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20E head vs 2.4 head.


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Hello all,

Not sure if this should go here or in the engine section. Please let me know if it should be somewhere else.

I've been struggling with a standard, non-unleaded cylinder head. I've got one valve I just can't get a 100% seal on. With a 100psi in the cylinder I can hear it passing slightly.

I'd decided to wait for a later unleaded head but in the meantime I've been doing a lot of reading on here and on the OpelGt forum.

Anyway, I have a 2.4 head with bigger valves and high ports and I understand it is possibly better flowing.  However the larger combustion chamber lowers the CR when stock 

So I've measured the combustion volume on both (see pictures) and I get GTE volume 50cc and 2.4 volume as 53cc. This is quite crude as I can only measure to the nearest cc.

First question is can anyone confirm or offer better/factory figures?

Secondly I've estimate the CSA of the combustion area tracing it with graph paper and counting up the squares. I get 51.6cm² 

Second question, can anyone provide a better value?

I calculate that to lower the volume of the 2.4 by 3cc I need to take 0.58mm off the head or 23 thou.

Would anyone like to check my maths?

I spoke to the machine shop today and he didn't see any problems physically removing this much.

Q3 Since I need to deal with cam timing would anyone suggest removing any more? Is a CR of 9.4 about right?

Finally, the Cam gear has an effective radius of 58.5mm which means a skim of 0.58mm will retard the timing by 0.57 degrees...I think.

Rallybob has a number of posts suggesting that advancing the timing a little is a good thing on these engines. About 3 deg is mentioned. Therefore retarding the timing at all doesn't sound good.  He had a great post about drilling out the locating hole on the cam gear and using offset bushings as a DIY friendly way of advancing the timing, so that's the plan.

As always, any thoughts or experience appreciated. Head is booked in for Friday to be skimmed and for 40 quid I think I'll give it a go as a little project.

The worst that can happen is I'm out £40 but I could end up with a big valve unleaded head and learn a few things along the way.

Photos and calcs

https://photos.app.goo.gl/3nafT3pqwjwVMsPS8

DIY adjustable cam.

https://www.opelgt.com/threads/source-for-cam-vernier-sprocket.26749/page-3 

Offset bushings

https://www.ebay.co.uk/itm/281727256845

 

cheers all

K

 

 

 

 

 

 

Edited by Nivlek2525
Lots of typos
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Problem I see is your about to make your 2.4 head none viable for the long term project you had planned. Not easy to come by or replace, although you could always use a copper 0.5mm head gasket I suppose .

however std CR is about 9.4:1 on GTE, so you are right that it would drop your CR to a smidge under 9:1.  But this will be offset by heads flow characteristics at high rpm range. 
edit. What I am talking about here is the effective CR at rpm, not static. As it depends on cylinder fill at rpm, the better breathing the head is at rpm, the higher the effective CR will remain through the rev range. E.g. if the head was so asthmatic that it was 50% at 5500rpm, then you would only have 1/2 the static CR. Keeping cylinder fill is more important that static CR (mostly). A change in 0.4/1 CR is negligible to a 5% flow improvement. 

You can buy a cam vernier still, that will alloy you to refine the camshaft, remember they do go out slightly as the chain stretches a little. Advancing the cam will bring back a bit of bhp in the rev range. https://mgispeedware.com/camshaft-calculator/ , although I would consider a slight retardation with the bigger valves better for lower rpm drive ability.

So to me the real cost is price to skim plus the 2,4 head. 

Also, have you got a suitable inlet to fit the 2.4head already? 
 

 

Edited by Jessopia74
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As stated above, the cost of the skim is not what you need to factor in but the cost on the inlet and thermostat housing as they are bespoke to the 2.4 with a higher inlet and a smaller thermostat inlet. I do have gaskets for the thermostat housing if you need one as i had to buy a pack of 10 🙂 so that will save you a couple of quid!!

And surely an adjustable vernier would not be far off the cost of modifying a static one?

What fuelling are you running?

Andy

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Thanks both, really appreciate the response. 

My thoughts were if I do go down the 2.4 route I'd try to start with a complete set up from a running frontera. In that case I'd have the head from that engine. If I decided to use the head I have for a 2.4 build then the skim raised the CR to about 9.7ish to 1 as the frontera is standard at 9.2 therefore I didn't feel like it was wasting or ruining the head for future use. You are right, I was very much focusing on static compression ratio and trying to get it back to standard. I may need to do a little more reading. 

The plan was to use the existing inlet manifold for now but mounted higher up on a spacer plate matching the 2.4 head to the 2.0 inlet. Again, this is described on OpelGt in a bit of detail an feels like something I could do myself with little outlay. I think you may even be able to buy them.

I have to admit I've not given too much thought to the thermostat housing.

With regards to the Vernier they are about £170 where as I think I can modify the pulley myself and buy the bushings for £20. So there is a bit of a different but agree it would make a good upgrade.

This is just something to keep me interested over the winter, with very little outlay and to allow me to try out some of the things I've read about on the forums. If it doesn't work, then it's not the end of the world. 

Maybe it's worth mocking up the head before committing to machining it down to see if I can get everything to hand together.

Many thanks both.

K.

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Seems reasonable. Just remember though that a CR change of such little will yield very little. A cam change would be more beneficial. Like the idea of the adjustable cam gear for £20 though, be interesting if you can keep it to such a budget 😎

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5 hours ago, Nivlek2525 said:

Thanks both, really appreciate the response. 

My thoughts were if I do go down the 2.4 route I'd try to start with a complete set up from a running frontera. In that case I'd have the head from that engine. If I decided to use the head I have for a 2.4 build then the skim raised the CR to about 9.7ish to 1 as the frontera is standard at 9.2 therefore I didn't feel like it was wasting or ruining the head for future use. You are right, I was very much focusing on static compression ratio and trying to get it back to standard. I may need to do a little more reading. 

The plan was to use the existing inlet manifold for now but mounted higher up on a spacer plate matching the 2.4 head to the 2.0 inlet. Again, this is described on OpelGt in a bit of detail an feels like something I could do myself with little outlay. I think you may even be able to buy them.

I have to admit I've not given too much thought to the thermostat housing.

With regards to the Vernier they are about £170 where as I think I can modify the pulley myself and buy the bushings for £20. So there is a bit of a different but agree it would make a good upgrade.

This is just something to keep me interested over the winter, with very little outlay and to allow me to try out some of the things I've read about on the forums. If it doesn't work, then it's not the end of the world. 

Maybe it's worth mocking up the head before committing to machining it down to see if I can get everything to hand together.

Many thanks both.

K.

Lots of great info over on the OpelGT forum for the 2.4, helped me out a lot. Got a few pics of my 2.4 on my blog that might help as well if you have not already headed over to take a look. http://theopelproject.com/

If you do go the 2.4 route and need pistons i think the best option is the Wossner ones, but a little pricey, but they have the skirts coated for longer life and the standard pistons (if you can find them) are a similar price now.

 

Andy

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Got it. £10 plus postage. Pm your email will send you pics first see of it's what you want instead of the nice whiney ones on German eBay. 

As said you can adapt a standard one to fit 2.4 

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I mocked this 10mm spacer up out of hardboard just to make sure it is possible. It's really rough but I just wanted to get a feel for what it would look like.  I'm happy I can make something suitable out of 10mm aluminium. I'll also need an equivalent spacer to apply pressure on the exhaust manifold. 10mm is just enough to get over the 2.4 dowel and I can add another dowel to the spacer to match up with the 2.0 gasket and manifold.

The ports are about the same overall height but the 2.4 ones are wider apart so the spacer just needs a slight taper to match up. It's not actually that much.

Cheers all.

https://photos.app.goo.gl/nFvfXJUfwgExLqGm6

 

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Looking good. 

Could you run the 2.4 head on the 2.0 block, or was that the plan anyway? if you already have the head then rather than spending the money on finding a complete 2.4 you could spend the money getting the 2.0 bored out to a decent size? probably more piston option for the 2.0 that might help to keep the cost down?

 

Andy

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5 hours ago, 611 said:

Lots of great info over on the OpelGT forum for the 2.4, helped me out a lot. Got a few pics of my 2.4 on my blog that might help as well if you have not already headed over to take a look. http://theopelproject.com/

If you do go the 2.4 route and need pistons i think the best option is the Wossner ones, but a little pricey, but they have the skirts coated for longer life and the standard pistons (if you can find them) are a similar price now.

 

Andy

Thanks Andy. I think I've read through most of your website now. It's very good and really informative. I had the same chain tensioner guide issue you had. Because I'd read through your site I knew what it was straight away. I meant to say thanks at the time.

8 hours ago, Jessopia74 said:

Seems reasonable. Just remember though that a CR change of such little will yield very little. A cam change would be more beneficial. Like the idea of the adjustable cam gear for £20 though, be interesting if you can keep it to such a budget 😎

Thanks J

Would you leave the head standard and not skim it? As I said I was just trying to get back to the 9.4 to 1 the GTE would have had so that I wasn't taking one step forward and one back.

K

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9 minutes ago, Nivlek2525 said:

Thanks Andy. I think I've read through most of your website now. It's very good and really informative. I had the same chain tensioner guide issue you had. Because I'd read through your site I knew what it was straight away. I meant to say thanks at the time.

Im glad it helped out. There was a lot of head scratching at the time until i finally figured it out. One of the reasons for having the blog was to be able to record all these findings and hopefully help others out and as the build has taken so long its handy for me to look back and see what i did 🙂

Its so much easier for me to record things and categories unlike having a post on here. and add all the extra stuff like the PDFs and parts links.

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14 minutes ago, Nivlek2525 said:

 

Would you leave the head standard and not skim it? As I said I was just trying to get back to the 9.4 to 1 the GTE would have had so that I wasn't taking one step forward and one back.

K

I think you will regret skimming that much off the head in the future for sure, you definitely would never notice 0.4/1 change in the CR, so it is not something that I would do (or consider a good use of the £40).  The mods for the rest is a great idea to mount inlet plenum though, as the 2.4 sits too high, so that would be useful.

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15 minutes ago, 611 said:

Looking good. 

Could you run the 2.4 head on the 2.0 block, or was that the plan anyway? if you already have the head then rather than spending the money on finding a complete 2.4 you could spend the money getting the 2.0 bored out to a decent size? probably more piston option for the 2.0 that might help to keep the cost down?

 

Andy

Hi Andy. 

Stage one is 2.4 head on a 2.0 block. My 2.0 head is leaded and one of the valves won't seat 100%. I have the 2.4 head sitting unused and it's unleaded. So I'm just trying to make it work and maybe get a slight advantage over a standard 2.0 head with bigger valves and a better flow. I think I can make it work with very little outlay. I'm just not sure whether to get it skimmed or not to raise the CR.

Any spare money is being spent on the car at the moment. Once that is finished I can then start savimg to put money into an engine build.

You never know, a really low mileage, one careful owner 2.4 frontera might turn up🤣.

2 minutes ago, Jessopia74 said:

I think you will regret skimming that much off the head in the future for sure, you definitely would never notice 0.4/1 change in the CR, so it is not something that I would do (or consider a good use of the £40).  The mods for the rest is a great idea to mount inlet plenum though, as the 2.4 sits too high, so that would be useful.

Cheers J

I'm convinced. I guess I can always take it off later....a lot harder to add back on. 

Really helpful 👍

I'll use the money to order the aluminium for the spacers.

Thanks.

K

 

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3 minutes ago, Nivlek2525 said:

Hi Andy. 

Stage one is 2.4 head on a 2.0 block. My 2.0 head is leaded and one of the valves won't seat 100%. I have the 2.4 head sitting unused and it's unleaded. So I'm just trying to make it work and maybe get a slight advantage over a standard 2.0 head with bigger valves and a better flow. I think I can make it work with very little outlay. I'm just not sure whether to get it skimmed or not to raise the CR.

Any spare money is being spent on the car at the moment. Once that is finished I can then start savimg to put money into an engine build.

You never know, a really low mileage, one careful owner 2.4 frontera might turn up🤣.

Good plan to keep the car going. If the head does work out ok then you could just look at getting the bottom end sorted and swap out the block, nice easy option.

You may be lucky and find one, but i think the old scrappage scheme got rid of a lot 🙂 

The problem you have is even if it is low mileage unless you know the history of the car you will never know how much work is needed until you take the head off. If its low mileage and been neglected you will probably be in the same boat as a high mileage one that's been looked after. Im not sure if this is the case for all of the 2.4's but from my research the rods dont have the oil squirter hole like the 2.0 so i think they suffer more if they are not kept up to scratch with oil changes. The Haynes manual says they have the squirter but everyone i spoke to said they didn't. Just another thing to keep in mind when you are considering the options for the bottom end.

The guys on the OpelGT site seems to mention a few piston options for the standard blocks with just a small amount of modification, so might be some other options than finding the manta pistons!

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Some info that can be usefull, the combustion chamber, the list is not complete...

A1.6N  46,2ccm

 16S     40,3ccm

17S  40,3ccm

16S 44,3ccm 

19N 52,7ccm

X19E 50,4ccm

19H 48,8ccm

X19 46,2ccm

X20 53,8ccm

X20S 53,8ccm

X20S 53,8ccm

X20E 49,8ccm

XR2E 49,8ccm

XR2EH 48,9ccm

P2 53,8ccm

P2E49,8ccm

XR22 55,0ccm

P22 55,0

X24 54,6ccm

Some data can be confusing, as an example the 1.6 had 80 Din Hp but later cause of enviroment rules 75 Din Hp. 

X means the camshaft has got 4 bearings, P is leadfree, E is injection 

 

 

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On 04/12/2020 at 17:43, H-400 said:

Some info that can be usefull, the combustion chamber, the list is not complete...

A1.6N  46,2ccm

 16S     40,3ccm

17S  40,3ccm

16S 44,3ccm 

19N 52,7ccm

X19E 50,4ccm

19H 48,8ccm

X19 46,2ccm

X20 53,8ccm

X20S 53,8ccm

X20S 53,8ccm

X20E 49,8ccm

XR2E 49,8ccm

XR2EH 48,9ccm

P2 53,8ccm

P2E49,8ccm

XR22 55,0ccm

P22 55,0

X24 54,6ccm

Some data can be confusing, as an example the 1.6 had 80 Din Hp but later cause of enviroment rules 75 Din Hp. 

X means the camshaft has got 4 bearings, P is leadfree, E is injection 

 

 

Great info Herman,

Using my crude method I got the XR2E measurement close at 50cc. I was quite far out on the x24, I measured 53. A syringe isn't the.most accurate way to do it I guess. 

Many thanks.

K.

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