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2.5 crank worth it in 2.3?

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  • 2.5 crank worth it in 2.3?

    Assuming you do not want to bore out to the max and just upgrade with higher compression pistons, new rods and some hotter than stock cams (evo springs etc) is it worth upgrading to a 2.5 crank? I do not want to bore out to the max allowable to do a true 2.5 but would that defeat the point? I'm running full standalone so tuning is not an issue.

  • #2
    Your new pistoms will require a different compression height. a 2.3 piston is 1.5mm taller from pin centre line to crown. So, in doing, you would need a specific piston design which is likely more expensive than a set of 2.5 pistons and the cost of boring to 95mm.
    Sport Evo No.47

    My Sport Evo Restoration

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    • #3
      Yes, I figured as much with the difference between the 87 and 84mm cranks that piston height will be custom. I actually found a thread from 2013 on the site that gives some great feedback. It seems like I really should focus on the top end as the 2.5 (crank only) doesn't seem to benefit nearly as much without going all the way on bore etc. I suppose I have answered my own question then but I do know the 2.5 crank is better all around. The gains probably don't justify the price and custom pistons though.

      I'm planning on getting a backup motor to slowly build as I drive mine into the ground is why I ask and a 2.5 crank was on offer.

      Here's the thread in case anyone else has the same thought:

      Also a interesting side bar about how to port the heads:

      Comment


      • #4
        Just out of curiosity, how many miles on the 2.3L? I've found that 100K miles is about the time the stock cylinder bores start to ovalize and need to be bored out. I pretty much always wind up at 94mm before the cyls are round again. So one of my favorite's is a 94mm 2.3L with 11:1 pistons, light head porting and a pair of cams. Put A-N on it and you're way beyond a basic 2.5L in performance.
        Ron ///Man

        • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
        • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
        • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
        • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
        • '89 M3 M3T / ITR Club Racer
        • '94 Spec E36 - Eh....
        • '09 M3 - Tarmac Terrorist
        • '04 330Xi Sport 6 Speed - Snowmobile
        • '07 530 Xi - Highway Star
        • http://www.imwcarparts.com/e30-m3-parts.htm


        Comment


        • dudley123
          dudley123 commented
          Editing a comment
          I've followed your recommended recipe along the last few years of reading your posts. This was the exact recipe I gave to my builder locally! So far it runs like a top!

      • #5
        Originally posted by Ron ///Man View Post
        Just out of curiosity, how many miles on the 2.3L? I've found that 100K miles is about the time the stock cylinder bores start to ovalize and need to be bored out. I pretty much always wind up at 94mm before the cyls are round again. So one of my favorite's is a 94mm 2.3L with 11:1 pistons, light head porting and a pair of cams. Put A-N on it and you're way beyond a basic 2.5L in performance.
        So 160k on original equipment though I already run standalone and carbon box. Shes puffing smoke on lift after hard acceleration so valve seals are definitely shot but some could be blowby... Running the no cat super sprint so I keep the mosquito at bay.

        Are you saying that when you punch out to 94mm you are still running the 2.3 crank with 11:1? That's sort of the direction I wanted to go along with valve job, better springs etc. Sort of an OEM ++
        But adding the cams... with that 2.5 it's like a stroker and you retain more of that lower end torque. Maybe it's a pipe dream though.

        Comment


        • #6
          Originally posted by proctor750 View Post

          So 160k on original equipment though I already run standalone and carbon box. Shes puffing smoke on lift after hard acceleration so valve seals are definitely shot but some could be blowby... Running the no cat super sprint so I keep the mosquito at bay.

          Are you saying that when you punch out to 94mm you are still running the 2.3 crank with 11:1? That's sort of the direction I wanted to go along with valve job, better springs etc. Sort of an OEM ++
          But adding the cams... with that 2.5 it's like a stroker and you retain more of that lower end torque. Maybe it's a pipe dream though.
          If you have never driven a brand new 2.3 that was properly built, back to stock specs even, you would be amazed at how different it feels than a worn out 160k 2.3.

          T

          Comment


          • #7
            Originally posted by proctor750 View Post

            So 160k on original equipment though I already run standalone and carbon box. Shes puffing smoke on lift after hard acceleration so valve seals are definitely shot but some could be blowby... Running the no cat super sprint so I keep the mosquito at bay.

            Are you saying that when you punch out to 94mm you are still running the 2.3 crank with 11:1? That's sort of the direction I wanted to go along with valve job, better springs etc. Sort of an OEM ++
            But adding the cams... with that 2.5 it's like a stroker and you retain more of that lower end torque. Maybe it's a pipe dream though.
            Not only valve seals are shot at 160K, so are the guides which probably is why the seals are shot. That is correct, 94mm with stock 2.3 crank and 11:1. If you do 2.5, you bore to 95mm and lose 2-3 .25mm overbores for future rebuilds, plus you get to spend a ton of $$$ on the 2.5 crank. I prefer to save as many overbores as possible given these blocks are unobtanium. Is the 2.5 better, sure, but the costs are high. Please define "better springs". Have you made a choice?
            Ron ///Man

            • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
            • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
            • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
            • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
            • '89 M3 M3T / ITR Club Racer
            • '94 Spec E36 - Eh....
            • '09 M3 - Tarmac Terrorist
            • '04 330Xi Sport 6 Speed - Snowmobile
            • '07 530 Xi - Highway Star
            • http://www.imwcarparts.com/e30-m3-parts.htm


            Comment


            • #8
              Originally posted by Ron ///Man View Post

              Not only valve seals are shot at 160K, so are the guides which probably is why the seals are shot. That is correct, 94mm with stock 2.3 crank and 11:1. If you do 2.5, you bore to 95mm and lose 2-3 .25mm overbores for future rebuilds, plus you get to spend a ton of $$$ on the 2.5 crank. I prefer to save as many overbores as possible given these blocks are unobtanium. Is the 2.5 better, sure, but the costs are high. Please define "better springs". Have you made a choice?
              Bingo. This is why I did not want to bore out to final bore to save future rebuilds if needed. So 2.5 crank not worth it with or without the full bore. Copy.


              As for springs I was thinking supertechs. I contemplated shim under bucket but won't ever run even the future built motor to 8k so not really necessary.

              I think you are right, stick to 2.3 crank, bore to match some nice 11.5 pistons, 2xx cams, refresh head, retune, done.

              Side note: Although smokey, she dynoed on a dynojet 186whp 170wtrq so she ain't dead yet.

              Comment


              • #9
                Evo valve springs are fine, preferable even. The Evo springs were designed (and homologated for Grp N) by BMW to work with stock valves and retainers and are good for 7800rpm on stock cams*. And they are reasonably priced.

                Group N homologation chip rev limit.
                Sport Evo No.47

                My Sport Evo Restoration

                Comment


                • #10
                  Originally posted by stevesingo View Post
                  Evo valve springs are fine, preferable even. The Evo springs were designed (and homologated for Grp N) by BMW to work with stock valves and retainers and are good for 7800rpm on stock cams*. And they are reasonably priced.

                  Group N homologation chip rev limit.
                  Im probably going to run 286/xxx cams, slightly larger valves etc. so unsure if the evo stuff is still going to be the best solution? I'm not even sure where to get those new anymore. The BW/turner stuff is shrick (Although I read somewhere on here the shricks worked well with shrick cams, go figure).

                  Comment


                  • #11
                    I have a set of EVO springs for sale if you want to go that route. Came out of Steve Dinan's club race engine so very low time on them.

                    T

                    Comment


                    • #12
                      Originally posted by stevesingo View Post
                      Evo valve springs are fine, preferable even. The Evo springs were designed (and homologated for Grp N) by BMW to work with stock valves and retainers and are good for 7800rpm on stock cams*. And they are reasonably priced.

                      Group N homologation chip rev limit.
                      Words of wisdom here. My go-to valve springs are Motorsport, unless it's a full-on race engine where I prefer the Schrick race valve trane setup - single groove valves, shim-under buckets etc. Big $$$. Deitrich's springs are incredible as well, and a step up from Motorsport's with better spring pressure, but unfortunately Dietrich only made them for a very short time. Motorsport springs are fine with 284/276 Schricks. As far as Supertech's go, I only used them in one engine and had two inner springs break.
                      Ron ///Man

                      • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
                      • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
                      • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
                      • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
                      • '89 M3 M3T / ITR Club Racer
                      • '94 Spec E36 - Eh....
                      • '09 M3 - Tarmac Terrorist
                      • '04 330Xi Sport 6 Speed - Snowmobile
                      • '07 530 Xi - Highway Star
                      • http://www.imwcarparts.com/e30-m3-parts.htm


                      Comment


                      • #13
                        Proctor,

                        Set goal with your engine. Goal/s are set often by the budget you have in mind. Goal/s is one large package what do you want from your engine?. Don't start with the unknown "Go" and then puzzle up the engine on the fly.

                        Never forget the DNA of the 4cyl engine and work around that, also the use. What power curve are you after? What rpm are you after ? so much to consider.

                        If I were you, I would use the 2.5 stroke. I promise you will have big smile on your face with 87mm stroke but one must take full advantages from it. Be after efficiency !!!

                        There is one for sale at present very clean crank for $2800obo on ebay probably a member here ? Have not check lately but how much is the 2.5 crank New ? perhaps out of stock with unknown ETA from BMW AG ? But if you can not justify the money vs the return then 2.5 crank is not an option.

                        Regards,
                        Anri
                        E30M3
                        E28M5
                        E24M6
                        E24M6
                        E24M6
                        E24M6
                        E31840Ci/S62.

                        https://www.youtube.com/channel/UCyh...=dd&shelf_id=0

                        Comment


                        • #14
                          Originally posted by First E30 M3 View Post


                          There is one for sale at present very clean crank for $2800obo on ebay probably a member here ? Have not check lately but how much is the 2.5 crank New ? perhaps out of stock with unknown ETA from BMW AG ? But if you can not justify the money vs the return then 2.5 crank is not an option.
                          New 2.5l crank with bearings costs ~3000 Euro these days
                          Still available
                          Last edited by Markus; 05-29-2022, 07:16 PM.

                          http://www.bmwm3shop.de

                          Comment


                          • #15
                            As Markus says, the 87mm crank will set you back 2700 plus about 300 fro main bearings. I bought the setup 12 months ago. If you are OK with the additional crank price, then go for it. Everything else will be the same cost as a 2.3 build. I built a bored out 2.3 last year and it went in the car 3 weeks ago and was mapped last week. In my experience the torque improvement is very much worth it and power delivery is significantly improved particularly above 5k revs. There’s lots of things people say to look out for when boring out a 2.3, but it all went smoothly for me and I had no issues at all. I spoke to a couple of very experienced engine builders here in the UK and they all told me not to worry, in their experience problems of porous blocks etc are extremely rare. I will post up a thread on my engine build soon. I also got my head ported by Moufang to 29.5mm, thanks to Markus who helped with arrangements. I used Evo springs with oversize super tech valves.

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