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Pedal Smasher
1973 Opel GT
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Discussion Starter · #1 ·
Howdy Everyone,

I tried to find a thread with this information and didn't have any luck finding it, if it's out there. I would like to get info on any of the following engine dimensions for a 2.4L CIH...



So stock: piston height, rod length, block height, stroke and piston diameter.

If anyone also has the typical cc's for the dome of a 2.4L head (stock or ported), that would be appreciated. I'm not sure how many on here would have the Wossner high compression pistons, but the loss in cc's for that piston would be nice too.

I'm aware that for blueprinting purposes, these would all need to be measured. It would be nice to know what they theoretically should be, as precise as possible. Just being able to do some rough number crunching can help determine certain things before buying parts that won't work well.
 

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The C24NE has a 95,00mm bore X 85,00mm stroke. The block height is 208mm from centerline of crank to deck. The piston compression height is 31,5mm and the rod length is 134,00mm. The diameter of the floating piston pins is 22,00mm. The combustion chamber size is about 55cm³.
 

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Pedal Smasher
1973 Opel GT
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Discussion Starter · #3 ·
That's a bunch for all that info!!! It really helps with compression ratio calculations, and a few other things. This gives me a good starting point to arrive at a rough dynamic CR.
 

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I forgot to mention that the C24NE pistons have an 11cm³ dish, which added together with the 7,24cm³ head gasket, gives a volume around 73,60cm³. A 20E or S piston has a flat top with valve reliefs and gives with a combustion chamber of 51,20cm³ and a 7,24cm³ head gasket, a volume around 58,74cm³.
 

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Just Some Dude in Jersey
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I can understand, sort of, the desire to "build your own" engine and learn all the little mm numbers and twist your brain into knots trying to make it all work, but wouldn't it be simpler to just have the machine shop do it? Presumably, you'll be buying one of Charlie's engines, so wouldn't it be simpler to just have him and his machine shop work it all out for you? He's got all these numbers already worked out and they're from a known "recipe". It seems that you've zero'd in on these Wossner pistons as your heart's desire, rather than just putting small block Chevy pistons in it as Charlie and his shop are doing. So, just tell them the type of Wossner pistons you want and have them order the sizes of things to make it all work. You really, REALLY, want a machine shop with experience with Opel engines to do the work for you. Don't forget, it would also be wise to have the oil passageway plugs replaced with screw-in pipe plugs. This is not easy to do yourself. It's really hard to beat Charlie's machine shop's prices and they now have experience with a dozen or more Opel engines doing all the machine work and calculations necessary to make the engine you want. The choice is whether to pay a shop at his end to do ALL the parts ordering and work and checking that it will all work with the compression ratio you desire and you simply receive your engine ready for install.....or.....receive the greasy used engine yourself and have to do EVERYTHING from scratch yourself and hope that the weenies at your local shop won't F it up, plus probably have to pay more. Charlie will inspect your engine and test a few things to make sure things are as they should be and the way you want and then ship you a nice spiffy, clean, engine ready for install.

Just a thought....
 

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Pedal Smasher
1973 Opel GT
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Discussion Starter · #6 · (Edited)
Hey Gordon,

I'm not dead-set on the Wossner pistons, but only math will say if they can be used and have to run race gas or not. If I do the math and a flat top is most sensible option, then that is what it will be. But I will only know that for myself, if I do the math. You'll know if things are going to get bad in a hurry, just from that.

Some people don’t want to build the engine, some people that’s what gets their blood pumping.

Sure, the easy thing to do would be to have someone else do it all. But... 1. I'm an engineer, I find stuff like this loads of fun. 2. This is the itch I've been wanting to scratch, doing all the math and blueprinting myself. With that said, I can see the logic in having the machine work that has to be done, done by Charles's shop. I know about the oil plugs, would make sense to have that done. Possible line and deck hones, and boring would make sense. I want to build the whole engine though, it saves me money and it's part of the reason why I'm going for a classic. This is where the fun is at.
 

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Rebuilding a 2.4 into a 2.5 is pretty straightforward.

Increasing the bore from 95 mm to 97 mm ups the displacement from 2410 cc's to 2512 cc's. It's very noticeable...

You could use stock rods and Wossner pistons.

Or aftermarket Maxspeeding rods and Wossner pistons...basically bulletproof.

Or alternatively custom pistons. Venolia has made me 2.5 pistons in 3 different compression ratios...heavily dished for turbo use, slightly dished for higher compression than stock, or flat tops for a bit more...

With modest compression you can use a stock 2.0/2.4 head gasket.

But for racing use or higher compression (or boost), I would go with an aftermarket Cometic MLS. They have a larger bore ID so the fire ring stays clear of the bore.
 
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These are the turbo 2.5 Venolia pistons. Next to a stock 2.4 piston for comparison. Ring stack was also lowered to keep the heat away from the rings.
 

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Here's the flat-top 2.5 Venolia piston. Valve notches are for 1.94"/1.60" Chevy valves, and an old Cam Techniques F324-12 camshaft. .504" lift with roller rockers, 257 degrees duration @ .050", 112 degree lobe separation.
 

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Pedal Smasher
1973 Opel GT
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Discussion Starter · #10 ·
Hey Bob,

Have you ever used the Wossner HC domed pistons in a 2.5? What what your static CR? The cam will be a hydraulic OR-77. Will compression be low enough for premium gas?
 

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Hey Bob,

Have you ever used the Wossner HC domed pistons in a 2.5? What what your static CR? The cam will be a hydraulic OR-77. Will compression be low enough for premium gas?
I have not used the Wossners, as they are much more expensive than Venolias.

With a dome I'm gonna say you are in the 11 -11.5:1 range on any 2.5. OR-77 may not be enough...

Even an OR-99 is on the small side for a 2.5 Opel.
 

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Pedal Smasher
1973 Opel GT
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Discussion Starter · #12 ·
What kind of hydraulic cams out there would be large enough? I want to stick to hydraulic, as I don't want to worry about regular lash checks.

I picked the OR-77H as Charles has seen some decent results with it o a 2.5L.

When I do the math, I'll be able to see how duration impacts dynamic CR. I know lift won't be taken into account in that however. I'll have the stock cam on hand to compare with.

I might end up creating a low cost flow bench to check some other ideas, and if that happens then the head would be checked too. I've got a couple ideas related to the intake needs for the CIH, that would need to be flow benched to see just how much of an improvement is made. The stock intake design is pretty inefficient and the Weber 38 DGV needs an air horn to improve flow. Stock, the DGV flows ~380 CFM from what I've read online which is enough for a CIH. But I'd want to check that myself, and then create an air horn base to replace the base of the Weber plenum. And a new dual plane intake just for the Weber 38, to improve air and fuel delivery. I've shared some rough CAD designs for this in the past. Some pics of roughly what I'm talking about are attached.
 

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What kind of hydraulic cams out there would be large enough? I want to stick to hydraulic, as I don't want to worry about regular lash checks.
None. You will need to make a custom grind to run that sort of compression ratio on the street with pump gas, especially on a larger displacement CIH engine. Nobody in Europe runs 'big' hydraulic cams because of the limitations of the hydraulic lifters (6800 rpms is considered their upper rpm limit). I toyed around with custom hi-performance CIH hydraulic cams back in the 1990's, and was always disappointed. Spring rates need to be *perfect*....too high or too low and the lifters can pump up or collapse. In one case swapping to a smaller solid lifter cam on a dyno session netted 30 more HP compared to the hi-po hydraulic cam.

I picked the OR-77H as Charles has seen some decent results with it o a 2.5L.
Charles also had issues with too much cylinder pressure early on, and had to machine a dish in the pistons to compensate. The big engines can be touchy when it comes to dynamic compression, even with modest static compression numbers.

When I do the math, I'll be able to see how duration impacts dynamic CR. I know lift won't be taken into account in that however. I'll have the stock cam on hand to compare with.
Duration, and lobe separation too. LSA changes the overlaps pretty quickly.

Don't forget the effect the induction and exhaust have on the dynamic compression. I've swapped out to a larger carburetor and seen increased cylinder pressures. Same with better flowing intakes.

HTH, Bob
 
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Just Some Dude in Jersey
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You appear to be planning on making a max power street engine with all the porting, cam, and piston mods........and you're planning on putting a downdraft Weber 38 on it?

Okay, if you're on a budget, that might work, but you'll be severely starving your engine for air. You'll have to weld "feet" onto the downdraft manifold to work on a 2.4 head, plus port it to match the 33% bigger ports.

Why not install a side draft(s) with a DCOE 45/48/50 carb on it? Going with a single side draft would cost about $750-$1000, going with duals would cost another $1000. Charlie has my chromed Midikit single side draft manifold that RallyBob modified, ported, and hogged out to fit and work on a 2.4/2.5 modified engine. You can buy a special solid linkage rod that will connect it up to the stock solid linkage set up. The jetting scenario has already been worked out(for a 45DCOE) by my dyno dude for a stock 2.4 and may or may not require any tweaking for your maxed out engine. The set up will be rock solid and start and work the same every time and your engine will get all the air/fuel it needs or wants. It doesn't appear that Bob will be doing anymore mods in the near future, so you might want to pounce on that manifold before it's gone. It's currently being offered as a package deal with his best used motor with the excellent Omega cam. The OR77 will lope like a mutha on a carbed engine.
 

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Just Some Dude in Jersey
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I just got done talking with Charlie and apparently you've already talked over this Weber 38 or Holley carb downdraft business. My contention is that, yes, they did run 8 cyl engines with 38's, but were these high power set ups or were they actually high fuel economy set ups.

Regardless, I've given you my observations and suggestions. I'm a reknowned non-motorhead and I usually don't get involved in these engine discussions, so I'll bow out at this point.

:veryhappy
 

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Stroker engines are able to rapidly build compression.
One of the reasons to use a camshaft with a late closing intake valve.
It'll help bleed down the rate a tad.
 

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Pedal Smasher
1973 Opel GT
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Discussion Starter · #17 · (Edited)
If you input some rather basic engine parameters into a carb CFM calculator, you'll see that the Weber 38 (which is said to flow ~380 CFM) is enough carb for the task. The problem is the incredibly crude intake manifold design. You have fuel and air slamming into the floor of a single plane intake, and then it's supposed to go right or left to enter the passenger side of the cylinder head. It's a horrible design, which is why some have modified it. The design I shared is rather crude itself but think tubular header for an intake, and you have the idea. It was created before I had SolidWorks. Any carb, mounted to a horrible intake manifold will flow like crap and people will think the carb just isn't enough for the job.

I will also add, that while the goal is for a performance oriented engine, I still have to like the way it looks in the engine bay. I've yet to see a good looking solution for a DCOE, that doesn't have the carb feeding from air that's been cooked by the exhaust headers. Dual DCOE's look great in a Manta, just not in a GT IMO. I like the way a Weber DGV looks in the engine bay, with the Weber snorkel to connect to the air cleaner. I'll just have to create some parts to improve this method of getting air and fuel to the engine.

Bob, I appreciate your thoughts on the pistons and cam. 11 to 11.5 static CR, is difficult to bring down with a cam for pump gas and still have decent street manners. If I was running a modern ECU that has VVT, spark timing, fuel delivery, etc then it would be less of an issue. For an old school engine, the cam would make it pretty difficult for street use or you'd have to run race gas to allow for a higher dynamic. I can get 100 octane at 2 VP Fuels gas stations in my city, but that's rather expensive for regular use. I am at a mile high in elevation, which can help with all this but I still need the car to be capable of driving at a lower altitude with some adjustments, or to be a little below optimum in town.

Later this week, I'll do all the math and put it into a report I've done in the past. Then let the forum scrutinize it. Doing the theoretical work, helps eliminate some of the guess work later.
 
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There is a lot of sense using hydraulic lifters for 2.4/2.5 street engine as those engines rarely spin above 6500 rpm. ENEM X5 is probably the biggest hydraulic cam in the market. At 300 degrees overlap and 108 LSA it might be a tad too big for a street engine.

I am running ENEM X1 in my 2.5 engine. At 284 degrees overlap and 109 LSA it is very tame but allows good engine breathing.

To go along RB’s remark regarding valve springs, it is important not to install too hard springs that will overcome hydraulic lifters. When I spoke to Jan Carneborn from ENEM he strongly suggested to purchase their valve springs that match X1 cam, rated pressure 40-42 kp (100 lbs) at closed valve, 120-125 kp (265 lbs) at 12 mm lift.

I found that combination perfect for street engine.
 

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Pedal Smasher
1973 Opel GT
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Discussion Starter · #20 ·
Thanks PJ for that intel. The Isky OR-77 has a duration of 284 with I believe a LSA of 110. Lift is 0.430. Sounds pretty similar to the X1.
 
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