Example:
-stock heads
-stock intake manifold
-cold air intake
-long tube headers
-aftermarket exhaust
-no cats

With that there, which side would you consider the restriction? The intake or the exhaust?




Motors with a restricted intake? The LS1?


But we can get it out, can we not?

 

duration has more to do with where the powerband is.

 

the exhaust side of the stock heads. remember you posted the flow percentages of the 5.3 head. in the .200-.500 range is was never over 75%. so you would need to add more to the exhaust side of the cam to help the head out.





if that was the case, then why is the LSx intake only giving 10hp? remember the truck intake is almost as good as the LS6 intake. it produced more tq and a little less hp. also, i gained .4 and 2.5 mph switching from the stock exhaust to a borla catback on the wife's 99 formula. that equates to about 30 rwhp. i haven't seen an intake do that yet on a stock cubic inch sized motor. http://www.stealthram.com/99formulatimeslip.html it's just not the restriction you think it is.


looking at your scenario above, the heads are restricting the exhaust side still. right? as i said above, using that rule you stated, the .200-.500 lift area is UNDER 75%. so you would need to add more to the exhaust side to compensate.

 

back on the reverse split cam thing. read this current thread.

https://ls1tech.com/forums/showthread.php?t=222222 i'll pull a quote right out of it.

 

just restating marc_w quote. mark can you explain a little more the differences you are noticing with the swap?

 

in response to this thread, VHP has added more to the tech and tunign page. this should help you understand more as to why they do the things they do. and it works.

http://www.vincihighperformance.com/...20PAGE%20.HTML

 

anyone know how long the deal is gonna last?

 

I agree that the exhaust side of the head is the restriction. With the exhaust system on and the intake manifold in place, the percentages would look alot different.


At what rpm? Have you tested this? I believe a test in Car Craft showed +21rwhp at 6600rpm and moved the tq curve up 1000rpm on a 5.3L w/ the Fast intake.
So you feel b/c the FAST manifold isn't making much power over GM's that the intake is not a restriction? Why are the carb, single and dual plane setups gaining so much? Its the design.


Obviously you feel the exhaust is the restriction, but your looking at the head flow numbers without a intake manifold and exhaust system installed. Finding the flow numbers with the bolt ons in place would show a much different ratio.

 

ok. so you would need to add more to the exhaust side of the cam to help the head out. based on the scenario you used in a previous post.


ok great. you can put a carb and intake on any fuel injected motor and do that. carbs always have, and always will make more horsepower than a fuel injection intake. here's the CHP article on intake only swaps. red is the truck intake, purple the LSx intake. you'll notice the truck intake kicks the LSx and the LS6 intake's butt all the way to 5000 rpm. so, it's great that it makes +21 hp @ 6600 rpm. but how long are you there? so, again, i will stand by my statement that the intake is not the restriction. the bad part of this test was the fact the test motor has headers on it. side note: the LS1 intake is the black line. the truck intake is less of a restriction than the LS1 intake i have on my car!!!



yes i feel the exhaust is the restriction. in your scenario, you took care of the external stuff. do this. put a vacuum gauge on the motor. go for a WOT run. it should stay at 0" the whole time. if it doesn't then you have an intake airflow problem. but why is it? is it the intake itself? the MAF? the throttle body? the intake routing? the size of the air intake duct? (this will help your point some. but, mainly mine) in the case of the wife's 99 formula, during the dyno testing, (only mods at time was borla catback and bassani headers) the PCM was reporting 5" of vacuum. so, VHP replaced the stock airlid and filter and MAF ends with their VHP airlid, polyfoam filter and ported MAF ends. the vacuum dropped to 1". so, yes there was an intake restriction. but not the intake itself. we still haven't replaced the throttle body with a larger one. and restating above what i said about the intake: the truck intake is less of a restriction than the LS1 intake i have on my car!!!

the head flow numbers are without any addons. this is to isolate what the head flow is. there are too many variables when adding aftermarket intakes and exhausts. so, yes the numbers will change. but that's because of the components own restriction. not the head. if the head can flow 250cfm, but the intake can only flow 200 cfm, that's the intakes fault. not the head. now, replace it with an intake that can flow 300 cfm. now the intake port of the head is the restriction. but now we get into air flow velocity. which is another thread someday.

 

now onto the next test CHP did. 3 cams and 4 intakes. unfortunately in this article, they didn't post the graphs. just peak numbers. which is only one part of the picture. this will help your statements more than it will me. to a point. if we could see the whole picture, i'm positive it would paint a way different picture than what the peak numbers are doing. i would venture to say the graphs would look almost the same as the intake test graphs. just with higher numbers in the upper rpms. when adding a cam to the mix, do aftermarket intakes raise the numbers? yes. do they increase the rpm range? no. remember these are all peak numbers only. but, what it does show is when changing to a higher duration cam, the powerband goes up. seeing as how this thread is in the truck section, unless this is a drag truck, i don't think anyone here with a truck wants higher rpm capability. they want existing rpm capability increased. the higher the rpm you run a motor, the more wear, tear, and stress you put on it. the lower the fuel economy gets.

look closely at this. even comp cams uses a large spread in their first cam. and in the other two cams, again the truck intake outdoes the LS1 intake on my car!!! in both hp and tq!!!! the truck intake is just not a restriction. unless you want to spend $900 for the LSx intake that only beats the truck intake AFTER 5000 rpms. i just can't see spending that much money for it. if anything, get a LS6 intake if you really want to change the intake. but look at the first graphs i posted. the LS6 just keeps up with the truck manifold.

and yes i see all the other intakes made way more power than the truck one in the small cam test. i really wish they would've posted the graphs.