Making LS7 more reliable and faster ? I hope so

[acammer]

Originally Posted by void_kp

as far as I understand (but can be wrong as I am new to these engines) it's ok up to 0.677 or even 0.700.
I'm sure some guru in the forum will have the answer

The LS has a few features going for it which make lift in the .650" range completely reasonable, even for street driven engines. The biggest factor is weight - the lack there-of. The lightweight nature of the valve-train means we can run with so much less spring pressure than most other pushrod combinations. This makes the scrub-nose style rocker very viable.

The other major factor is the cam lobe design itself. This is a CRITICAL piece to making any valve-train live a healthy life. This varies between various manufacturers, but a well developed and tested cam lobe will keep the valvetrain smooth and stable, even with big lift and RPM.

I've put 20k miles on a .650" lift cam setup, and my rocker tips still looked great on inspection. Sure - any time you crank up the rpm, lift, spring pressure, you're going to see more wear than a factory engine would. That's a fair trade-off, we're looking for performance well above and beyond what the factory gave us, and so we're willing to accept we won't get 150,000 miles out of some of the more critical wear parts.

One other note, because it's like to come up, regarding roller tipped rockers. It seems like an obvious solution, right? Replace a sliding surface with a rolling one, less friction is always good, right? Well, in this case, no. There is no way to add a roller tip to a rocker without adding weight of the roller and axle setup to support it. This added weight comes at the worst possible point on the rocker, right over the valve tip where it creates the most additional inertia to control. The translation is more spring pressure to achieve the same stability at a given RPM. Now, we're asking more of a fairly light duty hydraulic roller lifter. It introduces more trouble than it's worth.

We spintron test our hydraulic roller valve-train setups into the 9000+rpm range, and we've never found anything better than the factory style rockers for those hydraulic roller applications. The Comp BSR Max Lift shaft mount system is proving to be a good option for retaining that OEM style rocker on a more stable platform - and would be my go-to recommendation for rockers on higher RPM combinations.

[void_kp]

quick status update.

After some visual inspection I returned one of the heads and the rocker arms.
One of the heads was perfect, well machined, really nothing to standout. The other head has some significant metal shavings in the conducts, one 'bump" in one of the combustion chambers and a shaving on the flat surface of the head that prevented it from being leveled. It was as if there was no QC and the head was shipped before one last stage of finishing.

LS3 Rocker arms were shipped incorrectly as I asked for the LS7 ones.

MAST Motorsports personnel was very friendly and the return is in progress, I'm waiting for the tracking number. Return initiated on 1/9 on my end but shipment to MAST was significantly delayed due to bad weather and the long weekend for MLK day.

On the more positive news, I've received the 2" KOOKS headers with high flow cats.
They are ok-ish quality. My reference point was Mugen and Spoon headers for the B16 engine back in the day and Kooks do not have the same welding or finishing. Not that it matters in terms of performance as from a visual inspection they do not have steps or inconsistencies in the inside part of them.
The welding that connects tubes with the flange looks with a step but when touching it proves to be smooth, so everything is ok. They are not pretty but they will probably work well, which is the most important thing.

here's some content:
https://youtube.com/shorts/NvAZ3VjT98M?feature=share

https://imgur.com/JIoMvQS
https://imgur.com/VhMYPc0
https://imgur.com/4OQjb5y

[ariZona28]

If I'd laid out a huge amount of cash for a set of heads and they showed up in the condition you mentioned I'd be hesitant to install thier product on my engine especially if it's going to be spending a good amount of time near the rev limiter. Its not just what you found but what you CAN'T see that would stress me out. "Sorry Sir" just doesn't cut it at 7 grand. If you must mod, I still say go with a well coordinated package from one retailer whether it's Katech, GPI or one of the other respected names. I'm a bit disappointed in the finish quality of the Kooks. Once again you threw out some good coin for a product with a budget style final out.

[void_kp]

Originally Posted by ariZona28

.... I'd be hesitant to install thier product on my engine especially if it's going to be spending a good amount of time near the rev limiter. Its not just what you found but what you CAN'T see that would stress me out. "Sorry Sir" just doesn't cut it at 7 grand. If you must mod, I still say go with a well coordinated package from one retailer whether it's Katech, GPI or one of the other respected names. I'm a bit disappointed in the finish quality of the Kooks. Once again you threw out some good coin for a product with a budget style final out.

while I agree on general negative sentiment of spending for "not so high" quality, I have to put some things into perspective:
- Headers are less than $3K , so less than half of what you mentioned here.
- external finishing on headers is irrelevant to performance and flow, as I mentioned the key parts are smooth to the touch (which is good) even if you can see a different color (irrelevant to performance)
- headers have almost no impact on reliability... I will inspect the original GM ones, but usually (not sure LS7 qualifies for usually) the original headers are basically the worst possible in terms of weight and flow.
- in my past experience there's absolutely ZERO advantage of relying on "famous" tuners or shops, the world is full of passionate people that specialize in few parts and do the best on them. I don't know if Kooks is one of them, but those headers are good enough. Since I was more worried about the heads, I went for the "top" with MAST.
- I don't plan to be around the limiter all the time, you can check it in my videos that i posted. I am not fighting for the last tenth of a second on the lap, I don't need to stress the engine out, this is to have fun on track. We will see the torque curve with the cams, but in its stock form the LS7 is not really worth to pull to the limiter.

[ariZona28]

Sorry, when I mentioned 7 grand I ment the RPM, not cost. I definitely would have no problem with the headers but the heads? I'm WAY too picky (and I too have been burned by self ordained experts) to go with those even if just running it hard during street "therapy " sessions.

[void_kp]

Originally Posted by ariZona28

Sorry, when I mentioned 7 grand I ment the RPM, not cost. I definitely would have no problem with the headers but the heads? I'm WAY too picky (and I too have been burned by self ordained experts) to go with those even if just running it hard during street "therapy " sessions.

MAST won almost any comparison against other manufacturers when comparing heads for LS engines.
Although it must be noted that it as the "black label" heads, while I bought the newer product, the "Factory"

[void_kp]

update: seems like MAST shipped back the head that I returned + the correct (hopefully) rocker arm + CHE trunnion.
Installation will start on 3/12. Will dyno before and after.
Will keep you posted

[void_kp]

Update on the project. Today I've brought the Z/28 to install all components (BFD cam, MAST Factory heads, rocker arms with CHE trunnions, Kooks 2" headers and everything that is needed to do so).

We did a dyno run before , we will do a dyno run after.
Before looking at the run(s) I'd like to remind everyone that my purpose is not to get more horsepower, for this reason I won't increase limiter, especially given that I've not changed any engine internals. I don't need more power, this is just to fix heads and install the cam that I was gifted.

about the Dyno run:
I am AMAZED by the LS7 engine. This engine is a masterpiece. That torque curve is wonderful, it's almost too good to be true

Power is good, 460+ on the wheels is a solid result, in my past experience a +/- 5% error is something to consider everytime you compare across different dynos. Anyway, this is more than I expected, given powertrain loss this is well above the 505hp that Chevy declares.
Car is bone stock, Dyno run was made with exhaust flap open and the "track" setting to ensure there's no conservative timing or other "slower" ignition/fuel map setting.

Car should be ready in the next 2 to 3 weeks. I'll keep you posted

[highrevving]

Thanks for sharing!

Similar data from Motortrend comparison with GT350R:

[void_kp]

today I went to check on progress on my car and it was almost done (all assembled, ready for break in and tune).

I asked the guy to check the original heads and he identified valve play on exhaust one in cylinder 8. Not sure yet if it's due to the "dreaded" valve drop problem. Will do more tests and inspection when I will bring the heads (And the car) back home.

so far everything looks super neat. I'm close to Seattle and I've used Carburetor Connection (www.carbconn.com) , so far they have been great.
let's see how it ends. I'll keep you all posted.

[void_kp]

oh, another quick update that I forgot. The 2" Kooks headers didn't fit right away. they hit steering rack on one side and something else on the other side. They require modification to install (or to "bump" the headers).

[joelster]

You can really go down a rabbit hole when talking about LS7 engine issues. I watched the Richard Holdener video and from the results of his test I went with Lingenfelter heads. The turn around time was low, and they've done tons of them. They outflow the Mast heads you bought, and are significantly cheaper. I am running the TSP 3.2 cam which is a little milder than what you have. I race autocross and need low end.

I have the same headers/no cat setup that you have, but also have the MSD Atomic, and a 103mm TB. I made 588rwhp.

I've been around engines my whole life and a few things inside the LS7 really worried me. They run a ton of preload on the lifters right from the factory. Almost 2 full turns. That's a really big no-no when you're talking a high rpm, hydraulic roller screamer. It wouldn't surprise me in the least that a lot of these failures on stock engines are from a lifter pumping up, hanging a vlave open, and then the piston smacks the valve. I went with a full roller rocker setup from TSP. With a 1.8 rocker and a non-roller tip from the factory stuff, I figured that it "might" accelerate wear on the valve tips. I know that tons of guys have run the factory rockers for years with no issues, but I wanted that piece of mind. I also went with 2 different sized pushrods from BTR. I don't remember the lengths off of the top of my head, but my preload is at .035-.040".

[acammer]

Originally Posted by joelster

I've been around engines my whole life and a few things inside the LS7 really worried me. They run a ton of preload on the lifters right from the factory. Almost 2 full turns. That's a really big no-no when you're talking a high rpm, hydraulic roller screamer. It wouldn't surprise me in the least that a lot of these failures on stock engines are from a lifter pumping up, hanging a vlave open, and then the piston smacks the valve. I went with a full roller rocker setup from TSP. With a 1.8 rocker and a non-roller tip from the factory stuff, I figured that it "might" accelerate wear on the valve tips. I know that tons of guys have run the factory rockers for years with no issues, but I wanted that piece of mind. I also went with 2 different sized pushrods from BTR. I don't remember the lengths off of the top of my head, but my preload is at .035-.040".

It's a good point about preload - I would agree that anytime you have a hydraulic roller setup and a manual transmission with the potential of mechanical over-rev that you want to target a minimal-modest amount of lifter preload. Ideally a preload amount less than the piston to valve clearance you have so that even if you manage to float the pushrod completely off the lifter and pump it full of oil, it doesn't have the ability to take up all of your clearance. This really underscores the value of running a short travel lifter in applications that turn big rpm, and are at risk for over-rev. With the short travel you can have those nice light .030" range preload amounts, and still only have another .030" or so of available "squish" where you can lose lift and duration to aerated oil in the lifter - mostly like to be seen in the upper revs where you need every bit of camshaft you've got.

As for rockers, I struggle to get behind anything that adds weight to valvetrain, especially at the valve tip. At a given RPM, that rocker is going to take more valvespring pressure to control, and everything we do in LS engines is to keep the valve-train light so we can minimize that spring pressure and keep the everything happy. I appreciate the concept of minimizing friction and wear - but with good oil, appropriate spring pressure, and good valve-train control valve-tip wear is not a substantial issue that we see. Given lots and lots of miles over the life of a few sets of valvesprings, it could become a conversation point, but that is almost never the life these sort of combinations lead.

I watched your YouTube video and I came up with some different values for preload. On a 1.8 rocker, you'll have right about .076" of preload per turn, from zero lash. So, for your stock rocker you've got about .120" of preload based on 1 5/8ths turn from zero lash, which sounds exactly like what the factory typically does. On your aftermarket rocker you've got about 7/8ths of a turn from zero, so right about .067" of preload.

Looking forward to void_kp's results and impressions of the combination he's got coming together.

[joelster]

Originally Posted by acammer

It's a good point about preload - I would agree that anytime you have a hydraulic roller setup and a manual transmission with the potential of mechanical over-rev that you want to target a minimal-modest amount of lifter preload. Ideally a preload amount less than the piston to valve clearance you have so that even if you manage to float the pushrod completely off the lifter and pump it full of oil, it doesn't have the ability to take up all of your clearance. This really underscores the value of running a short travel lifter in applications that turn big rpm, and are at risk for over-rev. With the short travel you can have those nice light .030" range preload amounts, and still only have another .030" or so of available "squish" where you can lose lift and duration to aerated oil in the lifter - mostly like to be seen in the upper revs where you need every bit of camshaft you've got.

As for rockers, I struggle to get behind anything that adds weight to valvetrain, especially at the valve tip. At a given RPM, that rocker is going to take more valvespring pressure to control, and everything we do in LS engines is to keep the valve-train light so we can minimize that spring pressure and keep the everything happy. I appreciate the concept of minimizing friction and wear - but with good oil, appropriate spring pressure, and good valve-train control valve-tip wear is not a substantial issue that we see. Given lots and lots of miles over the life of a few sets of valvesprings, it could become a conversation point, but that is almost never the life these sort of combinations lead.

I watched your YouTube video and I came up with some different values for preload. On a 1.8 rocker, you'll have right about .076" of preload per turn, from zero lash. So, for your stock rocker you've got about .120" of preload based on 1 5/8ths turn from zero lash, which sounds exactly like what the factory typically does. On your aftermarket rocker you've got about 7/8ths of a turn from zero, so right about .067" of preload.

Looking forward to void_kp's results and impressions of the combination he's got coming together.

I do autocross, so my engine doesn't spend a whole lot of time at max rpm. A typical run only goes WOT for 2 or 3 short instances, and then you're right back on the brakes, hard. My engine is oversprung as it is. If it was a daily driver or an engine that I'd run 5000+miles a year, I would have a different approach for sure.

You're correct on the preload, I was simply going by the thread pitch, I totally forgot to multiply by the ratio lol. But factory preload at over a tenth is just nuts to me.

I see you're from GPI, they have an excellent write-up on what goes wrong with an LS7. I refered to that page a lot!