V7 SLR Posted November 1, 2003 Share Posted November 1, 2003 What's the optimum length trumpet for a 1.8K? ISTR someone (PC?) having experimented and coming up with a figure. Can't find this in the archive. Is there any benefit from going longer? Any deficit? Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
Jason Plato Posted November 1, 2003 Share Posted November 1, 2003 I was experimenting with trumpet lengths on my 1600K , I ended up using 130mm trumpets which I had made up especially for me plus 19mm spacers . These changed the tuned pulse to the tune of +22bhp and +24lb torque in the mid range vs 90mm trumpets . It also meant that the trumpets now poke out of the bonnet , which is fine as I want a cold air feed anyway . Peter was also at emerald on the same day and tried my trumpets - with no gains on his 1800 . Peter will tell you that my timing was not optimised -but I have failed to find any more power by using the timing since that day . I believe that the 1600 needs a different length to the 1800 ,and the exhaust , cams and head being used also has different requirements . I dont know of anyone else who has done any practical tuned length work on the 1800 , maybe you should do some experiments as I did Nige ? Just be aware that the length of trumpet will need to clear the crossmember and you will have to make your own backplate and filter arrangement to fix onto the trumpets . Plus the long trumpets are bloody loud !!! Dave Edited by - Dave Jackson on 1 Nov 2003 10:47:05 Link to comment Share on other sites More sharing options...
Steve-B Posted November 1, 2003 Share Posted November 1, 2003 didn't we have a debate on this on Tour7 about 3-4 months ago 🤔i can check to see if i ratholed away the articles.... Steve B Big Black Beast^3 SV VHPD Join us on the USA 2005 tour......HERE Link to comment Share on other sites More sharing options...
V7 SLR Posted November 1, 2003 Author Share Posted November 1, 2003 Thanks Dave. I may indeed have a play, however this is a question relating to a friend who has an ingeneous-looking home-made long-trumpet setup. Er, hyphen monitor..!! Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
oilyhands Posted November 2, 2003 Share Posted November 2, 2003 A friend has been playing with an unequal length trumpet setup, some extraordinarily long trumpets on two cylinders and some not quite so long trumpets on the other two. Together with cylinder trims for the fuelling this has produced some quite large gains at the bottom end and mid range with no loss of grunt at the top. His setup in other respects is near identical to yours Nigel. Oily Link to comment Share on other sites More sharing options...
Rob Walker Posted November 2, 2003 Share Posted November 2, 2003 Dave, I think you are forgetting the little fact that you also replaced your cams from the 740 to 1227 grind and this accounts for most of your gains. Link to comment Share on other sites More sharing options...
AMMO Posted November 2, 2003 Share Posted November 2, 2003 Oily I suggested an unequal set up some time ago. People seemed to poo poo it. Glad to see it that somebody has tried this in practice and that it worked. It is common on four cylinder Superbikes. My bellmouths are attached to the Weber throttle bodies with rubber hoses and clips. This means I can shorten or lengthen the induction system. On the rolling road it worked best with the system as long as it would go (not a surprise). Stupidly I never ran two long and two short. Must try this at some point. AMMO Link to comment Share on other sites More sharing options...
Steve-B Posted November 2, 2003 Share Posted November 2, 2003 oily, it would be very interesting to learn a bit more of this experiment. the trumpet sizes, etc. can you elaborate a bit more on this please 🤔 Steve B Big Black Beast^3 SV VHPD Join us on the USA 2005 tour......HERE Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted November 2, 2003 Share Posted November 2, 2003 Hope this doesn't come as a double post but seemed to loose my last one. someone in sweeden is now making a variable length trumpet system which could be of interest. Bill Link to comment Share on other sites More sharing options...
Steve-B Posted November 2, 2003 Share Posted November 2, 2003 bill, would that be telescopic / adjustable. if so that could have interesting uses for differing road situations. BTW, didn't one of the WRC teams get in trouble for some kind of variable trumpet or was it throat to a trumpet... Steve B Big Black Beast^3 SV VHPD Join us on the USA 2005 tour......HERE Link to comment Share on other sites More sharing options...
Jason Plato Posted November 2, 2003 Share Posted November 2, 2003 No your wrong Rob . The back to back tests on the trumpets were done with the 1227 cams installed . The 24lb torque and 24bhp gain was in the mid range . The peak bhp was 210. The swop from 740 cams to 1227 was done at the same time as relapping the valves , more head work , slight head skim , accralite pistons and remap . That produced 206 bhp up from 186 bhp , on 90mm trumpets . Lotus 7 Club Speed Champion 2003 South Wales Area Organiser C7 TOP Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted November 2, 2003 Share Posted November 2, 2003 http://home.swipnet.se/jpmotorsport/E/justerba.htm Link to comment Share on other sites More sharing options...
Steve-B Posted November 2, 2003 Share Posted November 2, 2003 wow--that's an amazing bit of kit Bill. seems one could take a tachometer feed if i read their site + 12VDC. any idea the cost, if you don't know i may contact them to find out. might be an amazing project Steve B Big Black Beast^3 SV VHPD Join us on the USA 2005 tour......HERE Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted November 2, 2003 Share Posted November 2, 2003 Its on my todo list to contact them to see if they have UK distribution and, if they don't if they want it :-) Particularly pertinent for me, as I have dyno evidence to show that a 2" change of length at 7000 RPM would give me 15HP more at 5500 than the optimum length for top end. I haven't looked at a plot for hopped up K to see what the effects could be though. Bill Link to comment Share on other sites More sharing options...
Jason Plato Posted November 3, 2003 Share Posted November 3, 2003 Bill do you want a copy of my graphs , with the comparative 90mm vs 130mm ?? Dave Link to comment Share on other sites More sharing options...
AMMO Posted November 3, 2003 Share Posted November 3, 2003 Bill and Steve We did a prototype variable length induction system for Suzuki in 1998. First of all we dynoed the engine with bellmouths that went up in length in 5 mm increments. We then overlaid the graphs to get the best midrange and top end power. This gave us the best lengths. The induction system was left short for top end. It had additional trumpets that dropped in to the fixed trumpets for the bottom end and midrange. These were all on a plate that was solenoid operated. It ran on the dyno fine. Due to the fact that that the injectors were external and the limited space available under the tank it never ran on a bike. Two long and two short trumpets were used instead. Dave I wouldn't mind seeing copies of your graphs too if that's OK. What duration and lift are 1227 cams? AMMO Link to comment Share on other sites More sharing options...
Jason Plato Posted November 3, 2003 Share Posted November 3, 2003 Ammo / Bill , I need your email address to send the graphs , please email me off line david.jackson@petersfood.com Ta Lotus 7 Club Speed Champion 2003 South Wales Area Organiser C7 TOP Link to comment Share on other sites More sharing options...
Mike Bees Posted November 3, 2003 Share Posted November 3, 2003 Ammo - #835 cam (virtually identical to #1227 I believe) is quoted as 280 deg. duration, 11.5mm lift. Don't know where the duration is quoted from (e.g. is it from fully closed). Mike Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted November 3, 2003 Share Posted November 3, 2003 Fascinating plots. Will need some time to work out what's what though. Please be patient Bill Link to comment Share on other sites More sharing options...
Peter Carmichael Posted November 3, 2003 Share Posted November 3, 2003 Dave's plots do make interesting reading. The torque on a tuned K tends to come in in a series of steps (usually 3 of them) depending on how the resonances build up. If you shift the steps further down the rev range, then the "riser" of the next step starts to take off where the torque was previously heading along the "tread" of the step. This can show some very big numbers for improvement in torque and power, as Dave's plots show. Usually it is the way with resonances that if you win at one point in the rev range you lose in another. The gain in mid-range torque has to be weighed against the possibility of more power right at the top end of the rev range. Again in Dave's case this didn't happen, so longer trumpets gave a clear advantage. Whn we tried this on my 1.8 there was no equivalent advantage. The give and take of the resonances were much smaller. I commented at the time that Dave's plots looked like mine before we sorted out the cam timing. It might take quite a bit of experimenting to find the sweet spot, but in my case, the power perked up from 238bhp to 253bhp as a result of a 1.5degree advance in exhaust cam timing as compared to the book spec for the cams. The torque was also up everywhere from 4000rpm, removing the up and down vagaries of the power delivery. Hmmm. Writing about it is making me kind of wistful and makes me wonder about the bits in the garage... Link to comment Share on other sites More sharing options...
V7 SLR Posted November 3, 2003 Author Share Posted November 3, 2003 Peter, don't you have a trick inlet or exhaust cam too? Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted November 4, 2003 Share Posted November 4, 2003 Computer committed suicide last night, so didn't get as far as I hoped but did sanity check the graphs and compare with the numbers I have for W111 FLY which is a broadly similar power curve with short trumpets and a 4-2-1 exhaust setup. I hoped to do some reverse engineering on the plots to try and work out which are the critical resonance modes, but this will have to wait. In the meantime an idea off the overall length from head to end of trumpet would be useful, so I can at least get the malboro packet out to see if we are dealing mainly with open or closed valve resonances. If I can get a handle on that, then we can start to match the mainly empirical results we have against theory and see if that sheds any light on things. In the mean time (and remembering that I am not a K owner so approaching this entirely from what the book says ,whilst noting that the engine hasn't read the book) I can say the following. 1. Torque is very flat above the peak 2. Power is still rising at peak RPM 3. The longer trumpets do give a handy additional power boost at 5500-6500 RPM (although it is possible that you needed more fuel for the shorter trumpet). So, assuming that you are not intending to rev to 8500 and that you want a fast road car as well as a track toy and are not totally obsessed with dyno headline w@nk value, I would try and drop the peak torque another 300-400RPM. This should fill in a bit more around 5000RPM as the power ramps up and only cost you maybe 1 or 2HP at the redline and will make the car quicker in real use. Basically its optimising the area between peak torque and peak power. So 20-40mm more on the inlet should do it. TWM do some spacers for this, and I'm sure jenvey has something. Bill Link to comment Share on other sites More sharing options...
Jason Plato Posted November 4, 2003 Share Posted November 4, 2003 Bill , Your comments on my graphs are welcome I have since also fitted a 4-2-1 manifold and on the road this *feels* as if the 2 dips have been reduced , for instance the rear wheels now light up in 3rd at 5000 rpm when exiting roundabouts where as before it wouldnt come alive untill 5750 rpm . Of course only the rolling road will tell if the manifold has improved things - this will be tested in the near future ....... I can easily extend the trumpets another 40mm with some spacers on the base of the existing trumpets . I may try and get these in readiness for the rollers I will measure the length of the total inlet tonite . So far we have 130mm trumpets + 19mm spacers + the depth of the DTHTB's Anyone know the depth of the DTHTB's ???? The power was still rising at peak : 7950rpm , I wish I could have reved it out to 8600rpm to see what happens but I'm afraid the crank may go pop Dave Lotus 7 Club Speed Champion 2003 South Wales Area Organiser C7 TOP Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted November 4, 2003 Share Posted November 4, 2003 Forgot to add. Those sliding trumpets are about a grand. If they get back to me I'll see what can be done about getting that a little cheaper with a change in materials. Still good value compared to carbon fibre wings though. Bill Link to comment Share on other sites More sharing options...
Jason Plato Posted November 6, 2003 Share Posted November 6, 2003 On the rollers I would also like to try the 2 x long trumpets @ 170 mm and 2 short trumpets @ 130mm . What will happen to the fueling ? Do you realy need individual cylinder control for this task ? So far on my plan of experiement I have 12 tests I would like to try , I think I'm gonna have to reduce these to 4 or 5 ..... Lotus 7 Club Speed Champion 2003 South Wales Area Organiser C7 TOP Link to comment Share on other sites More sharing options...
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