Making LS7 more reliable and faster ? I hope so

[void_kp]

Hey folks,
starting this thread to share my journey with LS7 mods.
Disclaimer:
I AM AGAINST ALL MODS on a well engineered car.
I use my Z/28 on the racetrack only (and to drive to/from there) and after reading here in the forum and talking with other LS7 owners (although Z06 vette ones, which is different vintage of LS7) I got quite scared about head problems. Btw It was also surprising to learn that there are rods problems too , but I am not willing to think about opening the block.

Anyway, in order to mitigate the risk of valve issues I decided to buy heads.
When I got the car, I also got some performance pieces with it (but uninstalled): a TSP BFD cam with all necessary accessories to install (pushrods, all bolts, gaskets...)

here's the cam specs:
https://imgur.com/JCy2ZfZ

I was looking around for heads, given that I will replace them and I have a cam already, it makes sense to install everything at once, right?
I'm not looking for horsepower but I suspect that this cam will still give me plenty.

I've looked to various heads and I was interested in the trickflow ones but then on black friday MAST motorsport made a 50% discount on the "factory" heads.

https://www.mastmotorsports.com/coll...-mast-head-305

I've purchased it with:

• Dual Valve Spring & Titanium Retainer Kit - 0.660 Lift
• LS7 Rocker w/ CHE Trunnion Kit & Rocker Bolts
• full assembly

here's the cam specs:

Dimensional Specs

Bore Size: 4.125 (+)
Weight: 28 lbs.
Intake Valve Size: 2.250"
Exhaust Valve Size: 1.600"
Valve Stem Diameter: 5/16"
Valve Length: 5.450"
Valve Angle: 12°
Valve Spring Pocket Diameter: 1.580"
Valve Spring Install Height: 1.800"
Head Stud Size: .4375"
Valve Guide OD: .502"
Valve Job Type: As Cast

Air Flow & Performance Criteria

Intake Max. Flow: 375 CFM @ 1.000"
Exhaust Max. Flow: 192 CFM @ 1.000"
Intake Average Flow: 288 CFM
Exhaust Average Flow: 165 CFM
Intake Seat Material: High Chrome Alloy Steel
Intake Port Volume: 292cc
Exhaust Port Volume: 104cc
Standard Chamber Volume: 71cc
Port Type: As Cast

Materials

Cylinder Head Material: A356-T6 Aluminum
Intake Valve Seat Material: High Chrome Alloy Steel
Exhaust Valve Seat Material: High Chrome Alloy Steel
Deck Thickness: .750"
Rocker Stand Type: Mast Billet
Rocker Arm Type: OE LS7 1.8 or Aftermarket
Guide Material: Bronze

General

Rocker Stand Type: Mast Billet
Rocker Stands Included: Yes
Rocker Stand Dowels Included: Yes
Uses Stock Rocker Bolts: No
Rocker Bolts Included: No
Rocker Arm Type: OE LS7 1.8 or Aftermarket
Head Bolt QTY: 6 Bolt Style
Valve Cover Rail Height: + ½ inch
Can use OE Valve Cover: Yes


the interesting part of the heads is the smaller valve angle compared to the stock one and the fact that they flow quite well.

I'm waiting for headers, I didn't buy a 102mm Throttle body and intake as I've read various VERY contrasting opinions about it.
I plan to dyno before and after, I'll post here to keep everyone updated

[ariZona28]

Wow, that is a pretty stout cam! I'd be a bit apprehensive about that much lift, valve train stress and longevity but I guess you're going for MAX N/A power. Can't wait to see some dyno and track results.

[void_kp]

here's an interesting YT video about various LS7 heads , how they compare and how much CFM (flow rate) influences power output.
A bit on the nerdy side for most of us, but there's a gold mine of information here for those who want to learn.

[ariZona28]

That's a good vid. Wish they included Katech. In the back of my mind I fantasize about Katech heads, the LS7 570 HP cam, Caddy lifters, Kooks or ARH headers, cat delete and a good tune. Then I get in the car and drive it and say "damn, this thing runs SO good as it is". That makes it difficult for me to crack into it AND I've already got a high maintenance LS3 powered C5 Z06 for track duty. I don't have the time and/or patience for another project vehicle.

[morepowerjoe]

Man that's a huge cam! Can't wait to see the results.

[acammer]

What valves did you get? I hope not the stainless option - that's going to be a heavy valve with a fairly modest spring.

The cam is a really interesting grind - it's got a pretty early IVC and late EVO, which is going to keep it from wanting to do big rpm in a 427, but it has ridiculous amounts of overlap (34.5*) that's going to make a pretty focused powerband in the 5800-7000 range. Reading the advertisement, the marketing matches - it seems primarily focused on sounding super aggressive. No doubt it will achieve that with the overlap, but it's gonna drive very aggressive in a manual car. I would not expect to enjoy just cruising around under 2600rpm anywhere.

I'm curious about your valve angle comment. Both the heads your bought and the factory LS7 cylinder head utilize a 12* valve angle, so not sure what you're seeing as different there.

It'll be an interesting combination - let us know how it turns out!

[void_kp]

Originally Posted by acammer

What valves did you get? I hope not the stainless option - that's going to be a heavy valve with a fairly modest spring.

unfortunately that's exactly what I did The MAST head had options for dual valve spring and titanium retainer, but not titanium valves.
the titanium valves were waaaaaay too expensive. Also, consider that the TSP kit came from an "insider" and they ok perfectly ok (from a reliability perspective too) to install it on standard heads+valves+valvesprings.

Originally Posted by acammer

The cam is a really interesting grind - it's got a pretty early IVC and late EVO, which is going to keep it from wanting to do big rpm in a 427, but it has ridiculous amounts of overlap (34.5*) that's going to make a pretty focused powerband in the 5800-7000 range.

This is correct. This is a cam meant to provide power on the stock engine top and bottom end (not increasing rpm) and to maximize the "choppy sound" at low end (hence the humongous overlap).

Originally Posted by acammer

Reading the advertisement, the marketing matches - it seems primarily focused on sounding super aggressive. No doubt it will achieve that with the overlap, but it's gonna drive very aggressive in a manual car. I would not expect to enjoy just cruising around under 2600rpm anywhere.

again, that is correct. It is expected to be bad drivability up to ~3000rpm. However I only use the car on the track and potentially to drive to/from the track (until I get a trailer and something to trail the heavy z28).

Originally Posted by acammer

I'm curious about your valve angle comment. Both the heads your bought and the factory LS7 cylinder head utilize a 12* valve angle, so not sure what you're seeing as different there.

It'll be an interesting combination - let us know how it turns out!

interesting, for some reason I cached that the stock valve angle was 14degrees. was I wrong?


Status update:
1/ I've inspected the heads and one of two seems to have a bit too many "Flaws" so I've reached out to MAST to get an explanation and potentially a substitution. The other head is perfect.
2/ the shop that will assemble everything recommended to not use the TSP head bolts (one time bolts) but to get some ARP ones:
"the ARP bolts are a hardened bolt with a recommend torque spec so we can get equal torque on all the bolts". I don't have any experience with either but what they explained to me about the head bolts made sense. I plan to take their advice.

[ariZona28]

That cam seems like more of a profile suited for drag racing. 10 seconds at max power then coasting for a cool down. Not sure what tracks you'll be running but when I'm on track I spend a LOT of time in the 3-5000 RPM range in both 3rd and 4th gear and my Z06 and Z/28 have similar RPMs/MPH in those gears. You'll need to be fairly skilled to keep downshifting to keep the engine in that rather high power band. Oil temps will probably need to be addressed. I'm keeping in mind your quest for reliability. With all of those aftermarket variables in place that may prove to be difficult. A few years back I talked to a gent with a gutted and caged Z/28. Engine was stock. He told me the reason he could compete with the Vettes, BMWs and Porches was because of the brakes as he could carry so much more speed into the turns and brake much later then use the big 427 to pull away on the straights. The Z with the LS7 was designed and engineered fairly well. Just watch that Nurburgring video and ask yourself if major improvements are really necessary.

[acammer]

Originally Posted by void_kp

unfortunately that's exactly what I did The MAST head had options for dual valve spring and titanium retainer, but not titanium valves.
the titanium valves were waaaaaay too expensive. Also, consider that the TSP kit came from an "insider" and they ok perfectly ok (from a reliability perspective too) to install it on standard heads+valves+valvesprings

This is correct. This is a cam meant to provide power on the stock engine top and bottom end (not increasing rpm) and to maximize the "choppy sound" at low end (hence the humongous overlap).

again, that is correct. It is expected to be bad drivability up to ~3000rpm. However I only use the car on the track and potentially to drive to/from the track (until I get a trailer and something to trail the heavy z28).

Sounds like you're eyes wide open about the cam. It's an interesting profile, it's definitely going to sign-off by 7000ish, so it probably works ok with the spring/valve combination from that perspective, and it should make a big upper mid-range and top end to 7000. The low-mid will be the part where it's going to be giving up some with that much overlap, 3-5000 is gonna be soft, and then come on really hard when the overlap starts to work for you, rather than against you.

I'd have like to seen similar durations, but split a few degrees from the intake to the exhaust, and on a 112ish LSA. It would top end better (with some more spring and/or ligther valves), and pick up the mid-range a earlier, not to mention drive nicer. I do think a cam like you have has the potential to make a pretty good dyno number, I just worry about the narrowness of the power band. Definitely interested to see your results. It should sound monstrous!

interesting, for some reason I cached that the stock valve angle was 14degrees. was I wrong?

I suspect you're thinking of regular cathedral or rectangular port heads, such as those found on the LS3, which have a 15* valve angle. For the LS7, GM went to a 12* valve angle to gain some PTV and open up the intake port. Other than the guide/valve issues with the factory head, the LS7 design is definitely the best of the LS heads in terms of outright flow and performance. I run aftermarket LS7 heads specifically designed for the LS3 on my car, I'm a big fan of what they have to offer when they are configured to be reliable.

Status update:
1/ I've inspected the heads and one of two seems to have a bit too many "Flaws" so I've reached out to MAST to get an explanation and potentially a substitution. The other head is perfect.
2/ the shop that will assemble everything recommended to not use the TSP head bolts (one time bolts) but to get some ARP ones:
"the ARP bolts are a hardened bolt with a recommend torque spec so we can get equal torque on all the bolts". I don't have any experience with either but what they explained to me about the head bolts made sense. I plan to take their advice.

Sounds like good advise on the ARP hardware. Essentially, the OEM bolts (and sounds like the TSP bolts) are a torque to yield bolt. This means they have a very specific torque procedure to get to the correct value, and they can only go through that process 1 time and produce a reliable torque value. I'm not sure about teh "equal torque" issue they described, as the TTY bolts are just fine when torqued properly, but the benefit of an ARP fastener is that it can be reused many times and will produce reliable, repeatable torque results. They are also overall a stronger, higher quality bolt.

[void_kp]

Originally Posted by arizona28

That cam seems like more of a profile suited for drag racing. 10 seconds at max power then coasting for a cool down.

what makes you say so? To be fair, to me this seems way more similar to a cam profile used in rally racing or track racing, the main difference with race engines is that in this cam the lift is close to the stock one (therefore does not require to change heads, rods, pistons).

Originally Posted by arizona28

Not sure what tracks you'll be running but when I'm on track I spend a LOT of time in the 3-5000 RPM range in both 3rd and 4th gear and my Z06 and Z/28 have similar RPMs/MPH in those gears. You'll need to be fairly skilled to keep downshifting to keep the engine in that rather high power band. Oil temps will probably need to be addressed.

this is an interesting point. Starting from bottom: I used to drive a Honda (B18C4 engine) on the track which needed to be kept between 7000 and 9000 rpm to do something ... I won't define myself as skilled but you are right, having low torque (more on this later) below 3000 will require to keep engine high revs to be fast.

my 2 main points are:
1/ will this engine have LESS torque in low end? I expect it to be quite similar, the main problem will be that the engine will "tend to stall" and the output will be irregular instead of smooth, but from a "time on track" perspective I'm not sure it will be much worse.
2/ I've checked some data and in the Seattle area there are 2 main tracks I'll use: The Ridge motorsport (fantastic) and Pacific Raceways.
I've downloaded data from my telemetry and at the Ridge I spend ~13.18% of the lap time below 3000rpm. I expect similar data to be at Pacific Raceways (won't download telemetry do to the same analysis right now). These are 2 hairpins that are usually done in 2nd gear (or 3rd if you want to be REALLY low revs) and will probably call for a 1st gear if you are as slow as I am.

For racetrack usage I think I should be ok... if it will become a hassle I will change cam in future.

Originally Posted by arizona28

I'm keeping in mind your quest for reliability. With all of those aftermarket variables in place that may prove to be difficult.

Totally agree with your concern. If it wasn't for vale drop and trunnions breaking I would NEVER have considered replacing heads or other mods.

Originally Posted by arizona28

The Z with the LS7 was designed and engineered fairly well. Just watch that Nurburgring video and ask yourself if major improvements are really necessary.

I agree with everything you wrote here, my answer is: I won't track a car that can drop a valve on me while I am there. It's a well known problem and it's serious enough that I am not willing to risk it, especially because the cost to "diagnose it" is not terribily different from replacing the heads.

Originally Posted by acammer

The low-mid will be the part where it's going to be giving up some with that much overlap, 3-5000 is gonna be soft, and then come on really hard when the overlap starts to work for you, rather than against you.

I am wondering if it will actually have lower torque than the stock cam at those ranges or if it will be all about perception given the (much) bigger torque we will see from 5000 on.

Originally Posted by acammer

I suspect you're thinking of regular cathedral or rectangular port heads, such as those found on the LS3, which have a 15* valve angle. For the LS7, GM went to a 12* valve angle to gain some PTV and open up the intake port. Other than the guide/valve issues with the factory head, the LS7 design is definitely the best of the LS heads in terms of outright flow and performance.

Yes I was probably confused with the LS3 heads. I'm aware of how good LS7 heads are from stock (btw they flow exceptionally well and can support much more HP than the stock, if I remember correctly they flow around 350cfm, which will support around 700hp NA). I would have never replaced them if it wasn't for the valve drop problem.

Originally Posted by acammer

Sounds like good advise on the ARP hardware. [...] I'm not sure about teh "equal torque" issue they described, as the TTY bolts are just fine when torqued properly, but the benefit of an ARP fastener is that it can be reused many times and will produce reliable, repeatable torque results. They are also overall a stronger, higher quality bolt.

I am aware of the OEM and TSP being torque to yeld bolts. Given that the ARP are higher quality and the fact that we are replacing heads I don't see a reason (beside cost of course) to not use higher quality bolts.
the only thing that comes to my mind is that if you do mistakes when torquing the OEM/TSP ones you cannot recover from mistake and have to replace them... while the ARP can be fixed
But this is me speculating.

I can't wait to share more info/data.

For the time being I am manging a replacement of one of the heads and the rocker arms because the rocker arms are wrong (LS3 instead of LS7) and one of the heads have some imperfections that I don't want to deal with, so they are replacing it.

My appointment to put everything together is on 3/12 , if the headers will come on time as well as the head replacement, we should be ok.

[acammer]

Originally Posted by void_kp

I am wondering if it will actually have lower torque than the stock cam at those ranges or if it will be all about perception given the (much) bigger torque we will see from 5000 on.

That's a fair point, I don't think you'll find it's under the stock cam, at least not by 3500rpm, and it definitely will have the feeling of coming on strong in that upper mid-range. Reading your post you've obviously given a fair bit of thought to your approach, and are pretty aware of the areas of the power band you use the most.

Average power is a critical piece to any sort of circle track or circuit car, where the engine has to operate over a sometimes fairly wide range - much wider than a drag engine that will have at most a 2400rpm window of operation for stick cars, and often under 1000rpm for really aggressive stall converter auto cars. This does make a case for cams that might actually sacrifice a bit of peak power from a broader curve that makes a better average. The "equalizer" in your case, to some extent, is the displacement, which will help torque production, and keep the RPM window modest.

A FAST LSXR or MSD Atomic Airforce with a 103mm throttle body would compliment that setup well. adding power across the curve. I agree that the big TB on the stock intake likely is worth little to no power. I tested this on an LS3 - results here if you're interested:

[void_kp]

The "equalizer" in your case, to some extent, is the displacement, which will help torque production, and keep the RPM window modest.

this is what I am hoping for, I hope to be correct

A FAST LSXR or MSD Atomic Airforce with a 103mm throttle body would compliment that setup well. adding power across the curve. I agree that the big TB on the stock intake likely is worth little to no power. I tested this on an LS3 - results here if you're interested:

Thank you for the video! Liked, I didn't know about your channel or company.
I always suspected that increasing TB size wouldn't provide significant benefits
For the time being I am not going to replace intake manifold... maybe in future.

[ariZona28]

Originally Posted by void_kp

what makes you say so? To be fair, to me this seems way more similar to a cam profile used in rally racing or track racing, the main difference with race engines is that in this cam the lift is close to the stock one (therefore does not require to change heads, rods, pistons).





.

Valve lift in the .650s harken back to the days of small block chevys with solid lifters ( my Father had a few). '57 Chevys and a '67 Chevelle. 7000 RPM works of art. The LS7 has a factory lift of .590 with 210/230 duration. .650s are a BIG jump, especially with all of that duration (245/256). I'm definitely no engine guru and I LOVE these forums as I continue to learn but do you need to be concerned about piston to valve clearance with such a radical cam?

[void_kp]

Originally Posted by ariZona28

Valve lift in the .650s harken back to the days of small block chevys with solid lifters ( my Father had a few). '57 Chevys and a '67 Chevelle. 7000 RPM works of art. The LS7 has a factory lift of .590 with 210/230 duration. .650s are a BIG jump, especially with all of that duration (245/256). I'm definitely no engine guru and I LOVE these forums as I continue to learn but do you need to be concerned about piston to valve clearance with such a radical cam?

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