Modern 2.5 -2.7L engine build thread
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Thread: Modern 2.5 -2.7L engine build thread

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    Opeler V6Opel's Avatar
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    Modern 2.5 -2.7L engine build thread

    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!
    Mike Pilkenton
    70 GT - Corvette Yellow
    72 GT - Roadster, 3.1L V6, T5
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    Just Some Dude in Jersey The Scifi Guy's Avatar
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    I'm looking forward to reading your adventure!

    A 2.4/2.5 sounds so much different than non-stroker CIH, I'm really curious what one of those super-stroker 2.7's would sound like.

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    Quote Originally Posted by The Scifi Guy View Post
    I'm really curious what one of those super-stroker 2.7's would sound like.
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    7,000 Post Club wrench459 (R.I.P.)'s Avatar
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    I would think that a high port cylinder head would work better.
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    Si vis pacem, para bellum "If you want peace, prepare for war"

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    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

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    Opeler V6Opel's Avatar
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    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?
    Mike Pilkenton
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    Project 1450 supporter... Site Supporter RallyBob's Avatar
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    Quote Originally Posted by V6Opel View Post

    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.
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    7,000 Post Club wrench459 (R.I.P.)'s Avatar
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    For a modern CIH
    I would think individual throttle bodies.
    Waste spark was cool at one time.
    Now today's coil-over-plug is sort of hot.

    Hey, it's your build so do what you want 2.
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    Just Some Dude in Jersey The Scifi Guy's Avatar
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    Quote Originally Posted by RallyBob View Post
    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.

    In my complete novice experience with 2.4's and side drafts, my throttle response was off the charts and I had to take steps to feather and soften my throttle response to make it more daily driverable.



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    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-Ind....c100508.m3226

    https://www.ebay.com/itm/OBX-Individ....c100005.m1851
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    Last edited by Mark B; 12-16-2017 at 10:01 AM.

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    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.

    https://www.opelgt.com/forums/general...onversion.html

    https://yoshifab.com/store/billet-re...s-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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    Quote Originally Posted by Mark B View Post
    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.
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    Thanks for the input RallyBob. Would it be worth considering using the matching Skunk B-series manifold plenum (1.82L) and fabricating the runners to fit the Opel head?

    https://www.ebay.com/itm/Skunk2-Ultr....c100506.m3226

    Or just go with the ITBs.

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    Quote Originally Posted by Mark B View Post
    Thanks for the input RallyBob. Would it be worth considering using the matching Skunk B-series manifold plenum (1.82L) and fabricating the runners to fit the Opel head?

    https://www.ebay.com/itm/Skunk2-Ultr....c100506.m3226

    Or just go with the ITBs.
    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.
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    Project 1450 supporter... Site Supporter RallyBob's Avatar
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    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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    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.
    Last edited by GoinManta; 12-16-2017 at 07:54 PM.
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    Quote Originally Posted by RallyBob View Post
    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.
    I am not building a 2.7 myself, but how do you size the plenum volume? Those Honda guys are nuts, you can get manifolds with up to 5.5L plenum and using Ford 90mm throttle.

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    7,000 Post Club wrench459 (R.I.P.)'s Avatar
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    A general rule of thumb with a single T/B 1.5 x swept.

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    Quote Originally Posted by Mark B View Post
    I am not building a 2.7 myself, but how do you size the plenum volume? Those Honda guys are nuts, you can get manifolds with up to 5.5L plenum and using Ford 90mm throttle.
    It all depends on your rpm range (camshaft and head breathing), and engine displacement. From this you can determine runner lengths, runner diameters, and plenum volume.

    A good rule of thumb is .8 to 1.2 times the engine displacement for the plenum volume.
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    Quote Originally Posted by RallyBob View Post
    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.
    Yeah, I had a set of GSXR 750 ITBs from a '98 that were 45mm, later ones were smaller. Sold them to a guy for his Toyota 2tg powered Lotus 7 clone. I have seen the BMW ones. The S65 V8 has two banks of four that would be good for two 4 cylinder Opels. But is that the TPS with 6 pins?
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