hard to decide anything without real world measurements. Maybe you could time your valve events to see what cam there really is in there.
Compression vs. Octane #2
Race Director
Joined: Oct 2000
Posts: 14,967
Likes: 79
From: central FL, near the beach.
if u want to tune it, i'll explain it.
i'll be at this # for the next 2 hrs.
386-(deleted)
nice talking to you Larry!
i'll be at this # for the next 2 hrs.
386-(deleted)
nice talking to you Larry!
Last edited by Matt Gruber; Dec 15, 2007 at 01:12 PM.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
My intention here was to find a way to tame this thing in a way to run pump gas. However, it is beginning to seem that may not be an acievable goal and still keep the power I would like to have I can stomach the octane cost if that is the only way to maintain performance.
so it seems like my options are:
1) keep running 100 (or whatever blend of octane keeps me from pinging) and reduce the size of the cam to bring my power range down to a more realistic level for the street. It sounds like I would have quite a few options here to adjust things. It also sounds like the LS-6 manifold would work well here. Is this a correct assumption?
2) Find a way to reduce compression through new pistons or shaving the existing pistons and then replace the cam. This would allow me to get power down where I want it AND run 93. This may be better in the long run. QUESTION: Will this approach net less power than option 1?
3) Get an L-88 hood and a hi-rise single plane and run like hell. I have 3.73 gears and a 4 speed Super T-10. I just don't have enough experience to know how this will be on the street. Seems I would be leaving a lot of rubber at each green light to get into the power range.
Thanks for all of your support here. I don't know what I would do without you guys.
so it seems like my options are:
1) keep running 100 (or whatever blend of octane keeps me from pinging) and reduce the size of the cam to bring my power range down to a more realistic level for the street. It sounds like I would have quite a few options here to adjust things. It also sounds like the LS-6 manifold would work well here. Is this a correct assumption?
2) Find a way to reduce compression through new pistons or shaving the existing pistons and then replace the cam. This would allow me to get power down where I want it AND run 93. This may be better in the long run. QUESTION: Will this approach net less power than option 1?
3) Get an L-88 hood and a hi-rise single plane and run like hell. I have 3.73 gears and a 4 speed Super T-10. I just don't have enough experience to know how this will be on the street. Seems I would be leaving a lot of rubber at each green light to get into the power range.
Thanks for all of your support here. I don't know what I would do without you guys.
Your car with 3.73s would run a lot stronger
overall with less cam, it might not make as much peak HP but
it will move the torque down lower accelerate your car better.
Last edited by Little Mouse; Dec 15, 2007 at 01:00 PM.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
My intention here was to find a way to tame this thing in a way to run pump gas. However, it is beginning to seem that may not be an acievable goal and still keep the power I would like to have I can stomach the octane cost if that is the only way to maintain performance.
so it seems like my options are:
1) keep running 100 (or whatever blend of octane keeps me from pinging) and reduce the size of the cam to bring my power range down to a more realistic level for the street. It sounds like I would have quite a few options here to adjust things. It also sounds like the LS-6 manifold would work well here. Is this a correct assumption?
2) Find a way to reduce compression through new pistons or shaving the existing pistons and then replace the cam. This would allow me to get power down where I want it AND run 93. This may be better in the long run. QUESTION: Will this approach net less power than option 1?
3) Get an L-88 hood and a hi-rise single plane and run like hell. I have 3.73 gears and a 4 speed Super T-10. I just don't have enough experience to know how this will be on the street. Seems I would be leaving a lot of rubber at each green light to get into the power range.
Thanks for all of your support here. I don't know what I would do without you guys.
so it seems like my options are:
1) keep running 100 (or whatever blend of octane keeps me from pinging) and reduce the size of the cam to bring my power range down to a more realistic level for the street. It sounds like I would have quite a few options here to adjust things. It also sounds like the LS-6 manifold would work well here. Is this a correct assumption?
2) Find a way to reduce compression through new pistons or shaving the existing pistons and then replace the cam. This would allow me to get power down where I want it AND run 93. This may be better in the long run. QUESTION: Will this approach net less power than option 1?
3) Get an L-88 hood and a hi-rise single plane and run like hell. I have 3.73 gears and a 4 speed Super T-10. I just don't have enough experience to know how this will be on the street. Seems I would be leaving a lot of rubber at each green light to get into the power range.
Thanks for all of your support here. I don't know what I would do without you guys.
1) As long as you keep running high octane fuel you can run a smaller cam to move your power range down, but your octane requirements may go higher. The only thing the LS6 intake is really good at is fitting under the stock hood. Of course, without having compared it to another design, it might still work plenty well enough to make you happy in moderate RPM ranges.
2)It will probably make less power than option 1 just because compression makes horsepower. But you already seem tired of paying for high dollar fuel, so loosing 20-30 hp probably wont be that big of a deal to you.
3) The L88 was actually designed to run with a high rise dual plane intake. While a single plane would work well at high rpms, it will give you even less torque in the low and mid RPM ranges. I would recommend either a Performer RPM or a Weiand Stealth.
If it were mine, and I wanted to drive it on the street, I would drop the compression to no more than 11 to 1, install a smaller modern grind cam with duration in the mid 240's intake / 250's exhaust, and run a high rise dual plane intake.
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
That is a good idea and something I will try. However, given that I was pulling 5" of vac at 1000 RPM, I figured the cam had to be pretty agressive and it seemed to validate to assertion that it was an L-88 cam (there were no vac leaks that I could identify).
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
Not necessarily, low vacuum could also be caused by other reasons, like a bad valve lash (i assume the L88 cam is a mech. one), bad ignition timing, ... but you're right that most of the time a cam could be the reason. I've seen variations of 5 inch of vacuum with my motor just by playing with ignition and valve lash... . Try to figure out what lash should be on yours, and reset lash on all of them, then time the cam, measure your cranking pressure.
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
Thanks for ideas. I set the valve lash about 100 miles ago. They are about .016-.018 cold. I have also worked on the timing curve and am running 18* initial and 36* all in, plus about 12 degrees vac adv.
At this point I am thinking of leaving the compression where it is at and experimenting with methods of bringing the power curve down. I think I will add a scoop of some sort (including cold air induction) before I paint and then put an RPM Air Gap (dual plane) on. I think that I may also experiment with a cam in the range that Little Mouse suggested.
Then I will try some of the suggestions in this thread to reduce my octane requirements.
At this point I am thinking of leaving the compression where it is at and experimenting with methods of bringing the power curve down. I think I will add a scoop of some sort (including cold air induction) before I paint and then put an RPM Air Gap (dual plane) on. I think that I may also experiment with a cam in the range that Little Mouse suggested.
Then I will try some of the suggestions in this thread to reduce my octane requirements.
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Instructor
Joined: Sep 2005
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Likes: 1
with the 074 heads, your lash will grow by .006 when it is hot. I checked this by warming the car up and then adjusting the lash hot. Left everything over night and the lash went down the .006. I have a 71 LS6 with the same heads and intake you have. I only have 9.0 to 1compression and must run on 94 sunoco at 38 total. My cam is 232/236 at .050. That intake dies above 6,000 rpm, why not make your car work with the intake, as it is the only gm intake that will fit under the hood
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
with the 074 heads, your lash will grow by .006 when it is hot. I checked this by warming the car up and then adjusting the lash hot. Left everything over night and the lash went down the .006. I have a 71 LS6 with the same heads and intake you have. I only have 9.0 to 1compression and must run on 94 sunoco at 38 total. My cam is 232/236 at .050. That intake dies above 6,000 rpm, why not make your car work with the intake, as it is the only gm intake that will fit under the hood
I was under the impression that the RPM Air Gap would give better performance than the LS6 because it is an alum. high rise. It is rated up to 6800. A scoop will be easy to add, as the car is currently stripped and will be getting paint in a month. This will give me many options for an intake that will give me the broadest power range.
I am interested to hear other suggestions on an intake that will help me bring my power range down a bit from where it is. I want to make a bit more power in the mid-range.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
I'd make a priority of getting that cold air induction done, as it will make a significant dent in lowering your octane requirement. Also, while increasing your lash may well move the torque curve down slightly and help tone down nasty drivability manners, keep in mind that the resulting earlier intake valve closing event could actually raise octane requirements, and that opening the lash up too far can put your lifters beyond the lash ramps at the point where lash reaches 0.000".
IMHO, if you really want to lower both the torque range and octane requirement, as well as improve idle quality, vacuum and such, you're going to have to seriously consider lowering compression and reducing duration. Short of that, you might as well come to accept that some VP 105 is likely to be in your future, as L88's and pump gas just don't make good mates.
BTW Matt, you were commenting/asking elsewhere about calculating VE's effect on compression... Not sure what to call it, but simply multiplying a given or projected VE% by the static CR may yield more of what you were looking for out of the DCR calculator...
IMHO, if you really want to lower both the torque range and octane requirement, as well as improve idle quality, vacuum and such, you're going to have to seriously consider lowering compression and reducing duration. Short of that, you might as well come to accept that some VP 105 is likely to be in your future, as L88's and pump gas just don't make good mates.
BTW Matt, you were commenting/asking elsewhere about calculating VE's effect on compression... Not sure what to call it, but simply multiplying a given or projected VE% by the static CR may yield more of what you were looking for out of the DCR calculator...
Last edited by TheSkunkWorks; Dec 17, 2007 at 03:18 AM.
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
I'd make a priority of getting that cold air induction done, as it will make a significant dent in lowering your octane requirement. Also, while increasing your lash may well move the torque curve down slightly and help tone down nasty drivability manners, keep in mind that the resulting earlier intake valve closing event could actually raise octane requirements, and that opening the lash up too far can put your lifters beyond the lash ramps at the point where lash reaches 0.000".
IMHO, if you really want to lower both the torque range and octane requirement, as well as improve idle quality, vacuum and such, you're going to have to seriously consider lowering compression and reducing duration. Short of that, you might as well come to accept that some VP 105 is likely to be in your future, as L88's and pump gas just don't make good mates.
BTW Matt, you were commenting/asking elsewhere about calculating VE's effect on compression... Not sure what to call it, but simply multiplying a given or projected VE% by the static CR may yield more of what you were looking for out of the DCR calculator...
IMHO, if you really want to lower both the torque range and octane requirement, as well as improve idle quality, vacuum and such, you're going to have to seriously consider lowering compression and reducing duration. Short of that, you might as well come to accept that some VP 105 is likely to be in your future, as L88's and pump gas just don't make good mates.
BTW Matt, you were commenting/asking elsewhere about calculating VE's effect on compression... Not sure what to call it, but simply multiplying a given or projected VE% by the static CR may yield more of what you were looking for out of the DCR calculator...
Thanks for the insight. I should probably start a new thread here. Given the guidance provided here my goal now is to run with the current compression and not worry about the octane requirements. Possibly next year I will look at reducing the compression with new pistons, etc. I am also not really concerned with idle quality or vacuum levels.
My current goal is to find ways to work with what is there but bring down the torque range into a more streetable level. I would be interested to hear your thoughts as well on recommended manifolds and cams for this goal.
Also, what do you think about advancing the valve timing; either with the L-88 cam or a smaller duration / less overlap cam (more LSA)? Is this typically successful in moving the torque range down?
Thanks.
Race Director
Joined: Oct 2000
Posts: 14,967
Likes: 79
From: central FL, near the beach.
Advancing the 264, 6 degrees will make it more like a 258.
Changing the lash to .024-028 will really help, .024 is stock.
With a new cam it should usually not need advancing if it is the right size. A smaller cam will ping easier around 3000 rpm, that is why i'd try advancing the 264. it might run fine on 93 whereas a new 245 might ping hoplessly at 3000 on 93.
The dilemma is, the car is apart and can't be tested; about all u can do is check cranking psi, which really will help.
once i ordered 3 cams and sent them all back without ever running the engine. i went with #4.
Changing the lash to .024-028 will really help, .024 is stock.
With a new cam it should usually not need advancing if it is the right size. A smaller cam will ping easier around 3000 rpm, that is why i'd try advancing the 264. it might run fine on 93 whereas a new 245 might ping hoplessly at 3000 on 93.
The dilemma is, the car is apart and can't be tested; about all u can do is check cranking psi, which really will help.
once i ordered 3 cams and sent them all back without ever running the engine. i went with #4.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
None of it matters as long as he keeps using high octain fuel,
shorter duration cam or advancing the cam. advancing the cam
will close the intake earlier build more comp. but advancing the cam
won't have as much affect as changing the shape of the cam lobe,
its just a crutch to try to help to much duration.
He can buy a new solid lift cam/lifters for less then $ 200.00 not likely to break the bank.
shorter duration cam or advancing the cam. advancing the cam
will close the intake earlier build more comp. but advancing the cam
won't have as much affect as changing the shape of the cam lobe,
its just a crutch to try to help to much duration.
He can buy a new solid lift cam/lifters for less then $ 200.00 not likely to break the bank.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 121
From: Millington Illinois
St. Jude Donor '08-'09
If you are using what you have and want to run lower octane, Back timing down a couple degrees, Run a little rich, Get cool air into the intake, Lower underhood temperatures as much as possible (ceramic coated headers will help), run a 165 degree thermostat, Good radiator, Colder spark plug. These will help but to run stronger midrange and bottom end you have to drop compression and change cams. Don't think opening up your lash is a good idea. Premature valvetrain wear. Advancing the cam will add to your detonation issues.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
he can afford to change to a little lower compression pistons, but
in the meantime to get rid of a miserable upper rpm range cam for
less the $200.00 he can get that big mu--her f--ker cam out of
his street car geared life. as long as he keeps high octain levels
he can advance the cam but that will just help a tiney bit, the fix is
a nice modern slightly higher lift shorter duration cam for $200.00
then later on down the road less compression to help get it on
pump fuel.
Race Director
Joined: Oct 2000
Posts: 14,967
Likes: 79
From: central FL, near the beach.
the car is snowed in, in chicago.
he has NEVER tried street gas
previous owner says it will ping.
myself, i'd tear it apart and check it out.
and i wouldn't violate the stock .024 and run .016. too tight, will make it into a dog.
but this is just talk for everyone on a cold day.
i agree cams are cheap! so are pistons!
so is street gas(vs race gas)
This is CHAT! Bench racing, whatever,
not
just passing the time until may 
he has NEVER tried street gas
previous owner says it will ping.
myself, i'd tear it apart and check it out.
and i wouldn't violate the stock .024 and run .016. too tight, will make it into a dog.
but this is just talk for everyone on a cold day.
i agree cams are cheap! so are pistons!
so is street gas(vs race gas)
This is CHAT! Bench racing, whatever,
not
just passing the time until may