JoeMonte

Hey y'all, I've got a 1985 Pontiac Trans Am, and it has the anemic LG4 engine with the tiny peanut cam. I want to purchase one that is far superior and wouldn't be too little cam for a 350 if I get one in the future. I was looking at the Summit K1104 cam with lifters, and I know I would need new valve springs because the stock ones float really easily, but other than that, would I need any more supporting mods? I'm about to install a set of headers and a complete exhaust, and I plan on the future to port my heads or pick up a decent set once I've got the cash. Would I need a new length of pushrods? Maybe some rocker arms? I'm not sure, thanks for the guidance.

MSgt Luttrell

I'm thinking that the advertised duration of that camshaft (298) is way too much for the stock compression of that engine, though the lobe separation of 114 may help somewhat. You'd be much happier and get way better performance out of a camshaft with 268-270 advertised duration. Also make sure to use a good zink additive in your engine oil or the new cam's life expectancy may be short.

Hopefully someone that has run that camshaft with the stock 9.5:1 compression of the LG4 will chime in, but I think that Summit camshaft will require closer to 10:1 compression to perform well.

dmccain

iTrader: (2)

I ran a K1103 in a stock LG4 and it did well with stock valve springs and all. With cheap summit shorty headers, a better intake and Holley 650 DP the car dropped a full second in the 1/4 mile.

JoeMonte

I read somewhere that for 9.5:1 compression and up the k1104 was the way to go. Would it be driveable? I'm not looking for a full on drag car but I would really like for this motor to not die off on the top end and this cam IIRC claims it is good until roughly six grand.

MSgt Luttrell

Sounds like the 114 lobe separation helps off set some of the compression loss that a 292 duration cam would normally have.

cosmick

86 was the only year that lg4s had 9.5;1, reports of '85 having it are false. i just installed the lunati 214/224-112 442/465 in my '86 lg4, same specs as one of summit's, but 8 degrees less advertised duration for like $7 extra, plus better stickers included.
the idle isn't bad, it is loud and noticeable, it lacks lower-rpm torque, the top-end pull is good, but i'm seriously considering pulling it for Comp's 210/218-111 447/462 254/262 grind, probably installed 4* delayed, to keep some top-end while restoring driveability, and it'll be the way to go if i add a turbo. i'm not doing another 2400-stall torque converter. 2000 is the stall for me.
When i had an l69, the stock cam had an ic of 36* and pulled hard well past 5500 rpm, even with stock exhaust manifolds. After a performer egr, hedman shorties and a comp 206/212-112, with an ic of 31*, it was done by 5000. So i ported the heads. i know that helped because i suddenly had a very fun traction problem, but it still wouldn't pull 5500. i nearly tried a comp 211/221-110 at 4* delayed, but got a 350 instead

cosmick

no, it makes the ic even later, intake closing is your dynamic compression.

JoeMonte

Do you have any specs/sources to back this up? I'm not trying to come off as rude I just had always read on TGO that '85 LG4's had the 9.5:1 compression ratio and it was never questioned.

IIRC 85's and 86's have flat top Pistons that give it the extra bump in compression

cosmick

How about GM's own tech info from their Vehicle Information Kits found in their Heritage Center? You can find alot more about the LG4s in the kits for Caprices, Monte Carlos, and the C-10s than in the Camaro kits.
How about my own experience pulling heads in salvage yards? Because 416 heads are a good-enough way to bump an 8:1 350 to 9.5:1 when you live above 4500' elevation, and even with no other changes will out-run the same engine with 624 heads, despite the smaller intake valves.
I will say there could well be some late '85s with the flat-tops, but I have yet to find one. So either get a bore-scope and have a look, or pull a head and have a look, or pick a cam that'll work with either. That Comp 12-388-4 would be a good example. Install it 4* delayed, it should get you to 5500 just fine, and it gave me 19" of idle vacuum.

JoeMonte

Thank you, that sounds like a very good cam. I certainly will be ordering it as soon as my paycheck comes. Do you have any recommendations for valve springs/rocker arms or anything of the sort that I would need?

I have also heard good things about the comp cams xe262h, which they sell as a kit with every bit of goodies imaginable, part K12-238-2. Anyone have any luck with that kit?

naf

iTrader: (7)

standard 'Z28' springs, lose the rotators, install good seals and shim to install height.

any other work to those heads, or replacement heads, gets you farther from a 350.

if you've still got the stock rear gears, which are likely 3:08, I'd go one step down from whichever cam I wanted. XE256 remains a solid choice for an otherwise stock LG4.

When you swap to a 350 you WILL be going with a roller cam, so re-use of this flat tappet cam isn't a consideration.

cosmick

Yes, the XE256H is a safe choice, and maybe slightly cheaper, I'd still install it 4* back, but it needs better springs. Have a look at Comp's own dyno charts. It needs beehives like the 26981s. Used stock LSx retainers have become cheap and easy to get.
If I go with the 12-235 I'll be running the 982s upside down with L31 retainers, I already have a cutter with arbor for the spring seats and valveguides.
And while I am planning to swap to an L31, I may give it my current Lunati cam with a new set of lifters, it'll save me $200 vs any HR cam.

JoeMonte

Okay, I looked up the RPO code a few days ago and I have 3:23 gears, probably once I have the big things sorted out I'll go with 3:73's

Fast355

iTrader: (2)

My 1983 G20 Van had factory flat top pistons and 53cc 601 heads with a steel shim headgasket.

Had a 1984 El Camino 305 I pulled apart that was a factory flat top engine too.

Also pulled apart a LG4 from a 1987 Monte Carlo LS that had dished pistons in it. Seems to be hit or miss.