converting an LS7 to 6 litres with a 96.9mm bore
Discussion
Ok I’m not an expert on the LS series of engines so I thought I’d post my idea here – I’m looking at creating a 6.0 Litre version of the LS7 engine, using the standard LS7 crank throw of 101.6mm……..therefore I will need to remove the standard press-in liners and reduce the bore size from 104.8 standard to 96.9mm therefore giving 6.0 litres in long stroke format……do the LS7 liners come out easily?…..I’m not interested in going the short stroke big bore route as I want the power delivered low down as this will be a normally aspirated race motor running air restrictors.
The only problems I can foresee are the LS cylinder heads and principally the valves fitting inside the bore size I require of 96.9mm – I have worked out I need 51mm inlet valves, with 43mm exhaust valves – so that will all be snug fit in a 96.9mm bore – I know I might need to come down on those valve sizes slightly, but that’s the ball park I’m heading in.
What I’m interested to know from you guys is based on your knowledge of all the variants of LS type cylinder heads, aftermarket too – do you think its possible to accommodate a 96.9mm bore with those sorts of valve sizes – or is it totally out of the question????........
Also – I was looking that the LS’s intake ports on boosteds website and I must say – they looked horrific as standard – by this I mean too big – has anyone yet made attempts to make the ports smaller for faster gas velocity?
Cheers
Knighty
The only problems I can foresee are the LS cylinder heads and principally the valves fitting inside the bore size I require of 96.9mm – I have worked out I need 51mm inlet valves, with 43mm exhaust valves – so that will all be snug fit in a 96.9mm bore – I know I might need to come down on those valve sizes slightly, but that’s the ball park I’m heading in.
What I’m interested to know from you guys is based on your knowledge of all the variants of LS type cylinder heads, aftermarket too – do you think its possible to accommodate a 96.9mm bore with those sorts of valve sizes – or is it totally out of the question????........
Also – I was looking that the LS’s intake ports on boosteds website and I must say – they looked horrific as standard – by this I mean too big – has anyone yet made attempts to make the ports smaller for faster gas velocity?
Cheers
Knighty
Your making a hell of work for yourself,why not get a standard bore ls engine and develop it from there,you can still fit ls7 style,afr or etp heads that flow big numbers.
I'm going the other way for a light racecar,sleeved 4.125 ls bore with 3.62" crank, yeilding just over 6ltrs to give me top end power and legs,torque breaks gear.
Go to www.ls1tech.com ,plenty of info there.
I'm going the other way for a light racecar,sleeved 4.125 ls bore with 3.62" crank, yeilding just over 6ltrs to give me top end power and legs,torque breaks gear.
Go to www.ls1tech.com ,plenty of info there.
I am pretty sure you cannot use the ls7 heads with an engine of that bore as the valves will not clear . If you want to go to 6L then you would be better of shortening the stroke which would also make it more willing to rev. I have a 3.41" stroke crank from a Le mans Lister which was running in the under 6L class. If you are interested in some kind of exchange you can contact me through my profile , David
ps . I do have some other very interesting c5r stuff
ps . I do have some other very interesting c5r stuff
The inlet ports look big because the top part is where the injector nozzle squirts. It's not really flowing any air. You can get a budget stroker crank for $800 or so. Ls7 crank has a long nose so you may have to shorten it plus it's balanced for lightweight componants. You'll have to rebalance it whatever you do and add weight. If you need smaller valves look to the smaller engine variants. In fact you could start with a smaller engine in the first place, downside is it will be iron block 
Boosted.
Boosted.
knightly said:
Ok I’m not an expert on the LS series of engines so I thought I’d post my idea here – I’m looking at creating a 6.0 Litre version of the LS7 engine, using the standard LS7 crank throw of 101.6mm……..therefore I will need to remove the standard press-in liners and reduce the bore size from 104.8 standard to 96.9mm therefore giving 6.0 litres in long stroke format……do the LS7 liners come out easily?…..I’m not interested in going the short stroke big bore route as I want the power delivered low down as this will be a normally aspirated race motor running air restrictors.
The only problems I can foresee are the LS cylinder heads and principally the valves fitting inside the bore size I require of 96.9mm – I have worked out I need 51mm inlet valves, with 43mm exhaust valves – so that will all be snug fit in a 96.9mm bore – I know I might need to come down on those valve sizes slightly, but that’s the ball park I’m heading in.
What I’m interested to know from you guys is based on your knowledge of all the variants of LS type cylinder heads, aftermarket too – do you think its possible to accommodate a 96.9mm bore with those sorts of valve sizes – or is it totally out of the question????........
Also – I was looking that the LS’s intake ports on boosteds website and I must say – they looked horrific as standard – by this I mean too big – has anyone yet made attempts to make the ports smaller for faster gas velocity?
Cheers
Knighty
The only problems I can foresee are the LS cylinder heads and principally the valves fitting inside the bore size I require of 96.9mm – I have worked out I need 51mm inlet valves, with 43mm exhaust valves – so that will all be snug fit in a 96.9mm bore – I know I might need to come down on those valve sizes slightly, but that’s the ball park I’m heading in.
What I’m interested to know from you guys is based on your knowledge of all the variants of LS type cylinder heads, aftermarket too – do you think its possible to accommodate a 96.9mm bore with those sorts of valve sizes – or is it totally out of the question????........
Also – I was looking that the LS’s intake ports on boosteds website and I must say – they looked horrific as standard – by this I mean too big – has anyone yet made attempts to make the ports smaller for faster gas velocity?
Cheers
Knighty
toooo much work IMO! go for a LS2 wich is 6.0ltr out the box. you can also get some LS7 style heads from ET (have a look on ls1tech for links). if you dont want them then i think the ET 24x heads will fit but they are pure race heads. also the LS7 heads WONT FIT with anything less than a 4.1 inch bore!
the blocks are very similar so there is not much advantage of using the 7 block. its not the expsencive to get a dry sump system for the LS2 and overall it will be MUCH cheaper than going a LS7. LS7 bare blocks are $6K!!!
thanks Chris.
interesting replies chaps - I may as well tell you what its for - a feasability study for a V8 push-rod 6.0 LeMans LMP1 engine - for an open top sports prototype - the only reasons I'm asking questions here is because of my lack of knowledge about the LS head variants - theres no point in creating a short stroke big bore engine that requires big revs, as the restrictor size will limit air flow at about 7500rpm........hence the engine must make peak power well under that figure - hence long stroke, small bore......I just need to find an LS head that can accomodate the valve sizes I require for a 96.9mm bore. in the past Lister, Mopar and Panoz have all gone the big bore short stroke route in LMP1, and they did not make comparable power with any of the top engines from Judd or Audi.....the mopar and Panoz motors appear to be 5.8 litre Nascar engines that they have bored out to 6.0litres and put restrictors on, and surprise surprise as they cannot rev over 9000rpm they dont make the power.
knightly said:
interesting replies chaps - I may as well tell you what its for - a feasability study for a V8 push-rod 6.0 LeMans LMP1 engine - for an open top sports prototype - the only reasons I'm asking questions here is because of my lack of knowledge about the LS head variants - theres no point in creating a short stroke big bore engine that requires big revs, as the restrictor size will limit air flow at about 7500rpm........hence the engine must make peak power well under that figure - hence long stroke, small bore......I just need to find an LS head that can accomodate the valve sizes I require for a 96.9mm bore. in the past Lister, Mopar and Panoz have all gone the big bore short stroke route in LMP1, and they did not make comparable power with any of the top engines from Judd or Audi.....the mopar and Panoz motors appear to be 5.8 litre Nascar engines that they have bored out to 6.0litres and put restrictors on, and surprise surprise as they cannot rev over 9000rpm they dont make the power.
How doe the chamber in the LS7 over lay the bore size you are after with the longer 7 stroke, any shoulding? Not an expert here, but we have always gone bigger bore and putting the valve in the best place for the chambers / bore we are using. If 7 head chamber to wide then presume it will not work hence Lister doing it the larger bore way (to match to bigger chamber? of the 7 heads?). Just some thoughts for what they might be worth.
Or just put a 7.0 in there and hope no one notices!!!!
going by the LS7 standard valve sizes of 56mm inlet and 41 exhaust, total = 97 therefore I'm quite sure the LS7 heads are a no-go on a 96.9 bore! ......nothing new to me there......but I'm interested to know if anyone thinks if any of the other LS heads, or aftermarket castings will accomodate my required bore size of 96.9mm????
knightly said:
going by the LS7 standard valve sizes of 56mm inlet and 41 exhaust, total = 97 therefore I'm quite sure the LS7 heads are a no-go on a 96.9 bore! ......nothing new to me there......but I'm interested to know if anyone thinks if any of the other LS heads, or aftermarket castings will accomodate my required bore size of 96.9mm????
Loads out there - Try checking if the New LSX head are out yet (these are alloy to go with the Drag racing LSX block just out). See www.pistonheads.com/gassing/topic.asp?t=338479&f=155&h=0
Edited by jellison on Tuesday 30th January 11:50
knightly said:
going by the LS7 standard valve sizes of 56mm inlet and 41 exhaust, total = 97 therefore I'm quite sure the LS7 heads are a no-go on a 96.9 bore! ......nothing new to me there......but I'm interested to know if anyone thinks if any of the other LS heads, or aftermarket castings will accomodate my required bore size of 96.9mm????
CHECK OUT LS1tech.com! there are serveal companies on there (Katech is one example) that build LM engine so they are the people you NEED to be talking to! from a pic i have seen of Katechs workshop they had about 20 C6R (the ones used in the covette ALMS cars) sat in storage. they also run their own cars i think.
also might be worth contacting GM as they offend do some very custom stuff for the race markets that the adverage pesron doesn't get to see!
all im saying is there are guys out there than are doing what your doing already.
thanks Chris.
knightly said:
going by the LS7 standard valve sizes of 56mm inlet and 41 exhaust, total = 97 therefore I'm quite sure the LS7 heads are a no-go on a 96.9 bore! ......nothing new to me there......but I'm interested to know if anyone thinks if any of the other LS heads, or aftermarket castings will accomodate my required bore size of 96.9mm????
Like I suggested earlier, you could look to the smaller engines. The 5.3 has smaller valves. Those heads should be cheap enough. As for ls1 heads they are 99mm across the chamber and the ls6 will probably be the same. 5.3 should be smaller across the chambers.
Boosted.
Edited by Boosted LS1 on Tuesday 30th January 14:15
Not an expert on the Chevy LS engines, but concur that there's definately a compromise of mean inlet gas velocity and low retriction/good flow coefficients. Alot of OEM get this wrong.
If the mean inlet gas velocity gets too high- you risk your mean inlet mach index number approaching above 0.5: Alot of Unis and tehcnical establishments during the 1950s and 60s did extensive studies and found that when inlet port mach number approached 0.5 relative to the local speed of sound Volumetric efficiencies would drop rapidly as the port choked.
On the other hand if flow coefficients are poor- this will effect top end breathing also. If the port sizes are too large, the air will lack ram energy (which is proportional to the square of the velocity) and combustion burn rate will become poor due to poor laminar burn velocities in the combustion chamber from poor induction turbulence.
You want to aim for a mean inlet gas velocity of about 88m/s (for inherently poor design of ports- poor angle, high intrusion of valve guide boss- with sharp area changes and poor finish) up to above 100 m/s for inherently good designed ports at peak power speed.
The other thing to be aware of if de boring a 2 valve engine like this is port flow shoruding from the bore which will hinder higher valve lift port flow characteristics. It's not likely to be as much of a problem on this two valve engine- with the valves closer to the centre line- but definately something to watch for on a pent roof or even a shallow angle hemi where the valves are closer to the bore walls.
I wouldnt dismiss the smaller bore option out of hand:
If I were evaluating both options: the larger bore application and the longer stroke application I would probably flow test the 51mm/96.9mm bore application -if possible- or failing that try to guestimate sensibly how the flow would be effected. Then I'd use these figures in cycle simulation software to see if I could achieve the top end air flow levels required with given restrictors.
Then I'd do a similar thing for the big bore variant . The bigger bore variant will possibly have poorer combustion due to lower mean piston speed and lower turbulence at higher engine speeds- as well as poorer surface to volume ratios. This is something Cycle simulation software can't evaluate. However the bigger bore variant will most likely have better flowing ports/bigger valves and may be able to afford a shorter duration cam profile .
Better flowing ports with shorter duration cams are nearly always a more preferably scenario to poor flowing ports/smaller valves and longer duration cams because the former usually gives a wider power band. Two valve engines with constrained valve sizes and a certain target HP/litre often have peak torque very close to peak power.
However IMO the deciding factor that would sway it would be the impact the different bore-stroke ratio will have on combustion efficiency and surface-to-volume ratios. This will effect Air utlisation- or how well the air flow or volumetric efficiency is converted to actual BMEP. Unfortunately these air utilisation and combustion efficiency effects aren't phenomenon that are easy to analyse easily...
If the mean inlet gas velocity gets too high- you risk your mean inlet mach index number approaching above 0.5: Alot of Unis and tehcnical establishments during the 1950s and 60s did extensive studies and found that when inlet port mach number approached 0.5 relative to the local speed of sound Volumetric efficiencies would drop rapidly as the port choked.
On the other hand if flow coefficients are poor- this will effect top end breathing also. If the port sizes are too large, the air will lack ram energy (which is proportional to the square of the velocity) and combustion burn rate will become poor due to poor laminar burn velocities in the combustion chamber from poor induction turbulence.
You want to aim for a mean inlet gas velocity of about 88m/s (for inherently poor design of ports- poor angle, high intrusion of valve guide boss- with sharp area changes and poor finish) up to above 100 m/s for inherently good designed ports at peak power speed.
The other thing to be aware of if de boring a 2 valve engine like this is port flow shoruding from the bore which will hinder higher valve lift port flow characteristics. It's not likely to be as much of a problem on this two valve engine- with the valves closer to the centre line- but definately something to watch for on a pent roof or even a shallow angle hemi where the valves are closer to the bore walls.
I wouldnt dismiss the smaller bore option out of hand:
If I were evaluating both options: the larger bore application and the longer stroke application I would probably flow test the 51mm/96.9mm bore application -if possible- or failing that try to guestimate sensibly how the flow would be effected. Then I'd use these figures in cycle simulation software to see if I could achieve the top end air flow levels required with given restrictors.
Then I'd do a similar thing for the big bore variant . The bigger bore variant will possibly have poorer combustion due to lower mean piston speed and lower turbulence at higher engine speeds- as well as poorer surface to volume ratios. This is something Cycle simulation software can't evaluate. However the bigger bore variant will most likely have better flowing ports/bigger valves and may be able to afford a shorter duration cam profile .
Better flowing ports with shorter duration cams are nearly always a more preferably scenario to poor flowing ports/smaller valves and longer duration cams because the former usually gives a wider power band. Two valve engines with constrained valve sizes and a certain target HP/litre often have peak torque very close to peak power.
However IMO the deciding factor that would sway it would be the impact the different bore-stroke ratio will have on combustion efficiency and surface-to-volume ratios. This will effect Air utlisation- or how well the air flow or volumetric efficiency is converted to actual BMEP. Unfortunately these air utilisation and combustion efficiency effects aren't phenomenon that are easy to analyse easily...
I think that your exhaust valve size is too large, take away 2mm which you could add to the intake valves.Of course you will have to offset the valve guides to acomplish all this. Also I think that you will have serious issues finding piston rings in a 96.9mm size. Custom pistons and liners are no problem, but rings are a different issue and you want them to be sized to the bore. It would definitely affect ring seal if you tried using rings that are designed for a reasonably close bore(i.e. 97mm only .0004in but still a big no-no). In the long run you will see more power and better results by sticking with Nascar hardware and tailoring it to your needs. Otherwise be prepared to spend millions on development to become competitive(where the Nascar guys already did most of the development work for you). As for long vs short stroke motors, a short stroke motor can make nearly the same amount of torque as a long stroke motor it just depends on your setup. With long stroke you are simply more limited in your selection of valve sizes and therefore limiting your power potential. Remember that the most competitive restrictor plate engines make near peak horsepower early,but keep it til redline, nice and flat power curve.
Ollies930 said:
I think that your exhaust valve size is too large, take away 2mm which you could add to the intake valves.Of course you will have to offset the valve guides to acomplish all this. Also I think that you will have serious issues finding piston rings in a 96.9mm size. Custom pistons and liners are no problem, but rings are a different issue and you want them to be sized to the bore. It would definitely affect ring seal if you tried using rings that are designed for a reasonably close bore(i.e. 97mm only .0004in but still a big no-no). In the long run you will see more power and better results by sticking with Nascar hardware and tailoring it to your needs. Otherwise be prepared to spend millions on development to become competitive(where the Nascar guys already did most of the development work for you). As for long vs short stroke motors, a short stroke motor can make nearly the same amount of torque as a long stroke motor it just depends on your setup. With long stroke you are simply more limited in your selection of valve sizes and therefore limiting your power potential. Remember that the most competitive restrictor plate engines make near peak horsepower early,but keep it til redline, nice and flat power curve.
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