ITB Jenvey Inlet Manifolds - Downdraft vs Crossover

ITB Jenvey Inlet Manifolds - Downdraft vs Crossover

Author
Discussion

Matthew Poxon

Original Poster:

5,277 posts

133 months

Sunday 9th September 2018
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Evening Gents

The engine in the Griff is sounding very unheathy at the moment so I am going to get it rebuilt. I am thinking of taking this opportunity to do something with the inlet manifold. Since seeing Ian Rose's and Andy Race's Griffiths with the individual throttle bodies I have had a burning desire to fit them to my Griff.

I am aware they are not going to add a massive amount of horsepower for the price, my primary goals are noise and throttle response.

I am looking for some advice for the pros and cons for each design. The solution I choose must fit under the bonnet of a TVR Griffith.

What I really fancy is a set of downdraft ITBs the same design as the TVR Tuscan Challenge 4.5 RV8s but instead of carbs fit Jenvey TBs.

I have found this picture and this looks like a good solution, my only concern is no airbox and short runners. I note the bonnet has been raised on this Griff but I have looked at mine and I believe the bonnet with standard catch should still close.



Ian Rose's car has the JE cross over manifold which features airboxes and definitely fits under the TVR bonnet. The runners are nice and long and also straighter. My only concern with this is that I do not think the taller TVR logo rocker covers will fit and I would like to run roller rockers.



Does anyone have any advice to help me make a decision.

Matthew

TV8

2,901 posts

135 months

Monday 10th September 2018
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Hi Matt,

I saw the video on Facebook and sorry that you need the rebuild. Who is going to build it for you?

Matthew Poxon

Original Poster:

5,277 posts

133 months

Monday 10th September 2018
quotequote all
Hi Graham,

Thank you sir. I knew it was coming as it is the original engine. I need to shop around but so far TVR Powers 5 year warranty is looking quite attractive.

QBee

17,903 posts

104 months

Monday 10th September 2018
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If it is merely in need of piston rings it might only cost you one limb - not two. wobble

Couple of years ago my Saab Turbo was drinking oil at one hell of a rate at 130,000 miles, and was diagnosed as piston rings by Mat Smith.
He was of course correct, he always is, and did the job without even removing the engine.
He also replaced the timing chain, as it was looser than a tart's trousseau, cleaned up the bores, changed the crankshaft shells and replaced the head gasket, as all were jobs that could be done while he was in there.

So perhaps initially worth going for a bit of a diagnose?

rev-erend

20,653 posts

244 months

Monday 10th September 2018
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Hi

I very much doubt if the down draft manifolds and TB's on top will fit under a standard bonnet without putting a bonnet scoop on it.

Dougal9887

223 posts

41 months

Wednesday 19th September 2018
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I'm looking at going to the JE crossover with gsxr 1000 throttle bodies and a Cerb style intake arrangement. Chimaera 500/Megasquirt.
This manifold is currently unavailable due to the casting mould having worn out. I spoke to JE earlier in the year, he'd taken the decision to have the mould remade, at considerable cost, and hopes to have new castings ready for machining by the end of this year.
I will be in his neck of the woods in November so am hoping to visit him, armed with the throttle bodies, and hope to measure up for cam cover clearance etc.
I could do a similar conversion using short inlet stubs and downdraft direction throttle bodies but I think torque would be compromised.

rev-erend

20,653 posts

244 months

Wednesday 19th September 2018
quotequote all
Take a look at the Rover V8 inlet archive..may things have en tried. The guy who did the bike TB's sold them soon after I believe.

http://www.mez.co.uk/ms12-new.html

Dougal9887

223 posts

41 months

Wednesday 19th September 2018
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Yes, I had seen that. Doesn't mean it can't work however. I have converted my Lotus Twincam to run on gsxr 600 tb's which is a huge success. Just need to transfer the technology to a V8 😀. As I see it a throttle body is a throttle body, it's all about the installation, setup and tuning.

rev-erend

20,653 posts

244 months

Wednesday 19th September 2018
quotequote all
Fair comment.

There was a nice lotus twin cam at the Brighton Speed trial, he did rather well.

My car is in the mainfold list. I now have an airbox.


Dougal9887

223 posts

41 months

Thursday 20th September 2018
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Supercool!

Slow M

2,581 posts

166 months

Tuesday 16th October 2018
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Dougal9887 said:
I'm looking at going to the JE crossover with gsxr 1000 throttle bodies and a Cerb style intake arrangement. Chimaera 500/Megasquirt.
This manifold is currently unavailable due to the casting mould having worn out. I spoke to JE earlier in the year, he'd taken the decision to have the mould remade, at considerable cost, and hopes to have new castings ready for machining by the end of this year.
I will be in his neck of the woods in November so am hoping to visit him, armed with the throttle bodies, and hope to measure up for cam cover clearance etc.
I could do a similar conversion using short inlet stubs and downdraft direction throttle bodies but I think torque would be compromised.
Shorter intake runners may not “compromise torque,” but quite likely will move the peak torque and peak hp higher in the rev band. If you know someone with the Pipemax software, they could run a simulation dyno sheet, to let you know what the new torque and power curves could be expected to look like.

My personal take, is that for a high performance car, area under the curve is much more important, than peak numbers. High peak numbers are good for dyno shoot-outs, and bragging rights. Considering that some dyno shoot-outs award cash prizes, I can see the point.

Best,
B.

spitfire4v8

3,441 posts

141 months

Tuesday 16th October 2018
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It's even easier than that .. it's the area under the curve in the rev range you're going to be using for performance. If you're foot to the floor at 2000rpm you either bought the wrong car, are lazy, or your gearlever has fallen off and you're stuck in too-high a gear.

phazed

19,272 posts

164 months

Tuesday 16th October 2018
quotequote all
spitfire4v8 said:
It's even easier than that .. If you're foot to the floor at 2000rpm you are lazy.
Are you alluding to my car Jooles? biggrin

spitfire4v8

3,441 posts

141 months

Tuesday 16th October 2018
quotequote all
phazed said:
spitfire4v8 said:
It's even easier than that .. If you're foot to the floor at 2000rpm you are lazy.
Are you alluding to my car Jooles? biggrin
hehe

Graham

16,340 posts

244 months

Wednesday 24th October 2018
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Ive got downdraft 45 jenvies on my 5 ltr in the challenge car. long trumpets two fiters and no air box. makes good power and transforms the thottle response. they do stick through my bonnet though..

a mate has cross over on his chimaera, under the bonnet but hes had a few issues getting everything to work

spitfire4v8

3,441 posts

141 months

Wednesday 24th October 2018
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I know certainly one car which had its crossover manifold replaced with a plenum. Long runners and injectors well upstream don't make happy bedfellows.

TarmacRV8

49 posts

33 months

Tuesday 6th November 2018
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Hi matt,
Short runners and downdraught are old school, will be good for throttle response but not power.
Long runners allow the air to build momentum(its a fluid)and inertia.
I have je crossover with 50mm itb.
Only prob is injector so far from intake valve which is not ideal for a street car seeing alot if low rpm.
Once on song its fine and becomes cleaner. There is a slight lag with throttle response due to distance.
Carbies or a plenum prob better in mist circumstances.
If serious about crossover and investing in cost. Do it properly ,Engine built as a complete system, ta heads, including equal length exhaust primaries, makes for a beautiful sounding rv8 with big gain in hp and torqueIf you have std rover casting heads it will be for looks and sound.
Roller rockers will fit with slight internal clearancing off rocker covers

griffdude

1,667 posts

208 months

Wednesday 7th November 2018
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Here you go, this chap’s got some for sale...

https://www.pistonheads.com/gassing/topic.asp?h=0&...

rev-erend

20,653 posts

244 months

Wednesday 7th November 2018
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That will get removed soon.. against posting rules.