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A local Opel-er, John Warga (aka "ftl" ) is approaching the completion of his "RallyBob 2.4 Stroker". He had been contemplating running the same cam as several of us Calgary Opel'ers have, the OGTS Combo Cam (aka Isky OR66) with a hydraulic grind. We all run the Comp Cams offset cam gear bushing, typically set to 4 degrees advanced.

That Combo cam is a mild upgrade to the stock cam (~0.395" valve lift) with 0.420" valve lift (hydraulic) and 268 degrees duration (seat to seat). I have recently read some suggestions regarding cams for a OEM 2.4 CIH, and while the Combo cam lift seems reasonable, the duration most typically quoted is 284 degrees. I believe the lobe separation angle is still typically 110 degrees. I think the OGTS "Max Comp" (aka Isky OR77) might be a good fit, with 284 degrees duration. He is ok with solid lifters, but I think he would be better off with the OR77H if that is available.

John's goal is a street engine with good "seat of the pants" power. That means low end torque is more important than +6000 rpm HP. He has a Getrag 5-speed, and this car will be a Foothills and Rocky Mountain cruiser (+3000' asl).

This engine is quite sophisticated, with full MegaSquirt EFI and spark control. The induction looks like a '75 Bosch LE, but only the intake is that. The ignition is EDIS "distributor-less" controlled by the MegaSquirt.

Here are the specs John provided. Please provide intelligent suggestions and sources for a cam, preferably one that can be acquired without too much drama. Grinding a cam locally isn't a practical option.

  • Bored to 3.769” (95.7 mm)
  • Pistons:
    • “Keith Black” hypereutectic
    • Chevy 305 pistons (+0.030”)
    • Shaved by .050” to sit .005 below deck for squish height around 0.037”
    • Stock rods with floating Chevy pins. Slightly lightened and balanced.
    • Stock Pistons & Pins: 734g Installed pistons & pins: 597g (137g lighter)
  • Crank stroked by 0.250” (0.500” total stroke increase) to 3.25” (82.6 mm)
  • Displacement: 2.38 litres.
  • Compression (see attached)
    • 9.9:1 static, Approx. 9:1 dynamic with OR-66 cam.
    • May go up very slightly with a 0.005” head shave to clean it up.
  • Valves:
    • SI Portflow stainless valves with undercut stem
    • Intake: Chevy - 1.84” (46.7 mm)
    • Exhaust: Chevy - 1.50” (38.1 mm)
  • Valve Springs – Dual Crane Springs: #99891 (Application: Buick V6)
    • Seat Pressure: 90-95lbs @ 1.510” Installed height
    • Open Pressure @ 0.430”: 200-210 lbs
    • Spring rate: about 270 lbs/in
  • Chrome Moly retainers (SI # SR-1230)
  • Combustion chamber:
    • Machined to 56.5cc to de-shroud valves and lower compression.
  • Minor head porting
    • Reduced valve guide bumps
    • Smoothed curves near valve seat.
    • Port matching on intake
  • Exhaust:
    • OGTS long 4:1 stainless header
    • 2” exhaust (planned)
  • Intake manifold:
    • 1975 Opel EFI manifold
    • Honda / Keihin Lo-Z Fuel Injectors (23 lb/hr – 240 cc/min)
    • 33 lb/hr – 345 cc/min are available from VTEC motors
    • MegaSquirt ECU
    • 60mm Throttle body (Nissan 240SX)
  • Ignition:
    • Dual wasted spark controlled by MegaSquirt.
    • Ford EDIS coils and 36-1 trigger wheel.
  • Camshaft:
    • Currently OR-66 hydraulic.
    • Considering OR-77 hydraulic or solid
  • Balanced rotating assembly
  • Flywheel & Clutch
    • Chevy S10 clutch & pressure plate.
    • Stock: 22.6lb (Keith’s)
    • After S10 machining: 17.6lb
    • Further lightened to: 16.2lb
    • With S10 pressure plate: 27.6 lbs.
  • Getrag 5-spd transmission
 

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Detritus Maximus
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Keith-

I see he is using one of the sheetmetal crank pulleys. How is the crank trigger wheel attached?
 

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Opeler
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Yes, the trigger wheel (from a Ford EDIS car - probably a 4-cyl Escort - it has been a few years) is TIG welded to the inside of the pulley. It was probably centered to within 0.025" after welding. After that was done, I mounted the pully in a lathe and did a small cut to the teeth to take out all the runout. It now spins with only a couple of thou of runout. The clearance to the Ford EDIS Variable Reluctance pickup is set at 0.030". It is spec'ed to be 0.025" - 0.050". Closer is better.

There is very little room on the timing case to mount the EDIS pickup sensor, so I made a bracket the attaches to the top of two (longer) oil pump cover bolts. It will probably end up quite close to the cross member that runs underneath the rad, but my measurements say this will work. We'll see. Fortunately, the MegaSquirt allows the pickup to be at any angle in relation to TDC. The Ford EDIS electronics are not forgiving on that.

When I put a MegaSquirt on my wife's MGB, I built an aluminum spacer to hold the trigger wheel to the centre of the vibration damper. I centered and machined a mating surface in the rough casting since you can't mount to the outside. I have since replaced the damper with a new one because the rubber was deteriorated. But it uses the same trigger mount.

Automotive tire Wood Automotive wheel system Auto part Circle


I didn't have a lathe when I made up the crank pulley and trigger wheel for the Opel (I used a friend's). The welding would not have worked on the MGB because of the rubber damper.

If I did it again for the Opel, I would build something similar to what I did for the MGB with an aluminum spacer going under the main crank bolt and keying to the crank. Moving the trigger wheel forward a bit would make it much easier to mount the crank position sensor as well.

Notes on Keith's pictures:
  • I'm using a GM 12SI alternator with a custom mounting brackets. There is a big piece of aluminum under the alternator, with a third bolt through the large hole in the flange near the oil pan. That was probably a positioning hole used during manufacturing. With all the loose alternators that have happened on GT's, I went with over kill.
  • There is no distributor. It will use two double-ended coils with wasted spark controlled by the MegaSquirt. The oil pump drive and distributor base remains to hold the oil pump drive.
  • The combustion chamber was opened up using a fly cutter in a milling machine. I went as far over as I could to de-shroud the larger valves.
  • The small sharp ridge on the outside of the valve seats has been smoothed out by installing an old valve that was cut to be a little smaller to protect the valve seats, then hitting it with a grinder wheel.
  • A very small amount of grinding has been done to the ports in these images. The only additional thing I'm planning to do is to go after the valve guide bump.
  • I will be sending the head out to get a very thin facing cut since the mating surface has a few small scratches from hanging around the shop for 12-ish years and surviving a shop move.
  • The bottom end of the motor is fully assembled. The top end seen in these pictures is just a trial assembly to see how everything fits. I may need to make a spacer for the throttle body to allow it to rotate a bit so the throttle cable does not stick up quite as high.
And not mentioned in the notes that Keith published, is I will not likely try to spin the engine past 6500 or so. I think it would hold together and the value train would work to 7000 or maybe even 7500, but I'm not likely to go that far. I will likely tune the MegaSquirt to do a severe ignition advance cut-off from 6500 through 6900-ish RPM, which should make it lose enough power to not go further under load. Then maybe a hard fuel cut-off at 6900 just in case I get too aggressive some day. All assuming, of course, that I ever finish this thing.

Edit: add last paragraph.
 

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Though I have mentioned it numerous times….

2” exhaust is small for a 2.4. I’d go with 2.25” if it’s ‘stock’, and 2.5” if it’s modified.

A 2.4 will tolerate a MUCH bigger cam than a 1.9 or 2.0 liter. In fact a 1.9 race cam in a 2.4 will still let grandma drive to church on Sunday.
Even an Isky MAX COMP cam is tame, I’d expect the powerband to be 2000-6000 rpms.
 

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Opeler
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I've done one MegaSquirt (wife's MGB via throttle body injection), and have everything organized for the Opel. Throttle body injection is super easy if you can find a GM throttle body from a mid to late 80's GM 2.5litre (in lots of small GM cars from that era, but most of those have already been melted down and re-sold as new Kia's). The MGB runs great with it and it is kinda cool to cruise around a mountain road with my wife driving and doing the tuning live from my laptop (in my lap) connected to the MegaSquirt via Bluetooth without getting my hands dirty. If I can help out with any suggestions on the MegaSquirt, just ask. I don't hang out at this site often, but Keith knows how to kick me back to attention.

I'm not sure of the source of these images, but this is how mine was done. The one showing the tack welds was downloaded from somewhere on this site (not my picture). The other two might be my trigger wheel. If not, it is exactly how I did mine. It was cut down a bit on the lathe so it not only centers on the pully, but that really helps keep it in place. It ends up really close to the belt, but should be OK.
 

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Opeler
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Thanks RB. Point taken on the bigger exhaust (I have not done it yet, only contemplated).

What about the muffler? I don't like noisy vehicles on the street. I WAS thinking of some sort of 2" in, dual 2" out that would then exit at the rear. Now more likely 2.5" from the header, but then what?
 

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Discussion Starter · #8 ·
A 2.4 will tolerate a MUCH bigger cam than a 1.9 or 2.0 liter. In fact a 1.9 race cam in a 2.4 will still let grandma drive to church on Sunday.
Even an Isky MAX COMP cam is tame, I’d expect the powerband to be 2000-6000 rpms.
Ahh, now that we have your attention, what cam spec might you suggest for John's engine?

If John actually WANTS the power band from 2000 to 6000 rpm, is the Isky Max Comp (OR77) a reasonable choice?
Or should he look for a cam with MORE duration, and/or more lift (limited by his valve spring parameters and piston to valve clearances)?
Is the OR77 LSA ok (and is it 110 degrees as I seem to recall)?
You have mentioned split profiles in the past. Should that be considered?
 
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Discussion Starter · #9 ·
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Ahh, now that we have your attention, what cam spec might you suggest for John's engine?

If John actually WANTS the power band from 2000 to 6000 rpm, is the Isky Max Comp (OR77) a reasonable choice?
Or should he look for a cam with MORE duration, and/or more lift (limited by his valve spring parameters and piston to valve clearances)?
Is the OR77 LSA ok (and is it 110 degrees as I seem to recall)?
You have mentioned split profiles in the past. Should that be considered?
I generally favor split profile cams for 1.9 - based cylinder heads. However the amount of deviation from intake to exhaust is established by flowbench testing of the ports on the cylinder head being used. Since I have no idea what the cylinder head in question flows, I have no solid advice to give.

In general any modern profile is going to be better than the old Isky profiles. Not because they are necessarily bad, but simply because they are 50 year old designs.

With the Isky cams, they are also all run at 110° LSA, but I’ve found the 2.4 liter engines make enough torque as it is. That said, you can run 112° LSA and achieve a smoother idle, higher vacuum, and broader powerband.
 

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Delta Camshaft in Tacoma, WA (DeltaCam.com) will weld and grind any profile you wish for about eighty bucks. Unless you have a blank. Not likely, RB bought them them all. They do not have any Opel cores. Doesn't cost much to ship a camshaft although I would slip it into a much larger box with some bubble wrap and lots of tape on the ends.
 

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Thanks RB. Point taken on the bigger exhaust (I have not done it yet, only contemplated).

What about the muffler? I don't like noisy vehicles on the street. I WAS thinking of some sort of 2" in, dual 2" out that would then exit at the rear. Now more likely 2.5" from the header, but then what?
I would run 2.5” in, 2.5” out. I prefer perforated core mufflers to louvered cores. The perforated core mufflers are a little bit louder unfortunately.

To help lower noise with a perforated core muffler, try using one with offset inlet/outlets as they are definitely quieter than a center inlet/outlet design.

You could then use a single over axle pipe, and converge into a rear resonator. An empty metal can will suffice (like the OEM resonators), and I’ve seen some folks use a stock type Bosal resonator, but they simple enlarged the inlet/outlet tubing sizes.

Another option would be to use a 2.5” inlet muffler with two 2” outlets, run the two tubes over the axle, then split into two separate resonated tips. Most aftermarket muffler manufacturers make some sort of resonated exhaust tips, in various diameters, lengths, and styles.
 

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I've done one MegaSquirt (wife's MGB via throttle body injection), and have everything organized for the Opel. Throttle body injection is super easy if you can find a GM throttle body from a mid to late 80's GM 2.5litre (in lots of small GM cars from that era, but most of those have already been melted down and re-sold as new Kia's). The MGB runs great with it and it is kinda cool to cruise around a mountain road with my wife driving and doing the tuning live from my laptop (in my lap) connected to the MegaSquirt via Bluetooth without getting my hands dirty. If I can help out with any suggestions on the MegaSquirt, just ask. I don't hang out at this site often, but Keith knows how to kick me back to attention.

I'm not sure of the source of these images, but this is how mine was done. The one showing the tack welds was downloaded from somewhere on this site (not my picture). The other two might be my trigger wheel. If not, it is exactly how I did mine. It was cut down a bit on the lathe so it not only centers on the pully, but that really helps keep it in place. It ends up really close to the belt, but should be OK.
I don't know if you can find a set of custom aluminum pulley and trigger wheel that a bunch of us did as a dual group buy several years ago. Very few that bought them ever used them.
BTW. The one shown is set up for EDIS4 and uses the special Opel oil pump cover that holds the VR sensor from a fuel injected Opel motor. I found a Ford Ranger VR sensor that I modified a little to fit.
 

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Opel Rallier since 1977
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In general any modern profile is going to be better than the old Isky profiles. Not because they are necessarily bad, but simply because they are 50 year old designs.

With the Isky cams, they are also all run at 110° LSA, but I’ve found the 2.4 liter engines make enough torque as it is. That said, you can run 112° LSA and achieve a smoother idle, higher vacuum, and broader powerband.
This ^^^^. Indeed the Isky profiles are old and worked with the weaker common valves springs of the late 1960's... which explains the slow opening and closing ramps. This is what makes these cams act like shorter duration cams... as much as a couple of steps smaller than the advertised duration.

For the application listed, where low RPM torque is empahsized over high RPM poeak power, going shorter than you might think is better. To get good torque below 3k RPM, the DCR needs to be kept up; the exhaust scavenging effect is not in play at the lower RPM's, so cylinder filling is not high and keeping DCR up is the only way to keep cylinder pressures high at the lower RPM's. If you ever use ther Wallace DCR computaiton sheets, they include an item called Volume-to-pressure ratio; this parameter is reflective of low RPM torque, below the RPM's where exhaust scavenging comes into play. You want that to stay as large as you can for low RPM torque.

As noted, a new cam profile with faster ramps off of and on to the seats is a good move here. Does not have to be the fastest... and too fast makes the springs more difficult. But it can be a lot than the old Isky grinds.I would be aiming for a true 268 advertised duration with a more modern grind, to keep the DCR up to 8.0. Too big and it lowers DCR, gives a lower V/P ratio, and hurts low RPM torque.

BTW, full fuel cuts can be very violent affairs if done at full song. Ask me how I know!
 
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