We just picked up a 99 Suburban LT K2500 454 w/3.73's. On the way home with it fairly empty, no trailer, we were getting 12.7-13.1 mpg, and that was dealing with rush hour traffic in DC, Chicago*(the Dan Ryan Messway) and rain and the mountains in between. We keep it around 72 mph when we could as the higher speed on cruise. But that was rare to be able to do. Any advice on tips to improve mpg, and to improve power? It seems like it isn't thrilled about revving higher than 3500 rpm, like it is out of breath. It will do it, but my old 96 350 Burb with same gears seemed to rev much easier (it would go to 5800 rpm fairly easily). Low end though, the 454 is so much nicer to drive. And mpg overall isn't much different so far, it is very early to tell. I was thinking of going to adjustable valvetrain and maybe some new rockers that are a blueprinted 1.73:1 ratio (stock for 454's so I am told). Does anyone know cam specs on the 96-99 454's? Are they very cam limited? Do they respond well to any mods like PCM tuning or cooler thermostats? Or K&N's? Or exhaust mods? We are hoping to pickup a 30-35 foot camper next year (if this truck will pull it ok) and start doing some camping with the kids. Thanks!!
We have a '98 C30 dually with an NV4500 and 4.10 gears. It definantly is a lower end motor. I think you are doing fairly good on mileage, especially at those high speeds. There really isn't much that is worth doing to boost mileage. A different exhaust and intake supposedly does, but you can buy a LOT of gas for what that stuff costs. As far as power, you are talking about changing cams, rockers.... With this particular engine I wouldn't mess with that stuff so I wouldn't know.
the only thing i would do is an exhaust and an intake... i don't think there is too much out there to improve mileage on a big block... maybe install a vacuum gauge so that you can have a reminder to stay off the gas a bit?
My thoughts are on going adjustable on the valvetrain is that I can pickup duration some by adjusting it looser. This can add as much as 3-4 degrees duration @ 0.050 (IIRC). Having that, it can move the powerband a little higher and possibly make it a little more efficient at slightly higher rpms. As well as unloading the lifter a little bit. And if I do go with some blueprinted rockers, can add a decent amount more lift. The stock rockers I am told are terrible at deflecting, and even though GM specs them to be 1.73:1, under load of the cam, they are often no more than 1.65:1. So a true 1.73:1 or 1.8:1 rocker can actually be a significant boost to power. I suspect the cam is around 200-205 duration @ 0.050, maybe as much as 210 @ 0.050, which for a 454, is terribly small, but I can't seem to find the OEM cam specs on it. I had a 455 Pontiac with a 228@0.050 cam and .480 lift and it made just as much low end power as my stock 067 cam did coming in at 208/215 @ 0.050 duration. There is just soo much bottom end on the 455 Pontiac, the bigger cam didn't hurt a thing, the smaller cam just restricted the upper end, and power fell off very very early compared to the larger cam, all other things being the same. I just feel for a 454 should make a ton more power than it does. It is rated 290hp/410 lb-ft torque, but sure feels like it isn't there. The low end is ok, but once you pass around 2500-3000 rpm, the power seems to drop off. Torque is ok, but HP just isn't. I think I will install a vacuum gauge, as my wife is the primary driver, if she could see what affected mpg, she might back off a tad. I have advised her to keep her speeds down and that will help dramatically, she said she would try. Just gets crazy in traffic when everyone is doing 85 and we try to go slower.... Anyone read that article in CarCraft/HotRod on the 455 Pontiac (1976 engine) that had such a small cam it made around 250 hp at WOT and 350 lb/ft torque? They added all kinds of mods on the stock cam and power just didn't change. Once they replaced the cam, they were up 100 hp. And power was UP everywhere in the powerband. Even over the stock small cam. I suspect that is what this needs. http://www.compcams.com/Community/Articles/Details.asp?ID=126369669 I drove my parents 8100/Allison 5sp RV and it was a monster even with 30000#, 75 mph was nothing for it (we kept a self imposed speed limit to 65, but I did get going faster once in traffic) and that thing did great on power. It was geared around the same effective gear as my truck would be with 4.10's. IIRC it ran 65 mph @ 2300-2500 rpm. My Sub runs 3.73's and is 2250@75 mph.
I did find the L29 454 cam specs. Valve Lift (Inlet/Exhaust): 0.480"/0.483" Duration at 0.050" cam lift (Inlet/Exhaust): 204/209 degrees The 502 uses this cam as well. Part Number: 12360893 Displacement: 8.2L or 502 cubic inches Compression Ratio: 8.75:1 Gross Horsepower: 320 at 4400 rpm Torque: 515 ft/lbs @ 2,800 RPM Bore/Stroke: 4.446 in./4.00 in. Engine Block: GEN 6 design with 4-bolt mains and siamesed cylinder bores Crankshaft: Forged 1053 steel, one-piece rear main seal Head, chamber size: Cast iron, 118cc open chamber Valve sizes (i/e): 2.065" / 1.720" Camshaft, lift (i/e): L29, Hydraulic roller, 0.480" / 0.483" hydraulic Cam duration (i/e): L29, 204 / 209 degrees @ 0.050 lift So GM feels the cam is worth making some decent truck power. But seeing that the peak hp comes in at 4400 rpm on the 502 with a much stouter 515 lb/ft torque at only 2800 rpm compared to the 4000 rpm on the 454 is only 290 hp and peak torque of 410 ft/lb @ 3200 rpm. Odd though, that the 454 with the same came peak power comes in at 400 rpm less. And peak torque is much less than the 502 and at 400 rpm higher. 454 L29 Specs: Gas-STD (L29) 454 CID (7.4) 290 hp @ 4000 rpm Torque 410 @3200 rpm Sequential-Port Fuel Injection Comp. Ratio 9.0:1 My thoughts are the cam isn't the weakest point, I think I need to address other issues to make the L29 454 sing....
I'll let you know how mine comes out. Mines a 1999 7.4 with Pro Topline heads, 1.8 rockers, stock cam, stroked to 496, larger injectors, etc. I'm building it in the garage to replace the one in my 1996, oh yeah, whipple supercharger too
Sounds sweet! Can you tow safely with a supercharger? I have always seen turbos and superchargers have significantly reduced tow ratings with gas engines. I was looking at head flow for the L29 and found conflicting #'s. One site said only around 215 cfm intake flow. Another (which I like more, and looked like they really flow benched it) came up with 242 intake cfm. They had more data to back it up, so I am leaning on believing that data. I can't buy into a BB head being so small.
Well I won't be towing with mine, it's in my off road truck. The problem I had with the heads were that the chambers were so small at 100cc, I could not find a piston that would net 8.5-9:1 compression with a 4.25 stroke. Lowest I could get down to was about 10:1. The Pro-Toplines have a 118cc chamber and the intake ports are 320cc and fully cnc ported and pollished. I'm still gathering parts, basically just need the pistons (didn't order till I had the heads) and the valvetrain for the heads, have everything else.
There is a 99 LT (not a loaded LT like mine) for sale in Decatuer, IL. 454 w/4.10's, 120K miles for $7000 (asking $7K, so he might come down) with less than 1000 miles on tires on it. Looked well taken care of, aftermarket running boards, pretty much standard LT. I can dig up contact info if someone is interested. It has been for sale for a while (9 months). I am noticing that this year the Subs with 454's are not selling well at all. Many dealers have 350 and 454 Burbs that are sitting for a long time without being sold. They keep trying to get a high price for them compared to what they should be realistically be trying to get. Sorry to the dealers that are trying to get more, but if you are STARTING to ask for a stupid high price like $9999 on a 97 K1500 with 150K miles, then they don't even get to consider my business. And the dealers love to give the excuse "well, that is the internet price, we don't have any room to budge on price" Ok, keep that truck for a long long time, or just wholesale it off and lose on it anyway. We almost bought a 97 K2500, "stripper LT" as I call them, LT with only LS type options, that the dealer was asking $5999, we would have bought in a heartbeat for $5300, but they would not budge in price lower than $5800, and they were trying to play the game "I have to go ask if we can do that price". Ahhh, another missed sale... http://tompeckford.com/pages/presen....asp?orgid=1721&vin=1GNGK26R0VJ330918&photo=5 if you want to take a look. It is a 350 4.10 truck. Nice, very clean, has some bad overspray on hood like someone tried to cover up something, probably the rust at the end of the hood that seems so common on the OBS trucks, the front header is loose at the bottom (many are), weak on power for a 4.10 truck IMHO, just feels heavy, my 96 was much more powerful, has a small dent in the left rear (90% of the Burbs we looked at did have some damage in the left rear...). But not many, if any, options over base LT. AC didn't work and they didn't want to even look at it. This truck has been there since March or so. Yes, the truck we found probably is the exceptional good price. LT with nearly every possible option (ok, it is missing engine block heater and 4.10's. I didn't want 4.10's and avoided them). Even has dimming outside mirrors that are heated. Heated leather, etc. But, it has a few minor dings, and a small dent in the left rear bumper. I'll take the hit to fix later to get the price of the truck down. Our last one was like that, 2 years ago and paid $5500 for a 96 K1500. It had 178K miles on it. But it ran good and we drove it till last month and sold it with 235K. And still runs like new. Revs fine to 5800 rpm. Pulls fine, has decent power even at that age.
