Gruvin84SS

You learn something new every day. The 1982-1984 LG4's had 8.6 to 1 compression and 145HP(in 1982) and 150HP in 1983-4. The 1985-1986 LG4s had 9.5 to 1 compression and 155HP. the 1987 LG4 had 9.3 to 1 compression and 170HP. In 1988, the LG4 was replaced with the LO3 which also had 9.3 to compression which also had 170HP(remained the same fron 1988-1992).

https://www.thirdgen.org/newdesign/tech/techdb.shtml

83 Crossfire TA

iTrader: (2)

More actual facts:
LG4 compression: 8.6:1
LG4 heads typically flow better then L98 heads, even the aluminum vette L98’s, ex, at .450” typically, the vette L98 will be at about 175cfm (and topped out) where the LG4’s will be between 185 and just short of 200cfm.

Opinion:
- for 90% out there, a 305 (even an LG4) is probably a better start then a 350. Very few really are pushing ‘ragged edge’ performance out of anything and can get the performance that they have out of a 305 or 350. At the same time, a lot of these cars are used as daily drivers or at least see a lot of miles…. 305 parts are DIRT cheap if you look around. Often you can get complete engines, which just need a hone, rings and bearings to be a good engine for FREE (I know of 2 that were just thrown out). 305’s tend to get much better mileage then comparable 350’s and tend to last longer. Yes, often you can find performance parts on sale for a 350 for slightly cheaper, but most of these are interchangeable between a 305 and 350 and those that aren’t (pistons, rings…) the slight cost difference is more then offset by the couple of hundred that you’ll pay for a good 350 core.

Fact:
- very few of the mild performance engines that most people build need heads that flow more then the low 200cfm range for the intake ports. Putting better flowing heads on most of these engines doesn't get you anything unless you change everything else to allow it to spin at a higher rpm to take advantage of the extra flow that you have.
- Very few inexpensive (read, mostly stock rebuild… heads) actually flow better with 2.02/1.6 valves without some additional port work. At a minimum they’ll need a good bowl blend.
- Stock vortec truck heads will flow 230cfm on the intake ports, will fit on a 305, and can be milled enough to retain the stock compression with the stock pistons. These heads (possibly with different springs/seals to allow a little more lift) will support the power produced by 99% of the performance builds out there, without resorting to larger, less responsive intake ports. Again, they’ll work great on a 305, and the performer rpm intake that everyone keeps mentioning is available in a vortec version… see where I’m going?

Oh, and as with every f-body package that I've seen, a good cold air iduction and well flowing exhaust will make a big difference (not sure why they didn't come that way fromt the factory).

Gruvin84SS

83 Crossfire TA ,
You state this as if it is a across the board til 1988 when it was replaced with the LO3.

In searching, I have found about 10 seperate websites other than the tech page on this site that denotes the later LG4's as having the CR that I posted in my previous post.

There was a HP change from 1984 to 1985 as well as a CR change is noted to the motor between those two years.

If you look at the HP jump from 85-6 to 87, this also helps to verify the post made by 87Formula4bbl.

85transamtpi

I stand corrected...but have a few ?'s. Do the heads still use 58cc chambers? Do LG4's come stock with flat top pistons or dished? The LG4 I tore into had dished pistons...which gave me the impression that the CR was less than my LB9 that used flat top pistons and heads with 58cc chambers.

And sure, everyone knows a old dirt tracker that swears by 305 heads on a 350.

However, the idea of 2.02/1.60 valves shouldnt even be brought up when talking 305's...we all know you cant use them.

Also I think we may have different ideas of a "street" cam. IMO putting a cam with less than .480 lift and 230* of duration is a waste of time. In my experience, building a 300hp+ small block is easy. "street" + decent heads + good flow in and out of engine.

Traction and gear gets ya 13's.

-Doug

83 Crossfire TA

iTrader: (2)

Gruvin, you’re right. The ’85 and ’86 was identical to the earlier one except for the compression was bumped to 9.5:1. As far as I can tell, the ’87 was identical to the LB9 (tpi) except with the LG4 manifolds.

In retrospect, most of the LG4’s that I’ve seen apart have been ’84 and older.

Hum, I just looked at the thirdgen.org chart… and it pretty much matches that. The HP differences would be fairly self explanatory:
- Everything gained from ’82-’83 because they changed the exhaust to a freer flowing, but not as good sounding single muffler.
- ’83 -84 stayed the same, ’85 it got 9.5:1 compression (from what I can tell from the factory part #’s this was just a piston change, same cam, heads…), which explains the HP gain.
- in ’87 it basically was a different engine. Worse heads, but much bigger cam…

the odd thing was that in a lot of places this doesn’t match the GM #’s, ex, the LU5 is listed as having 9.8:1 compression where the chart shows it as having 9.5:1… and in assorted places GM lists the TPI’s as having 9.5:1 where the internet standard seems to be 9.3:1…

85transamtpi, I’m not sure that I’d believe ‘old dirtracker tales….’ Most traditional smog 350 heads will flow about the same as the original LG4/L69/LU5 heads (if I remember right, there were at least 3 part #’s for those 305 heads, but they were used across the models), the only difference would be the chamber size (small 305 chambers are usually between 53 and 58cc, smog early smog 350 heads are around 76cc, and earlier and later 350 heads are 63-64cc). If you can handle the higher compression then go for it, if not then the lower timing that you’d have to run would probably hurt more then the gain from the compression.

I’m not sure that I have a problem with your definition of street cam. Those lifts or higher you’d end up having to swap springs and/or modify the stem seals to give you the clearance. The nice thing about the LG4 is that with proper carb tuning you can do pretty much anything you want to the engine below the carb, the computer doesn’t have that much control over it and won’t flake out like with FI setups. Honestly, I considered responding earlier with something with about that duration, 110 LSA (plus or minus a little depending on what you end up with for compression after any head milling, thinner gaskets… tighter LSA lets you build more cylinder pressure and make up for low compression)…. I think that with the right mods, starting with a ’82-86 LG4 f-body and not messing with the bottom end you could build a car that would run 12.0’s or maybe even a little better.

85transamtpi

crossfire,
I couldnt agree with you more about the ultra high compression motors. As I said earlier, I know people who swear by this combo...but strangely enough none of their cars are all that impressive to me.

Also, It is my opinion that any thirdgen doing a cam swap should also change springs anyway. Thirdgens are just plain getting older...11 years old is the newest they can possibly be. There are a lot of high mileage cars that were most likely beat on at some point in their life. I am sure most cars have tired springs. I know when I changed mine on my '85, it gave me a kick in the pants (with stock cam).

Im not going to disagree with you here...but I have yet to see a N/A 305 powered thirdgen run any better than 13's. But then again I've never seen the great wall of China, and Im pretty sure it exists.

later,
Doug

87Formula4bbl

Hey while we are on the subject, I have a quick question for anyone really knowledgable about cams. I'm lookin for a good one for my 305 while retaining my stock converter and all. I've got headers, full 3" exhaust so no problems there. The cam I am looking at is the xr252 by Crane I believe. I found this cam while looking through possible setups in DD2000 (don't even go there, for whoever is going to say it). I too belive that DD2000 isnt totally correct in everything, BUT, when I plugged in this cam with my setup, in respect to all other cams I've tried, including the xe256 and xe260 and xe268, it blew these others out of the water. Tons of low end torque (really flat torque curve) and excellent HP curve. The specs for the cam are:

LSA: 110 deg

Int. Dur: 252
Ex. Dur: 258

Int. Lift: .472
Ex. Lift: .480

As far as I can tell, it is very simiilar to the xe 256, who's specs are:

LSA: 110 deg

Int. Dur: 256
Ex. Dur: 268

Int. Lift: .477
Ex. Lift: .484

The only main diff. I can see is the shorter duration but slightly smaller lift for the xr252. Oh ya, and I want something that will 'slide right in' for now, can't afford springs and head work at the moment.

Any help greatly appreciated.

Thanks,
Ben

87Formula4bbl

Oh ya, and the xr252 is rated at 600-4x00rpms, whereas the xe256 is slightly higher, I think around 1200-5000 or so, so as you can see, the xr252, from what I can tell, is made for gobs of low end? Anyone also have any experience with this particular cam?

Thanks again.
Ben

83 Crossfire TA

iTrader: (2)

You don’t have to preach to me… I always tend to have a couple of sets of extra good springs sitting on the shelf just for that reason…

Like I’ve already said, I’m SOOO tempted to build one just to prove that it could be done… Hell, maybe I should find someone that has a 305 f-body and talk them into paying me to ‘fix’ their engine/drivetrain…

83 Crossfire TA

iTrader: (2)

87Formula4bbl, you're not really giving enough detail to answer the question. What about headers and that good stuff. I could see that being the case with manifolds, ports that stall early, low compression...

I'm curious (and can't seem to find my copy of DD2000)... what happens if you decrease the LSA to 108 or advance the cam a couple of degrees?

87Formula4bbl

No, Im saying I have Heddman Headers (shorties) and 3" Y-Pipe back exhaust with Flowmasters, so I will have no problems with exhaust flow. I've gotten many different answers on compression (tech articles all vary) but I seem to think that my compression is 9.3:1 for the '87 LG4.
I have all emissions removed, retuned CC QuadraJet. Also functional cowl unduction, so no intake flow problems either.

I've found (and I'm curious as to why) that when you retard the timing on the stock LG4 setup in DD2000, it helps a lot with the numbers, but when I run this cam, amongst others, it usually drops numbers, I have no idea why.

What other info do you need?

All my other valvetrain and heads are stock for now, thats why I dont want to go too radical or anything, I dont have funds to go changing everything around right now, just looking for a good solid upgrade from the original peanut cam.

If you need any other info, let me know.

Thanks,
Ben

83 Crossfire TA

iTrader: (2)

rule of thumb that you might find helpfull:
if retarding cam timing seems to reslut in more power then your cam is probably too small, if advancing it makes more power it's probably too big (relative to the normal 4 degrees advanced).

I'm guessing that in your case it's some combination of the modeled head flow, manifold design and low compression...

1986BANDIT

wrong,a dyno is an engine brake,hence the "brake horsepower".

//<86TA>\\

iTrader: (14)

This thread is 15 years old....

1986BANDIT

i forgot to wear my glasses yesterday,that's it

B4Ctom1

Thread necromancy is the worst form of pedantry.