ITB Jenvey Inlet Manifolds - Downdraft vs Crossover
Discussion
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
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
If it is merely in need of piston rings it might only cost you one limb - not two. 
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?
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?
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.
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.
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
http://www.mez.co.uk/ms12-new.html
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.
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. 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.
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.
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
a mate has cross over on his chimaera, under the bonnet but hes had a few issues getting everything to work
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
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
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