Dobey, have you thought about a custom grind? comp will custom grind a cam for your car, the lobe choices are damn near infinite. you could get more than the L92 cam, and still not blow the budget, and retain full VVT range.
Originally posted by ericjon262: Dobey, have you thought about a custom grind? comp will custom grind a cam for your car, the lobe choices are damn near infinite. you could get more than the L92 cam, and still not blow the budget, and retain full VVT range.
I have, but I want to do all the math to figure out what acceptable lift, duration, and LSA will fit my needs. I don't want to go too big on lift (around 0.550 total), or duration and LSA, as I'd like a nice smooth and quiet idle that sounds similar enough to the stock 2.8, for the sleeper goodness. The stock L92 cam with 1.8 rockers will be about 0.530 lift, and I've already had the heads milled 0.015" to bump the compression a tiny bit. I've also been thinking about maybe having them milled a bit more, to bump the compression even further.
On the other hand, the stock L92 cam with 1.8 rockers, compression bump, intake swap, vvt retrofit, and custom headers should be enough to make 400 HP/TQ at the crank, and have quite a nice, broad and nearly flat, torque curve already, even with the displacement drop to 4.8L. I guess I just need to decide if that's enough, or if I want a little bit more out of it.
Fair enough, I just hadn't even seen the mention of custom grinds, thought I'd throw it out there. any updates otherwise?
------------------ "I'm not what is called a "civilized man" professor, I have done with society for reasons that seem good to me therefore I do not obey it's laws."
we're in desperate need of a little more religion to nurse your god-like point of view...
Guess I need to get new pistons, or otherwise the VVT won't be usable, as the VVT engines all have pistons with indentations for valve clearance. So even with a stock L92 cam, I'd probably have clearance issues with the current flat-top pistons. :-/
Guess I need to get new pistons, or otherwise the VVT won't be usable, as the VVT engines all have pistons with indentations for valve clearance. So even with a stock L92 cam, I'd probably have clearance issues with the current flat-top pistons. :-/
Rather than stock VVT pistons, look at pistons with deeper clearance cuts. Part of the reason specialty cam designers use little or no VVT is they have to grind for stock valve clearance cuts in the pistons to be applicable to a wide market. With extra valve clearance you will have flexibility they don't.
Now is a good time to figure out the compression ratio you want as well. -Paul
------------------ 1988 Fiero Formula 25k miles, garaged since 1988
Originally posted by Paul.S: Rather than stock VVT pistons, look at pistons with deeper clearance cuts. Part of the reason specialty cam designers use little or no VVT is they have to grind for stock valve clearance cuts in the pistons to be applicable to a wide market. With extra valve clearance you will have flexibility they don't.
Now is a good time to figure out the compression ratio you want as well. -Paul
That's the problem. I want more compression, not less. If I could get to 11:1, that'd be awesome. It might be difficult to manage though, on a Gen IV block with Gen III heads, and adding VVT, thanks to clearance issues. The new Gen V 6.2 is 11.5:1, and the 5.3 is 11:1, but they're also direct injected and have very different heads than the Gen III/IV does. I think the Gen IV L99 is around 10.4:1.
Anyway, I'll do the math and figure out a good combination to go with, for cam, pistons, and what VVT range to use. Since I want to build it to be able have at least an 8000 RPM fuel cut, being able to keep as much retard as possible in the VVT would be best, for being able to keep the power coming out way up there.
That's the problem. I want more compression, not less. If I could get to 11:1, that'd be awesome.
Way back when, when I followed high performance engine building more closely, you could get custom SBC pistons with deep valve relief and a slanted dome for compression over 12:1 Is there anything like that for LSx?
------------------ 1988 Fiero Formula 25k miles, garaged since 1988
Originally posted by Paul.S: Way back when, when I followed high performance engine building more closely, you could get custom SBC pistons with deep valve relief and a slanted dome for compression over 12:1 Is there anything like that for LSx?
Yeah, I've built BBC race engines before that had like 16:1 compression. But those didn't have VVT, and PTV clearance was much more straightforward. There's nothing particularly special about the LSx pistons versus classic SBC pistons; just that the dome shape will be slightly different to match the different chambers on the different heads. Wiseco has some at least, for 11.8:1, but they only sell them for the larger bores, and I don't think they'd work well with VVT at all. I could probably get custom pistons made but those are $$$. I can get the stock VVT 4.8/5.3 pistons new for about $300. A set of the pre-made aftermarkets for the larger bore are about $650-800 depending on type and maker.
I can just go with stock VVT pistons and then get the heads milled a bit more (I've already got them milled a tiny bit). Another 0.030 off should give me right around 11:1. As it sits right now, even with the stock VVT pistons I should still be just over 10:1.
Originally posted by Paul.S: What is the most you can mill off total without causing problems?
I'm not sure exactly. I've already taken off 0.015. I don't think I'd go more than another 0.030 total for a street car though. It's supposed to be a little warmer here tomorrow, so maybe I'll see if I can't pull a head off the shelf and measure the chamber depth on it.
Looks like a since wave would have problems with the fully retarded curves.
Can you install the cam 13 degrees advanced relative to the phaser? That way it would have 31 degrees each of advance and retard and you wouldn't be as close on the fully retarded end of travel.
ALSO, piston motion isn't a since wave. The angularity of the conrod causes the piston to be "slower" than a sine through TDC and faster through BDC.
Looks like a since wave would have problems with the fully retarded curves.
Can you install the cam 13 degrees advanced relative to the phaser? That way it would have 31 degrees each of advance and retard and you wouldn't be as close on the fully retarded end of travel.
ALSO, piston motion isn't a since wave. The angularity of the conrod causes the piston to be "slower" than a sine through TDC and faster through BDC.
If I understand you right, you're asking if I can change the unaltered timing of the phaser. I don't think that's possible without building a custom phaser with different timing than the OEM one. I'm not sure if I would want to install it at that much advance anyway. What's important to me is keeping as much of the OEM retard in the phaser as possible, as I'm trying to build it to have a quite high redline. So I'd like to be able to still make power up at that end of the spectrum, too.
And yeah, it's not a perfect sine wave, but it should be much closer to a sine wave, than a straight line between two points. I could write a program to render everything properly, and calculate the correct wave for the piston motion, and try to calculate the correct curves for the cam lobes, but that takes much longer to do, and I just wanted a quick "close enough" approximation to see what was going on.
With the Wiseco pistons, and the valve pockets in them, I should have plenty of clearance with a custom cam grind, to keep the full range of factory VVT, and make plenty of power throughout the entire range.
just build that lil' small block up as a 327 and put a turbo on it. screw all that VVT crap. you've been building it now for 5+ years, just get er' done. Work on the "Dream motor" after you get this one done. get this one done, install it behind the F40 and then put another 4.8/5.3 on the engine stand to build. Once done, swap them out. Come on man!!!!
Originally posted by dobey: If I understand you right, you're asking if I can change the unaltered timing of the phaser.
He saying to rotate the camshaft vs. the cam gear. 13 degree might be to much for off-the-shelf parts, but you can always redrill the dowel pin location in the cam gear to get the desired installed advance/retard (that's how I did mine - installed 16 degrees advanced).
At 5 degrees of crankshaft rotation, the piston is pulled .008" down from TDC on the 4.8. At 10 degrees its down .031" At 15 degrees its down .067" At 20 degrees its down .123"
He saying to rotate the camshaft vs. the cam gear. 13 degree might be to much for off-the-shelf parts, but you can always redrill the dowel pin location in the cam gear to get the desired installed advance/retard (that's how I did mine - installed 16 degrees advanced).
But that wouldn't change the phaser range to have 31 degrees of advance and retard. It would still have the same as stock. To get 31 in both directions, I am pretty sure the internals of the phaser would need to be changed, no?
If I just advanced the cam position on the gear right now, the ECM would still advance it another 18 degrees (without some serious reprogramming anyway), in the low end. I don't think running that much advance would be a good idea, and it would definitely result in the intake valve hitting the piston, with the L92 cam anyway.
Well, if Isky can do a custom VVT grind cam for me, I think if I get the exhaust lobe max lift point matched up with the exhaust lobe on the L92 cam, and get a bit larger LSA than the L92, clearance shouldn't be an issue, and it should get me the power I want, and I should be able to retain the full VVT range of the phaser. So we'll see what they say about the cam.
I also put an e-mail in to SCAT about a crank and rods. Hopefully will hear back from them and Callies soon, and can do it for a decent price (or let my engine be the test mule for it and sponsor me a crank and rods).
But that wouldn't change the phaser range to have 31 degrees of advance and retard.
Yes, it would.
quote
Originally posted by dobey: (without some serious reprogramming anyway)
I thought that was an obvious requirement for pretty much anything that's been discussed in this thread.
Yes, it would require shifting the cam phasing map such that the new "zero" for the phaser put the cam back where it was prior to changing the cam angle relative to the phaser hub.
[This message has been edited by Will (edited 01-05-2015).]
Originally posted by Will: Yes, it would require shifting the cam phasing map such that the new "zero" for the phaser put the cam back where it was prior to changing the cam angle relative to the phaser hub.
I looked at a couple of tunes and there appears to be 3 main VVT maps (for 3 different MAP levels), so it would be simple to apply a constant adjustment to every cell.
The other noteworthy item is the values were 12 in the higher RPMs, but in the mid 20's in the cruise RPM/cylinder airmass areas. The values never went negative.
Originally posted by fieroguru: I looked at a couple of tunes and there appears to be 3 main VVT maps (for 3 different MAP levels), so it would be simple to apply a constant adjustment to every cell.
The other noteworthy item is the values were 12 in the higher RPMs, but in the mid 20's in the cruise RPM/cylinder airmass areas. The values never went negative.
Interesting. I wonder if those maps have the same numbers in the 08-09 Escalade, or 2010-2013 trucks or Camaro/Corvette, as the Avalanche didn't have VVT at all until 2010.
Interesting. I wonder if those maps have the same numbers in the 08-09 Escalade, or 2010-2013 trucks or Camaro/Corvette, as the Avalanche didn't have VVT at all until 2010.
I looked at one Vette and its values were pretty much the same, but I can check some others this weekend and get some screen shots of the tables and the subsequent values. I haven't downloaded the latest version of HP tuners (but can this weekend), so it wouldn't let me open the 2014 or 2015 calibrations to see what those looked like.
Here are the High and Low MAP VVT tables for three 2010 applications. There is a 3rd table (medium), but I didn't show it. The theshold values for the low, Med & High tables are 75kPa, 84kPa and 94kPa for all 3 applications.
The three applications are 5.3 Tahoe, Camaro 6 speed, Vette 6 speed:
Originally posted by fieroguru: Here are the High and Low MAP VVT tables for three 2010 applications. There is a 3rd table (medium), but I didn't show it. The theshold values for the low, Med & High tables are 75kPa, 84kPa and 94kPa for all 3 applications.
The three applications are 5.3 Tahoe, Camaro 6 speed, Vette 6 speed:
Those are some interesting numbers. I take it those are all timing retard values for the phaser, and negative would be advance? I wonder why they never advance the cam from centerline in the low end, and don't go as far out on the retard as they could in the top end. Piston clearance maybe? Or just typical conservative numbers for OEM programming, to minimize chance of recalls or warranty work, and get a little MPG improvement to satisfy the CAFE requirements?
BTW, who manufactured your custom grind cam, fieroguru? I know Pat G specced it for you, but are the lobes and core made by Comp? Isky hasn't replied to me yet, and I've been thinking about their lobes a little more, and the numbers on their lobe sheet seem to result in a slightly odd lobe shape that increases duration at very low lifts, and can make for a bit more overlap than I might want, so I might need to go with a different set of lobes. If your cam was made by Comp, how is it holding up? I was looking for some more custom cam info, and ran across several threads on other sites of people complaining about cam failures with some of Comp's stuff. Thanks.
Originally posted by dobey: Those are some interesting numbers. I take it those are all timing retard values for the phaser, and negative would be advance? I wonder why they never advance the cam from centerline in the low end, and don't go as far out on the retard as they could in the top end. Piston clearance maybe? Or just typical conservative numbers for OEM programming, to minimize chance of recalls or warranty work, and get a little MPG improvement to satisfy the CAFE requirements?
BTW, who manufactured your custom grind cam, fieroguru? I know Pat G specced it for you, but are the lobes and core made by Comp? Isky hasn't replied to me yet, and I've been thinking about their lobes a little more, and the numbers on their lobe sheet seem to result in a slightly odd lobe shape that increases duration at very low lifts, and can make for a bit more overlap than I might want, so I might need to go with a different set of lobes. If your cam was made by Comp, how is it holding up? I was looking for some more custom cam info, and ran across several threads on other sites of people complaining about cam failures with some of Comp's stuff. Thanks.
Yes, the positive values should be retarding the camshaft. With the small stock cams, there probably isn't any benefit to advancing them, where as on some of the more aggressive aftermarket camshafts there might be some. As for why they don't retard further at higher RPM, it must be they run out of benefit, it hurts emissions, or they are intentionally leaving power on the table. Its not PTV clearance as they go much further at lower RPM. You might want to discuss your goals with Pat G and get his thoughts on the VVT camshaft.
I haven't had my custom camshaft made yet... been too busy. Mine uses proprietary EPS lobe profiles that offer more valve train stability at higher RPMs. So when I go have it made, I will have to have EPS make the camshaft, but I think almost everyone uses Comps cores (my current New Era camshaft is from a Comp core).
Emissions and CAFE affect EVERY aspect of an OE calibration. The rule is that the calibration will have the best power it can give within emissions rules.
Expect to remap the entire VVT map if you're swapping cams and looking for best power without regard to emissions.
Originally posted by Will: Emissions and CAFE affect EVERY aspect of an OE calibration. The rule is that the calibration will have the best power it can give within emissions rules.
Expect to remap the entire VVT map if you're swapping cams and looking for best power without regard to emissions.
I do care about emissions. I'll be installing the modern emissions equipment used on new LSx based cars along with my LS4, making aero mods to the car, and trying to squeeze out very high MPG numbers for a V8.
I expect to do a lot of VVT, fuel, etc… map changes, not just power and emissions, but just to make it run decent, with the changes from stock that I'm doing. I guess I just wish that GM (and other manufacturers) would publish full power/emissions data from testing that led to the default numbers in the programming, so it would be easier to understand what they were thinking when they made those decisions, and make better decisions about where those numbers should be for my build, without having to spend some insane amount of hours and dollars on dynos, to get to the same conclusions.
You don't care the way OEM's care... so the compromises made in the calibration are very different. Sniffer equipment at your local emissions check station isn't even close to the level of equipment used to evaluate OE powertrain configurations.
Originally posted by Will: You don't care the way OEM's care... so the compromises made in the calibration are very different. Sniffer equipment at your local emissions check station isn't even close to the level of equipment used to evaluate OE powertrain configurations.
I don't have a local emissions check station (emissions checks aren't required where I am, and now that my Fiero is over 25, she doesn't have to bother with the yearly state safety inspections either).
While the equipment available to me to check emissions outputs may not be anywhere near the OEM's stuff, the basic principles of timing in the engine are the same. I also don't have to worry about warranty claims on millions of vehicles, or getting the right mix of HP and MPG numbers to maybe sell a few more cars than the competitor in the same class based on marketing. I do have loose goals I'd like to be able to reach, though, and understanding the numbers better will let me make better decisions about how to reach my own goals.
Anyway, I'll continue doing what I've been doing, and do what I know to do, and alter what I'm doing as new info and ideas become available.
