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St170 Inlet Manifold


MarkB
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The set up I have is bike carbs that have been poorly spaced, so I'm weighing my options up at the moment, getting the original throttle bodies is one option I'm considering, replacing the current carbs with fireblade carbs is another

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Hi Mark

The ST has much bigger inlets ,The manifold would have to be port matched to cylinder head.

Regards Paul

 

Hi Paul,

Please can you delineate between head port size and manifold port size.

 

The 2 part Silvertop aluminum inlet manifold, the part which bolts to the head has bigger ports than the horrid Blcaktop plastic thing by some way. Hence my thirst for knowledge.

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I've just fitted my spare ST engine. I've been fiddling with it for the last three months. Slight rise in CR to 10.8:1, inlet ports cleaned up, exhausts ports opened up from 22mm to 25mm. Fixed adjustable pulley on inlet. Exhaust changed to 4:2:1 with 1.75" primaries, 2" secondaries and 2.25" tail. Ports and manifolds matched and dowelled. Jenvies and omex. As usual full of hope that this is going to perform well.

You look at the ST engine and think it must be way more powerful than a blacktop. Then you run them on the rollers and they always disappoint (so far). I still think a blacktop engine is the better base. The ST suffers such a sharp power drop off at 6000rpm that it's like hitting a brick wall when the engine has only just come on cam and it just won't rev. Safe to 7,500 but not worth going over 6000! What's that all about? I can't work out if it's the cams or the tiny exhaust ports. (The standard ST exhaust valve should have a port that's a minimum of 26mm diameter. From the factory it comes with 22mm! Is this for emissions?)

I know I hear people who have the ST fitted rave about it. Lots quote near 200 bhp for a standard engine and 20 more for a little extra work. It is the highest BHP figure engine I have had in the car. The car is fast. Corners come towards you too quickly. Why don't I love it? To add to the woes I've just found a report that the ST head is a bit bendy if skimmed. Brilliant, not!

I still think a standard blacktop is a better drive. Way broader power band and revs to 7500. Better torque. Less power sure but more usable. Add in some cams and a little head work and you have a genuine 220 and a far better drive.

This engine is my last effort at making the ST perform as it seems it should. If it doesn't rev on the rollers next week then it's losing its head and a standard blacktop head is going on in it's place.

Just needed to get that off my chest!

 

Nigel

 

In answer to the original question, yes, all inlet bolt holes match up and it fits fine. You will need to port match quite a bit.

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The ST170 has much bigger ports... The manifold pattern is the same however.

 

The ST170 will make just shy of 200bhp on throttle bodies, wheras a blacktop will make 170bhp, thats the tried and tested differences, and shows how much better the head on the ST is.

 

The ST170 bottom end is steel as well IIRC, and substantially stronger, allowing higher RPM range.

 

Nigel is right though, if we were recommending to a customer, we would say start with the blacktop, and go from there. Cams and TBs see similar power to the ST, without the hassle of VVT lockout etc.

 

Matt

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The ST170 will make just shy of 200bhp on throttle bodies

My engine was obviously very very shy. My point about the ST is the way the power crashes above 6000rpm.

The ST170 bottom end is steel as well IIRC, and substantially stronger, allowing higher RPM range.

Hardly worth having the steel crank and flash rods. I think Ford must have sussed that because they didn't bother to put decent pistons in! Why would you if the thing only produces power to 6000? Maybe it ran better with fully variable cam advance in the focus.

 

Nigel

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Ours seems to stay very (hp wise) level up until 7k, but yes, the torque was falling.

 

http://www.rhocar.org/index.php?showtopic=21527&view=findpost&p=171142

 

The VVT was only really did something around idle and up to around 1500rpm, was more for emissions than anything else. Drive an ST170 focus, they are gutless! Fors 'could' of made a good job of it, maybe they ran out of development money :)

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