TBI305Camaro

exactly what the title says. I was just wondering. is it because its roller motor? how do the heads and cam compare on these two motors?

vic_V8

they had a post on here not to long ago with the different heads on there lg4, lo3, l98s


I'm guess fuel injection alone could make up 10 horses

iroc22

Keep in mind that in 1987 the LG4 made 165hp, but only 245ft-lbs of torque. The difference in torque is the fuel injection. But I think the real difference in hp is the v-belt to serpentine switch. I can't account though why the L03 can outperform the LG4 with the 187 heads.

TBI305Camaro

was just wondering because there is some buildups that got a lg4 to 325hp so i figured maybe the lo3 could squeeze alittle more out. i decided i dont need a extremely fast car so im just gonna mess with the lo3 more and be happy. makes a great daily driver

iroc22

Fuel injection is a lot more worry free over a carb. Expecially for a daily driver. No one has actually dyno'd a built up L03 to compare side by side with a LG4. So who knows.

jase

did'nt the lo3 hve more compression than the LG4?Thats not because it fuel injected is it?

iroc22

No and no.

Actually the LG4 uses true flat top pistons to obtain a compression ratio of 9.5:1 in the years of 85-87. L03's have a 9.3:1 compression ratio with 4 vavle reliefs in the pistons.

Dave_A

But prior to that most LG4's had 8.6:1...

Slade1

Actually we had a good comparison of a LG4 and LO3 at the last dyno day I went to a few weeks ago.

LG4

No A/C on belt, Holley 650 Carb, Accel wires, 160 stat, K&N Extreme Lid and Flow Filter

147 RWHP @ 4500 RPM
232 RW FT/LB @ 2700 RPM

LO3

March Crank Underpulley, K&N Air filter, Flowmaster 80, Dynomax Cat, K&N Filter, Stock Everything Else

150 RWHP @ 4000 RPM
255 RW FT/LB @ 2400 RPM

The fuel injection setup holds quite a bit of an edge over a carb, the torque and hp curves were a lot smoother for the TBI vs the jagged curve of a LG4. This can be attributed to the minute fuel corrections the TBI can make per ms over the LG4. The LO3 also makes more torque at a lower RPM. This would give the LO3 an advantage of gaining more HP per RPM than the LG4 at all RPM. The edge in peak RPM of the LG4 is the advantage of a 650 CFM over the stock 480 CFM TBI. I'm not entirely convinced the Underpulley can account for the significant difference in torque. I'd have to say the lightly freed up air system contributed a lot more than the pulley alone. From the results of TBI owners with the Holley 670 TBI, if the peak is moved up into the 5000 RPM range than the HP curve will be significantly higher, while the torque curve will gain only a small amount. I think from calculations, this LO3 would gain up to 30 RWHP from the extra 1000 RPM peak. That would put it in TPI 305 territory without having the TPI 305 hotter cam they got compared to the TBI. The LO3 in my opinion is a fairly restricted engine and has a lot more to gain from all mods since it starts out with a lot less than other engines. The LG4 engine is in the same boat as the LO3, it suffers from air restrictions and an efficiency issue since its a carb. All things considered, if today's modern engines with less ci generate more torque and hp, imagine if the 305 got today's air flow technology... it'd be one hell of an engine... take it a step up to 350 and it'd have even more.

iroc22

That's a really good comparison. The Holley would make a huge difference on the LG4, so the hp numbers for a stock LG4 would be lower. That's a great representation of numbers though. Although the 650cfm and 480cfm(If seen 520cfm with injectors in place, but whatever) can't be directly compared. The difference in delta flow between the 4 bbl and 2 bbl's makes a difference.

Keith5

The ealier L03's had 9.5:1 compression, it changed in '90 or '91, I think because of the type of head gasekts or something, but there wasn't any change in the horsepower ratings.

iroc22

No they didn't. They've always had a 9.3:1 compression ratio, with the same pistons and same thickness head gaskets.

Pony Killer

Why the heck were they running a 650 holley on there, did it mention what type of distrubutor they were running?

Anyway, Back to what i was going to chew at, The LG4 system is a very reliable, smoothly working system with very little modification, the CCQjet on there will flow 750 Cfm, The management system, was just fine for performance, it went into a modified open loop mode where the secondaries could be tuned like every other Rochester, and the timing curve went into a fairly agressive curve for the later ones with the knock sensors.
Which made them very easy to modify, extraordinarly cheap to modify, and a great platform to put a stronger motor under it... the management system didn't care... Mid low 14's are runnable on the stock chips..

Mileage was excellent, My Z got 18-19 round town, 25-29 on the highway. With the original, and the later modified engine.

As Far as Airflow restirictions... the stock carbs only suffered from poor aircleaner designs, and a holley suffers no air flow restrictions...

The stock designs Qjets were efficient carbs, however what damned them is what dammed all carbs, they still flow fuel when the throttle blades are shut, and that's what got them nixed.

But from an ease of modifying, and tuning stand point they are superior.... even without a holley on top .

Keith5

My factory book on my '89 that came with the car in '89 says 9.5:1

iroc22

I don't know why. In all other publications and this site it states 9.3:1 ratios for all L03's.

Slade1

I have an 88 SC built probably early 88 late 87 as its still has the wing where late 88's have spoilers. I tested it a few months ago at a good 9.5:1 compression, but that was when cold (like 40 degree cold) so I figure when hot its like 9.3:1 like stock is supposed to be.

The holley setup had vacuum advance timing I believe, but I'm not sure. It was an 87 TA and even with the difference in heads, the LO3 still did those numbers like a walk in the park with only when hot dipping slightly in numbers but all in all a decent motor for daily driving.

Pony Killer

At least they used the right type distributor

I bet if they did some tuning to it, it would have been far closer, or hell left the stock carb, and distributor in.. and tuned it, it woulda been dead even, or better..

But.... .. I didn't do the testing nor did i do the tuning.

evil t/a

How did you test your compression ratio?

graebz28

iTrader: (5)

I think a large difference is in the exhaust size. GM has been known to put the same motor in F-body's and the Vette, and just restrict the intake and exhaust on our cars. Same with the LS1 today.

I just retired a 89 TPI and adopted a 90 TBI. My tuned senses can hear and feel the exhaust restricting esp when down shifting or WOT.

With a full 3" TPI exhaust and an open element or cold air intake set-up, I think you could make up 15-20 horse. Primarily since the exhaust that is on my car right now is only 2 1/4. And the TBI exhaust manifolds are supposed to be more restrictive. And the heads..... And the ............