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Modern 2.5 -2.7L engine build thread

25K views 115 replies 16 participants last post by  V6Opel 
#1 ·
Well I know there are a ton of threads on all kinds of builds and opinions but I thought I would start a consolidated thread on building a 2.5 to 2.7L engine for my 70 GT restoration. I'll be working with Charles Goin extensively on this build over the winter and hope to have this baby running next spring. Here's the basic recipe:

- start with a good 1.9 engine core with X19 head
- bore to max and use the chevy 305 pistons
- Install the 2.3L diesel crank reground to specs
- install big valve package and port the head
- Induction I have not decided on so definitely looking for opinions here. I would love to go EFI with waste spark DIS.

Looking for any and all ideas!
 
#5 ·
the word modern got my attention

Rally Bob is a wealth of info we used to talk about long rod motors years ago

also I was able to order custom pistons for my Toyota 4AGE for under $550 a set

I miss so many good threads with good info on this forum I hope I can stay tuned

good luck
 
#6 ·
I've had several conversations with Charles and hope to meet up sometime over the holidays. Charles, how about describing your current thoughts on the recipe!

Wrench, what high port cylinder head are you referring to? A 2.4L Opel head?
 
#7 ·
Wrench, what high port cylinder head are you referring to? A 2.4L Opel head?
Either a 2.2 or 2.4 is considered a 'high port' CIH head. Airflow from either head can be substantial, though I prefer the 2.2 head for throttle response due to smaller exhaust port volume.
 
#10 · (Edited)
As far as the induction system is concerned, I am considering two options. The first is using the manifold from a 75 Manta and a 70mm Skunk throttle for a Honda, cheap and brand new and can be used with Megasquirt efi. The second would be a ITB setup, sexier and more performance oriented. Most of the ITB options are pretty expensive but I found the OBX systems to be attractively priced. Of course they don't have one for the Opel CIH, but depending on your fabrication skills (mainly to fab a manifold), it would be possible to make one fit. The BMW kit is 40mm throttles, up to the Honda H22 with 52mm throttles. A nice thing about using the Honda TPS and MAP sensors and I assume the injectors, they are plentiful and cheap.

https://www.ebay.com/itm/OBX-ITB-In...08&rk=1&rkt=1&&_trksid=p2045573.c100508.m3226

https://www.ebay.com/itm/OBX-Indivi...d=232361491882&_trksid=p2047675.c100005.m1851
 

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#12 ·
As far as the induction system is concerned, I am considering two options. The first is using the manifold from a 75 Manta and a 70mm Skunk throttle for a Honda, cheap and brand new and can be used with Megasquirt efi.
Don't waste your time with a 70 mm TB on the stock 1975 EFI intake. The intake is the restriction...not the throttle body at that point.

However if you fabricate an intake and the head is modified to flow better, there may be some benefit to the larger TB.
 
#11 ·
For the ignition side of things I would agree with Dan that coil on plug is the way to go. GM LS style coils are an easy and cheap option. The only thing is I think the best way is to have a cam angle sensor as well as a crank angle sensor. The trigger wheel only gives a crank angle. You can use the CAS from Mitsubishi to give both cam and crank positions and have sequential fuel and ignition timing. See this thread on the Yoshifab CAS adapter that replaces the distributor. You can get brackets that relocate LS coils and mount them to the brake bar since you won't have a voltage reg or normal coil anymore.

http://www.opelgt.com/forums/genera...shifab-dsm-crank-angle-sensor-conversion.html

https://yoshifab.com/store/billet-redblock-dsm-cas-adapter.html

Josh told me in a email that the adapter to use a DSM CAS would be $250 and to make a revised one with the CAS guts built in would be $330. I already bought an NOS CAS so will probably send that and a distributor core and see what he charges me.
 

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#14 ·
Depends what you are doing to the engine. Big cam? Go with ITB's, response and idle will be way better.

Forced induction? Plenum might be better. 1.8 liter plenum is too small for a 2.7 liter engine BTW...so just build your own.
 
#15 ·
BTW, motorcycle ITB'S....way cheaper and plentiful.

GSXR 600 and 750 use 38 mm
GSXR 1000 uses 42 mm
Hayabusa uses 46 mm

Keep in mind there's no venturi in an ITB, so they flow more than a comparable DCOE Weber.

Alternatively, BMW uses 50 mm ITB's on their 6 cylinder M3 engines.
 
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#16 · (Edited)
Not sure what I will have.. machine shop had problems sourcing correct pistons and rods based on the online info I gave him. But he is trying to come up with something and he is pretty sure he can have it figured out.

That said, in regards to using a 1.9L Core, I realized I was listening but not hearing when talking to Bob on the subject.

The 1.9L and the 2.0L have the same thickness walls, thats what I heard.

What it meant was STOCK they have the same thickness walls. So cutting a 1.9L to 2.0L ends up being similar to cutting a 2.0L the extra to get to the STOCK 305 Pistons. In anotherwoards there isn't anymore meat on a 2.0L than a 1.9L BUT you don't have to cut a 2.0L to get to 2.0L you DO have to cut a 1.9L to get to 2.0L specs.. THUS a 2.0L has thicker walls than a 2.0L Built from a 1.9L Core.

Which isn't an issue making a 1.9L to a 2.4L based on Bobs' original article : http://clubs.hemmings.com/oana/tech/24l.pdf

BUT going with even more stroke or more bore, and you could run into issues with a 1.9L Core.

But whats done is done, and Ballos and I are still working on a 2.7L built off a 1.9L Core that was bored to 98mm. But unless there is an "Ah Ha" moment and he finds a cheap off the shelf set of components. It maybe a one off.

Going much bigger than 2.5 ( or 2.46 in the case of the 2.4L builds I have been doing ), is proving to be not as straight forward as I had envisioned. That said its not going to stop me in seeing what my machine shop can come up with using a 1.9L Core and a 2.3TD Crank..

BUT What the 1.9L Core becomes will be known sooner than later, once he has the parts that work and the math lets him know the ccs. I will then run it on the Red Baron, and after I get it installed.. I will find how well it can handle the needs of someone that is only going to stress it as far as it can handle on the interstate, not the racetrack.

I know that the stroker 2.5L builds based off the 2.4L Core have so far proven to be a hell of a lot of fun.. but given that I can only bring over 6 motors at a time and they are expensive, that limits what others can do. That said I will have 7 2.3TD Cranks coming in the same batch and they are much easier to ship.
 
#22 ·
6 cylinder M3 tbrottle bodies can be separated. More modular by design.
 

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#23 ·
The dynamics change from throttle body to ITB's.

If you want to play around with some of the variables get a engine performance program.
Plug in changes in the intake runner length and cross-section.
You'll notice the difference in torque and horse power curves.
 
#26 ·
What type of intake design would it take to utilize a single throttle body versus four? And what are the pros and cons of both methods? It seems to me that most modern cars use a single TB and a lot of intake manifolds are now some type of molded plastic. Must be some high temp stuff.
 
#28 ·
Single TB's and plenum intakes are cheaper than ITB's. Hence most OEM's use them. Long runners favor torque, and a common plenum is a nice compromise for top end power too. Idle quality suffers when a big cam is used due to reversion in the plenum from cam overlap

ITB's can be placed closer to the valves, and tend to have very good throttle response. Lack of a common vacuum plenum means they aren't as sensitive to cam overlap. But it all comes at a cost.
 
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#29 ·
For an economy option, I am planning on using a stock Opel manifold welding in bungs for ford injectors.

The tenting the manifold like was done for the Holley.

But instead of a Holley flange the EFI TB flange that Bob made, so an Nissan Throttle body can be used.

Should be a cost effective solution, given the 1.9L/2.0L intakes are starting to get harder to find and with that more expensive.

As for throttle response, etc.. I think the average person wont notice the difference driving the car to a show or to get groceries. :)
 
#33 · (Edited)
How do the two manifolds differ? Since the 3.0L is now effectively a 2.0L by being cut down, how do the plenum and runners compare to the 2.2L and even the 1.9L? Is it possible to modify the 3.0L to fit the low port head? I think if you are not looking for the max on a 2.0L engine or even Mike's 2.7L, the cut down 3.0L would flow plenty. What is the availability of the 3.0L mainfolds?
 
#35 ·
2.2 EFI intake flows the worst.

1.9/2.0 intakes are essentially the same, and flow better than the 2.2 intakes.

2.4 intake flows better than all of these, but is very tall as it is designed for a truck.

3.0 intake is similar to the 2.4 in terms of flow, but is shorter in height. High port design like the 2.2/2.4.

None of them will touch a decent DSD intake with carbs or ITB's.

Cut down 3.0 intake below.
 

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#36 ·
Bad is all relative..

Here is the thing to consider..

Most these things would be never ever be noticed by the average Opel owner.

No Opel owner will push thier car to 6000+ RPM, except when possibly doing a 1-2 or 2-3 shift.

Maybe when on the interstate and drop shifting for 5-4 or 4-3..

Most Opel owners will never have more than 20,000 miles on thier new motors. So the "extreme wear" issues I feel are also overly exaggerated.

The Average Opel owner, with a stock 2.4L, using a stock efi system wouldnt even push it to 100% for that long.

Would the difference between a custom plenum or custom side draft efi system get more power or throttle response over a modified carb intake or just a bone stock EFI manifold? Sure, if a professional was dynoing it or driving it.

The average Opel Owner is looking for performance improvement over stock.

A 2.0L build with a 32/36 vs a stock 1.9L with a Solex is night and day

That 2.0L vs a 2.4L with Motronic is equally a night and day difference.

These are differences anyone could notice.

The difference between a 2.6-2.7L over a 2.4L-2.5L not so much. Will it be there, sure. Will it be as big a difference to the average Opel owner/driver as the other examples ? I highly doubt it.

These HUGE and BAD differences are parsing things that make the most subtle of differences, that you have to be a professional to even notice. Even then the only way a professional will really notice is on a Race Track.

But that just my take on it.
 
#38 ·
Apples to apples, a DSD with ITB setup versus a 2.2 EFI intake on a mildly prepped 2.4 big valve head should make 50-55 more hp.

Don't tell me you won't feel that...
 
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#40 ·
What cam ? Valves ? Who did the porting and deshrouding ? How is exhaust setup.. ? Etc.. etc..

See I do listen..

;)

Now that said, cost ? How streetable is ITB setup.. Will it cruise at 3500 rpm and still behave at stoplights. For most Opel Owners that matters more.
 
#41 · (Edited)
I would think ITBs are very streetable going by the number of BMWs that are running them. Low speed driveability problems with DSD setups are more a camshaft issue I think due to the carbs being governed by vacuum. With stand-alone EFI you can force the fuel curve you want and it doesn't go out of tune on a humid day. Besides, if I had that kind of power I would be pushing it any chance I got. My Vibe GT sees the 8500 redline all the time, it's a rush when the lift kicks in.
 
#42 ·
ITB's are indeed very driveable and flexible. True they cost more than a plenum intake and. But there is a reason BMW uses them on production cars, every sportbike for the past ten years uses them, and virtually every modern motorsports engine uses them. They work.

Sportbikes with 200 hp per liter output, steady 900 rpm idle, razor sharp throttle response, and 14,000 rpm redlines. I'd say that covers all the bases...

Initial costs and setup are higher. No doubt about that!
 
#44 ·
Because the 2.3 crank already has a longer stroke and is much easier to grind for the rebuild than welding and modding a 2.4 crank. At least this is what I've been told.
 
#47 ·
The 2.3 crank has much larger journals which can be offset machined down much easier than welding up and regrinding the 1.9 crank. The result is a gain in stroke. Again, this is what I'm told.
 
#48 ·
That is correct. The larger journals allow for offset grinding without having to weld material. So your not limited to what stroke or rod length you want.

The 2.4L crank is quite a bit different than the stock 1.9L crank, where as the 2.3L weights are about the same and other than the rod journals, its bout the same. Bob would know more about the specific differences.
 
#50 ·
" There is No replacement for Displacement" - Anon ;)

That said, its only 0.2 than the 2.5, once at 2.5L your already a stroker.

The real difference is the CAM.. driving the 2.4L with the stock cam vs the 2.5l with the OR-77 was a night and day difference. Given the cam was similar to yours. I would say if all you did was bump your displacement from 2.5 to 2.7 you would only notice a small difference overall.

The reason I am designing the 2.7L off the 2.3L crank is the same reason I went to 2.5L when rebuilding the 2.4L. Working on building a recipe that uses quality but less expensive off the shelf components.

Will know more once I get the 2.7L in my hands and assembled and that SHOULD be this week. I have a new cam coming for it as well designed by Isky for this motor.
 
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