blower cam?
07-11-2002, 05:19 PM
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blower cam? I'm doing an ARE 360 with 9:1 comp, T-trim with around 15 lb. boost. I'm looking for the optimal cam for this setup. They are putting in a 226/226 .561/.561 114. I'm concerned that this is a bit conservative for what I want to do, Any suggestions? I run a T-1 right now with H/C and a g-trim. I have had pretty good luck with that combo.
07-13-2002, 09:59 PM
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Re: blower cam? Thanks, that sounds like a good cam, I'm still looking at options right now. I know its stupid, but I'd hate to lose the lope that comes with the 112 LSA.
07-16-2002, 02:09 PM
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Re: blower cam? When I was choosing a blower cam alot of the info on how a NA car and a blower car worked was unclear. Then I found this info and it pretty much tells you everything you want to know. I know this info is for an LT1 but the concepts are the same and the information should be true for LS1s as well.
The abbreviated long version of "choosing a blower cam for an LT1" is based on a couple of things. In terms of the cam itself you need to pick a cam that has very little overlap. The reason is to avoid blowing the intake charge right out the exhaust port. Unilke an NA motor you are not depending on scavenging by the exhaust port to empty the combustion chamber and to fill it with the intake charge - the blower does that. Closer LSA = more overlap = more power at high revs on an NA motor due to this scavenging. But to a degree the oposite will occur with a blower car. Another issue is that a large spread between the exhaust and intake duration is needed. All LT1's have pretty efficient induction systems with a high VE. The normal 80% ratio of exhaust/intake flow provided by the heads isn't enough to fully empty the cylinder on the exhaust stroke in this situation. That's why all decent LT1 cams are "dual pattern". And you don't want to push it out with the intake charge either (see above). This is especially true when you are using a "street" type exahust system with it's added resistance to flow. If you think of the SC as a device that drastically increases VE (and hence intake flow) you can see that a set of heads that have good exhaust flow and an even more exaggerated split bewteen the exhaust and intake durations are needed. A 10-12 degree spread with more exhaust lift is best.
The XE lobes on this cam are also tailor made for a SC car. The steep ramps limit the rpm range, but with a blower you don't need to rev the snot out of the motor to make power. That's what the blower is for. Just set up the blower to max out where the cam does (~6,200rpm in this case) and you'll have phenomenal mid-range torque. I think you will love this cam. But use the right springs and don't try to rev it past ~6,500rpm.
In terms of peak power, it a "matter of degree" (pun intended). At some point for a given setup there will be an optimum LSA for maximum peak power, as there will be for maximum "area under the (power) curve". Remember that it's the latter that determines acceleration. As far as for this particular cam, in your particular application, it's somewhat of a guess. Keep in mind before freaking out about 116 degrees that the stock cams for LT1's are up to 117 degrees LSA (I forget which year used that, don't have the file of cam stuff with me). And these stock cams are short duration, so they have "negative" overlap. That's part of the reason for the flat torque curve that makes the LT1 such a delightful driver, even in stock form.
In terms of performance cams, there are some significant differences between optimal blower and NA cams. For NA you must sacrifice low end to get power at the top of the rev range. Overlap is needed to fill the cylinder on the intake stroke and empty the exhaust gasses by way of exhaust "scavenging" and by way of timing the intake pulse to coincide with intake valve opening . But remember that the manifold on a blower car is under pressure all the time (when under boost) and that the pressure increases as the revs rise. So the rate of increase in the intake flow is much faster than in an NA motor as the revs rise. Peak and average cylinder pressure are much greater and increase faster as well. End result: overlap bleeds off cylinder pressure more and more as the revs rise and is not needed to fill the cylinder or force out the exhaust gasses. This is the opposite of NA where a cam with more overlap will have a relatively narrow (1-1,500rpm) band in which there is an optimal relationship between the intake and exhaust tuning and the amount of overlap. Within that range everything works together to maximize cylinder pressure (and power). The more the overlap the narrower the range but the higher the peak in terms of amplitude (max power) and where it sits in the rev range. On a blower car the peak will be [bl]lower[/b] with more overlap and as distinct from the NA paradigm the midrange will also suffer. As with all things, if you go too far in any direction the generalization starts to fall apart as second and third order effects come into play. But that's the basic idea.
If you look at overlap at 0.050" a 224/236 cam with have zero overlap at 115 degreess LSA. So when I think about it that may be the "best" way to have this cam ground if you go for it. 114 will be fine, but I think you will gain a couple of HP if you go a bit wider. Certainly do not go narrower than 114.
(This is the cam that I use <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> ) And all the credit for this post goes to Rich Krause. Hes the cam guru! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />
The abbreviated long version of "choosing a blower cam for an LT1" is based on a couple of things. In terms of the cam itself you need to pick a cam that has very little overlap. The reason is to avoid blowing the intake charge right out the exhaust port. Unilke an NA motor you are not depending on scavenging by the exhaust port to empty the combustion chamber and to fill it with the intake charge - the blower does that. Closer LSA = more overlap = more power at high revs on an NA motor due to this scavenging. But to a degree the oposite will occur with a blower car. Another issue is that a large spread between the exhaust and intake duration is needed. All LT1's have pretty efficient induction systems with a high VE. The normal 80% ratio of exhaust/intake flow provided by the heads isn't enough to fully empty the cylinder on the exhaust stroke in this situation. That's why all decent LT1 cams are "dual pattern". And you don't want to push it out with the intake charge either (see above). This is especially true when you are using a "street" type exahust system with it's added resistance to flow. If you think of the SC as a device that drastically increases VE (and hence intake flow) you can see that a set of heads that have good exhaust flow and an even more exaggerated split bewteen the exhaust and intake durations are needed. A 10-12 degree spread with more exhaust lift is best.
The XE lobes on this cam are also tailor made for a SC car. The steep ramps limit the rpm range, but with a blower you don't need to rev the snot out of the motor to make power. That's what the blower is for. Just set up the blower to max out where the cam does (~6,200rpm in this case) and you'll have phenomenal mid-range torque. I think you will love this cam. But use the right springs and don't try to rev it past ~6,500rpm.
In terms of peak power, it a "matter of degree" (pun intended). At some point for a given setup there will be an optimum LSA for maximum peak power, as there will be for maximum "area under the (power) curve". Remember that it's the latter that determines acceleration. As far as for this particular cam, in your particular application, it's somewhat of a guess. Keep in mind before freaking out about 116 degrees that the stock cams for LT1's are up to 117 degrees LSA (I forget which year used that, don't have the file of cam stuff with me). And these stock cams are short duration, so they have "negative" overlap. That's part of the reason for the flat torque curve that makes the LT1 such a delightful driver, even in stock form.
In terms of performance cams, there are some significant differences between optimal blower and NA cams. For NA you must sacrifice low end to get power at the top of the rev range. Overlap is needed to fill the cylinder on the intake stroke and empty the exhaust gasses by way of exhaust "scavenging" and by way of timing the intake pulse to coincide with intake valve opening . But remember that the manifold on a blower car is under pressure all the time (when under boost) and that the pressure increases as the revs rise. So the rate of increase in the intake flow is much faster than in an NA motor as the revs rise. Peak and average cylinder pressure are much greater and increase faster as well. End result: overlap bleeds off cylinder pressure more and more as the revs rise and is not needed to fill the cylinder or force out the exhaust gasses. This is the opposite of NA where a cam with more overlap will have a relatively narrow (1-1,500rpm) band in which there is an optimal relationship between the intake and exhaust tuning and the amount of overlap. Within that range everything works together to maximize cylinder pressure (and power). The more the overlap the narrower the range but the higher the peak in terms of amplitude (max power) and where it sits in the rev range. On a blower car the peak will be [bl]lower[/b] with more overlap and as distinct from the NA paradigm the midrange will also suffer. As with all things, if you go too far in any direction the generalization starts to fall apart as second and third order effects come into play. But that's the basic idea.
If you look at overlap at 0.050" a 224/236 cam with have zero overlap at 115 degreess LSA. So when I think about it that may be the "best" way to have this cam ground if you go for it. 114 will be fine, but I think you will gain a couple of HP if you go a bit wider. Certainly do not go narrower than 114.
(This is the cam that I use <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> ) And all the credit for this post goes to Rich Krause. Hes the cam guru! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />
07-16-2002, 05:02 PM
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Re: blower cam? Thanks NeedforSpd_Z, Points well taken. I do know that a wider LSA will be better with a blower, I just wanted to keep the 112 LSA for the "lope". I did point out that yes this was not the smartest thing to do. I will probably go with a 114 LSA, no higher than that. I will probably go with a split duration/lift, Nick Agostino is going to recomend what to do on that end. He is doing some research on this. I have seen a few grinds that I think would work well, but I'll leave it to the pro(s) at Agostino. Good reading on N/A vs. SC cams. I have read some good stuff in the magazines, but of course when you want to find a certain article, good luck!
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07-16-2002, 05:42 PM
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Re: blower cam? I would go XE-R 226/234 on a 114LSA
That will get the exhaust out and the car will FLY under boost <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
Chris
That will get the exhaust out and the car will FLY under boost <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
Chris
07-16-2002, 11:08 PM
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Re: blower cam? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by CoopDog:
<strong>I'm doing an ARE 360 with 9:1 comp, T-trim with around 15 lb. boost.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong>
I have been told a T-trim will not fit/work under the hood of an LS1, were there any major mods needed to get this to work?
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"><strong>I run a T-1 right now with H/C and a g-trim. I have had pretty good luck with that combo.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">What sort of rwhp / 1/4 mile numbers have you gotten out of it? I've been thinking about that same combo...
<small>[ July 16, 2002, 11:19 PM: Message edited by: jhelms ]</small>
<strong>I'm doing an ARE 360 with 9:1 comp, T-trim with around 15 lb. boost.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong>
I have been told a T-trim will not fit/work under the hood of an LS1, were there any major mods needed to get this to work?
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"><strong>I run a T-1 right now with H/C and a g-trim. I have had pretty good luck with that combo.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">What sort of rwhp / 1/4 mile numbers have you gotten out of it? I've been thinking about that same combo...
<small>[ July 16, 2002, 11:19 PM: Message edited by: jhelms ]</small>
07-17-2002, 02:45 PM
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Re: blower cam? Chris, that sounds like a tasty cam, I like the duration numbers, what about lift?
jhelms- The T-Trim is a custom setup that will be offered by an authorized Vortech dealer. There is some info on this on LS1.com. I talked to the owner/developer and he has it fit under all hoods except for SS possibly (will still require cutting of the hood.) There are a few prototypes running now, one posts on this board. I'd be interested to hear more from him. The kits won't be available for a month or so. I'm not in a huge hurry.
jhelms- The T-Trim is a custom setup that will be offered by an authorized Vortech dealer. There is some info on this on LS1.com. I talked to the owner/developer and he has it fit under all hoods except for SS possibly (will still require cutting of the hood.) There are a few prototypes running now, one posts on this board. I'd be interested to hear more from him. The kits won't be available for a month or so. I'm not in a huge hurry.
