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Hi all, I know the subject may seem a bit out there but that's why I'm here! This site has been instrumental for me since I was a teenager. Anyhow...

I'm trying to choose a cam. Please read on...

I'm working on putting an engine together for my 2 seat Chenowth buggy. It's a play car and gets trailered to/from the trail.
It is primarily used in the tight and steep wooded "Jeep" trails up here in the PNW with less frequent dunes and open trails. All that said to try and give an idea of what I'm trying to accomplish, which is not an all-out screamer. Lots of 1st gear driving with most of the power being needed to keep momentum up on steep climbs. So it's gotta have a nice smooth idle along with good low end (has 5.38:1 final drive 002 trans). Planning on under 10psi boost from a Subaru turbo I've got lying around. Doesn't need to rev over 5000.

All the new parts I have now I bought over 5 years ago when I was going to build a mostly stock motor for/from a Baja I used to have. I'm hoping to use what I've got. Operating on a tighter budget these days...

The engine is a 1800 with a stock crank, AA 96mm slip-ins and flat-top pistons (Not ideal but it's what I have).
Stock 1800 AMC heads rebuilt with new guides, seats and valves. Smoothed ports.
I'm shooting for 8.0:1 or 8.25:1ish compression ratio.

Already running MSD 6A box and Blaster coil.
Propane kit from gotpropane.com set up for about 100HP. No intercooler required. Will probably heat the regulator with engine oil. I'm tired of carburetors off-road and this isn't the right vehicle for aftermarket EFI, IMO.

So, cams. I'm looking for a cam with under 0.450" lift, 240ish duration @0.050 and 112 lobe centers. I'm hoping to run just a single HD valve spring.
Let me know if I'm off base here.
The Scat C25 p/n 20086 seems like a nice grind but it's on a 108 lobe centers. 0.430", 234 @ 0.050
The Webcam 119 is stated as a turbo grind but also on 108 lobe centers. 0.499", 240 @ 0.050. I'm under the impression that 0.499" requires more machine work on the heads. Correct?

Thoughts?

I just realized I should call both and see if they can be ground on 112 LC...

Thanks!
-Levi

The 119 requires dual springs, but it's an excellent all-rounder, if a bit hard on the valvetrain.
With propane, you have ~120 octane fuel, so limiting yourself to near stock compression ratio, particularly with a 119 on 112 degree lobe centers is a waste, 10:1 or more would be called for, even mildly boosted.

If you are crawling jeep trails, and given your target cr and engine, a web 73 would be a far better choice.
I'd keep my eyes open for a 2L crank/rod setup, perhaps even a mild stroker combo for low end tq and a bit more compression to take advantage of the fuel.

Thanks for the reply, Pile.

I do have a 2.0l crank and rods in good used condition, I was saving it for... well I don't know. I'll dig it out and consider it.

I see what you're saying about compression and lobe separation. I hadn't really put it together that widening the lobes retards the intake valve so I'm certainly willing to change my target compression ratio. I am trying to stick to a single valve spring.

I've read a fair bit on TSF about turbo cams. Seems more people are running a tighter lobe sep. Maybe because a turbo was an afterthought for many. I understand why a wider lobe sep is ideal for forced induction, but having zero experience with turbo VWs I'm wondering how much it really matters. Pick a cam that works for my application and let the turbo do what it's gonna do?

-Levi

A factor with turbo engines is how much back pressure you have in the header. That depends on the turbo design & the header / exhaust. A very well chosen combo will have low back pressure, so the cam can have a more NA profile
. With increased back pressure (very common, even on OE
Engines) the exhaust flows back into the head on overlap mixing dirty air with the intake charge. So less overlap is needed / necessary to prevent backflow

Thanks, Bruce. I will be building my own exhaust system. I imagine that long primary tubes would be ideal to help prevent exhaust pulses, from other cylinders, from back-flowing the cylinder with the exhaust valve open? specifically with a cam with more overlap.

-Levi

First you need to figure out what you want, crawl trails or run at the drag strip.
A low restriction turbo setup will make for great high RPM power and nothing on the bottom end.
A turbo that will give good low end grunt will be the opposite of that setup.

A long runner turbo header on an ACVW is almost unavoidable due to engine layout, unless you run with a pair of the ICTU sized mini turbos with a crossover pipe. Would actually be easiest on an open buggy, you could use a short pipe dual bazooka exhaust setup with a header on either side except the turbos go at the collectors, just above the rocker box height, that way you have a short drain line etc..

Twin baby turbos would be pretty cool…

The goal is crawl trails with help from the turbo for mid to upper end for hill climbs.

I think I have been overthinking the cam situation. The 96x66 1913 is going to push this 1500# buggy around just fine even n/a. The worn out 1600 still gets the job done. So, I’m going to put it together with the parts I’ve got and paid for and put a mild n/a cam in and let the turbo be what it is. I can always swap turbos, redesign the exhaust, two minis, etc.

The theoretical compression ratio with 57cc chambers (that’s an educated guess) and 0.030” deck height maths out to 8.64:1. With propane this allows some room for tuning error from the mechanically controlled boost and fuel system. Trying to keep it simple and reliable.

Sane choice.
Sometimes less is more.
Use good rod bolts, have them rebuilt/prepped (by someone good)
New ex valves etc.(does not always require new quides, the stems actually shrink as the valves stretch)
(sometimes a little bit more is good)

All the machine work was completed over 5 years ago.

The rods have been checked and sized. Piston pin bushings measured out fine. Heads had the seats ground and new valves all around. I’d never seen intake valves so hammered.

I assembled the crank today along with the rods. Stock bolts and some good condition nuts. Bearing clearances measured out in spec. I’ll plastigage the center main tomorrow, hopefully. I’m at home on medical leave after back surgery. Recovery is going well but I have to wait for help from my wife or a friend to move anything over 20lbs.

Pile, what would your rod bolt recommendation have been?

If you are staying stockish new replacement bolts/rebuild would have been fine.
(the big ends can stretch at high mileage, but have never seen a 2L rod big end stretch, could happen...)

ARP makes "replacement" bolts, although the price is about what a set of T1 H-beams go for.
I and some other folk have used ARP2000 waveloks for an early BBC. The holes in the rods have to be honed out .005" IIRC (must actually measure as the rods vary) then the rods needs rebuilt. I scored a full set cheap on ebay years back, half of them went to Europe and found their way into a 411 that saw some road racing action.

There is also a Carrillo replacement bolt set that fits ACVWs RIMCO used to put in their "Super rods" (lightened, balanced, shot peened etc) but you'd have to talk to Carrillo or a shop that reps them for the # as Rimco wasn't telling.

Shouldn't really be a secret as anyone with good calipers and an old rod bolt has the dimensions, and I'm pretty sure there is a catalog somewhere... Most 1968++ VWs used the same or compatible rod bolts.

I got the case assembled a few weeks ago. Scat C25 cam was what I went with. Also cleaned up the exhaust flanges using my brother in laws lathe. Spent a lot of time on the heads cleaning up the casting flaws, smoothing/gasket matching the intake and exhaust ports. I have new Scat singles and new keepers/retainers to use.

I’ve been working through compression ratio numbers and it seems I need to fly it the heads or turn the cylinders down. Clatter mentioned in his sweep-the-floor build thread that AA cylinders run long to make up for cases being decked. Mine has not been decked hence some of my issues.

Average deck height numbers are 0.056”. The heads have a 0.026” step in them. The measured combustion chamber volume including that area inside the step is 59ccs. This makes for a compression ratio of 7.85:1. Too low for my liking. Also the valve train geometry is soooo far off that it confirms something has to change.

If I have the step milled out of the head it makes for 54.2cc chambers and 8.4:1. I’ll probably just have the machinist take off 0.030” for good measure.

Does anyone know the length for stock cylinders from case to head mounting surfaces?

Your best option would probably be having the jugs turned down to achieve zero deck (even with the tops of the cylinders) and use the machined in step as most of the "deck height", perhaps using the stock .010" aluminum base gaskets. for total deck of .036".(I ran .028" on a 1700 for ~150K miles, then another 100k with 1800 p&l)

I'm not sure why the head shops build in that step, it's not unusual and a PITA/extra expense if you didn't ask for it.
You don't want to flycut T4 heads except to clean up--- there is not enough metal in the deck as it is.
It's not just the cheap shops that do it.

Pile, thank you.

The issue I have with the step in the head is it was cast in, not machined. You can see it in one of the pics. It also has a smaller ID that the cylinder ID so it protrudes into the bore. Would machining out just the step really be too much material loss?

Now, it just got deeper... I discovered that the odd deck height measurements I was getting is because the case deck is not straight. Its 0.0025" concaved (for lack of a better term) between the cylinder spigots on one side and convex about the same amount on the other side... dammit...! ugh... sigh... I checked this with a machinists straight edge across the top of the cylinders and feeler gauges, then across the case with the cylinders removed. It all points at the case deck. The machinist had said the case didn't need to be decked but I'm beginning to disagree.

I put some plastigage on the head sealing surfaces on the "low spots" and torqued the heads. Seems the cylinders square up in the head when torqued. As much as I don't want to tear down the freshly assembled bottom end, I may have to. Since these are thin wall cylinders and the engine will see mild boost, I really need good head sealing.

Decking the case 0.010 or so and machining out the step in the head would make everything square, make the deck height better and fix my compression ratio numbers.

The machine shop is 75 miles away. So I'll talk with him this week about options.

-Levi

The cases have usually collapsed a bit at the center main... Bowing out I have not seen.
You should probably have the crank bore checked for size and straightness before spending money on decking.
(your machinist can do that)

I'm now assuming they AA, AMC or other aftermarket heads?
I have never seen a step in actual VW made head that wasn't machined in.

(I think I see the "A" of the AMC logo in one of the pics, those are better castings than the originals, although the steel parts...seats, springs/keepers and rocker/exhaust studs were garbage on the older units, they corrected that eventually)
AA head castings are sadly identical to the OGs.

You can likely get away with the cut on AMC heads.as IIRC they added some material vs. the originals in appropriate places, but I'd still try and figure out how to open the step to bore size and cut the jugs.. although it would cost more..

Yes, these are AMC heads. I have no idea how old they are. This engine originally came out of a burned out ‘74 bus I bought for $200 when I was just out of high school. I ran the engine and the 5 rib trans in by Baja for a long time. The seats have been ground and new intake valves SS exhaust valves. I’ve got Scat springs and things.

Here’s a few pics of the future recipient. Dig my last minute “temporary” intake piping. It works so well and has really grown on me.