Discussion in 'Mech Tech' started by Gnasha, Feb 25, 2019.
@Gnasha You have another vote for a Web 86a from GARRICK.CLARK.
Have you made a decision yet?
77westy once again thank you for your valued input.
I'm in the fortunate position to have two 2.0 engines both stripped and awaiting assembly when they return from machining. One is hydraulic cam (which I was favouring) and the other solid cam, GD & GE. the cam from the Hydraulic was a wrecked. I'm left with a decent solid cam for what was going to be a standby engine. I have new parts followers etc for both arrangements. If I choose the solid arrangement I need a new improved solid cam which leaves me with new set of hydraulic followers and the need for a hydraulic cam to build a standby engine. Or build two solids and bite the costs for the hydraulic parts. I need to think this one out.
This was the distributor.
Thanks for the vents and mains info. I'd read somewhere it was advisable to increase both, ill do that at some point.
I'll certainly look for a 123 programable dizzy, is that electronic ignition, having the capability to be programed?
Yes I see Garrick's response after your comments re hyd vs solid I'm thinking about the consequences. Maybe I need to measure the CR and see what range I have first?
That hydraulic cam shows typical wear, both the heal and the nose are pitted, the follower never leaves the cam and the oil film is wiped off.
If you need two engines – you’re obviously not confident about reliability – you could have one with a mild cam for touring and one with a wild cam for a bit of fun and just swap them, it’s only four bolts. Seriously, I’d build them both with solid cams (and sell one).
This is a 123 programmable distributor http://www.123ignition.nl/product.phtml?id=199
If I did go the solid route, I'd prefer to keep things simple.
86 Good overall performance for carbureted mechanical street engines. RPM range 2500-5500. The perfect street cam! Requires New lifters (rev range is too high)
86A Strong mid and upper end performance for high performance street engines. Requires Exhaust System, Performance Valve Spring Kit, and New lifters required.
86B Strong mid and upper end performance for small displacement racing engines. Requires Exhaust System, High Compression Piston, Performance Valve Spring Kit, and New lifters
91 Hydraulic profile for high performance street engines. Requires Programmable Injection or Carbs, and New lifters required.
At first glance it looks like 86 or 91, although I'd like the rev range to start earlier. 86a & B require signficant additional work as above.
Exhaust system, I dont want to appear completly dumb here, so here goes. I intend to run heat exchangers and a type 4 into ghia bespoke exhaust system, will this meet the requirements of the Webcam selection?
Am I correct in thinking type 4 springs are stronger or is that just 1800cc?
This appears to be taking longer than expected, thanks to those who have contributed so far and their on-going patience
I'm leaning towards the dark side of solids and build one as standard and one that provides some seat of the pants stuff, bearing in mind I'm no youngster anymore. Anybody need a set of hydraulic lifters?
The 123 programable dizzy is a must, already tracked down a supplier Vintagespeed.
This is my first aircooled build, I chose what I thought would be an easy engine build, how wrong I was. The second engine came cheap after hearing it running.
"its only 4 bolts" must be the quote of the year so far
You really mean you’re leaning away from the dark side of hydraulics.
Be careful you don’t end up with two engines you’re unhappy with. A standard spec type 4 is very mild and lazy but with a wild cam you’ll need to keep the revs high – and it will be more difficult to build. To ensure compatibility whatever cam you decide on, buy the lifters from the same manufacturer.
Rather than getting confused with cam choice have you considered simply making the engine bigger with a longer stroke crank and/or pistons and barrels? There’s no replacement for displacement.
77Westy I feel I've been ridng a wild horse, and now I have a tiger by the tail
Is a Webcam 86 considered "wild"? why would I need to keep the revs high? because the torque band has moved up the rev range?
I may consider 2056, just a "simple" barrel and piston (flat top) change but I'll still need a cam.
I’ve been following the replies on the other forums and I think at least one guy has missed that you have a 2.0l engine with bus pistons and you’re fitting bus 1800 heads to it. They’ll bolt straight on of course (and that’s probably what a lot of people do) and the engine will run but the performance might be disappointing.
With 2.0l dished bus pistons and 1800 heads, it may be difficult to get the compression ratio high enough for even a standard cam to work. And if you change to a cam with more lift and duration (and you should) then it becomes even more difficult. Do some research on static and dynamic compression ratios and you’ll understand why a ‘performance’ cam needs more static CR to have the same dynamic CR as a standard cam. http://johnmaherracing.com/tech-talk/what-effect-does-compression-ratio-have-on-bhp/
Now, increasing the capacity with flat top pistons and 96mm barrels may give you the opposite problem; too much static CR unless you increase the deck height, but it’s probably easier to reduce the CR by making the combustion chamber bigger than it is to increase the CR.
A Webcam 86 is not wild at all, it would work well in a bus engine, but it still needs more static CR than a standard cam. That’s really why I said at the beginning that you can’t start with the CR and select a cam, it’s just the wrong way around. You choose the cam to get the engine characterises you want then adjust the CR so the cam works at its best.
There are dozens of solid cams that will provide more or less the engine characteristic that you want but there are subtle differences between each and that’s where it gets confusing but for a road engine they’re maybe not significant enough to worry about. You might lose 5bhp – so what, how often will the engine be run at maximum power? Possibly never, and the bigger and more powerful the engine is the less likely it will be used balls to the wall – unless you’re an adolescent and /or hooligan.
Play around with an engine calculator to see what can work. I’d keep the deck to as close to 0.050” as possible, too big and the squish is lost, too little and there may be a risk of pistons hitting heads. http://johnmaherracing.com/calculators/engine-calculator/ A cam with around 275deg duration and 0.430” lift will idle well, pull from low revs and make a little more power but a cam with more duration and lift might suit your needs better.
I was just about to ask what the minimum safe deck height is.... Think you have just answered my question
0.040” (1mm) is generally accepted as the minimum deck although there are plenty of engines running with less. How lucky are you?
See where i am at 1mm, think I could struggle to get to 8.5.1 cr with the dished pistons. Haven’t measured dish volume yet, do you know where its at on std Mahle pistons. Sorry being lazy now but its warmer sat on the sofa than in a cold garage on a Saturday evening.
I’m as lazy as you, I could go and measure the dished pistons but… 0.040” deck is what I’ve run my 2.0l with dished pistons and a C25 cam for the last few years, the CR is probably too low but I wasn’t happy running with less deck. I have the opposite problem with the 2.3l and flat top pistons; it’s difficult to get the CR low enough.
So with a 1mm deck i am calculating a CR of 7.4:1 . The piston dish measures 14cc & the AMC head according to MarkC68 are 56cc. I don’t know if that measurement included the machined sealing step.
The deck i am measuring at the cylinders is 0.5mm. I Presume the machined raised part of the AMC head that replaces the gasket is included in the deck height? Question is does the piston clear it? As mentioned previously the heads are still on the engine in the bus so i am unable to measure at the moment.
In hindsight I maybe would have been better using flat top pistons with the C25 cam.
The step in the AMC heads replaces the gasket and the pistons do clear, I expect @MorkC68 measured the combustion chamber volume from the step so don’t include it in the deck. That makes your CR 7.7:1, still too low for the C25 to work well but what you could do is machine 0.05mm from the top of the pistons; that would bump the CR up to about 8.0:1, if you can keep the total deck at 1mm.
John at aircooled.net says the C25 works between 7.5 and 8:1 https://vwparts.aircooled.net/SCAT-C25-Type-4-Camshaft-1-3-1-Rockers-20086-p/20086.htm I think that’s too low but if you agree with him you’re not far off. But read that tech article on dynamic CR on the link I gave up there^.
I have found the step height on AMC heads is 0.7-0.8 mm deep, so if i have 0.5 in the cylinder am I correct in thinking that i have 1.2-1.3mm deck height/clearance. Don’t want to risk piston to head contact.
As for CR will probably give it a go at 7.5-7.7:1. Want to avoid having the pistons machined if possible.
Get the deck down to 1mm, there is no risk of pistons hitting heads unless the engine suffers a catastrophic failure and the couple of points CR could make a difference. But you need to measure the combustion chamber volume of your heads.
Yes i will check the cc of my heads to be sure.
I have checked the cylinder deck with pre used base gaskets. Cyl 1&2 are at .5mm 3&4 are at .7mm. I was thinking of leaving the base gasket off cyl 3&4 & just use permatex to hopefully get them all to 0.5. Does this sound feasible?
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