Im collecting bits again

And wondered if any one had sucessfully fitted a jenvey plenum to an rs turbo (with cvh)... You can buy them with blank back plates so it wouldn't bee too much of a faf to get them machined to fit a cvh....

I was more concerned with whether they can be squeezed in rather than how well they flow etc, as every thing I've seen suggests they flow very well etc.

Pics would be great too


Cheers

Rob,

 

I would love one but with itb's it would never fit. Would hit bulkhead

 

Yes I think I remember you saying that in the past, Im not going to run ITB's tho, just one on the inlet.... Reckon it would fit?

 

Hello Rob,

The cvh head - even when properly ported is still a relatively poor flowing cylinder head.
The Jenvey plenum inlet manifolds are designed to flow far in excess of what any CVH head would flow. This would largely be a waste of well earned money - and a mismatch of inlet port cross sectional areas (very important if one is looking for power gains)

Too big an inlet is just as bad as too small an inlet - they must be matched and designed for specific rpm range and engine sizes.

Just my opinion of course.

 

Hi Perry,

Thanks for the reply!

I'm a bit of a gas flow novice tbh but could you tell me why an inlet that outflows a head would be a bad thing?

The runners would be specific to this inlet, ie) have the correct cross sectional area to match the ports so a mismatch wouldn't be present, im aware of the damage mismatched ports etc can do to flow.

Are there any good books/papers specifically about inlet manifold design etc that you could recommend? I have heard so many conflicting opinions about manifold design!

You mention design for a specific power band etc? What design considerations are we talking about? restricting max flow to closer match a head, tailoring plenum volume for a specific application or choosing runner length carefully...? Im assuming that runner length plays a smaller part on a boosted engine than for N/A, IE) long runners wouldn't have such a great effect on low/midrange torque compared to longer runners on the n/a engine.

Would a manifold that could flow a lot (more air than my application needs) be detrimental to power due to a drop in gas velocity? So designing a manifold that could flow a similar amount as my head would presumably mean the highest possible gas velocity as runners etc would be as small as possible whilst not 'strangling' the head?

I've always been under the assumption that reducing flow restriction whilst maintaining an even flow to all cylinders would increase VE, I hadn't considered that one could go too far.... thinking about it though it makes sense, just the same with heads, a massive port means massive flow... but damages gas speed etc.

Cheers

Rob,

 

I remember reading that the plenum volume should be at lease half the engine capacity for a 4 cyl, would a plenum with much larger volume be a bad thing?... I assume turbo lag would be increased with a very big plenum.

 

now this is getting deep

looking forward to reply

i thought a longer runner length (even on a forced induction) would promote higher torque

wish i had the time and money to go in depth with everything

 

as gus said, in a nut shell, longer inlet trumpets/tracts promotote midrange power where a shorter increase peak hp. not sure how this fares in the forced induction world. would speculate its much the same. but i always thought a turbocharged engine can still produce rlatively huge hp/torque on the shittiest of flowing engines compared to n/a equivelant. higher boost rs turbo vs gas flowed xr3i for instance. anyway sorry for the drift, how much are these inlets rob? what is the std inlets max ability in terms hp. i know the head on the rst can manage 250hp before its restrictive.

 

they aint cheap thats for sure

 

They aren't outrageous, I started looking at them because the burton catalog lists them for £600, however this is without a machined back plate (no port holes, trumpets etc) so maybe even cheaper if you go jenvey direct...

The stuff you mention regarding port length is true, I believe it may have a larger effect on a n/a engine... it would be good to get input from some one who specialises in this kind of thing, but they tend to keep their hard earned knowledge to them selves (fair enough i guess).

I don't totally agree with the rst head being restrictive at 250 bhp... its restrictive at lower HP figures too. Its just that it becomes a problem around that figure, ie having to use more and more boost for a smaller HP gain.

IMO, a decent head and inlet manifold would still be advantageous on lower bhp engines, not just because they are more efficient but because they can be tailored to your application as Perry says...

My general aim is for a high 200's (260-280 bhp) car that drives like a 200 bhp escort does with a stage 2 t3.... just faster obviously. So really responsive, nice wide power band etc... compared to most 300 bhp rs turbos which are very peaky and not particularly rewarding to drive on the road, bar the occasional run up a dual carriage way.

 

Yes they do mate, my above sentence was badly written. I've added to the sentence to make it clearer.

 

Karls pushing 400 bhp I'm a Ford inlet manifold all beit highly ported and he has no issues achieving this power. He says its one of the few standard inlets that actually works!!

 

i have always said this

my old engine made 311bhp with a god knows what spec t3 was awesome

very responive and went vey well, should of stayed with that but onwards and upwards

 

not doubing karls work


but

what boost is he running to achieve 400+

with a better flowing inlet could you not achieve similare power with less boost

or what ever power

 

Interesting stuff, its defiantly time to find someone close with a flow bench, it would be great to get some official figures for all the common manifolds.

Rob,

 

I know what ur saying and I'm not doubting anything people say but all Karls figures are done with the o/e manifold both exhaust and inlet. Two of the most commonly changed items on RS turbo's.

The 400 bhp conversion from what Karl tells me has many custom bits but all based around the standard equipment.
I think there's just that many options and opinions here its all down to tuners choice and what think works best.

Roll on another RS turbo thrash in a couple of years I say there's plenty of nice cars in the pipework

 

Hello Rob,

I took a look at the jenvey plenum, and it does look like a good piece.
You are correct that it will require some work - machining and or welding
to get it to work with a CVH. You can certainly modify an existing CVH manifold (lower portion) to work with the plenum. Bell mouths would probably be best? inside the plenum.

Looks like a neat project if you get one.
Be interesting to do a before and after test with a regular manifold and a much modified one with the jenvey plenum up top.