CNC Porting- The Best?

[Bob Eyres]

Since the advent of computer aided porting has happened since the introduction of the LT5, I would have expected that in recent years programs to have been developed that greatly improved the breathing of our engines. Programs that would be far superior and repeatable over the hit or miss results of porting by hand. Yet it seems as though many LT5's still get ported manually. Why is this?

You would think that, over time, ideal programs would have been developed for relatively stock engines, as well as moderate, and big displacement LT5's. Programs that would perfectly match the 16 separate runners in ways far superior to hand grinding. Not to mention all the other operations applied to the heads and other parts in the air stream.

Can someone school me as to why this seems to still be such a "black art" rather than an easily predictable upgrade?:confused:

[Hog]

Because it takes cubic dollars to develop an effective CNC program with only a handful of prospective buyers. Anyone can make a CNC program, but engineering one that produces desired results, let alone 2 or 3 different levels. As with anything, junk in, junk out.

I disagree that hand porting is hit or miss. An experienced "chip maker" can produce repeatable results and is also the basis for many CNC programs.

Notice how everyone and their Brother sells a CNC ported head for the GEN 3/4 and soon GEN 5 heads. Thats because there are literally millions of these engine in circulation with many more possible customers. Heck even GM does CNC ported heads now.

[XfireZ51]

Bob,

The problem is that components like the plenum, IHs and heads are not as consistent as would be needed for CNC. Castings vary and runner walls can have pockets or be thin in different places. Even experienced tuners that have ported
many intakes and heads will tell you that even they run into unforeseen issues at times. Particularly if you are attempting to take porting to more extreme levels. CNC would be used to give you a start, but in the end, manual is how you finish it off. I'll let other more experienced players give you their opinion.

[Locobob]

You'd have to do a lot of testing and development, it would never be cost effective given the small production numbers. Hand porting can be very consistent with attention to detail and careful measuring.

[Paul Workman]

Well, IIRC, Pete had his heads digitized, and some number of heads out there have been cut - at least initially - using his CNC program. In fact, I believe I saw some pricing for CNC'ing the heads; pricing that ranged depending on whether he had to pull the heads off your motor, or not.

With regard to the variances in castings dimensions (aka "core shift"), it does exist. In fact, I believe it was after cutting Bob Gillig's 427 LT5 runners with the CNC map that some of that core shifting became evident. As I recall, he had to repair some seepage resulting from the program grazing the oil side of one of the head runners.

I'll leave it to Pete to put the light on this...

But, with regard to hand grinding vs. CNC: What comes first? Hand grinding or CNC mapping? And, is there just one and only one pattern to optimize the LT5, or is there room for improvements? Pete's CNC sets the bar pretty high, but I wouldn't go so far as to say it can't be improved upon. JMO.

Paul.

[rkreigh]

generally heads are hand ported, flowed, digitized, and then the CNC program can be generated

the modern technology makes this much easier. a digitizer pen is used to trace the port and put together a 3d cad image which can be refined and adjusted all you want to test with

but since there aren't a whole lot of people stepping up in line waiting to get their heads ported AT ALL we're durn lucky Pete took the time to capture a CNC of his handiwork

we were "debating" LS vs LT5 cyl head flow. while we clearly have improved flow quality and velocity 330 cfm is a starting point for a good head

we seem to be "flow limited" to around 750 hp with the heads

you can go up in displacement, but not see much additional HP due to the flow limitation

I think it's time for a billet head, using an improved chain drive, with a better port design

nelson has done it, and with the modern tooling the cost of this debauchery will eventually come down

my old crusty hands (like phrogs) are salavating as we see more ZR-1s getting parted out and the lt5 parts hitting the pipeline

"experimental" builds become more affordable

I'm doing LS motors right now (because I can) not by choice

one day I hope to boostamuv on a stock block LT5 on E85 and see if I can get it to live at 800 with stock internals

my bet is it will do just fine, factory cams and all

looking for a decent price on a crate motor or good used one (high miles ok too, just want good cyl sealing!!)

we are doing this with 4.8 LS iron block motors and finding the limits are quite high for the 2004 and up motors with the better pistons and ls2 rods

and many people are literally throwing these engines away because they are so plentiful I have 3 of them in the garage right now if anyone needs one. a few sets of forged internals, ect...

I'm really thinking of pushing a stock short block with studs and wider ring gaps to 800 hp which is nothing new to these guys and seeing what happens!!

[tpepmeie]

we were "debating" LS vs LT5 cyl head flow. while we clearly have improved flow quality and velocity 330 cfm is a starting point for a good head

we seem to be "flow limited" to around 750 hp with the heads

you can go up in displacement, but not see much additional HP due to the flow limitation

I think it's time for a billet head, using an improved chain drive, with a better port design

nelson has done it, and with the modern tooling the cost of this debauchery will eventually come down

Ron,
I'll be pushing the limit upwards to (hopefully) 800 this time. Bigger valves and 400 cfm should do it easily. When you get to those levels, the camshafts present more of a constraint then the headflow--the duration required to efficiently fill the cylinder at 7000 rpm with anything above a 3.75 stroke exceeds 300 degrees seat-to-seat, and you need to lift the valve proportionately higher with larger valves. Most people don't want to run something like that around the street. Stage 3's are something like 282 degrees seat-to-seat; my current cams are 297.

As far as the heads go, the main limitation is the valve spacing and port angles. You can't get more than 42mm inlet valves in there--period. The intake port angles are too low to use the really high airspeeds you see with the best 4-valve heads. Still good, but not ideal.

We'll see what 427 version 2.0 makes next year.

Todd

[Harvie]

The bottom end strength of the lt5 sleeved blocks and the sizes of their crankshaft journals are the large limiting factors along with the induction systems multiple sharp turns in air low.

Over 750HP power requires a bigger steel crank with large dia full radiused crank journals to last. Then blocks would then have to be fitted with a strong steel girdle and studded.

[tpepmeie]

The bottom end strength of the lt5 sleeved blocks and the sizes of their crankshaft journals are the large limiting factors along with the induction systems multiple sharp turns in air low.

Over 750HP power requires a bigger steel crank with large dia full radiused crank journals to last. Then blocks would then have to be fitted with a strong steel girdle and studded.

Well, I was assuming at the power levels we're talking about a new crank was a given. Which journals specifically do you think need to be "bigger"?

The LT5 bottom end has been proven to handle >1000 in boosted applications. None of us are building 24hr endurance engines, so sustained high rpm, high load conditions are rare anyway. Now that we have studs, the bottom end isn't a worry.

For NA power, the limiting factors are the cylinder head geometry, and the user's tolerance for extra large camshafts. Always has been, always will be.

[FU]

IMO FWIW any thing above 3.80 stroke offers little ROI.

[Kevin]

The bottom end strength of the lt5 sleeved blocks and the sizes of their crankshaft journals are the large limiting factors along with the induction systems multiple sharp turns in air low.

Over 750HP power requires a bigger steel crank with large dia full radiused crank journals to last. Then blocks would then have to be fitted with a strong steel girdle and studded.

sprayed 408 and 415 cube cars were popping head gaskets, not cranks. TT's car are making well over 800 with no issues. I think you're wrong

[Harvie]

All the main journal widths and diameters on the LT5 are smallish compared to the extreme high horse power motors I see running for more than a few mins, between rebuilds freshen ups.

These LT5 engines were built for endurance and longevity and they compromised peak HP for various factors, not to mention that the hood would have to be modified to allow for more direct airflow.

Reversing and going for real high peak hp requires strength in the block and bottom end (plus rotating assembly) that the LT5 blocks never had.

Sorta like 350 2bolt vrs 350 4 bolt vrs 350 4bolt truck vrs SB2 blocks vrs current Nascar blacks the more power required the more material and strength moves towards the bottom end, while the air/fuel passages are straightened/enlarged/optomized.

If you look at the marine extreme high hp motors (made by any manufacturer) you will see where the materials are put when there is constant stress on the motors, they are good for about 50 hours running time, between freshenups.

[Harvie]

sprayed 408 and 415 cube cars were popping head gaskets, not cranks. TT's car are making well over 800 with no issues. I think you're wrong

Put one of those engines on a dyno take it to your "800HP level", set the throttle, and let it run for just 5-10 Mins. Then come back let us know.

[Kevin]

Put one of those engines on a dyno take it to your "800HP level", set the throttle, and let it run for just 5-10 Mins. Then come back let us know.

you pony up the money and I'll be happy to

[Harvie]

you pony up the money and I'll be happy to

Post the dyno run sheets, showing that motor making 800HP you want me to pay to see. (So, I know you are not just pretending.)

Then you arrange its transport and we will hook it up to the Superflow. I have the wiring harness and flywheels from previous runs. We will video tape it, started and pegged at 95% power (that would be where it is making 760 hp) running for 10 mins for everyones' enjoyment.

If it does not get to that 760HP, the motor comes right off and you pay the $2500 for the dyno hookup and runs...

next...

[Kevin]

Post the dyno run sheets, showing that motor making 800HP you want me to pay to see. (So, I know you are not just pretending.)

Then you arrange its transport and we will hook it up to the Superflow. I have the wiring harness and flywheels from previous runs. We will video tape it, started and pegged at 95% power (that would be where it is making 760 hp) running for 10 mins for everyones' enjoyment.

If it does not get to that 760HP, the motor comes right off and you pay the $2500 for the dyno hookup and runs...

next...

Money shouldn't be a worry for you so you fund it, personally I don't care about this that much. If it mean that much to you pony up. I've not heard of any LT5 spitting a crank so feel free to find some for me since you're so sure of yourself.

[rhipsher]

Me being a CNC programmer/Machinist all my life and one who has done porting on the LT5 the problem is that you can only go so far down on a cnc before it turns into a 90 degree corner with the plenum. And unless they make a tool that can cut around corners the rest has to be done by hand. And at that point you have to use a ball gage. I made one for Pete and one for me. I know that some have used a telescoping gage. But you can't get a true 360 degree circumference with a gage that can only take a measurement 180 degrees at two tiny points.
http://i301.photobucket.com/albums/nn63/keeno1970/imageCAH2QHZK.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/5.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/8.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/100_0115.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/Picture054.jpg
I charged $850 to do the IH and plenum/Siamese. And it took me 16 hours to do it right. It just wasn't profitable enough for me to keep doing. Mark H. Charges $1800 to do it. Corey charges $950. I would say $1500 is worth the trouble. And with porting alone your looking at maybe 15-20HP gain. With Jeal headers and A 3" B&B added along with a good tune your looking at 40hp gain realistically. 385-400rwhp

This was with top end porting only. I was able to pull an extra 15rwhp and some more torque out of my 90 Z. And here's the proof at Corey Hendersons. The before and after overlay dynoes. No tune. No nothing and I was running lean on top of it.
http://i301.photobucket.com/albums/nn63/keeno1970/P1010024.jpg

[Hog]

Did I read here that Extrude hone will no longer do LT5 plenums due on their process causing damage?

[XfireZ51]

When I modified/ported my 84 Xfire manifold, EH is one thing I had done to it. Once I bought a ZR, I thought of doing the same thing. I contacted EH and was told they were no longer doing the LT-5 plenum because the pressure used in squeezing their abrasive through the plenum was cracking the runners from the main body of the plenum. True or not, don't know but that was the reason given. This was 7-8 years ago.

[Paul Workman]

Me being a CNC programmer/Machinist all my life and one who has done porting on the LT5 the problem is that you can only go so far down on a cnc before it turns into a 90 degree corner with the plenum. And unless they make a tool that can cut around corners the rest has to be done by hand....*

Yep! I recognize those balls! I may have been the first to use one of your creations when porting mine, back in 09 (I think it was?)...

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Headporting1.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/Headporting1.jpg.html)

It was a 37.5mm gauge, as I recall.

Some, like you too, have gone bigger - actually siamese'ing some or all of the runner length. And, apparently from what we saw in the LT5 2.0 AND at Mercury Racing last Friday, opening the runners to a single oval runner has merit. MM has eliminated the IH by placing the the injector directly in the head, just as the LT5 "2.0" (tho MM claims there is no DNA from the LT5 in their new line of 4-valve DOHC V8 racing motor...yeah, right!)

One thing that has always been a bottle neck of LT5 mod information is the number of LT5s is so limited. Limited numbers brings relatively high cost and a smaller number of people that ported their motors. Consequently, specific porting experiment results has only been at a comparatively trickle pace, compared to say the "LSx" developments. Early on some deep pocket, big name shops like Lingenfelter and Calloway played a more active role and pushed the envelope agressively. But, that effort seemed to stop short of what is becoming more common now, far as development goes. (limiting discussion to stock bottom 5.7L motors).

There are still some ponies to be dug out of the stock 5.7L top end for street driven cars. For example, Marc Haibeck upped his 500 crank hp package to 510 hp, due at least in part to some improvements to his previous porting architecture. And, then there's Pete with the help of cams and phasing is in the 560 hp range on a stock bottom LT5.

So, there are still some ponies to be had. So, there is still a certain amount of had grinding/experimenting beyond what CNC maps are available. But, it seems the pickin is getting slim for a 5.7L block, normally aspirated. BOOST would appear to be a relatively open field for the 5.7L LT5, at this point.

Porting: Always a very interesting topic...

[Pete]

To get the best performing heads could be done but would cost time and money.

We would probably need a couple sets of heads, flow bench, engine dyno, gaskets, lots of labor,etc.

Flow bench doesn't always tell the whole story you do need to put it on dyno.

All of the above still does not guarantee you will get better then what we have now.
Lets just say we do all of the above and gain 3-4 hp would it be worth/cost affective.

I have spend lots of money and time on cam research trying to get the most out of a LT5 350 we did discover a few things, now can there be more power in cams? again goes back to cost affective.

Pete