TrophyJem
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| posted on 20/3/14 at 12:48 PM |
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Can I cut down my trumpets?
I acquired a set of AT Power throttle bodies with my engine, but the trumpets are far too long (100mm).
The cost of a shorter set is way prohibitive, so I was wondering if I could just cut them down (ideally to 50mm), by taking a section out of the
middle?
They are not the usual bolt on affair with a flange they are threaded instead. They have a pretty thick wall so I was thinking of cutting them and
then either have them welded or even glue them together.
Thoughts please.....
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Jenko
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| posted on 20/3/14 at 01:16 PM |
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You can do what you want as they are yours :-)
There is no good reason why you cannot shorten them (assume they are parallel rather than tapered). Why do you want to shorten them?....Other thing to
consider is if anyone wants to do a trade for some shorter ones.
MY BLOG - http://westfieldv8.blogspot.co.uk/
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TrophyJem
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| posted on 20/3/14 at 01:25 PM |
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quote:
Originally posted by Jenko
You can do what you want as they are yours :-)
There is no good reason why you cannot shorten them (assume they are parallel rather than tapered). Why do you want to shorten them?....Other thing to
consider is if anyone wants to do a trade for some shorter ones.
I need to shorten them to avoid them sticking out of the side of the bonnet. I already have a hole in the bonnet from the old install, but
unfortunately it doesn't line up, so I'm think a piece of mesh over the current hole and shorter trumpets with the air filter inside the
bonnet.
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jeffw
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| posted on 20/3/14 at 01:40 PM |
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Trumpet length has an effect on the torque curve of an engine. They are almost certainly tapered and I very much doubt you will be able to cut them
and remake them shorter without causing engine issues.
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Jenko
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| posted on 20/3/14 at 01:42 PM |
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Just a thought.....could you keep the length, cut the bonett to fit, then make a plate up with somthing like carbon which covers the old hole and
creates the new one....
MY BLOG - http://westfieldv8.blogspot.co.uk/
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TrophyJem
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| posted on 20/3/14 at 01:45 PM |
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quote:
Originally posted by Jenko
Just a thought.....could you keep the length, cut the bonett to fit, then make a plate up with somthing like carbon which covers the old hole and
creates the new one....
Yes that is the other option I had considered. Just a bit worried about how it would look.
I originally asked for hole filling ideas a while back
http://www.locostbuilders.co.uk/viewthread.php?tid=189339
I was just exploring alternatives
Cheers
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bi22le
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| posted on 20/3/14 at 01:55 PM |
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I went down the longer trumpet and cutting larger hole in bonnet route.
I made a plate up and wrapped it in carbon to make it look smart. having the air filter protrude through the bonnet gaurentees cold air.
The length is critical to where the torque curve peaks. With in reason, the monger the trumpet the more desirable the curve.
If they are cut to 20mm or non existant the engine will still drive but you will notice the difference.
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1
Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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r1_pete
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| posted on 20/3/14 at 01:59 PM |
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This might help you decide, it shows the effect on flow rate of various trumpet designs.
 
Trumpets
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jeffw
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| posted on 20/3/14 at 02:16 PM |
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Bottom line....naffing about with the trumpets will result in a set of wrecked trumpets and you buying a new set...
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TrophyJem
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| posted on 20/3/14 at 02:18 PM |
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There is a definite straight section to the trumpet lower down (away from the mouth). The mouth is tapered.
I am concerned that cutting them down to 50mm long may cause me problems.
If I leave them at 100mm and have them stick through the side of the bonnet then I need to find a very deep air filter.
On the picture below only the right most one has the trumpet fitted, as that was the only one that would fit behind the bonnet.
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40inches
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| posted on 20/3/14 at 02:28 PM |
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Look at the differences between 7,8 & 9 in Pete's diagram, doesn't seem enough to worry about.
And isn't it the complete inlet tract length that governs torque?
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TheGiantTribble
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| posted on 20/3/14 at 02:34 PM |
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Trumpets should be polished and on show.
I mean think of all those beautiful F1 cars from the 1960/1970s all had a row or two of shiny trumpets
and didn't they look grand.
Yes polish your trumpet and flash at the passing pedestrians 
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Jenko
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| posted on 20/3/14 at 03:42 PM |
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There is lots of gumpf out there regarding longer = more torque, smaller = more topend. But most people are restricted by thier cars design in
relation to the inlet. For example, on my build I have very little space for a long inlet, and no doubt I will loose some hp, but there is nothing I
can do about it.....In your case, if it were me, I would figure out a way to keep the length and have the filter poking out into the nice cool air.
I've seen a few cars with made up plates to cover holes and make new ones, and done correctly (with carbon of course), it actually looks quite
good (IMHO).
That said, to shorten them, you would need to cut and weld, and then machine any weld from the inside of the trumpet.....but I don't think this
wouls be the best solution.
MY BLOG - http://westfieldv8.blogspot.co.uk/
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TrophyJem
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| posted on 20/3/14 at 03:47 PM |
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quote:
Originally posted by Jenko
There is lots of gumpf out there regarding longer = more torque, smaller = more topend. But most people are restricted by thier cars design in
relation to the inlet. For example, on my build I have very little space for a long inlet, and no doubt I will loose some hp, but there is nothing I
can do about it.....In your case, if it were me, I would figure out a way to keep the length and have the filter poking out into the nice cool air.
I've seen a few cars with made up plates to cover holes and make new ones, and done correctly (with carbon of course), it actually looks quite
good (IMHO).
That said, to shorten them, you would need to cut and weld, and then machine any weld from the inside of the trumpet.....but I don't think this
wouls be the best solution.
That probably does make a lot of sense.
I just need to find a filter that's over 100mm deep so my trumpets will fit inside. They are proper long!
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theduck
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| posted on 20/3/14 at 03:50 PM |
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Cut hole bigger so that trumpets are central on new big hole. Fill hole with contrasting material (carbon) with smaller hole in middle the right size
for trumpets. Job jobbed.
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Rod Ends
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 posted on 20/3/14 at 04:33 PM |
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Emerald Adjustable Length Intake Trumpet Development
quote:
Based on the testing we have done to date we can draw certain conclusions:
1. The tapered trumpets work no better than the parallel ones.
2. It is the overall length of the induction that is the single most important feature of any throttle body system.
3. A change of just 4mm in overall length gives a measurable change in the torque curve.
4. You only need to re-map the wider throttle settings of the fuel and ignition maps when you change the induction length.
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Slimy38
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| posted on 20/3/14 at 04:55 PM |
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quote:
Originally posted by TrophyJem
I just need to find a filter that's over 100mm deep so my trumpets will fit inside. They are proper long!
Just as a side question, why do you need a deep filter? Don't filters just need to cover the ends?
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TrophyJem
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| posted on 20/3/14 at 05:16 PM |
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quote:
Originally posted by Slimy38
quote:
Originally posted by TrophyJem
I just need to find a filter that's over 100mm deep so my trumpets will fit inside. They are proper long!
Just as a side question, why do you need a deep filter? Don't filters just need to cover the ends?
Because the filter backplate has to be sandwiched between the trumpets and the throttle body pipes.
At least I think it does.
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paulf
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| posted on 20/3/14 at 09:51 PM |
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I would keep them as long as possible, although I worked out that to get the best torque they actually need to stick out of the bonnet by about a foot
which is clearly not possible.If you want to shorten them it looks to me as if the part attached to the manifold is parallel and could easily be
machined shorter and then re threaded to suit the trumpet.
Paul
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pmc_3
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| posted on 21/3/14 at 08:06 AM |
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Could you mesh the existing hole and then use some sock filters inside the bay on the trumpets?
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TrophyJem
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| posted on 21/3/14 at 09:02 AM |
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quote:
Originally posted by pmc_3
Could you mesh the existing hole and then use some sock filters inside the bay on the trumpets?
The trumpets would need cutting down for this, as only one of them will fit inside the bonnet.
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scudderfish
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| posted on 21/3/14 at 11:18 AM |
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Can you not cut them so they are no longer at 90 degrees to the head, but a bit lower so they come out of the hole you have. It should only be a few
degrees.
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sam919
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| posted on 21/3/14 at 01:18 PM |
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Its all been said and some very good points made.
shorter = better bhp less torque
Longer = better torque less bhp/ restriction to amount of air flow.
I doubt unless your racing you'd notice any difference, the links above to emerald are proven and very good info. If you just cut them from the
rolled / trumpet end, you can roll the cut again for a smoother edge, it takes a bit of time but achievable.
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MikeRJ
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| posted on 21/3/14 at 05:39 PM |
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quote:
Originally posted by pmc_3
Could you mesh the existing hole and then use some sock filters inside the bay on the trumpets?
Only if he wants to really strangle the engine. Sock filters flow about as well as a cork.
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