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Overbore 4.0
- Thread starter profonde
- Start date
5-90
NAXJA Forum User
- Location
- Hammerspace
Bring out the cylinders should pose no trouble - but the power gain will be minimal. You're increasing displacement slightly, but that's about it.
Boring out the cylinders is the usual method to "clean up" the cylinder walls, but that's about it. It is only really an advantage when done in conjunction with a stroker crank - then, you get enough increased displacement to really shine!
Given that the OEM 4.0 bore is 3.875" and the stroke is (on average - I've seen different figures for this) 3.41", let's look at a few numbers:
3.41 x 3.875 x 6 cylinders = 241.29ci. Just short of 242ci, or right around 4.0 litres. (3.9556L)
3.41 x 3.905 x 6 cylinders = 245.04ci, or just a shade over 4.0 litres even (4.01705L)
3.41 x 3.935 x 6 cylinders = 248.82ci (4.079L)
So you see, just boring out the cylinder doesn't really increase displacement much - so you won't notice much in the way of power gains (except in the driver's seat, but that's what I consider "psychosomatic" power - you did all the work, so you want the engine to have more power. Perception becomes reality...
Now, let's compare the same figures, but using the "stroker" figure (258ci crankshaft) of 3.895" - this is the most common stroker going - but there's another crank you can use, and I'll get to that in a minute:
3.895 x 3.875 x 6 cylinders = 275.61ci - and that's without boring out the block! (4.518L)
3.895 x 3.905 x 6 cylinders = 279.892ci This is a fairly common stroker build, using the 258 crankshaft and rods, and having the block bored out +.030" (4.588L)
3.895 x 3.935 x 6 cylinders = 284.209ci. This is a +.060" bore job, and about as far as I'd take a block I didn't do an ultrasonic inspection on myself - especially with later engines.
However, there was a guy who actually took an early AMC 242ci engine out to a bore of 4.000" and put in a stroker crank - so let's look at that for a monent (this requires boring your engine out +.125" - not for the faint of heart, and not to be done with just any block!)
3.410 x 4.000 x 6 cylinders = 257.108ci, or 4.21L
3.895 x 4.000 x 6 cylinders = 293.676ci, or 4.81L
See where this is going? It gets big a lot faster when you lenghten the stroke.
The other option I'd mentioned was the use of an AMC232ci crankshaft - may or may not be more plentiful in junkyards you may have in your area, or with "salvage parts dealers" (although I doubt it...) The 232 had a stroke of 3.500", which gives us:
3.875 x 3.500 x 6 cylinders = 241.29ci/3.956L. Not much increase with the stock bore...
3.905 x 3.500 x 6 cylinders = 251.51ci/4.123L. Slower building up with the 232...
3.935 x 3.500 x 6 cylinders = 255.39ci/4.187L
And, since the AMC 232 I6 went out of production, I think, in the late 1970's (here
while the AMC 258 I6 was in production to about 1990, I probably misspoke on the availabiliy of it earlier. However, I'm relying more upon domestic production - and I note you're in Istanbul, so I could be wrong. However, it is something of an option - you can push displacement up just a little bit...
Here's a recap:
Stroke Bore Total Displacement Crankshaft Overbore
3.410 3.875 241.29ci AMC242 +.000"
3.410 3.905 245.04ci AMC242 +.030"
3.410 3.935 248.82ci AMC242 +.060"
3.895 3.875 275.61ci AMC258 +.000"
3.895 3.905 279.89ci AMC258 +.030"
3.895 3.935 284.21ci AMC258 +.060"
3.500 3.875 247.66ci AMC232 +.000"
3.500 3.905 251.51ci AMC232 +.030"
3.500 3.935 255.39ci AMC232 +.060"
Since you don't say what year XJ you have (or what year of engine,) I can't tell you whether or not to even bother getting your block checked, if you have a shop that can do so. If your block casting number indicates that it was made in 1990 or earlier, then the cylinder walls are thicker and have more material to work with - that's how Mike Parrish (formerly Accurate Power) was able to bore his engine so far. However, you do need to leave at least .100" of cylinder wall thickness, and if the cores have shifted, you'll have to make sure you have more material on the "major thrust side" (I'd have to check my notes, but I think it's the passenger side of the block. Don't hold me to it tho - I haven't had to think about that stuff for a little while, so it's slipped.)
Anyhow, a conventional formula is that "displacement = power." With the stock crankshaft, you might get an extra 7 or 8 cubic inches - or not quite a 3% increase in displacement. That's not enough to worry about.
Bore the block +.030" with a 258/4.2L crankshaft, and you can pick up a 14% increase in displacement - which becomes significant. It's possible to go farther still, but the parts to do so are probably not available to you over there...
Good luck! This is a whole chapter in my book, and I'm still thinking of things I've missed. Glad I made it updatable for things like this...
Boring out the cylinders is the usual method to "clean up" the cylinder walls, but that's about it. It is only really an advantage when done in conjunction with a stroker crank - then, you get enough increased displacement to really shine!
Given that the OEM 4.0 bore is 3.875" and the stroke is (on average - I've seen different figures for this) 3.41", let's look at a few numbers:
3.41 x 3.875 x 6 cylinders = 241.29ci. Just short of 242ci, or right around 4.0 litres. (3.9556L)
3.41 x 3.905 x 6 cylinders = 245.04ci, or just a shade over 4.0 litres even (4.01705L)
3.41 x 3.935 x 6 cylinders = 248.82ci (4.079L)
So you see, just boring out the cylinder doesn't really increase displacement much - so you won't notice much in the way of power gains (except in the driver's seat, but that's what I consider "psychosomatic" power - you did all the work, so you want the engine to have more power. Perception becomes reality...
Now, let's compare the same figures, but using the "stroker" figure (258ci crankshaft) of 3.895" - this is the most common stroker going - but there's another crank you can use, and I'll get to that in a minute:
3.895 x 3.875 x 6 cylinders = 275.61ci - and that's without boring out the block! (4.518L)
3.895 x 3.905 x 6 cylinders = 279.892ci This is a fairly common stroker build, using the 258 crankshaft and rods, and having the block bored out +.030" (4.588L)
3.895 x 3.935 x 6 cylinders = 284.209ci. This is a +.060" bore job, and about as far as I'd take a block I didn't do an ultrasonic inspection on myself - especially with later engines.
However, there was a guy who actually took an early AMC 242ci engine out to a bore of 4.000" and put in a stroker crank - so let's look at that for a monent (this requires boring your engine out +.125" - not for the faint of heart, and not to be done with just any block!)
3.410 x 4.000 x 6 cylinders = 257.108ci, or 4.21L
3.895 x 4.000 x 6 cylinders = 293.676ci, or 4.81L
See where this is going? It gets big a lot faster when you lenghten the stroke.
The other option I'd mentioned was the use of an AMC232ci crankshaft - may or may not be more plentiful in junkyards you may have in your area, or with "salvage parts dealers" (although I doubt it...) The 232 had a stroke of 3.500", which gives us:
3.875 x 3.500 x 6 cylinders = 241.29ci/3.956L. Not much increase with the stock bore...
3.905 x 3.500 x 6 cylinders = 251.51ci/4.123L. Slower building up with the 232...
3.935 x 3.500 x 6 cylinders = 255.39ci/4.187L
And, since the AMC 232 I6 went out of production, I think, in the late 1970's (here
while the AMC 258 I6 was in production to about 1990, I probably misspoke on the availabiliy of it earlier. However, I'm relying more upon domestic production - and I note you're in Istanbul, so I could be wrong. However, it is something of an option - you can push displacement up just a little bit...Here's a recap:
Stroke Bore Total Displacement Crankshaft Overbore
3.410 3.875 241.29ci AMC242 +.000"
3.410 3.905 245.04ci AMC242 +.030"
3.410 3.935 248.82ci AMC242 +.060"
3.895 3.875 275.61ci AMC258 +.000"
3.895 3.905 279.89ci AMC258 +.030"
3.895 3.935 284.21ci AMC258 +.060"
3.500 3.875 247.66ci AMC232 +.000"
3.500 3.905 251.51ci AMC232 +.030"
3.500 3.935 255.39ci AMC232 +.060"
Since you don't say what year XJ you have (or what year of engine,) I can't tell you whether or not to even bother getting your block checked, if you have a shop that can do so. If your block casting number indicates that it was made in 1990 or earlier, then the cylinder walls are thicker and have more material to work with - that's how Mike Parrish (formerly Accurate Power) was able to bore his engine so far. However, you do need to leave at least .100" of cylinder wall thickness, and if the cores have shifted, you'll have to make sure you have more material on the "major thrust side" (I'd have to check my notes, but I think it's the passenger side of the block. Don't hold me to it tho - I haven't had to think about that stuff for a little while, so it's slipped.)
Anyhow, a conventional formula is that "displacement = power." With the stock crankshaft, you might get an extra 7 or 8 cubic inches - or not quite a 3% increase in displacement. That's not enough to worry about.
Bore the block +.030" with a 258/4.2L crankshaft, and you can pick up a 14% increase in displacement - which becomes significant. It's possible to go farther still, but the parts to do so are probably not available to you over there...
Good luck! This is a whole chapter in my book, and I'm still thinking of things I've missed. Glad I made it updatable for things like this...
Dear 5-90 thanks a lot for the time you invested replying my email... I really appreciate that
Coming to the subject, maybe i should have given you more detailed info...
1) The car is 90 model.. so it has a renix.
2) Its actualy used in our race car. (The type of racing we do might be
explained similar to rallying).
3) It has 170 Hp when we dynoed the car.. (not rwhp)
4) The car is running on 31" of rubber with 4.88 gearing and an AW4.
We are now going to our 3th season race and we figured out that the cars engine is holding us in fast stages. So we need more power
But reliability is a main concern here because in racing to finish first you have to finish first
Thats why i am a little bit of concerned at strokers. Many racers think here, playing with the engine that much will only get problems. There might be two problems..
1) The engine will fail itself in the race after becoming a stroker. (I dont
have the financial budget to order a crate engine from golen or hesco,
they cost more than 6k after importing etc..)
2) The cars drivetrain will not hold the extra torque. and fail. I have a super
35 kit at the back by the way..
And i also should remind you that i can not make a HO head conversion(very difficult here).
Regarding to my concerns i would really like to hear your expertise for building a stroker or not?
Thanks in advance...
Coming to the subject, maybe i should have given you more detailed info...
1) The car is 90 model.. so it has a renix.
2) Its actualy used in our race car. (The type of racing we do might be
explained similar to rallying).
3) It has 170 Hp when we dynoed the car.. (not rwhp)
4) The car is running on 31" of rubber with 4.88 gearing and an AW4.
We are now going to our 3th season race and we figured out that the cars engine is holding us in fast stages. So we need more power
But reliability is a main concern here because in racing to finish first you have to finish first
Thats why i am a little bit of concerned at strokers. Many racers think here, playing with the engine that much will only get problems. There might be two problems..
1) The engine will fail itself in the race after becoming a stroker. (I dont
have the financial budget to order a crate engine from golen or hesco,
they cost more than 6k after importing etc..)
2) The cars drivetrain will not hold the extra torque. and fail. I have a super
35 kit at the back by the way..
And i also should remind you that i can not make a HO head conversion(very difficult here).
Regarding to my concerns i would really like to hear your expertise for building a stroker or not?
Thanks in advance...
seanyb505
NAXJA Forum User
- Location
- Simpsonville, SC
I believe theres a shop called Titan here in Florida which makes a 4.6 or a 4.7 stroker with a 3yr/36000 mile warranty. On ebay they only run about 2100USD, but shipping may significantly add onto the price.
5-90
NAXJA Forum User
- Location
- Hammerspace
Hoo, boy. This is gonna get fun!
OK - do you have access to AMC258 engine parts there? You don't need the whole engine - just the crankshaft and connecting rods. You'll use the pistons from your 242ci engine (unless you bore over - then you need new slugs and rings,) the wrist pins from either engine will work, so check them all out and take your best six. Scrap the pistons from the 258 - they should be worth a few bucks as scrap metal, since they're aluminum alloy.
You'd get more from a crankshaft swap than you would from boring out the engine, and it's less work. However, boring and stroking the engine will give you significant increases - and make the bore job worth the money you spend on it. You don't need to do anything to the bottom end to fit the 258ci crankshaft, although you may require a "spacer" for the harmonic damper (just cut 1cm off of the old damper, and put it behind the new one when you put it on.) This is because the crankshaft snout on the 258 is 1cm longer than the later 242, because the 258 used a V-belt setup (while youre 242, as you know, uses a serpentine or "flat" belt.)
Since you have the earlier block, you'll have plenty of material in the cylinder walls after you bore the engine out. Going +.060" presents no problem at all - and you should still be able to find pistons in that size. Going to 4.000" even (+.125") requires modified Small Block Chevrolet slugs, which may not be available to you easily.
However, there is no reason whatever why you should expect engine failure just because you built a stroker - especially considering you can use entirely off-the-shelf parts, if you don't get too silly. There are people here who have accumulated upwards of 200Kmiles (as I recall) on strokers without any trouble. This would include both on-road and off-road driving. You may also want to check with the guys at JeepSpeed (www.jeepspeed.com, I think) and strokers (groups.yahoo.com/group/strokers) for more information and direct stroker experience - the strokers group is dedicated to that, and the JeepSpeed guys probably run similar racing to what you're trying to do. I don't recall offhand if strokers are legal in JeepSpeed, but do check anyhow. They can probably give you some other tips and tricks.
The power curve on the stroker variations runs right about the same as for the original engine - just higher. So, you'll still have horsepower where you're used to it, and torque where you're used to it - just more of both. You will need to install larger fuel injectors if you do the stroker (I'd have to check my notes, and it would help if you decided on an option and told me, so I could work some numbers over for you...) but all other sensors and control units would remain the same.
You'd also note an addition increase in power if you installed a later-model cylinder head - the HO heads do flow more air - but that would require switching out the head and intake - the HO throttle body, as I recall, has the throttle linkage hookup on the other side, and the TPS is different, you'll have to adapt the RENIX TPS to the HO tbody (it's been covered here, with pictures, so pillage around and see what you can find out.)
The RENIX throttle body bore should be able to handle a stroker just fine without work - again, unless you get silly. I don't think the 258 crank and +.030" bore will post any trouble at all, but you might be "on the edge" if you go +.060" - I'd have to check. I'm fairly sure I've got flow data for the RENIX throttle body around here somewhere...
I'm perfectly willing to help you crunch numbers and select parts - just be sure you have a solid idea of what you want before you tell me. I can also run engine simulations - so let me know what parts are available to you. I may have profiles and data for stuff you just can't get - so I need to know (so I don't suggest something to you that you can't get your hands on.)
I'd have to look up the specs on the "Super 35" kit (I've heard of it, I just don't have useful data...) but if you're worried about drivetrain, plan on updating the rear axle to either a Dana 44 or a Ford 8.8" or 9" - depending on what's available to you. The front axle should hold up, once you upgrade the rear (but going to a 44 front, while difficult to find a source for, should prove rewarding in terms of reliability.) Still, if you do the stroker properly, I think you can just cross "engine reliability" right off of you list of concerns.
OK - do you have access to AMC258 engine parts there? You don't need the whole engine - just the crankshaft and connecting rods. You'll use the pistons from your 242ci engine (unless you bore over - then you need new slugs and rings,) the wrist pins from either engine will work, so check them all out and take your best six. Scrap the pistons from the 258 - they should be worth a few bucks as scrap metal, since they're aluminum alloy.
You'd get more from a crankshaft swap than you would from boring out the engine, and it's less work. However, boring and stroking the engine will give you significant increases - and make the bore job worth the money you spend on it. You don't need to do anything to the bottom end to fit the 258ci crankshaft, although you may require a "spacer" for the harmonic damper (just cut 1cm off of the old damper, and put it behind the new one when you put it on.) This is because the crankshaft snout on the 258 is 1cm longer than the later 242, because the 258 used a V-belt setup (while youre 242, as you know, uses a serpentine or "flat" belt.)
Since you have the earlier block, you'll have plenty of material in the cylinder walls after you bore the engine out. Going +.060" presents no problem at all - and you should still be able to find pistons in that size. Going to 4.000" even (+.125") requires modified Small Block Chevrolet slugs, which may not be available to you easily.
However, there is no reason whatever why you should expect engine failure just because you built a stroker - especially considering you can use entirely off-the-shelf parts, if you don't get too silly. There are people here who have accumulated upwards of 200Kmiles (as I recall) on strokers without any trouble. This would include both on-road and off-road driving. You may also want to check with the guys at JeepSpeed (www.jeepspeed.com, I think) and strokers (groups.yahoo.com/group/strokers) for more information and direct stroker experience - the strokers group is dedicated to that, and the JeepSpeed guys probably run similar racing to what you're trying to do. I don't recall offhand if strokers are legal in JeepSpeed, but do check anyhow. They can probably give you some other tips and tricks.
The power curve on the stroker variations runs right about the same as for the original engine - just higher. So, you'll still have horsepower where you're used to it, and torque where you're used to it - just more of both. You will need to install larger fuel injectors if you do the stroker (I'd have to check my notes, and it would help if you decided on an option and told me, so I could work some numbers over for you...) but all other sensors and control units would remain the same.
You'd also note an addition increase in power if you installed a later-model cylinder head - the HO heads do flow more air - but that would require switching out the head and intake - the HO throttle body, as I recall, has the throttle linkage hookup on the other side, and the TPS is different, you'll have to adapt the RENIX TPS to the HO tbody (it's been covered here, with pictures, so pillage around and see what you can find out.)
The RENIX throttle body bore should be able to handle a stroker just fine without work - again, unless you get silly. I don't think the 258 crank and +.030" bore will post any trouble at all, but you might be "on the edge" if you go +.060" - I'd have to check. I'm fairly sure I've got flow data for the RENIX throttle body around here somewhere...
I'm perfectly willing to help you crunch numbers and select parts - just be sure you have a solid idea of what you want before you tell me. I can also run engine simulations - so let me know what parts are available to you. I may have profiles and data for stuff you just can't get - so I need to know (so I don't suggest something to you that you can't get your hands on.)
I'd have to look up the specs on the "Super 35" kit (I've heard of it, I just don't have useful data...) but if you're worried about drivetrain, plan on updating the rear axle to either a Dana 44 or a Ford 8.8" or 9" - depending on what's available to you. The front axle should hold up, once you upgrade the rear (but going to a 44 front, while difficult to find a source for, should prove rewarding in terms of reliability.) Still, if you do the stroker properly, I think you can just cross "engine reliability" right off of you list of concerns.
- Location
- Roanoke VA
profonde said:
I had to bore my 90' due to burnt pistons(previous owner drove 50 miles with no coolant). Punched it 40 and also had to deck the block and mill the head(20 each) It runs great but I don't think it gave me any significant power increases. I drove this Jeep the day it was bought new, it runs the way it did that day (my dad was the first owner). The second owner blew it up, I bought it back.
