Anybody made their own plenum spacer?
Discussion
I did a CAD profile and thanks to afriend of Dave (V8GRF) we had some cut out. They were cut from 12mm thick marine Tufnol. I ran mine for a while and it seemed ok. The car ran the same but the plenum was noticeably cooler.
I now run a spacer under the trumpet base made from the same material.
I now run a spacer under the trumpet base made from the same material.
I was reading somewhere that the 5.0 benefits slightly from a larger volume within the plenum and there's a company that sells a space, but it it work out around £120. I've ordered a thermal plate with my induction kit, so that should help with the hear transfer. I was just wondering about increasing the height of the plenum a little?
Just remove the damned ellusive trumpets & blend the base, saves you a fortune as well as weight & less parts = less weight, less to go wrong, no shrouding......
It also allows you to increase the CSA of the trumpet base to inlet manifold throat once you can profile the shape rather than be forced into using circles. Not just the CSA but also you can begin to flow the air towards the manifold bends to help.
You certainly would pick up on these flow deficiencies on any head porting ~ why do you think the trumpet base & manifold should be that much different in approach?
It also allows you to increase the CSA of the trumpet base to inlet manifold throat once you can profile the shape rather than be forced into using circles. Not just the CSA but also you can begin to flow the air towards the manifold bends to help.
You certainly would pick up on these flow deficiencies on any head porting ~ why do you think the trumpet base & manifold should be that much different in approach?
I'm no expert David, in fact fairly new to the world of TVR. I have been reading a lot, but as usual there are a lot of different theories and it is difficult to make sense of what is best and what isn't. One of the things I have read about reducing the size of the trumpets or blending the base is a loss of torque. It's one of the things I like about my car. How much would a blended effect the torque by? It's obviously a cheaper route than the trumpets.
Folks will tell you all sorts, but AFIK I am the only person that has ever significantly altered the inside of the inlet manifold and that is always going to limit the flow changes you make to the trumpets/upper inlet manifold tracts.
Joo did quite a lot of testing with his rolling road on this area. When he stuck a 5 litre engine in his own V8S, suffice it to say he used a blended base. Don't confuse that with some of the reports on him testing a plastic insert to create a blended base (which he wasn't too impressed with). As a rough guide you may lose a little torque, it'll just shift higher in the range, but gain significant bhp generally. Each base has been done differently, I would imagine a mildly ported base would have similar torque to the 500 flared trumpet configs, just making a radius at the top and tapering out the step that the trumpets sit in should be enough. I would advise having the base welded up first though ~ needs bits of ally cutting / grinding to fill the voids & then welding into place + filling, so you can grind on solid metal.
Joo did quite a lot of testing with his rolling road on this area. When he stuck a 5 litre engine in his own V8S, suffice it to say he used a blended base. Don't confuse that with some of the reports on him testing a plastic insert to create a blended base (which he wasn't too impressed with). As a rough guide you may lose a little torque, it'll just shift higher in the range, but gain significant bhp generally. Each base has been done differently, I would imagine a mildly ported base would have similar torque to the 500 flared trumpet configs, just making a radius at the top and tapering out the step that the trumpets sit in should be enough. I would advise having the base welded up first though ~ needs bits of ally cutting / grinding to fill the voids & then welding into place + filling, so you can grind on solid metal.
chris1972 said:
That's interesting. Aren't you a little worried about the bit breaking off and being sucked into the engine?
I am a little worried about most things with my track record 
No. As i said i drilled the voids open so a whole piece cannot break away. I cant see a reason for smaller pieces breaking off. The chemical metal was added in one go and worked back to profile.
You will see a few areas that could be a little tidier but i am happy with it. If i do another i know i can do a neater job and will take into account Daves comments on blending towards the ports.
My 4.6 runs very well with it and torque is good throughout.
A thick nylon chef's chopping board can be used to make a plenum spacer. My own car suffered no loss of response for the fitting of one, quite the opposite (it did coincide with shortening the trumpets however).
Now use the alloy 45mm trumpets with enlarged base openings matched to a ported inlet manifold - whilst I expect a trumpetless base would flow just as well or better, I prefer to keep trumpets for the simple reason I still use manifold vacuum driven crankcase breathing and no matter what traps are used, oil residue will find its way into the plenum. This (mostly) will pool on the base srface (or in the inter-trumpet voids), whereas without trumpets it would mostly be going into the chambers. There's also the fact that Helmholz theory says a clearly defined tube termination gives a stronger pulse signal... whether the pulses are working for or agianst you is another matter of course
Having got it working how I like it, I expect a whole new can of worms will open once the hair-drier is added...
Now use the alloy 45mm trumpets with enlarged base openings matched to a ported inlet manifold - whilst I expect a trumpetless base would flow just as well or better, I prefer to keep trumpets for the simple reason I still use manifold vacuum driven crankcase breathing and no matter what traps are used, oil residue will find its way into the plenum. This (mostly) will pool on the base srface (or in the inter-trumpet voids), whereas without trumpets it would mostly be going into the chambers. There's also the fact that Helmholz theory says a clearly defined tube termination gives a stronger pulse signal... whether the pulses are working for or agianst you is another matter of course
Having got it working how I like it, I expect a whole new can of worms will open once the hair-drier is added...
Pupp said:
..I prefer to keep trumpets for the simple reason I still use manifold vacuum driven crankcase breathing and no matter what traps are used, oil residue will find its way into the plenum. This (mostly) will pool on the base srface (or in the inter-trumpet voids), whereas without trumpets it would mostly be going into the chambers.
Sounds logical, but those voids have drain holes at the bottom so the oil ends up in the inlet tract anyway... so no difference in reality...As for Helmholtz, the radius on the end is what counts ~ the tube is the trumpet base. Consider trumpets fitted to carbs/TBs that sit on a blanking plate to enclose the air filter?
V8 GRF said:
As mentioned by Derek we made one from Tufnol but I ended up taking it off as it didn't seem to make any noticeable difference. I still have the CAD profile somewhere.
ETA it ended up considerably cheaper than the £120 you mention
Looked at the Tufnol. A £15 sheet and a jigsaw and you're away!ETA it ended up considerably cheaper than the £120 you mention
Edited by V8 GRF on Thursday 25th April 12:00
spend said:
Sounds logical, but those voids have drain holes at the bottom so the oil ends up in the inlet tract anyway... so no difference in reality...
As for Helmholtz, the radius on the end is what counts ~ the tube is the trumpet base. Consider trumpets fitted to carbs/TBs that sit on a blanking plate to enclose the air filter?
Think someone must have blocked my void holes then; maybe they're full of spare mushroom breather valves! As for Helmholtz, the radius on the end is what counts ~ the tube is the trumpet base. Consider trumpets fitted to carbs/TBs that sit on a blanking plate to enclose the air filter?
db418BHP said:
I am a little worried about most things with my track record
No. As i said i drilled the voids open so a whole piece cannot break away. I cant see a reason for smaller pieces breaking off. The chemical metal was added in one go and worked back to profile.
You will see a few areas that could be a little tidier but i am happy with it. If i do another i know i can do a neater job and will take into account Daves comments on blending towards the ports.
My 4.6 runs very well with it and torque is good throughout.
What did you use to machine the ports? Die grinder?No. As i said i drilled the voids open so a whole piece cannot break away. I cant see a reason for smaller pieces breaking off. The chemical metal was added in one go and worked back to profile.
You will see a few areas that could be a little tidier but i am happy with it. If i do another i know i can do a neater job and will take into account Daves comments on blending towards the ports.
My 4.6 runs very well with it and torque is good throughout.
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