LS7 - Help Me Analyze

[da z06]

Ok. Let me answer some of the questions.

EEC is stock E38, HP Tuners (latest edition) for tuning.

Injectors are FIC850cc, fuel pressure was within specs.

AF and Timing table or logs I don't have access to at this moment (Im at the office) don't have access to them. But AF/Timing @ peak TQ, peak HP, on top and mid-range was played with no significant changes to where the power band levels.

The Ferrera HS 2042P is (on my scale) 85g:



The PSI LS1515ML is 76g:



Runner length on the Holly Hi-Ram is significantly shorter than that of the MSD intake, (I know I measured it but cant recall), therefore not requiring that much intake timing for higher RPM power and I get your point in regards. With current set-up, power band seems to start falling at ~7200RPMs.



I been thinking about these specs:

Intake open BTC: 14.5
Intake close ABC: 58.5
Exhaust open BBC: 68.5
Exhaust close ATC: 12.5
Intake center: 112
Exhaust center: 118
Degrees overlap: 27
In: 174@.200
Ex: 181@.200

[wyrmrider]

Let's recapitulate
Lifters not collapsing but may have stability problems
HR lifters are subject to collapsing due to many factors, too much spring, too much acceleration or rocker, too much valve weight so BVVC
Those lobes are pushing 10 years old and are from the early days of LS- have the camgrinders learned anything in the last 10 years, different springs available etc?
did you say who's spring and part number you have or just quote the specs
you might pull and test a couple if you have been ruining them for awhile
7-8 years ago duals were recommended to solve all the worlds ills like heavy valves or Comp 26918 or PAC 1518 with light valves- there has to have been some progress with springs
918 or 26926 came along- what now?
what retainers?
are these the lobe you are currently using
.006? 50 200 lobe
13020R 289 239 162 .367” .624”
13024R 305 255 176 .367” .624” looks about right with change to 1.8 rockers
small typo on the intake 200 in your post
is you have a 114 LCA- is this required for computer or brakes or what?
did you dbl check the rocker geometry- stock base circle on the cam?

[RW TECH]

The same 233° cam I was talking about made peak HP at 6900 in a 450 CID combination with LSX 102 intake so I still believe you're not miles off with 239° @ .050".

ou should get the valvetrain sorted out on a spin rig if at all possible. I've seen combinations like that (based on your .200" duration numbers) slam into a wall just above 7K RPM, especially with the heavier exhaust valve.

The cam you're looking at - I would try to get the exhaust valve closing a little closer to 15° ATDC and the intake opening closer to 10° BTDC.

The situation at high engine speed sometimes involves cyl. pressure purging into the intake port when intake valve opens.

Something like this:





Y

[da z06]

Let's recapitulate
Lifters not collapsing but may have stability problems
HR lifters are subject to collapsing due to many factors, too much spring, too much acceleration or rocker, too much valve weight so BVVC
Those lobes are pushing 10 years old and are from the early days of LS- have the camgrinders learned anything in the last 10 years, different springs available etc?
did you say who's spring and part number you have or just quote the specs
you might pull and test a couple if you have been ruining them for awhile
7-8 years ago duals were recommended to solve all the worlds ills like heavy valves or Comp 26918 or PAC 1518 with light valves- there has to have been some progress with springs
918 or 26926 came along- what now?
what retainers?
are these the lobe you are currently using
.006? 50 200 lobe
13020R 289 239 162 .367” .624”
13024R 305 255 176 .367” .624” looks about right with change to 1.8 rockers
small typo on the intake 200 in your post
is you have a 114 LCA- is this required for computer or brakes or what?
did you dbl check the rocker geometry- stock base circle on the cam?

The springs on those dyno runs were fresh with less than 2500 miles on them. They are a NEW (within the last year) release by PSI specific for the LS7 folks:

LS1515ML (Beehive) OD: 1.290", IDO: .630 140lb@1.950, 405lb@1.300, Rate: 408, Max Lift .650", Blind 1.225"

The Ferrera Hollow Stem may be a few grams heavier than the Stock Hollow Stem, but still way lighter than a solid SS for the same application.

Spintron testing is out the question.

I prefer to run a Single just for the better valvetrain control over a dual. As I listed earlier, leaning towards the PSI LS1516ML on the new combo.

LC is 114/ICL 110, car is not a dedicated racer, and drive it easy 10K miles per year. Has to deal with stop-and-go traffic, and has to have AC in SATX heat! jejeje!

[Newold1]

Having now seen the added pics you posted. If that is the MSD intake manifold with the interchangeable runners, try a set of the short runners and retest you might just find the results you are looking for.

[wyrmrider]

Conventional wisdom from the good old days would be to add some exhaust duration to extend the power curve
today exhaust ports are more efficient
and the header change may do the same thing and adding duration may be too much
so easiest thing first may be those shorter rams
then the headers
then fool with the cam- you are running 4 degrees advanced now
how about straight up or split overlap
saying that with as these are not single pattern symmetrical lobes
asymmetrical lobes are not really where you think they are in the first place
but given that a test is still in order before thinking about new lobes
there is another thread with stock rocker issues above 630 lift
other threads with guide wear
and guide wear leads to detached valve heads
so take a look at all the aspects
cheers
do you have approximate head flows? from similar work?

[da z06]

Having now seen the added pics you posted. If that is the MSD intake manifold with the interchangeable runners, try a set of the short runners and retest you might just find the results you are looking for.

Unfortunately the MSD runners are not interchangeable like the FAST, and the FAST with the extra runners is only for the LS3 as of yet.

[da z06]

Conventional wisdom from the good old days would be to add some exhaust duration to extend the power curve
today exhaust ports are more efficient
and the header change may do the same thing and adding duration may be too much
so easiest thing first may be those shorter rams
then the headers
then fool with the cam- you are running 4 degrees advanced now
how about straight up or split overlap
saying that with as these are not single pattern symmetrical lobes
asymmetrical lobes are not really where you think they are in the first place
but given that a test is still in order before thinking about new lobes
there is another thread with stock rocker issues above 630 lift
other threads with guide wear
and guide wear leads to detached valve heads
so take a look at all the aspects
cheers

do you have approximate head flows? from similar work?

Per TSP, the flow data advertised is as follows:

Flow Data: @ 4.125" Bore Plate Superflow 600 LS7 Head

Stock In/Ex vs CNC In/CNC Ex
.200 161 114 169 119
.300 227 171 248 179
.400 291 193 308 211
.500 330 203 351 224
.600 351 209 383 235
.650 353 204 388 241
.700 353 209 393 246

[RW TECH]

Conventional wisdom from the good old days would be to add some exhaust duration to extend the power curve
today exhaust ports are more efficient
and the header change may do the same thing and adding duration may be too much

Take a look at the graph I posted earlier....that was an LS7 with porting. Headers didn't make that go away.

[Newold1]

Ah yes, that is that MSD Atomic intake manifold. Better than the stock GM LS7 intake even with a 90mm throttle body, but even with a 102 mm big mouth throttle body and your head and cam combo it will be power peaking at about 6500 or so rpms and power is falling slowly from 6500 to 7000rpms. If you find some dyno reports on the LS7 builds with lets say the Holley Hi=Ram cast intake for the LS7 with short runners it is power peaking at about 6800-7000rpms and climbing all the way there with little or no plateauing. Damn that Corvette low hood clearance. Will be nice when GM finally puts the engine midship and really allows it to breathe! I am not sure you would want to try but it might be possible to cut and shorten those runners about 2-3 inches and epoxy them back on for a higher rpm peak power range and create a little more plenum volume in the process. When I have seen the dyno testing results on Fast's short runner equipped version LS3 that allowed manifold switching between the runner lengths, the higher rpm power points were achieved with the right camshaft profiles and the shorter runners.

[KnightEngines]

The little wobbles in the power curve up top suggest there is an issue with the valve train - it's a giveaway when the power stops before you think it should, but doesn't drop off just flatlines & goes wobbly.

I don't like behive springs, I think you'll be happier with duals. Short travel lifters would probably be on the shopping list as well.

I'd do springs & lifters 1st, then retest so you got a real idea of where the cam is giving up & can think about a new cam with correct info for a basis.

[fdicrasto]

The LS7 hyd. roller lifter is an excellent piece with one minor mod. Limiting plunger travel. You would need adjustable rockers to finish the deal.

[wyrmrider]

Sorry RW
these old eyes don't quite get your post
I think I'm looking at 8 pressure traces
your comment that sometimes cylinder pressure gets into the intake when the intake opens
is that not what the exhaust suck is supposed to prevent?
but also why randy goes to steeper seats
or go to an IR cam and have a later seat opening
it will be interesting to see where this ends up
If you want to explain I'm listening
thanks

[Newold1]

Hey da z06:

Talk to Marcella about this intake manifold. He makes it for a LS7 head and it will fit under the corvette's hood. Its pricey but it will get you where you want to go!

[Newold1]

Sorry da z06

You need the inside shot to know why it works!