Does anyone have the GM part number for the LT4 cam that everyone talks about installing?

How about the cam specs as well?

Looking at putting one into a 87 305 LG4 block.


Thanks.

Jeff

 

GM # 12551142. 203/210 duration @.050, .476/.480 lift using 1.6 rockers.
btw- you'll get basically the same cam if you use a 95-97 LT1 cam with 1.6 ratio rockers. I only mention this because you can pick up a used lt1 cam for $30, as opposed to the lt4.

 

Thanks Five Point.

 

Is the LG4 motor a roller motor? I always get confused with engine codes. I thought the LG4 was the early low output 305? If so, it's not a roller motor and you'll have some trouble using that cam in it. In that case, summit sells cams that come with lifters for $79.

 

I figure the LT4 is a poor return on investment for the effort required to re-cam an f-body be it a 305, 350 or otherwise. I also wouldn't waste coin on a roller setup cost of the lifters will pay for a decent set of headers, rear gears, whatever.

If I had an LG4 I'd go with top notch exhaust system, manifold and a cam with something in the mid teens, say 214-216 intake @ .050 and around .470 or .480 lift.

92RSFivePointSlow -- The LG4 is non-roller, L03 and LB9 are rollers.

adious,
RP.

 

OK .. I probably stated wrong block numbers here.

The question was really for my brother, he has an 1987 firebird.

The motor is roller setup, whether the block is LG4 or not I'm not 100% sure. He just had his heads done, so he's sure it's a roller block - I'll have to check his codes again so I don't confuse any further - maybe it's the LB9 - I see that as another option in the Tech Data section here.

He was looking at a Comp Cams that had almost the same numbers as the LT4, but at a much higher cost. I suggested he look into an LT4 cam for some savings - I see everyone here discussing LT4 cams alot, be it the "hot" cam or the standard one. I told him the numbers on the LT4 and he was impressed with the "bang-for-the-buck" ratio. $150 brand new LT4 (and cheaper used) vs. $240 Comp Cam is a deal. He has access to a shop, lifts, tools, etc. so a cam swap is no biggie for him.

He's in a non-emmisions county, so he can do the cheaper headers and such with ease to the wallet (unlike myself who has to get TES for a similar effect).

Sorry for confusing anyone.

 

Too broad a brush. '87 LG4's are roller blocks.

 

I've spent enough time around LG4s. Never heard of or seen a carb'd LG4 with a factory roller setup. There was rollers as far back as '85 the TPI was called LB9 it's low output carb'd contemporary was LG4 etc. In my book LG4's and rollers didn't happen.

Might have been some in the switchover year ('87-'88) like I said never seen or heard of it.

In any event IMO the LT4 is cam-lite for the amount of work you are doing to swap it out. Not enough gains for your efforts. Specs are roughly 201/209 and mid .400s without 1.6s. I can do that with my L98 cam (203/209 .415/.430) -- better off with the ZZ4 208/221 or LT4 hot 218/228 assuming you have no ECM to deal with ?

my farthings worth,
RP.

 

I have one.....1987 Z-28 305 roller motor LG4 cc q-jet. The LT1 or LT4 cams with 1.8 roller rockers are an excellent upgrade. You will see 25 to 35 hp.




Brian

 

I'll take your word for it then and stand corrected.

About the LT1 and LT4 cams... wait while dig up the specs... ok:

LT1 - PN 12551705, 201/208 @.050, .447/.459 @ 1.5
LT4 - PN 12551142, 203/210 @.050, .446/.450 @ 1.5 ratio, .476/.480 at 1.6 ratio.
LT4 HOT - PN 24502586 218/228 @.050, .492/.492 @ 1.5, .525/.525 @ 1.6
ZZ4 - PN 10185071, 208/221 @.050, .474/.510 @ 1.5

My factory roller cam is somewhere around 203/209 .415/.430 (depending on sources). Throw on some 1.6RRs to get a little more duration & lift and it starts to look like an LT1 or LT4 cam. I don't think the LT4 cam carries enough of an increase to justify the cost, time and effort required to re & re your cam.

The LT4 HOT on the other hand, would really wake up your LG4 -- assuming you are not limited by ECM and PROM issues ? 218 degrees on the intake will introduce some manifold vacuum issues on any 305.

Oh yeah there are no 1.8 roller rockers for our 87-92 sbc centerbolt heads.

my .02 cents worth,
RP.

 

Yeah that was a typo I ment 1.6 The duration is not changed by the ratio of the rocker, only lift .030 from 1.5 to 1.6 Computers are not friendly to duration on a cam if you do not do your own chips. The lift makes up for the duration in some aspects. I would go with the LT1 & 1.6's however if you are not using a computer then the duration is not limited. With the zz4 & LT4 hot you will run into spring & guide clearance issues on stock heads.




Brian

 

You might be surprised to hear that upgrading rockers (1.5 to 1.6) does have the 'effect' (using the term carefully) of increasing duration by 1.5 to 2.5 degrees at the valve on the SBC.

Just went through quite the debate on this on the Ontario Board. You can do a search or read all about it in David Vizard's "SmallBlock Chevy Camshafts and Valvetrain book".

I'm curious if you heard of anyone trying the LT4 HOT on an LB9 TPI ? Looking for a cam solution myself and am at a roadblock maybe the HOT might clear up ? I figure 218 degrees on the intake will destroy neccessary MAP at idle for a stock chip.

thx,
RP.

 

sure you can run a hot cam on the LB9 you will just need a custom chip to use the vac. signal. I am using the hot cam in my 350 and I get 15 in of vac at idle 12 in in gear idling at 750. With the standard LT4 I got 19 to 21 inches.



Brian

 

yep I HAD i a 87 LG4 roller block. STill looking for a car f7