The conventional wisdom over in the TBI forum is that LO3 heads can't handle more than .480" of lift. My questions are what is the problem and what can be done about it? Reason being, that a lot of off the self cams are in the cams are in the .500" and beyond lift. I want to try a Comp Magnum 270HR as I think a large single pattern cam would suit the flow characteristics of the LO3 heads.

Basically, what I'm interested in discovering is just how much power one can eek for a LO3. People bolt stock vortec heads on 383's and 400's and make in excess of 400 hp, so why can't 300 be be possible with LO3 heads. If you look at intake flows relative to displacement, a LO3 is a 3/4 model of a 400 with vortec heads with better exhaust flow.

 

Two issues with valve lift:

1) Mechanical interference between the top of the valve guide and the bottom of the valve spring retainer (assuming you have valve springs that can handle the lift w/o coil bind).

2) Swirlport head port flow doesn't improve with lift over about .450" - any more cam lift than that is wasted motion.

As for 383 power with Vortecs vs. LO3 power, there's more to power than steady-state port flow. Chamber design has a lot to do with it as well.

 

I've pulled rockers studs out of stock L98 heads with 0.510" lift. Costly mistake. I would not approach that kind of lift with pressed in rocker studs.

 

1) Can a different valve guide be substituted to fix this issue.

2) I agree, but it high lift means more time spent in the areas of peak flow.

3) The chamber design seems to be exactly the same as a 305 Vortec heads. The spark plug is mounted more towards the center and everything.

Thanks for that, I'll take that into consideration.

 

Saabster you've brought up an interesting topic IMO. The 187's have mediocre flow ##'s on intake but great on exhaust. While other 305 heads, 416 casting for example, has good intake lift and very poor exhaust. So in theory with the right cam and good exhaust the 187's should make more power.

Playing with DD2000 to my surprise it fully supports this idea. Using the stock 187's flow data, with small tube headers and mufflers, and the cam you suggest, the peak flywheel estimates are 332hp @ 5500rpm and 361trq @ 4000rpm. The torque curve is nice looking too it starts at 333 @ 2000rpm.

I'm not saying this is fact of anything like that but just what the tool suggest could be done with perfect tuning. Which it would be needing a lot of that.

Couldn't you always use offset valve locks to compensate for the lift? You could always pin the rocker studs too to solve that issue.

 

You've hit upon what I've noticed. I've always been a believer in the "you can only get in what you can get out" theory of engine design. The 187's fit this with exhaust flow that's slightly worse than intake flow, which is consistent with the fact that the engine has less gasses coming out of it that went into it.

I really do think that 300 hp and plenty of torque should be doable. Look at what they did with Vortec heads on a 400.

 

But Vortec heads have completely different intake ports? How is this an apples to apples comparison?

 

They're both "Swirl Ports," the Vortec is just a much improved design that flows better. Both should swirl the air and fuel nicely and produce the desired "fast-burn" combustion.

How much compression do people think is too much? I can leave it stock which is 8.8:1. Do a light with flat tops and a large .080" quench for 9.3: or a tight quench for 10.2:1.

 

Unless you were getting coil bind or retainers hitting guides, lift isn't at issue, it's your open spring pressure. 300 pounds is a realistic upper limit for pressed studs with 1.5:1 rockers

 

Vortecs really aren't enough head for a 400, so you're proving the common wisdom with that comparison. Your oops.
With proper machine work, there's no good reason you can't run 0.560" lift with LO3 heads. Like a COMP 08-000-8, 3012/3033-110 with 1.6:1 rockers.
If you're really serious, get the heads Extrude-Honed.

 

Vortec 350 heads, '96-up, with casting numbers ending in 906 or 062, are NOT swirl ports. They do give good swirl, but far out-flow the '87-'95 truck 350 swirl-port heads, which usually have a casting number in 193.
In '88, the Vortec name was introduced for the swirl-port 4.3L V6/90, but these days it only refers to the '96-up with good heads. Swirl ports can never be good heads.

 

428 HP from a 406 is crap. Go look in my best builds sticky. That 400 is at 525 hp, and 525 ft-lbs, with Dart 180 Platinum heads. And it does those 525 horses at just 5800 rpm.

 

I've never once seen DD2K get within 10% of what I get from a real engine dyno. It's among the worst of the sim programs. Exhaust flow is necessary for good HP, but Jud Massengill is correct when he says to keep improving the intake port as far as possible, no matter what it does ti the I/E relationship. And stock LO3 exh. port flow just isn't enough for a 330 hp 305 with a COMP Magnum 270 HR cam. With good valves, porting and polishing, it is, but the problem remains getting enough air in. With LO3 heads, the bottleneck is the intake ports of the heads, Even Extrude-Honed, they'll still lag behind what the Edelbrock TBI intake flows as it arrives in it's box.

 

Why do I let you armchair warriors get me going? Raise your hand if you're a professional engine builder. Mine's up.

 

I'm not saying they're "good" so much as saying they'll work up to a point, around 300 hp. We're constantly inundated with people asking how to make their LO3 faster, and we tell them all to get new heads. Most of them either can't afford heads or are scared of the changing cylinder heads. So what I want to do is figure out how to extract all the power I can from what the LO3. Basically make power on the cheap.

I don't want to argue with you. How about this. I have a LO3 with shorties and a 3" exhaust. I want to make as much power as I can. What cam and intake would you run?

 

Does that mean you aren't open to changing the heads?

 

I am, but in the interest of experimentation and science I want to see just how much power can be had out of LO3 heads. It costs me little to nothing to work with what I currently have and I can always change them out later.

 

Atilla-

I think that I qualified my statement well.

On the contrary to your results I get low ball estimates using DD2000 on some other TGO members builds, FAST355 being a prominent one. There is no way to exactly simulate reality and since no one tried this exact build, or atleast chimed in, I think this tool would work well for sake of discussion.

Have you tried this build already? I'm not trolling you I'm just curious because in you're "builds" thread you said you didn't do 305's or something along those lines.

 

Or course it was the spring pressure that pulled out stud. But if you are running a .5" lift cam, you aren't going to be using stock springs. Please don't give this guy the impression he won't run into press in stud problems with 0.5" lift cam and appropriate springs.

No I am not a professional engine builder. That doesn't make my personal experience any less valuable. I would not pretend to give advice on something I knew nothing about.

Do you know who told ME that the press in studs would be fine. You guessed it, a professional engine builder. I am not saying you aren't a great engine builder. I am just saying in my experience just because you do something for a living doesn't mean you are good at it. I know a lot of crappy engineers at my company.

 

Attila-

Just for the sake of discussion I worked up your first 350 Vortec build in your thread to see what DD2000 thought. Thanks to your awesomely thorough information it was easy to put in exact data.

I'm just posting peaks so not to clutter the post so much, but if your interested I saved the data.

Reality vs DD2000 (DD2k only does 500rpm increments)

401hp @ 5600rpm vs 417hp @ 6000rpm

428tq @ 4200rpm vs 425tq @ 4500rpm

 

This is going to end really well.

 

Saabster....i would run a Comp Magnum 292 and a Victor Jr Intake

 

Saabster -

Sorry I'm not trying to troll your thread or anyone I'm just kicking around the same idea you are right now. This Trick Flow Track Max cam is what I was thinking about, and summit has it on sale for 120$ right now.

http://www.summitracing.com/parts/TFS-31402000/

Int Duration 270
Exh Duration 276

Int lift 0.452
Exh lift 0.465

LSA 110

 

...and dont forget to have those heads Milled!

 

That seems like a safe cam with stock heads. And it will certainly do better than the stocker.

 

Okay, now I see it differently than before. The 270 Magnum HR makes more sense, as does using a set of "plus fifty" locks. But they still need to change springs. I say these would be fine:
http://www.competitionproducts.com/H...uctinfo/98111/ They'd have to be shimmed up to maintain the correct installed height, but this would keep the retainers off the seals, in theory. I don't have an lO3 on hand right now, or I'd check.
Now we need to come up with a ready-to-go, smog-legal tune to go with this cam, the Edelbrock TBI intake, and shorty headers, and the stock TB and injectors, with an L69 air cleaner, but with the spark stack pulled out. And some way for them to get this tune into their cars.

 

Those theoretical guys Saabster just fussed at me about, they aren't gonna want to pull the heads and have them milled. And really, there's no need.

 

You're sharp, but I'm confusing. I used to do 305s, but not anymore. I haven't dyno-verified any of the popular 305 build articles floating around. I do believe the 372 horse build, I helped a friend copy it. I don't think the driveability of it qualifies as daily driver.
If anyone can find the '99 or '00 article where CarCraft got 325 hp from a 305 with an XE262, that's one worth copying.

 

That's funny because Chevy High Performance magazine reported that Tim Moore did an extremely similar build, and made 418 or so horses at 6200 or so. I lost that article years ago. Look at GM's ZZ430 crate engine. Those FastBurn heads don't equal the truck Vortecs on the intake side, despite the volume and valves.
The HOT cam is good for a shift point of 6200, but with Vortecs, run a 26915 spring at 1.75", and 1.50:1 rockers if you want it to feel happy turning 6200.

 

He won't have problems if he keeps the springs under 300# and out of coil bind, and keeps the retainers off the seals.

 

Seems good, but the loss of 0.048/0.035 lift could be 10 HP. "Plus fifty" locks are so cheap that he may as well stick to COMP's Magnum 270 HR. It works out to about $1/hp by my figuring.

 

I wonder if it's a better idea to go with the slightly lower lift cam just to keep the stress on the studs down. Hmmm.

Also these are self-aligning rocker heads, are they gonna play nice with the "plus fifty" locks you're suggesting?

As for a smog-legal tune, ummmmm, forgot about California.

 

I've already explained about the quasi-relationship between lift and studs.
The stock rail rockers will work fine with "plus fifty" locks on valves with stock-length tips. The only possible issue for some will be between the retainer and the rocker, due to production variance in the rockers. But going to roller rockers would net about 10 HP just from reduced friction. The cost being over $200 makes it less of a value, but roller rockers generate less heat into the oil.
Passing emissions is mostly about overlap, and the Magnum 270 HR certainly will be clean enough, even for Cali. So will that other cam that Doom suggested.

 

Are you saying that Vortecs perform better than Fast burns?

 

And I understood it perfectly, I'm just pondering if I should run it near the limit, or be a bit more conservative to avoid mechanical failure. Or maybe I should just go for broke since if I break it they're just LO3 heads, who cares.

I like roller rockers, but given the "on the cheap" theme I think I'll pass for now. I think given the low RPM nature of this build (5000 max) I don't need to worry too much about the heat from the rockers.

Yeah, but I was thinking of ditching the A.I.R. system for a modern 3 way cat and a careful tune. It is a plan that just gives Cali members the finger.

 

Under 4000 rpm they most definitely do, in ALL instances. Above 4000 rpm, it does depend on the exact specific engine combination.