41mn vs 45mm throttle bodies
Discussion
Simply...power.
You won't be making the most of your 1585cc engine as you are not allowing it to breath to its full potential.
As an estimate you would be talking around 5-10hp.
On the other hand it will start work and should be up on your 1500, just make sure you get it mapped to suit.
You won't be making the most of your 1585cc engine as you are not allowing it to breath to its full potential.
As an estimate you would be talking around 5-10hp.
On the other hand it will start work and should be up on your 1500, just make sure you get it mapped to suit.
Do the bored out Gen 1 TBs actually work?
Quite a few years ago I did a load of flowbench development on a Gen 1 cylinder head (including big valves) and found the standard 46mm TBs restricted the developed head flow considerably. So we bored the TBs out and fitted the 48mm butterflies, back on the flow bench found absolutely zero flow increase. To find out what was going on we took the butterflies and spindles out of a standard TB and a bored out TB (plugged spindle holes obviously) and then found that the bored out TBs did then give a good flow increase over the standard ones. Thats no good though if you can't have spindles and butterflies installed to realise the improvement.
My conclusion was that the spindles and butterflies were too close to the rubber mounts to the head making the taper too short messing the flow up. We ended up ditching the bored out TBs and went straight to 50mm TBs to reduce the restriction. Even on the 1400cc engine it would still take full throttle at 3000 rpm and rev to well over 11000 rpm.
Quite a few years ago I did a load of flowbench development on a Gen 1 cylinder head (including big valves) and found the standard 46mm TBs restricted the developed head flow considerably. So we bored the TBs out and fitted the 48mm butterflies, back on the flow bench found absolutely zero flow increase. To find out what was going on we took the butterflies and spindles out of a standard TB and a bored out TB (plugged spindle holes obviously) and then found that the bored out TBs did then give a good flow increase over the standard ones. Thats no good though if you can't have spindles and butterflies installed to realise the improvement.
My conclusion was that the spindles and butterflies were too close to the rubber mounts to the head making the taper too short messing the flow up. We ended up ditching the bored out TBs and went straight to 50mm TBs to reduce the restriction. Even on the 1400cc engine it would still take full throttle at 3000 rpm and rev to well over 11000 rpm.
I just wondered if anyone had found that the bored out throttle bodies actually worked or not as it is quite a bit of work to do and then find they don't make any difference. Following my flow tests I personally wouldn't bother with them but we never actually ran them on the engine, only on the cylinder head on the flow bench. The flow bench is steady state flow whereas running the engine isn't so there may be a difference, unlikely though but if someone has genuine data to prove different or to prove either way that would be great.
I think the 50s were SBD/Jenvey items but it was about 8 years ago I did these tests so there might be other ones (or proper 48s that will do the same job) available now. It will also depend on the spec of the head as to whether it needs bigger TBs at all.
Hopefully Dan will be able to provide more info for you?
I think the 50s were SBD/Jenvey items but it was about 8 years ago I did these tests so there might be other ones (or proper 48s that will do the same job) available now. It will also depend on the spec of the head as to whether it needs bigger TBs at all.
Hopefully Dan will be able to provide more info for you?
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