Modern 2.5 -2.7L engine build thread - Page 5
OpelGT.com is the premier Opel GT Forum on the internet. Registered Users do not see the above ads.
Thanks Thanks:  0
Likes Likes:  0
Dislikes Dislikes:  0
Page 5 of 5 FirstFirst 12345
Results 81 to 87 of 87
Like Tree32Likes

Thread: Modern 2.5 -2.7L engine build thread

  1. #81
    Opel Rallier since 1977
    Join Date
    Aug 2006
    Location
    Afton VA
    Posts
    841
    Downloads
    0
    Uploads
    0
    Quote Originally Posted by V6Opel View Post
    Those DSS pistons are available in several compression heights and dish volumes so it would be easy to achieve pretty much any desirable CR from below 8 to as high as 13. This is based on a bunch of numbers I ran last night from the Summit website. So given a can such as the GM77 which Charles says runs about between the OR 66 and OR77 specs, what target CR do you think one should shoot for?
    I'd have to run some numbers and it might take a couple of days to get the time.... have a project to build at Ft Knox this week.... not in the gold vault! LOL I need to dig back into those cam specs too.

    But generally, in the upper 9's for SCR is where I would head just at first guess based on other motor work. Are you going to run that Sniper system?

    BTW you can take your static CR and the cam specs and work through any good DCR calculator and look to get a DCR of high 7's to 8. The trick is to interpret the Opel cam specs, which give duration as seat-to-seat, but you need more like .006" lift duration numbers to get an accurate DCR. (The .006" number is for a hydraulic lifter cam; a solid would be different.)

    Just be aware that your rod-stroke ratio is getting low, down close to 1.5, as opposed to the stock 1.9L rod-stroke ratio of 1.8. So it will be the typical low rod-stroke ratio stroker.... it'll not rev as high before starting to flatten out. (There is a reason that a 2.6L Misubishi kept a longer rod and deck height...to keep the rod-stroke ratio up.) So, you'll want to keep the low RPM torque good to keep a reasonable total RPM range. Of course, 2.6L in a light GT will no doubt move along.

  2. Remove Advertisements
    OpelGT.com
    Advertisements
     

  3. #82
    Opel Rallier since 1977
    Join Date
    Aug 2006
    Location
    Afton VA
    Posts
    841
    Downloads
    0
    Uploads
    0
    OK, just managed to dig out those GM77 cam specs and took a stab (educated guess) at the .006" lift duration as being in the 285-290 range. If that is the case, your DCR ends up in the 7.7-7.9 range at first cut without any chamber opening, etc. So not bad.

    But, the overlap is possibly an issue for EFI: 65-75 degrees which is very large for EFI.

  4. #83
    Opeler V6Opel's Avatar
    Join Date
    Aug 2006
    Location
    Dayton OH
    Posts
    333
    Real Name
    Mike Pilkenton
    Downloads
    1
    Uploads
    0
    Quote Originally Posted by Manta Rallier View Post
    I'd have to run some numbers and it might take a couple of days to get the time.... have a project to build at Ft Knox this week.... not in the gold vault! LOL I need to dig back into those cam specs too.

    But generally, in the upper 9's for SCR is where I would head just at first guess based on other motor work. Are you going to run that Sniper system?

    BTW you can take your static CR and the cam specs and work through any good DCR calculator and look to get a DCR of high 7's to 8. The trick is to interpret the Opel cam specs, which give duration as seat-to-seat, but you need more like .006" lift duration numbers to get an accurate DCR. (The .006" number is for a hydraulic lifter cam; a solid would be different.)

    Just be aware that your rod-stroke ratio is getting low, down close to 1.5, as opposed to the stock 1.9L rod-stroke ratio of 1.8. So it will be the typical low rod-stroke ratio stroker.... it'll not rev as high before starting to flatten out. (There is a reason that a 2.6L Misubishi kept a longer rod and deck height...to keep the rod-stroke ratio up.) So, you'll want to keep the low RPM torque good to keep a reasonable total RPM range. Of course, 2.6L in a light GT will no doubt move along.
    Agree on the rod/stroke ratios. I did some research on these and the rule of thumb for engine builders is to hit 1.5 - 1.8 with 1.75 being the optimum ratios. Different pros and cons and depends what you want. Several Honda 4 cylinders are down in the 1.49 - 1.54 ratios and they are screamers. The Opel ratios are 1.83 for the 1.9L, 1.65 for the 2.2L and 1.576 for the 2.4L.

    The biggest issue with the Opel engine I'm learning is the short block. With only 208 deck height to work with and piston compression heights no lower than 27.7 mm (1.09") there is little room for increasing the engine displacement without sacrificing the above ratio.

    And yes I will be running the Sniper EFI system.
    Manta Rallier likes this.
    Mike Pilkenton
    70 GT - Corvette Yellow
    72 GT - Roadster, 3.1L V6, T5
    2008 Opel GT (w/ SKY badges)

  5. Remove Advertisements
    OpelGT.com
    Advertisements
     

  6. #84
    Opel Tinkerer and Rescuer GoinManta's Avatar
    Join Date
    Mar 2002
    Location
    Midlothian, Virginia, United States
    Posts
    7,371
    Real Name
    Charles Goin
    Downloads
    5
    Uploads
    0
    Quote Originally Posted by Manta Rallier View Post
    OK, just managed to dig out those GM77 cam specs and took a stab (educated guess) at the .006" lift duration as being in the 285-290 range. If that is the case, your DCR ends up in the 7.7-7.9 range at first cut without any chamber opening, etc. So not bad.

    But, the overlap is possibly an issue for EFI: 65-75 degrees which is very large for EFI.
    have a more aggressive OR77 on EFI and it didnt seem to have a problem at all

    Had some timing issues with the Motronic, but not the EFI itself.
    CURRENT
    '71 Opel Kadett 4 Door 36D (2.0 L w/ EFI & Auto) - "Mary Ann"
    '92 Senator B - "Professor"
    '74 Opel Manta - "Barbara"
    '72 Opel GT - "Red Baron"

    In the past owned:
    '04, '05, '06 Pontiac GTO
    2 Bitters (#491/#439)
    '73 Commodore GS
    ATLAS ( 74 Manta w/ 2.8L LK5 )
    & many many other Opels and a even few GTs

  7. #85
    Opel Tinkerer and Rescuer GoinManta's Avatar
    Join Date
    Mar 2002
    Location
    Midlothian, Virginia, United States
    Posts
    7,371
    Real Name
    Charles Goin
    Downloads
    5
    Uploads
    0
    Quote Originally Posted by V6Opel View Post
    The biggest issue with the Opel engine I'm learning is the short block. With only 208 deck height to work with and piston compression heights no lower than 27.7 mm (1.09") there is little room for increasing the engine displacement without sacrificing the above ratio.
    You can twist yourself in knots, and go down a million rabbit holes trying to figure out every single hundredth of a CC. But, Math is math, parts are parts, the blocks all have their limitations, and the crank is what the crank is..

    Anything more complex requires custom rods, custom pistons, etc.. A lot of work and cost for a street motor. $ years and 13 motors and I still don't know all of it.. but it still pretty much comes down to variations on what has already been done.

    Everything is a compromise, Cost to Performance to Reliability all have to be considered.. then there is the time it takes the shop to do the work all factor in.

    There is a reason I keep the compression in the 9:1 region, there is a reason for most everything I or the machine shop have done. See the above statement.

    Teasing out those extra HP due to flow benching the head or porting the intake just right so you don't make it worse instead of better, etc.. etc.. is all theoretical to us..

    I mean if you have Bobs skills, and all the tools or have a machine shop at your beck and call, or unlimited money laying around, then that's one thing.

    But I and most everyone else have to pay a machine shop to do the work so that has to factor in as well. Where do you get the greatest improvement.. Where is that spot for diminishing returns on time and money..

    These are all as big of factors as what to build as the smaller details.

    Seriously though, what you do to the intake, what you do to the exhaust, what you do the ignition, all will have a far, far, greater affect on performance than a extra 40 ccs here or there.
    Last edited by GoinManta; 36 Minutes Ago at 10:09 PM.
    Manta Rallier likes this.
    CURRENT
    '71 Opel Kadett 4 Door 36D (2.0 L w/ EFI & Auto) - "Mary Ann"
    '92 Senator B - "Professor"
    '74 Opel Manta - "Barbara"
    '72 Opel GT - "Red Baron"

    In the past owned:
    '04, '05, '06 Pontiac GTO
    2 Bitters (#491/#439)
    '73 Commodore GS
    ATLAS ( 74 Manta w/ 2.8L LK5 )
    & many many other Opels and a even few GTs

  8. #86
    Opel Rallier since 1977
    Join Date
    Aug 2006
    Location
    Afton VA
    Posts
    841
    Downloads
    0
    Uploads
    0
    It's just the matter that an EFI using manifold pressure can see some instability in MP at low-moderate throttle openings and RPM if there is a lot of overlap and thus reversion. (Once the rev's get up and the exhaust pull-through get going, that helps reduce the reversion.) I can only guess how a given system will handle any MP instability...so IMHO is is bit of a 'try it an see' thing.

    And as to the Honda's being screamers with their ratios.... look at the bore and head chamber sizes more to understand them. Small chambers and smaller bores don't suffer as much. The physics of what is going on around TDC has to do with chamber width, shape and size, finite combustion speeds and how fast the piston is pulled down once past TDC, and you are dealing with a wider chamber with the CIH so it is apples to oranges to bring in the Honda's. The more compact the chamber, the more quickly the flame can burn through the whole charge, and so the piston can be jerked down from TDC faster (which is what happens with a low rod-stroke ratio) but still not compromise the peak pressures. (Hope that makes some sense...)

    And, the Hondas are not all down around 1.5 by any means.... and we might as well throw in F1 engines with their high ratios....15K+ RPM. So the Honda's are really just low RPM engines after all LOL
    GoinManta likes this.

  9. #87
    Opel Tinkerer and Rescuer GoinManta's Avatar
    Join Date
    Mar 2002
    Location
    Midlothian, Virginia, United States
    Posts
    7,371
    Real Name
    Charles Goin
    Downloads
    5
    Uploads
    0
    Quote Originally Posted by Manta Rallier View Post
    It's just the matter that an EFI using manifold pressure can see some instability in MP at low-moderate throttle openings and RPM if there is a lot of overlap and thus reversion. (Once the rev's get up and the exhaust pull-through get going, that helps reduce the reversion.) I can only guess how a given system will handle any MP instability...so IMHO is is bit of a 'try it an see' thing.

    And as to the Honda's being screamers with their ratios.... look at the bore and head chamber sizes more to understand them. Small chambers and smaller bores don't suffer as much. The physics of what is going on around TDC has to do with chamber width, shape and size, finite combustion speeds and how fast the piston is pulled down once past TDC, and you are dealing with a wider chamber with the CIH so it is apples to oranges to bring in the Honda's. The more compact the chamber, the more quickly the flame can burn through the whole charge, and so the piston can be jerked down from TDC faster (which is what happens with a low rod-stroke ratio) but still not compromise the peak pressures. (Hope that makes some sense...)

    And, the Hondas are not all down around 1.5 by any means.... and we might as well throw in F1 engines with their high ratios....15K+ RPM. So the Honda's are really just low RPM engines after all LOL
    Given the sniper is designed for bigger motors I think it will be more than fine, and the stupid Motornic with its ancient AFM was fine.

    Its all about going up to the edge, and not crossing it. Thats why Isky designed the Cam for me. The OR-77 Hydraulic worked well but was a big rough around the edges, mainly at cold start and idle. We brought it down from the OR-77 specs to halfway between the tried and true OR-66 and the larger OR-77.

    Everything I have tried to do in my designs was keep the cost within reason, the work the machine shop had to do repeatable.. and make it a streetable motor. The target was for it to perform as well as a 90s BMW motor. Never the intent to be a circle track or road racing motor.
    Last edited by GoinManta; 46 Minutes Ago at 09:59 PM.
    CURRENT
    '71 Opel Kadett 4 Door 36D (2.0 L w/ EFI & Auto) - "Mary Ann"
    '92 Senator B - "Professor"
    '74 Opel Manta - "Barbara"
    '72 Opel GT - "Red Baron"

    In the past owned:
    '04, '05, '06 Pontiac GTO
    2 Bitters (#491/#439)
    '73 Commodore GS
    ATLAS ( 74 Manta w/ 2.8L LK5 )
    & many many other Opels and a even few GTs

Page 5 of 5 FirstFirst 12345

Thread Information

Users Browsing this Thread

There are currently 8 users browsing this thread. (2 members and 6 guests)

  1. GoinManta,
  2. Manta Rallier

Similar Threads

  1. My engine build thread.
    By First opel 1981 in forum 6F - Engine Rebuilding
    Replies: 204
    Last Post: 01-30-2016, 06:09 PM
  2. GeorgeOpel Opel build thread
    By GeorgeOpel in forum Member Projects
    Replies: 22
    Last Post: 06-25-2015, 05:35 PM
  3. Ubernoob's Engine Build Thread
    By ubernoob51 in forum Member Projects
    Replies: 95
    Last Post: 06-07-2015, 01:10 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •