooth the walls - and in that last pic above - you can see how if you fit the thick plastic spacer and then grind into the wall at the edge and part way through the spacer - you can easily improve the flow at each side. Only relevant if using an HIF44 of course!

Post by **GeorgeHurst** » Thu Dec 17, 2009 10:38 pm

No probs

I'm going to sell it as I bought an HIF38 with manifold, heatshield, spacer etc as one let on eBay so it's now surplus to requirement

Post by **MikeNash** » Fri Dec 18, 2009 1:31 pm

George,
Hope this gets through! If the intake is still available I'll buy it! But clearly its first come first served. Regards, MikeN.

I'm on 01264 -736530 if that helps.

Post by **GeorgeHurst** » Fri Dec 18, 2009 1:46 pm

Please note, manifold now sold to Mike