Hi there! I am rebuilding a 1986 corvette, and I'm looking to upgrade some stuff along the way. Right now I am looking for some advice on the L98 valve train. specifically the rockers, pushrods, and lifters. Is it safe to reuse any of the afore mentioned parts? the engine has 160,000 miles on it, and the previous owner did not take care of it.

I am looking to use a Howards Cams 110245-12 they advertise: Lift: .500 / .510, Duration @ .050: 225 / 231 on their website, and have pretty good reviews. Doing some research on here I came across an article titled: "SBC Camshafts – A primer," this article stated that a compression ratio of 9.5:1 should have around 210-220 duration. Does anyone think I am going with too much of a cam, I was looking for something to take advantage of the max-ish lift that the heads can accommodate.

https://www.summitracing.com/parts/hrs-112901-12 (cam)

For reference I am also looking to get FLOTEK 180cc Small Block Chevy Cylinder Heads 102-505FT heads, and keeping the stock TPI, aside from injectors; which will be 24lbs instead of stock.

https://www.summitracing.com/parts/flk-102-505ft (heads)

A google search says the stock rocker arms would have to be replaced, with stud mount rockers. However it looks like they are currently mounted on a stud, and the heads I would be buying look like they have a similar way of bolting on the rockers. Am I wrong in thinking like this?

Any help is much appreciated as this is my first time building an engine, and thank you in advance to anyone who responds!

 

That would be a no, another no, and a HELL NO. All of that goes in the trash.

A generic cam may or may not work well with TPI. It's not like carb setups where you can jam just anything in there and it'll make more power. Lots of people over the years have reported how much power they LOST by installing an inappropriate cam. It's not so much a question of "too much" cam, as such; more a matter of, does it support the TUNED aspect (the "T" in TPI) of those SOOOOOOOPER LONG runners? I'd suggest looking at Comp for cams that are SPECIFICALLY designed with TPI in mind.

I know nothing about Flotek. Sounds like one of those generic Chinese copies of copied copies of head casting copies. No idea whether they're any good or not. I don't see any reason they COULDN'T be, butt also, about a million reasons why they MIGHT BE total crap. Tread carefully. One truism that's nearly universally true in this hobby is "you get what you pay for". I would however amend that to, "you get AT BEST what you pay for, and usually somewhat less than that". Meaning, if you pay the least, you get, AT BEST, ... you plug that into the truism.

Of course. Stock ones are stamped out of sheet rubber. Looking at them with a Strobotach while the engine is running is ... scary. Makes no sense to put that floppy s*** back in there.

Virtually ALL SBC rockers go onto the studs. So even without knowing what rockers you're looking at, you're probably not wrong in thinking like that. Don't get aluminum ones if you intend to drive it on the street though. While those are just fine for racing, on the street, where they get operated MILLIONS of times over their lifetime, they tend to fail, by way of metal fatigue. Look at steel ones such as from Comp or Crower.

 

You can reuse those components if they are in good condition, if they are roller lifters, and you want a generally stock rebuild. If you don't know or can't tell, replacing them with new is best.
However, it sounds like you want to "mod" your car. I don't have much advice for that. Usually a slap upside the back of head (aka dope-slap) is best, but I don't feel like making the drive over there.

 

I've reused all of that junk many-a-time, and it's always worked just "fine". Is the the best way? No, but it'll work fine, last longer than long enough, and probably get you the goals you want.

I think the cam you're looking at is too big for a TPI engine.

 

Reuse valve train parts with 160,000 poorly maintained miles on them?

 

Sure. Yes? No? All of that. Personal preference and risk tolerance.

What's the difference between "re-using valve train parts" at 160k, during a parts swap, and just continuing to drive the car, starting at 160k? I had a prof in auto skool who constantly used to talk about "guys who'd do a mod at 100k, then blow the bottom end out of it". Say WHAT!? One day I asked him: What if you drove a car for 100k, never above 1/2 throttle....then after 100k you start flooring it?....is that going to blow the bottom end out of it? No. I knew he was full of it and so when my TA had 180k, I had NO PROBLEM with throwing a cam/lifter kit into it, re-using everything; pushrods, rockers, springs, everything. The only "might as well" that I did was a $15 timing chain set and gaskets. The last I heard of that car (after it got sold twice from me) was that had blown a head gasket at ~245k miles, which had nothing to do with the 180k mile cam swap of course. Everything worked great and the mod, "re-using valvetrain parts" was totally worth it. Had I changed springs, pushrods, rockers, retainers, keepers etc....it wouldn't have made one whit of diff in the car's performance and all that $$$ would have drifted down the toilet when the car was sold.

So....personal preference. And tolerance for risk vs. budget.

 

I wouldn't be willing to risk an old lifter, regardless of how it 'looked,' wiping out a cam lobe. OP may be more of a gambler than I; engines are expensive.

 

Aren't 1986 L98 Vette engine flat tappet cam and lifters?

At 160k miles and not very well maintained all the stock valvetrain goes straight into the trash can.

That aftermarket Howard's cam is not suitable for TPI.

 

^^^ This ^^^

In the trash. All of it. Valve springs included.

 

I agree, if we're talking flat tappet lifters.


Some are. Not "160,000 poorly maintained miles" engines, though. For engines like those, who cares? I don't. Giv'r hell and see what you get out of it. IMO.

 

I wouldn't reuse a non roller camshaft and lifters either, which is why I like to provide this disclaimer:

Both of my Thirdgens are running rebuilt engines with reused valvetrain components. My 1985 had who knows how many miles on that poorly maintained engine before I rebuilt it. I reused the rocker arms and push rods but put new cam and lifters in because it is flat tappet. 50k or so on the rebuild and no indication those reused parts will ever fail. I've never even changed the oil since the initial break in. I wish it would fail so I could build a bigger engine for it, but no matter how many times I rev that engine to 6k it just won't break any of those old parts.

 

Okay, point taken no re-using parts! I will look more into the headers and a comp camshaft instead. Thank you muchly for the advice everyone!

I don't really have the money to blow stuff up and rebuild it all the time so I will try and keep the risks low....

 

What makes it too big? The duration? And thank you for the response!

 

[QUOTE=sofakingdom;6556838]That would be a no, another no, and a HELL NO. All of that goes in the trash.

Okay lol that made me laugh when reading it

"It's not like carb setups where you can jam just anything in there and it'll make more power." (QUOTE

Would trying to carb swap it be a bad idea?

"does it support the TUNED aspect (the "T" in TPI) of those SOOOOOOOPER LONG runners? I'd suggest looking at Comp for cams that are SPECIFICALLY designed with TPI in mind."

What would you suggest to try and accommodate the runners? And thank you for the response I appreciate the advice!

 

The duration, IMO....b/c of the runners, as SOFA has suggested. I'd try to get something that is a proven TPI "winner" (people have loved it over the years). The first thing that comes to mind is the LINGENFELTER 211 cam. Something like that is "mild-mid" (for a stockish 350) and will still make a good difference.

 

Depends. If all you're after is "max power", then, it'd be the way to go. OTOH if you're after making a significant improvement while not sodomizing and bastardizing the car, then no. From what's written in all the white space around the words you typed, looks to me like, probably not what you're interested in.

TPI is "tuned". Think of those runners as being like a musical instrument; they behave EXACTLY the same way. Like an organ pipe for example. The pitch - frequency - that a pipe makes is determined by its LENGTH. The diameter almost doesn't matter to the pitch it produces. It's all about the speed of sound, and how long it takes a sound wave (a compression / rarefaction wave) to travel from one end to the other, bounce off of the discontinuity (open hole at the end), and return to the source, just in time for the next repetitive wave created by the same source to begin travelling the same way. When the waves line up like that, they reinforce each other. We call that "resonance". TPI does EXACTLY the same thing.

The speed of sound at room temperature and pressure is 1100 ft/sec more or less. As pressure decreases, the speed also decreases. In the intake system of an engine, the pressure is ALWAYS lower than atmospheric, because the engine is extracting air from it faster than the atmosphere can push it back in... sometimes not less by very much, butt ALWAYS lower than atmospheric. OTOH, it's also warmer than room temperature, which tends to make the speed GREATER than in the open atmosphere. So just for the halibut, and to keep the numbers simple, let's call it 1200 ft/sec inside the intake tract.

Inside the engine, during the intake stroke, the air/fuel mixture flows down the intake runner and fills up the cylinder. The more of that mixture that gets packed into there, the more power it makes. Pretty simple really; power comes from releasing the energy stored in the fuel molecules, and turning it into heat, which then raises the pressure in the cyl and pushes the piston down. It's all about heat and pressure, NOT "explosion". The more fuel molecules we can burn (which of course requires oxygen, which we get from air) the more power we get. The limit to an engine's output is almost always how much air we can get through it, NOT how much fuel we can feed.

So, the air in the runner has mass, and therefore inertia. As it rushes down that tube, eventually the engine reaches the end of the intake stroke, and the intake valve closes. At that time, the air gets STOPPED COLD IN ITS TRACKS by the closed valve. It produces a giant pulse of positive pressure as the rest of the air in the runner tries to force the air right near the valve to keep going, which it cannot do. Instead, we get this pulse of pressure, which travels back up the runner as the air in the runner comes to a halt. This is a compression wave - aka SOUND. This is why all of that about sound and music is applicable to TPI.

The pressure wave travels back up the tube, reaches the plenum, and pressurizes it a little bit. That would be the end of it all if that's all there was to it. BUTT: what happens if that wave arrives at the plenum and reaches the NEXT runner in the engine's cycle (firing order), and JOINS the wave that's going down THAT runner? Right: just like the organ pipe, it REINFORCES that NEXT wave, and helps push the air in that NEXT runner down towards its cyl. Then when that one's int valve closes, the process repeats for the NEXT cyl in the firing order. And so on.

Keeping in mind that the wave travels at a finite speed, at exactly what interval between cyl intake events, does this reinforcement reach its peak? If we know THAT, then we know how far apart those events will be at that peak, right??? Easy enough to calculate. All we need to know, is how long the runners are.

It just so happens, the length of the part of the runner you can see, plus the part in the intake base, plus the part in the head, is 22". Don't forget that number, it's IMPORTANT. 22" from the top of the runner where it meets the plenum, to the intake valve. The distance inside the plenum from one runner to another is a few more inches; again, just to keep the numbers simple, let's call it 4", on average. 22", + 4", + 22" more, = 48". 4' on the nose.

At 1200 ft/sec, the sound wave travels .833' (1 ÷ 1200) per millisecond (thousandth of a second). So it takes 3.3 milliseconds or so to get from one intake valve making the pulse when it closes, to the NEXT intake valve in the firing order, to arrive at EXACTLY the right moment to REINFORCE the filling event in THAT cylinder, when the cylinders fire 3.3 milliseconds apart. Right? Well, there are 4 firing events per engine revolution, in a V8 motor, since the crank makes 2 full revolutions per each cylinder's cycle. Suck, squeeze, bang, blow: each of those strokes takes HALF of one revolution. That means 300 firing events (1000 milliseconds ÷ 3.3 milliseconds) per second, which then means 600 crank revolutions per second. There are 60 seconds in a minute, therefore there are 600 × 60, or 3600, revolutions per minute aka RPM occurring at this resonance, at which RPM peak cyl fill, therefore peak torque, will occur.

That's why TPI generates this Mount Everest peak of torque at 3600 RPM, give or take.

We all know that nothing in life is free. There's a penalty for this, as there always is; no good deed ever goes unpunished. The penalty is, that as engine RPMs increase past 3600, the reinforcement effect DECREASES, and at 4500 RPM, the net effect is ZERO; and once the RPMs increase past 4500, the effect becomes NEGATIVE, i.e. DECREASING that next cyl's fill, i.e. DECREASING the engine's output. Which is why TPI falls flat on its face at that RPM. You own the car and drive it, so I'm sure you've noticed this; if you hold it in low gear too long, the car quits accelerating until you shift, at which point you get that nice rush of power again.

Now in all this discussion, did the diameter, or ANY OTHER PROPERTY of the runners besides their length, enter into the discussion? NO. The behavior of TPI is determined by the frequency (pitch if you will, like a musical instrument) that they are TUNED to. You could theoretically improve the AMOUNT of air that could travel down the tube by making it larger, butt NOT the frequency at which it resonates. As long as those 22" runners are there, the engine is going to make peak torque at 3600 RPM. PERIOD. No way around it.

Furthermore, to get the biggest baddest most effective pulse of sound travelling back up that runner to reinforce the next one, it's important to close the intake valve at just the right moment: early enough that the air is still moving down the tube pretty fast, butt late enough that THAT cyl isn't starved while reinforcing the next one. Therefore it's important that the cam WORK WITH the exact behavior that TPI imposes on it, and NOT fight it.

That's the reason for choosing a TPI-specific cam. In 2025, TPI is seriously ANTIQUE, so there aren't all that many cams around SPECIFICALLY for it, even to the limited extent that there ever were. Worse still, you have a NON-roller-tappet motor, and TPI was only available in such motors for 2 years out of its 8 yr run, and there NEVER WERE very many at all for the flat-tappet system you have. Comp still makes some roller ones; not sure they ever did make any flat-tappet ones. TPiS, Lingenfelter, and SLP were other sources, butt AFAIK ALL of theirs were for roller motors also, which you can't use without some rather $$$special$$$ parts. Your car is the last year of the old flat-tappet system. Specifically, you need what's now called "retrofit" roller lifters like these https://www.summitracing.com/parts/cca-85301-16, with link bars instead of the factory's figure-8 retainer thing; and a cam button at the front, instead of the factory roller system's retainer plate. A cam button is cheeeep though. This is what we were all using for all the years before the factories (not just GM; they all use a similar system, and all changed to it around the same time) introduced their system in the mid - late 80s; 87 for GM. For that matter, I'm pretty sure the cam you posted, is also a roller; and will need those $$$retrofit lifters$$$. Might be cheeeeeper from some source other than Comp, butt I guarantee they'll still hurt your bank account. I have no clue whether the Howard's cam is SPECIFICALLY for TPI, butt I kinda doubt it

I would also note, BE CAREFUL with Lingenfelter. They made a system called the Superram (later sold to Accel) designed to go onto TPI engines that was QUITE DIFFERENT from TPI proper. It was a MAJOR upgrade to TPI, butt was the kind of thing that the super rich "hobbyists", the kind that pay somebody else to do their work for them, would buy. It is long since discontinued, AFAIK you can't even get any of the piece parts for it nowadays from either Lingenfelter or Accel butt don't hold me to that, and was stuuuupid expensive even back in its day. It's quite difficult to work on not only for itself butt because it gets in the way of everything it makes the whole engine a PITA to deal with, not terribly reliable (uses a giant flat plate about a foot square to seal the plenum for example, which is all butt impossible to keep from leaking for very long), and there is no support for it whatsoever anymore (like, gaskets). Butt they offered a bunch of cams SPECIFICALLY for THAT setup, which being DIFFERENT from TPI, those cams don't work well at all in a stock TPI. You'd have to be careful with them to pick one SPECIFICALLY for TPI and NOT for the SuperPITAram. Whether those are still available, I don't know. TPiS (Tuned Port Injection Specialties) and SLP were other sources for cams, again, no idea whether they're actually still making them or not.

So there ya go. Choose wisely..