I am looking into converting an LG4 performance motor into a TPI motor in my race car.

First thing I need to figure out is what heads to use.

The LG4 is from a 82 or 83 Z28. I am assuming the heads are 58cc, right?

And valve sizes are 1.84/1.50.

Also I have heard these are close to 167cc intake ports.

Which all sounds pretty much identical to the 081 centerbolt LB9 TPI heads.

So - question is, any advantage to switch to the TPI heads, or will the LG4 heads work just as well?

I am limited to stock heads, so I can't port them or go to any aftermarket head.

 

Yeah they're pretty much the same except the change from perimeter bolt valve covers to center bolt valve covers.

 

not quite true - I found some flow data for both that suggests that the 081 heads flow 20cfm better on the intake side.

Also - I have empirical data from somebody who dyno'ed with the 187 heads and the smaller 305 cam and made 197hp, then switched to the 081 heads and larger cam and retested - pulled 232hp, so it was worth 35hp. Also the power curve died after 3500rpm with the smaller cam / heads and had a good 1000-1500 more useable RPM with the bigger cam / 081 heads. Hard to say how much was heads vs. the cam, but I am not taking any chances and will just go with the 081 heads to be sure. The port design is also a bit different and optimized for TPI, so that should work better as a system.

 

That's not specific to LB9/LG4. I had an 87 LG4 with the centerbolt valve covers.

IIRC, the 187's were the TBI swirl-port heads, which is yet another different head from the two previously mentioned.

LB9's and LG4's should have the same head. The only difference should be the valve covers/manifold bolts, which changed from 86->87, not from LG4<->LB9

 

Only '87 LG4's have the 14101081 305 TPI heads.

 

I have taken apart stock LG4s from 1987-1988 Caprices that had 187s heads. I have also seen 1987-1988 Monte Carlos with 081s on the L69 and 187s on the LG4.

416s were used on the following

1982-1986 305 LG4
1982-1986 305 L69
1985-1986 305 Lb9
1982-1986 305 LF3 Truck

601s were used on the following
1982-1984 305 LU3 Crossfire
1981-1986 305 LE9 Truck
1979-1981 267

I have also seen alot of 1992 era trucks that had 081/083 heads on them stock. GM using up excess stock?

 

blah blah blah

race car

stock heads

no porting

who are you gonna race?

 

It is a spec class with stock motors in NASA called CMC - Camaro Mustang Challenge. Road racing. We get about 15-20 cars per event in CA, so there are plenty of people to race!! Very popular series with great driving and competition.

 

I have seen stock 416s, 601s, and 081s, support over 400 FWHP.

 

You're probably correct, but since this is a thirdgen website, so what came on Caprices and Monte Carlo's isnt relevant. I would agree GM used up whatever stock they had left, using the good stuff on better cars and the rest on other cars.

The Camaro-Mustang Challenge is a lot of fun! I've been out to their races several times helping my friend Nick Steel. They're limited to 230 RWHP and 300 RWTQ, but there's no limit on area under the curve. I still wouldnt know which heads are better, but the new-tech guy in me would say to use the newer heads.

 

Yes it is a Camaro/Firebird website, BUT I feel the fact that LG4s came with 187s is VERY RELEVANT. It has been 20 years since the general built the last of the LG4s and MANY of the engines have been rebuilt and swapped around. Unless it is a documented stock car, it very well could have 187s on it. I've even seen 193 and 083 350 heads on rebuilt 305 engines.