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Post by Zed on Dec 5, 2018 15:16:33 GMT
77westy C25, 234° @ 0.05" = 3000 -6500rpm What say you? This is often recommended as a mild cam suitable for buses but mild compared to what I wonder? You called. I’ve been lurking here a long time and I suppose I’d better say something. So… I have a C25 cam in 2.0l with 1800 heads, twin 40 IDFs with 30 vents and a CSP Python exhaust. It pulls well from just above idle and runs out of steam at around 4,500 and that suits what I use the bus for pretty well, it’s seldom on a motorway but climbs a lot of Cols. John at Aircooled.Net says “This is a nice upgrade on stockish engines, it's an outstanding bus cam!” I’ll be using the same cam in a 2,316cc that I will eventually get around to building – I’ve had the parts for 18 months. I’ve measured the new cam and it has slightly less lift than advertised and that probably means it has a degree or two less duration too. It’s easy on the valve gear and only needs single springs. A cam with a lot of duration tends to produce power and heat at higher revs, a mild cam makes power (and heat) at low revs. VW wanted heat at low revs to help with emissions so used a cam with not much duration but in my opinion it’s too mild for a big engine. The larger the capacity the more torque the engine will make and it will make maximum torque at low revs, of course in an ideal world we’d have variable valve timing, just like a modern engine. Your engine with almost all VW parts - the 104mm pistons are big and relatively heavy compared to the standard 94mm, it made sense to use H beam rods because they’re lighter so the reciprocating mass is similar to a 2.0l and the crank will tolerate the same revs. H beam rods are not as strong as the standard I beam but they’re certainly strong enough. My 2316cc engine – I no longer have access to a machine workshop and I’m too tight to pay someone to do any machining so the biggest engine I could make has a 80mm stroke crankshaft with 96mm pistons. Bigger stroke cranks are available but then there are clearance issues with the crankcase and the cam – no. 2 and 4 rods get very close to the cam. The crankcase and the heads are VW but almost everything else is from all over the world; the cam, followers, pistons and rings from the US, crank from Taiwan, rods and cylinders (double cast biral that everybody tells me not to use but can’t tell me why not) are from China. Bearings from Brazil and Mexico, the valves, pushrods and swivel foot adjusters from Germany but not VW and the distributor is from the Netherlands. Thread from the dead... I've been plotting to change my engine. What's wrong with it...or irks me because it causes inefficiency... Big deck Cam needs more duration, particularly the exhaust on a type-4 which is a known bottleneck that can't be ported out of a stock bus head, but both due to stockish valves and increased capacity. I can't justify happy Jim's reasonable £1050 a pair AA 412 casting 42x36 much as I'd like to. They'd need your exhaust and new 3 hole manifolds. Despite Rob failing to find my build calculations, I've pretty well worked out what I have. I found my AA cylinders wete/are supplied 2mm over stock length. I can't have the tops machined without machining off the top fin. I can't machine the bases or the rings will hit any step that may have worn at the top. Even if I could, to get to 8:1 with a tight deck would need a huge dish in the pistons and or more carving from the already weakened heads. I'm guessing the heads are around 60cc - could be more. I have to keep them as if I'm honest my engine does what I want already. So, new b&p's are a requirement and as I can get to 8:1 more easily with 102's which will fit my holes (I hope) and have thicker walls (I hope) I'll be loosing about 100cc. But hopefully improved efficiency will mop that up. Cam : I've been chatting with modok for a while, he understands that I'm trying to tweek for effiency without spoiling what I like about it more than anyone I think and specs his own engines off the wall He doesn't post about them because he knows he'd be told he was doing it all wrong. He's encouraging that I should follow my nose/own path hoping for good results that might confound accepted beliefs...a bit anyway. All good fun. So, he reckons I should get a split duration Webcam 73/86 and get them to add an extra 4 degrees of duration, which they for free. Expensive, but they are patkorised (sp!) which I was going to do anyway. No running in and I see no reason not to reuse my refaced stock followers which saves. I can also reuse my stock wheel and I'm told by them that know that I get to keep my stock oil pump too. 73/86 with the extra duration is (In/Ex) .426/.423" Valve Lift with stock 1.3:1 Rockers, 254/264 degrees of advertised duration, and 228/238 degrees of duration at .050". Aircooled net say hogh rev valve springs, modok says type-1 stock springs but don't say I said that, I say sod it, I've revved a stock 2l to the red line, no probs so they'll be fine to my 4500 even with the slightly higher lift. vwparts.aircooled.net/Web-Cam-Type-4-Camshaft-73-86-Grind-p/web-cam-73-86-split-duration.htmI've got a local vw drag racing machine shop lined up to shorten the cylinders and dish pistons. What do you think to the cam? Webcam also do hotter split diration cams for type-4 but they're too hot for me but could be good for your new fire breathing monster with it's racing exhaust. Your exhaust* - they sell 3 different collectors for it I believe. I asked them for advice "buy them all and try them". Yeah right! How did you decide? * I'm pretty sure it was that exhaust.
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Post by Zed on Dec 5, 2018 15:26:29 GMT
Before you say it, Yeah I know - my cam plan makes a mockery of that chart. For an accurate chart you'd have to specify more than just the cam duration. I still stand by keeping it mild for a bus engine, I've just reassesed my particular combo (as they say).
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Post by 77westy on Dec 5, 2018 20:57:15 GMT
Before you say it, Yeah I know - my cam plan makes a mockery of that chart. For an accurate chart you'd have to specify more than just the cam duration. I still stand by keeping it mild for a bus engine, I've just reassesed my particular combo (as they say). That cam chart is wrong IMHO, or at least not completely correct because it does not consider the capacity. The more capacity you have the more duration you can have, the torque lost at low revs is made up by the capacity and the duration extends the useable power at the top end. Your engine will run out of puff relatively quickly but it will have bucket loads of torque at very low revs that you can’t use. A Web 73/86 should work well, it’s still mild but if you use standard valve springs be careful they are not coil bound at full lift, I use HD single springs with a Scat C25 cam and that only has 0.004” more lift than the Web 73/86. It’s not necessarily the revs it’s the distance between the coils. And I’d definitely use a new set of Web lifters to go with a new Web cam. I’ve just pulled the 2.0l from my bus that has had standard lifters in it for about 30k miles, the cam looks fine but some of the lifters are pitted. Scat lube-a-lobe lifters with a Scat C25 cam are in the new engine (yet to fitted but getting close). Deck height is your problem, the engine will have very poor efficiency because there is no squish and the flame spread in those big cylinders will be slow, but you knew that when you built it. Is there enough meat in the piston crown to get a decent dish? Smaller cylinders would help but obviously you’d lose capacity – and there’s no replacement for displacement. 102mm cylinders will give you about 2321cc, my engine is 2316 but I’ve gone for stroke not bore. 80mm counterweighted crank with 96mm cylinders. It’s a pretty straightforward build really but clearances are tight and it couldn’t be much bigger but deck height and CR are a challenge with the flat top pistons. I can’t get the deck as tight as I’d like with a CR that the cam needs to work well, the same problem that you have but at least I can open up the combustion chambers in the 1800 heads. A standard cam gear is fine for whatever cam you use, as is a standard 24mm oil pump but I’m using a 26mm pump because I had it on the shelf, and an oil cooler for the new engine. Those that fit 30mm pumps are bonkers - and wonder why they have high oil temps. I use the smaller diameter CSP Python exhaust without a cone insert, it works fine and head temperatures are 50F lower compared to the truly awful EMPI twin I had before. CSP wanted to sell me the larger diameter exhaust for the 2.3 but I want to keep the heat exchangers and they are the restriction. They also wanted me to buy the 3 sizes of cone inserts, I didn’t do that.
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Post by Zed on Dec 6, 2018 9:35:47 GMT
Before you say it, Yeah I know - my cam plan makes a mockery of that chart. For an accurate chart you'd have to specify more than just the cam duration. I still stand by keeping it mild for a bus engine, I've just reassesed my particular combo (as they say). That cam chart is wrong IMHO, or at least not completely correct because it does not consider the capacity. The more capacity you have the more duration you can have, the torque lost at low revs is made up by the capacity and the duration extends the useable power at the top end. Your engine will run out of puff relatively quickly but it will have bucket loads of torque at very low revs that you can’t use. A Web 73/86 should work well, it’s still mild but if you use standard valve springs be careful they are not coil bound at full lift, I use HD single springs with a Scat C25 cam and that only has 0.004” more lift than the Web 73/86. It’s not necessarily the revs it’s the distance between the coils. And I’d definitely use a new set of Web lifters to go with a new Web cam. I’ve just pulled the 2.0l from my bus that has had standard lifters in it for about 30k miles, the cam looks fine but some of the lifters are pitted. Scat lube-a-lobe lifters with a Scat C25 cam are in the new engine (yet to fitted but getting close). Deck height is your problem, the engine will have very poor efficiency because there is no squish and the flame spread in those big cylinders will be slow, but you knew that when you built it. Is there enough meat in the piston crown to get a decent dish? Smaller cylinders would help but obviously you’d lose capacity – and there’s no replacement for displacement. 102mm cylinders will give you about 2321cc, my engine is 2316 but I’ve gone for stroke not bore. 80mm counterweighted crank with 96mm cylinders. It’s a pretty straightforward build really but clearances are tight and it couldn’t be much bigger but deck height and CR are a challenge with the flat top pistons. I can’t get the deck as tight as I’d like with a CR that the cam needs to work well, the same problem that you have but at least I can open up the combustion chambers in the 1800 heads. A standard cam gear is fine for whatever cam you use, as is a standard 24mm oil pump but I’m using a 26mm pump because I had it on the shelf, and an oil cooler for the new engine. Those that fit 30mm pumps are bonkers - and wonder why they have high oil temps. I use the smaller diameter CSP Python exhaust without a cone insert, it works fine and head temperatures are 50F lower compared to the truly awful EMPI twin I had before. CSP wanted to sell me the larger diameter exhaust for the 2.3 but I want to keep the heat exchangers and they are the restriction. They also wanted me to buy the 3 sizes of cone inserts, I didn’t do that. Big engine, tight deck - as you say, difficult. I can get to 1.5mm, but I don't think I can get 1.2mm which I'd like. 102-104 are perceived as big but they're not really that much bigger? 102 are only 3mm biigger radius than stock, hardly a show stopper for flame travel? Mine will still be a low revver when I've done, I'd be disappointed if it weren't. Same thing as you - heat exchangers - do you know the size of type-4 hx primeries? I have another chart for primeries/capacity/rev range that you'd like. According to said chart (I'll post when I find it), if we assume 1 1/2" you'll be strangled above (around) 4,000rpm. When I checked mine existing on chart it says 2000-3900rpm - spookyily an exact match to my dino chart...
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Post by 77westy on Dec 6, 2018 16:21:59 GMT
You won’t convince me that 102/104 cylinders are not big. I have pattern heat exchangers and I was led to believe that they were smaller than original VW, but they aren’t, both are 38mm OD – a lot less than 1½” ID for your chart. The Python is 42mm OD, 4 into 63mm. The EMPI was 34mm with horrible bends and very restrictive.
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Post by Zed on Dec 6, 2018 16:44:32 GMT
You won’t convince me that 102/104 cylinders are not big. I have pattern heat exchangers and I was led to believe that they were smaller than original VW, but they aren’t, both are 38mm OD – a lot less than 1½” ID for your chart. The Python is 42mm OD, 4 into 63mm. The EMPI was 34mm with horrible bends and very restrictive. The pattern ones are 10% bigger than the originals so you have the best ones. 👍 I know because I used pattern to replace part of my og ones. So I have the worse choice in that respect. I think "that chart" is OD, the way primeries are aleays discussed. 38mm = 1 1/2". Do you think your exhaust will be compromised if you don't go up a size? I don't know, just asking.
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Post by 77westy on Dec 6, 2018 19:47:01 GMT
I’ve got a pair of original heat exchanger internals and the pipe size is the same as the pattern ones – 38mm OD. What size are yours?
It might but I don’t think the smaller exhaust will compromise performance, the pipe size increases from heat exchangers to primaries to collector so the gases expand throughout the system. Maybe if I was looking for maximum bhp from the engine it would, but I’m not. Time will tell, if I lose a bit so be it, I’m not going to buy another exhaust the Python was an arm and a leg and I want it to last as long as the bus, or me.
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Post by Zed on Dec 6, 2018 20:13:17 GMT
When I fixed mine I found this. It'a poor photo but the pattern donor chunk on the end ia about 2mm bigger. Maybe they increased the size at some point.
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Post by 77westy on Dec 7, 2018 8:08:08 GMT
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Post by Zed on Dec 7, 2018 8:46:51 GMT
Think you misunderstood... I'd blurry love a python exhaust, but with heat exchangers?
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Post by 77westy on Dec 7, 2018 15:55:16 GMT
Think you misunderstood... I'd blurry love a python exhaust, but with heat exchangers? Maybe I did misunderstand – it happens a lot. I was trying to answer your question “Do you think your exhaust will be compromised if you don't go up a size?” Short answer - no. Longer answer – No, but I don’t know for sure. I was trying to demonstrate that a 42mm exhaust was capable of flowing enough gas for far more torque/bhp than I’m expecting from a 2.3l engine. I have 38mm heat exchangers and a 42mm Python exhaust, I don’t think it’s the exhaust that will limit the engine performance, it’s more likely the heat exchangers. There is no doubt in my mind that the Python is more efficient than a Vintage Speed or a standard VW exhaust and far better than the EMPI I had before. Money well spent with CSP, but I’m not buying another one.
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Post by Zed on Dec 18, 2018 12:29:05 GMT
Back to cams. Having nothing better to do, after coming across some equations for calculating Dynamic CR, I'm working up to making a spreadsheet for bunging in all the varibles to save repeating this fairly complicated calculation. It's a lesson I learned when I did repetitive CAD work. I got so fast (if I may say so ) at AutoLisp programming if I saw I'd have to do something more than twice I'd write a program in less time. One took a month to write but saved me an additional 1500 hours that I still got paid for. Happy days. I do realise that DCR is not the whole story, but anything deeper (cylinder pressure) is just about impossible, probably 100% impossible and Static CR is next to meaningless being so cam dependent and should be back calculated from Dynamic. What we all do though is head for "aircooled.net" and read John's recommendations for static CR for a particular cam. It will be interesting...to me anyway...to see real numbers calulated from valve closing times, taking into acount stroke length, rod length etc which all change the Dynamic CR and are not taken into account other than by giving an SCR operating range for the cam. That range must also encompass the quality of the combustion chamber design so for me, knowing next to bugger all, I'm be going for the lower end of recommendation if not calculating myself. This is getting heavy! Part of me wants to feed in my numbers for my previous engine to see if I ended up with a really low dynamic CR that could have been the cause of it's gutless lower rev action and general hot running. Somewhere in that engine was a mistake I don't want to repeat.
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Post by Zed on Dec 18, 2018 17:26:15 GMT
Hmmm. This is sending me batty.
New plan is draw it on CAD and measure the effective stroke length then bung it in an engine calculator and reverse out to static cr... but CADs on a laptop that's seen less confused days, the battery is shagged and the mains charger wire has to be balanced "just so". It's locked up and won't turn off now so I'm waiting for the battery to peg out. Rome wasn't built in a day.
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Post by 77westy on Dec 18, 2018 18:15:31 GMT
I like John Maher’s Tech Talk articles, this one on static and dynamic CR is interesting. johnmaherracing.com/tech-talk/what-effect-does-compression-ratio-have-on-bhp/I think John's (aircooled.net) static CR recommendations are conservative, especially as cam duration increases. I hope they are anyway because I’m having difficulty getting the static CR he suggests for a C25 while having a reasonable deck height.
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Post by Zed on Dec 19, 2018 8:44:15 GMT
I like John Maher’s Tech Talk articles, this one on static and dynamic CR is interesting. johnmaherracing.com/tech-talk/what-effect-does-compression-ratio-have-on-bhp/I think John's (aircooled.net) static CR recommendations are conservative, especially as cam duration increases. I hope they are anyway because I’m having difficulty getting the static CR he suggests for a C25 while having a reasonable deck height. From a few quick calcs I think you're right about Johns figures. I also noticed the 73 grind offers different numbers for duration to the 73 part of the 73/86 which is also confusing. So... I managed to make some headway and worked out valve closing crank angles for all durations on 108 centres. These would apply to any cam, any engine and it's weird that they're not on the net somewhere though it's a simple formula. Then using CAD the effective stroke for each closing time for my engine and any other stock crank/rods type-4. Now I just substitute effective stroke in the normal calculators...later.
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