29.5 degrees of overlap + Boost-?
29.5 degrees of overlap + Boost-? So I ran into an article that GM High-Tech Performance put out awhile back where they built a LS 383 with flat top pistons (high CR) and tested out two cam profiles for a single turbo setup; one with a traditional aggressive NA profile, with 29.5 degrees of overlap, the other a more conservative turbo cam. As it turns out the more aggressive cam netted more Tq and Hp throughout. Any thoughts?
http://www.gmhightechperformance.com...t/viewall.html
So I've got an LS2 with a MS4 cam with about 33 degrees of overlap and 10.9 CR. I know this cam shouldn't work well for a turbo setup....but just curious what would be the difference. Perhaps the larger displacement of the 383 in the above article would tend to tame the cam a bit..?
http://www.gmhightechperformance.com...t/viewall.html
So I've got an LS2 with a MS4 cam with about 33 degrees of overlap and 10.9 CR. I know this cam shouldn't work well for a turbo setup....but just curious what would be the difference. Perhaps the larger displacement of the 383 in the above article would tend to tame the cam a bit..?
Yea, I've been scouring the net for something like this. Mostly because I'm trying to convince myself to do this since I purchased both a relatively fresh LS2 and a single turbo setup minus the turbo. I was under the impression that the lower the LSA with boost the more tq/hp you give up down low but it adds to the top end.
So here are the valve events for the 281LRHR13 cam, I'm having a bit of difficulty find them for the MS4.
Valve Timing @ 0.006 Lift:
Exhaust
Closes 28
ATDC
Opens 81
BBDC 109
Intake
30 Opens
BTDC
70 Closes
ABDC
Valve Timing @ 0.006 Lift:
Exhaust
Closes 28
ATDC
Opens 81
BBDC 109
Intake
30 Opens
BTDC
70 Closes
ABDC
As easy as the cams are to change in these motors I dont have any issues running basically ANY cam. If it doesnt work well change it later.
You are going to need a turbo with a BIG turbine wheel for that cam to work, I suggest the 97mm S400 setup with whatever compressor you need for your HP goals.
I ran a s475 1.32 97mm turbine on my 6.0 with this cam (.006")
IVO is 33.5 ° BTDC
IVC is 69.5 ° ABDC
EVO is 82.5 ° ATDC
EVC is 30.5 ° BBDC
Overlap is 64 °
And it was perfect, low backpressure, and made more hp/psi than the z06 cam I had in there by a long shot. around 540whp at 12# with the z06 and 620whp at 12# with the big NA cam
You are going to need a turbo with a BIG turbine wheel for that cam to work, I suggest the 97mm S400 setup with whatever compressor you need for your HP goals.
I ran a s475 1.32 97mm turbine on my 6.0 with this cam (.006")
IVO is 33.5 ° BTDC
IVC is 69.5 ° ABDC
EVO is 82.5 ° ATDC
EVC is 30.5 ° BBDC
Overlap is 64 °
And it was perfect, low backpressure, and made more hp/psi than the z06 cam I had in there by a long shot. around 540whp at 12# with the z06 and 620whp at 12# with the big NA cam
As easy as the cams are to change in these motors I dont have any issues running basically ANY cam. If it doesnt work well change it later.
You are going to need a turbo with a BIG turbine wheel for that cam to work, I suggest the 97mm S400 setup with whatever compressor you need for your HP goals.
I ran a s475 1.32 97mm turbine on my 6.0 with this cam (.006")
IVO is 33.5 ° BTDC
IVC is 69.5 ° ABDC
EVO is 82.5 ° ATDC
EVC is 30.5 ° BBDC
Overlap is 64 °
And it was perfect, low backpressure, and made more hp/psi than the z06 cam I had in there by a long shot. around 540whp at 12# with the z06 and 620whp at 12# with the big NA cam
You are going to need a turbo with a BIG turbine wheel for that cam to work, I suggest the 97mm S400 setup with whatever compressor you need for your HP goals.
I ran a s475 1.32 97mm turbine on my 6.0 with this cam (.006")
IVO is 33.5 ° BTDC
IVC is 69.5 ° ABDC
EVO is 82.5 ° ATDC
EVC is 30.5 ° BBDC
Overlap is 64 °
And it was perfect, low backpressure, and made more hp/psi than the z06 cam I had in there by a long shot. around 540whp at 12# with the z06 and 620whp at 12# with the big NA cam
Thanks for the info, I will probably just go ahead and see how it works out. I however did find the full specs on the MS4 cam, let me know what you think.
@ .05
8 ° BTDC
50° ABDC
51° BBDC
9° ATDC
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I just went ahead and double checked how to calculate overlap, if I'm not mistaken it's BTDC+ATDC. If that's correct then the MS4 cam only has 17 degrees of overlap, and I'm slightly confused since duration ((289+291)/4)-111 LSA= 33 degrees of overlap.
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You're jumping back and forth between 0.050" of lift and 0.006" of lift... thats where you're getting confused.
The ((281+291)/4)-111 formula erroneously gives you 34* of overlap at 0.006" of lobe lift. I use this formula with 0.050 numbers, but you forgot to add a "x2" around the whole equation. So, you would actually have 68* of overlap at 0.006" lift with the MS4.
Then you mentioned 17* of overlap using 0.050 numbers with the MS4. I've never heard of computing valve events to get overlap, but then again I'm a newb. The number I get is (((239+242)/4)-111)x2= 18.5* of overlap at 0.050" lift with the MS4. Just use 0.050" numbers and everyone will be on the same page. 0.050" numbers are more commonly used for general cam discussion nowadays.
Either way, the MS4 is one bad top-end mother (depending on the cubes).
The ((281+291)/4)-111 formula erroneously gives you 34* of overlap at 0.006" of lobe lift. I use this formula with 0.050 numbers, but you forgot to add a "x2" around the whole equation. So, you would actually have 68* of overlap at 0.006" lift with the MS4.
Then you mentioned 17* of overlap using 0.050 numbers with the MS4. I've never heard of computing valve events to get overlap, but then again I'm a newb. The number I get is (((239+242)/4)-111)x2= 18.5* of overlap at 0.050" lift with the MS4. Just use 0.050" numbers and everyone will be on the same page. 0.050" numbers are more commonly used for general cam discussion nowadays.
Either way, the MS4 is one bad top-end mother (depending on the cubes).
You're jumping back and forth between 0.050" of lift and 0.006" of lift... thats where you're getting confused.
The ((281+291)/4)-111 formula erroneously gives you 34* of overlap at 0.006" of lobe lift. I use this formula with 0.050 numbers, but you forgot to add a "x2" around the whole equation. So, you would actually have 68* of overlap at 0.006" lift with the MS4.
Then you mentioned 17* of overlap using 0.050 numbers with the MS4. I've never heard of computing valve events to get overlap, but then again I'm a newb. The number I get is (((239+242)/4)-111)x2= 18.5* of overlap at 0.050" lift with the MS4. Just use 0.050" numbers and everyone will be on the same page. 0.050" numbers are more commonly used for general cam discussion nowadays.
Either way, the MS4 is one bad top-end mother (depending on the cubes).
The ((281+291)/4)-111 formula erroneously gives you 34* of overlap at 0.006" of lobe lift. I use this formula with 0.050 numbers, but you forgot to add a "x2" around the whole equation. So, you would actually have 68* of overlap at 0.006" lift with the MS4.
Then you mentioned 17* of overlap using 0.050 numbers with the MS4. I've never heard of computing valve events to get overlap, but then again I'm a newb. The number I get is (((239+242)/4)-111)x2= 18.5* of overlap at 0.050" lift with the MS4. Just use 0.050" numbers and everyone will be on the same page. 0.050" numbers are more commonly used for general cam discussion nowadays.
Either way, the MS4 is one bad top-end mother (depending on the cubes).
All I need now is to pick out a compressor and figure out what I'm going to drop it in, probably a chevelle.
Thanks for the info, I've read over some of you posts when researching and you seem to be quite knowledgeable about turbo dynamics so I appreciate the feedback.
I'm running a 2.5in crossover pipe I'm not sure whether this would reduce the velocity of the charge enough to effect spooling. The intake is off of a LS6 and has been port matched to the reworked 243 heads.
I'm running a 2.5in crossover pipe I'm not sure whether this would reduce the velocity of the charge enough to effect spooling. The intake is off of a LS6 and has been port matched to the reworked 243 heads.
Ehh, that test of the N/A cam versus the "turbo" cam wasn't what I consider fair. You've got a cam that has 212/218 degrees of duration @.050" versus a cam that's 231/239 @.050" and compare them? That's not even taking into consideration LSA and ICL and the duration difference alone is huge. Holdener has always done great tests IMO, but that one doesn't make me feel warm and fuzzy.
I'd like to see that same 231/239 113LSA cam versus the 234/239 114+3 or 234/237 115+4 cam I do for a lot of the S400 BW stuff and see how it would compare in a back to back dyno test. I can say I've done a nearly identical cam to that 231/239 113lsa cam they used in a few turbo engines and it versus the slightly larger slightly wider LSA 234/237 and 234/239 cams I mentioned make within 5-10rwhp of each other with slightly different characteristics.
When you take two extremes and test them against one another of course the results will be vastly different. You can also talk to 10 different cam grinders and you'll get 10 pretty much diferent answers at every stop along the way. Everyone of those cam grinders version of a "turbo" cam will be different.
I'd like to see that same 231/239 113LSA cam versus the 234/239 114+3 or 234/237 115+4 cam I do for a lot of the S400 BW stuff and see how it would compare in a back to back dyno test. I can say I've done a nearly identical cam to that 231/239 113lsa cam they used in a few turbo engines and it versus the slightly larger slightly wider LSA 234/237 and 234/239 cams I mentioned make within 5-10rwhp of each other with slightly different characteristics.
When you take two extremes and test them against one another of course the results will be vastly different. You can also talk to 10 different cam grinders and you'll get 10 pretty much diferent answers at every stop along the way. Everyone of those cam grinders version of a "turbo" cam will be different.
Just to clarify I'm looking to get around 700hp at the wheels, it looks as though this turbo supports quite a bit more. I'm also running a high SCR of 10:9:1 and I don't have access to E85 in NC so it will be limited to pump gas so low boost. The car will be mostly street driven, should I look toward another turbo?
Last edited by Chevyguy358; Feb 14, 2013 at 07:15 PM.
