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Topic: 24V Cossie (SaveTheNight) (Read 710 times) |
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howiedintheplace
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Based near Evesham
 
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24V Cossie (SaveTheNight)
« on: Jun 8th, 2005, 3:25pm » |
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Anyone got any ideas, I think Bill may have the answers thou?
Firstly I am building a 3.7L 24V Cosworth BOB.
Using the 4.0L crank, forged pistons with total seals, brand new Std heads, a girdle brace to support the bottom end so it can rev @ 7000rpm & new valve timming gear. It will also be turbo charged using 2x T3's & running Emerald engine management.
Firstly the cams: they are ground with a autobox in mind but I am fitting a manual so any ideas for after market cams?
Second. I was intending to use some cast manifolds for the turbo's, BOA's redrilled to suit the BOB as they are easy to get but is there any point going tubaluar tuned lengths on a turbo car? Don't have much space.
Also back pressure? I will have no CATS & the engine is designed for them so the loss in back pressure will mean the engine will not be as good as it could be as I will loose half my fuel down the exhaust. Any ideas?
I know the turbo's will generate some.
STN how you getting on with the chain guide testing?
Any other surgestions.
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Dave
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DJWerkz
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Re: 24V Cossie (SaveTheNight)
« Reply #2 on: Jun 9th, 2005, 10:46pm » |
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A 'stroked' turbo Cossie, sounds very interesting, I would much rather see someone go naturaly aspirated with a 'stroked' 350 V8 block though.
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Baz
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S Reg. 1998 24v Cosworth S2.9 COS (Deceased)
Posts: 4009
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Re: 24V Cossie (SaveTheNight)
« Reply #3 on: Jun 10th, 2005, 1:57am » |
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It amazes me why someone would want to take a car that does 18mpg round town and then deliberately make it do even less!!!
£1.34 a mile for the new charges would probably be cheaper than the petrol duty!
But it really does sound interesting...............any pictures?
Baz
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howiedintheplace
Senior Member
Based near Evesham
Posts: 1194
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Re: 24V Cossie (SaveTheNight)
« Reply #4 on: Jun 11th, 2005, 10:10pm » |
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Baz this engine is not about fuel economy mate thou it will be running 3.13 diffs & a 0.75 top gear. Will be about 2300 rpm at 70 mph so should not be too bad on the motorway. Computer reckons it will be about 14 mpg on average. This car is not meant for going down the shops in?
Here is some pics
Piston
Cast manifolds
Tube Manifolds
New BOB engine
3.7L BOB
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Dave
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craig
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Re: 24V Cossie (SaveTheNight)
« Reply #5 on: Jun 12th, 2005, 8:09am » |
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that looks a bit tasty..
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Ultima_Alan
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2.0i 16v Ultima
Posts: 66
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Re: 24V Cossie (SaveTheNight)
« Reply #6 on: Jun 12th, 2005, 9:38am » |
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Thats looks very pretty
Any chance of building me one when your done with yours ??.... LOL
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SaveTheNight
Senior Member
I can resist anything ...except temptation !!
 
Posts: 1961
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Re: 24V Cossie (SaveTheNight)
« Reply #7 on: Jun 12th, 2005, 10:12am » |
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Hiya Dave .. I presume that you're using an Explorer crank ? .. obviously the cams are pretty important and as Snoopy says, Piper is certainly worth an enquiry as they know their stuff but the cams can be experimented with later if necessary ..maybe even think about using BOA timing settings instead of the BOB plates < we can have a natter about that later though > .. the manifolds worry me quite a bit but I guess you are very aware of what will be going on there .. the collection is a bit suspect and fairly certainly not strong enough for the turbo < but I haven't seen the turbo configuration yet > ..they look like Fitz's Top Boss manifolds I think ? ..are you after torque or power and where ? .. I'm afraid that I disagree about back pressure and apart from two-strokes.. it's my opinion that no engine built ever required back pressure and back pressure cannot scientifically create HP.. EVER !! .. the turbos self created back pressure will assist of course but ONLY in silencing which as you know will give you loads of choices in silencers , mufflers or none at all ..as you aren't going to have noise problems like a normally apirated motor ... I would probably run a race cat and very little else perhaps other than a very good resonator .. we can talk about it anyway ... take care mate ... regards ........ STN
looking forward to seeing it progress and on the road !! nice one Dave .........
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howiedintheplace
Senior Member
Based near Evesham
Posts: 1194
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Re: 24V Cossie (SaveTheNight)
« Reply #8 on: Jun 13th, 2005, 12:07am » |
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STN
I am trying to decide on a exhaust which is why I'm thinking about the back pressure thing. Anyway it's true 99% of engines don't need back pressure but going on what others have found with the BOA Cossie it does?
It appears to need some, otherwise the fuel economy gets worse & power drops as well. I guess it's the same for the BOB as they are very close?
My understanding of why the BOB needs back pressure is this:
The 24v engine is designed for silencers and cats in standard form and only at its best with back pressure, with a large overlap the valves are both open for a short time to scavenge any spent gases, or to put it another way, to allow all the burned gasses to escape down the exhaust the inlet is opend to stop the vacum in the chamber and assist in a full chamber fill!
It is only at its best with back pressure to stop over scavenging, or in other words air/fuel mix passing though the cylinder and out the exhaust.
The loss of power is due to the cylinder not having a full chamber of air/fuel mix (some being lost down the exhaust)?
Low back pressure causes, a drop in power, poor fuel economy & the power band can shift. Yeap just like a 2 stroke?
Have I got that right STN as my thery is based upon it?
Yes it is an explorer crank, engine has done 130,000 miles as a 3.7 with no problems but now needs a rebuild for more power.
Cams? Can't see anything on the piper site (thanks Snoopy) I have emailed them as I do remember they did some for the BOA once upon a time?
Manifolds yeap the tube one is top boss, does look a little weak don't it?
Power well as a 3.7 N/A it made 278 bhp & 290 lbs. If you allow 50 - 75% for 1 bar of boost it should be somewhere about 460 bhp & 480 lbs. Cause I have the girdle I can take the revs upto 7000 rpm & as you know the engine will make more power the higher you go as it is 24V. 
STN do you do anything turbo manifold wise & how are you getting on with them chain guides?
Girdle pic.
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Dave
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Baz
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S Reg. 1998 24v Cosworth S2.9 COS (Deceased)
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Re: 24V Cossie (SaveTheNight)
« Reply #9 on: Jun 13th, 2005, 12:25am » |
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Hope you are putting the thermostat in a more sensible position!!!
Looks good though. I may one day rebuild the engine on mine when I have the time/space/money.
Bill, I am still looking to get one of your nice engine covers!!
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SaveTheNight
Senior Member
I can resist anything ...except temptation !!
Posts: 1961
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Re: 24V Cossie (SaveTheNight)
« Reply #10 on: Jun 13th, 2005, 7:04am » |
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Hi Dave ... well ... I didn't realise the engine had been running 3.7 already so I presume it's one of Chris's at " Power Engineering " conversions originally ? .. the theory you are referring to regarding back-pressure is generally accepted by some but as I say ..I don't agree ..if you had a choice of running optimum power with no noise restriction then open short headers would
be the choice in most cases as in dragsters .. I can go into my own theories if necessary but the simple fact is that exhaust gases are pulses because of the valves as you rightly say .. and not a gush of air as people would first think ..those pulses and the gases are very hot and high pressure ..the prime objective is to keep them hot throughout the exhaust system until they are out ! .. back pressure and silencers have a cooling effect immediately ..cool gases are dense ..and dense is heavier ..therefore you are trying to push a heavier mass throughout the system ..most exhausts will not reach optimum performance partly due to the cooling effect but it pays to attempt to, if poss .. in your case the turbo will supply enough back pressure and especially if you run race cats to acheive some economy < you're right about the economy > .. my point is that you certainly don't want to be pushing mass at those short manifolds although the turbo is in fact sucking them out .. it's sometimes easy to forget that you are only dealing with a three cylinder engine at each manifold despite your inlet valve comment .. the leading edge of each exhaust pulse must be above astmospheric pressure ..the middle is approx ambient ..and the tail of the pulse is low pressure ..low enough almost to create a total vacuum ..opposites attract and that low pressure sucks the high pressure leading edge of the next pulse and so on ... this is what makes them move , hence manifold " tuning " .. the secret is to get the pulses nicely " lined up " ..back pressure prevents this ..ask any tech with a dyno and he will agree that the best silencer is NO silencer at all .. the turbo's will aid this of course on your 2 ..three cylinder engines !! .. if the headers are too short or badly flowed ..then the chaos of pulses will waste time efficiency and bhp .. ooops ..i'm rambling again !! gotta goooooo ...more later ... looks like you're doing great Dave anyway ... see ya laterrrrrrrrrrrrrrr ...... cheers ... STN
Baz ... sorry mate ..so hectic down here ..but I'll get a pic off to you asap ...
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