DPG Posted May 13, 2012 Share Posted May 13, 2012 (edited) Hi guys, I have been doing some research online and just wanted to get the forums opinion on this. I am building an L28 N42, bored to 89mm, L28 crank, and am debating on the rods to use. Seeing as I have to do custom pistons, I can do whatever I want with them. I have read that a longer rod will benefit me in a higher RPM set-up. I'm looking for 8000rpm, so would using 133mm L24 rods with a shorter piston be better for me in making power compared to an L28 rod with standard L28 pin height? I have read that long rods will give better TDC dwell resulting in longer combustion time, allowing more efficient power to be made, and a short rod will give slightly better torque down low. Also, would the Fj20 rods and custom piston give the best combo bc of the 140mm length? Any hardcore engineers here to shed some light on the L6 engine and what I should do? Thanks! Edited May 13, 2012 by DPG Quote Link to comment Share on other sites More sharing options...
PMC raceengines Posted May 13, 2012 Share Posted May 13, 2012 (edited) I have done so many tests on this ,, and L24 rods are not long in the hole sceem of things and there is hardly a diffrence in hp not worth talking about Edited May 13, 2012 by PMC raceengines Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted May 13, 2012 Share Posted May 13, 2012 (edited) I would definitely trust pmc. Also you're "higher rpm" set up involves a lot more than just rods, such as cam, head work, intake, and exhaust. I'm sure for what you want, you can easily get it with either l24 rods and custom pistons, or some l28 rods with much cheaper ready-to-order forged pistons edit: if you're boring to 89, then you can just use forged 240sx pistons which are plentiful. Edited May 13, 2012 by BluDestiny Quote Link to comment Share on other sites More sharing options...
PMC raceengines Posted May 13, 2012 Share Posted May 13, 2012 (edited) Over the Last 25 years i have built many L28 motors with diffrent rod lenth from 130 133 137 140 mm and my normal combo i run 140mm fj20 rods and a custom piston ,, is it better than other combos ,im not so shore if its better but it makes good hp and it revs very nice . I seen this combo many years ago in GTU cars and its been good to me . One time i built a motor to find out if the rods made a difrance and i set it up with L28 rods and pistons to set a bench mark , then we put 133mm l24 rods in with custom pistons .. gess whot no change . with in 3hp and no real gains ,to keep it fair i used the same rings on the pistons . Then i went to 140mm custom rods and a 28mm comp hight piston , the test was not so fair as the last test piston and rod were much lighter , and power and torque were better not by much only very small amounts ... Its the exhaust that makes or breaks a good engine at 8000 . And port volume. The rod has little afect over it ,,, But a nice piston thats short and light will make more power ... Edited May 13, 2012 by PMC raceengines Quote Link to comment Share on other sites More sharing options...
DPG Posted May 13, 2012 Author Share Posted May 13, 2012 The head is going to get a full job done on it. E31 with 45/36 valves, full port and polish, etc. I'm not worried about the flow. I'm having Isky do a custom cam for me. So the real advantage would be only to go with the Fj20 140mm rods is what seems to be the situation? Quote Link to comment Share on other sites More sharing options...
DPG Posted May 13, 2012 Author Share Posted May 13, 2012 I would definitely trust pmc. Also you're "higher rpm" set up involves a lot more than just rods, such as cam, head work, intake, and exhaust. I'm sure for what you want, you can easily get it with either l24 rods and custom pistons, or some l28 rods with much cheaper ready-to-order forged pistons edit: if you're boring to 89, then you can just use forged 240sx pistons which are plentiful. Using these you are still left with a recessed deck height of 1.4mm, so the compression is not where I want it to be. Plus I would like to have forged for the sake of revving above 7200. Quote Link to comment Share on other sites More sharing options...
PMC raceengines Posted May 13, 2012 Share Posted May 13, 2012 Well its not the only way to go but it works well for me , JE do a good piston with this combo , that is very light and strong and they will make it to sute your head combo and valve size no problem ,, And there are a lot of fj20 custom rods on the market. But like i said there is very little in it over a normal rod , just a better piston and ring size Quote Link to comment Share on other sites More sharing options...
Leon Posted May 14, 2012 Share Posted May 14, 2012 I have done so many tests on this ,, and L24 rods are not long in the hole sceem of things and there is hardly a diffrence in hp not worth talking about THANK YOU. Many get so caught up in R/S ratios as if it's some holy grail. It's not, so forget about it. A well built engine will have everything sized to everything else. Worry about making things work together. PMC mentions exhaust tuning, and I'll add intake tuning to that as well, as it's the same thing for all intents and purposes. Make the cam, intake and exhaust work in harmony, get pistons that wont explode at the high rpms you want to spin and you're set. Quote Link to comment Share on other sites More sharing options...
DPG Posted May 15, 2012 Author Share Posted May 15, 2012 Well its not the only way to go but it works well for me , JE do a good piston with this combo , that is very light and strong and they will make it to sute your head combo and valve size no problem ,, And there are a lot of fj20 custom rods on the market. But like i said there is very little in it over a normal rod , just a better piston and ring size Thanks for your input Quote Link to comment Share on other sites More sharing options...
rsicard Posted May 15, 2012 Share Posted May 15, 2012 Concentrate on getting the top of the piston level with the top of the block or slightly above same. Get as much squish as possible between the piston and cylinder head. If using all forged bottom end components, shoot for .030 inches between the piston and cylinder head with as much area of the squish pads piston and cylinder as possible. This should greatly reduce tendency to ping. Check for adequate valve to piston clearance with piston at 10 degrees before and after TDC taking into account the total valve lift plus 0.100 inch clearance. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 15, 2012 Share Posted May 15, 2012 The "How to Modify" book says to never get less than .050" clearance between piston and head, .055" in a race engine. .030" is asking for problems isn't it? Quote Link to comment Share on other sites More sharing options...
rsicard Posted May 16, 2012 Share Posted May 16, 2012 Notice that "If using all forged bottom end components," was stated. Forged bottom end, crankshaft, con rods and pistons will stretch MUCH LESS than non-forged components. 0.025" or less is pushing the limit. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 16, 2012 Share Posted May 16, 2012 Thanks. Interesting. That's a tight fit. Quote Link to comment Share on other sites More sharing options...
DPG Posted May 16, 2012 Author Share Posted May 16, 2012 (edited) Concentrate on getting the top of the piston level with the top of the block or slightly above same. Get as much squish as possible between the piston and cylinder head. If using all forged bottom end components, shoot for .030 inches between the piston and cylinder head with as much area of the squish pads piston and cylinder as possible. This should greatly reduce tendency to ping. Check for adequate valve to piston clearance with piston at 10 degrees before and after TDC taking into account the total valve lift plus 0.100 inch clearance. Thank you for the info. I ordered the FJ20 rods today, pistons next. Slowly but surely... I have been messing with the engine calculator. I assume it is correct... http://atlanticz.ca/zclub/techtips/calcs/engine%20builder/index.html So for the .030 inches of clearance, you are including the head gasket height correct? This would be 0.762mm between the head and top of the piston. So assuming I am using a 1mm gasket, I would shoot for about 0.24mm rise above the deck for the piston? Edited May 16, 2012 by DPG Quote Link to comment Share on other sites More sharing options...
PMC raceengines Posted May 16, 2012 Share Posted May 16, 2012 Thank you for the info. I ordered the FJ20 rods today, pistons next. Slowly but surely... I have been messing with the engine calculator. I assume it is correct... http://atlanticz.ca/zclub/techtips/calcs/engine%20builder/index.html So for the .030 inches of clearance, you are including the head gasket height correct? This would be 0.762mm between the head and top of the piston. So assuming I am using a 1mm gasket, I would shoot for about 0.24mm rise above the deck for the piston? I have been running as close as .028in with my combos and had no problems. Just make make shore your ptv clearance is good ... Also if your pistons have large piston to bore clearance you will need more piston to head clearance , as the piston rocks it gets very close to the head . Just make shore you check the deck hight of your block before you order the pistons , and give the specs to the piston maker so you get what you need Quote Link to comment Share on other sites More sharing options...
JCan Posted January 7, 2013 Share Posted January 7, 2013 I am not sure that the piston to head gap is the problem I am having (see quote from Braap below). However it is the best idea I have. See quoted text below. Jim Quote Link to comment Share on other sites More sharing options...
PMC raceengines Posted January 7, 2013 Share Posted January 7, 2013 If it tuches it will leave a shiny mark , thats very easy to pic , ,,, Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 7, 2013 Share Posted January 7, 2013 If it touches, you will HEAR it as well. I don't even want to get into how I know this...but suffice to say even if you find the SLIGHTEST 'hitch' in rolling the engine over by hand....INVESTIGATE THOROUGHLY! Quote Link to comment Share on other sites More sharing options...
ozconnection Posted January 9, 2013 Share Posted January 9, 2013 If it touches, you will HEAR it as well. I don't even want to get into how I know this...but suffice to say even if you find the SLIGHTEST 'hitch' in rolling the engine over by hand....INVESTIGATE THOROUGHLY! ...and you started an engine without checking this??? I'm surprised at you Tony, not up to usual high standards mate Quote Link to comment Share on other sites More sharing options...
SlowRob Posted January 18, 2013 Share Posted January 18, 2013 The main benefits of longer rods are increased T&B dwell and reduced piston acceleration. Both increase resistance to detonation and reduce wear. I built a 383 SBC using 6.0 rods (over 5.7 stock) running 11.3CR on pump gas. Output was >500hp and >500lbft, spinning to 9000rpm. Motor has been together for over 50k miles and still pulls like an elephant and is still making >200psi static. If I ever build the L28, I'll be looking at long rod combinations. Quote Link to comment Share on other sites More sharing options...
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