My Mechanic stats tomorrow swaping my 305 Lg4 for my new bulit 350/355 the block came out of a 1974 Z-28 there takeing out all the smog crap. I got some pace setter headers i order from jet hot so they should go good with my high flow cat 3 inch pipeing flowmaster 80s muffler. How many HP do you think i'll have? Well it be a big diffrance from my Lg4 with 181,000 miles? Thanks

PS i'll be useing the OEM 4bbl carb i had it rebulit a year ago how do you think that well work with it? Sitting on a Edelbrock RPM intake.

 

Horsepower is highly dependant upon the heads and cam. You didn't give us any information on those.

The small Pacesetter primaries will limit HP. You'll probably have more than the LG4 had, but probably not as much as possible with better headers.

The CC q-jet handles a healthy 350 just fine, as long as you use an air cleaner that doesn't choke the airflow like the stock single snorkel unit does.

 

The cam is a "151" cam, used in the L79 in the mid 60s its brand new. The heads are stock but had them rebulit they are like new whats wrong with the pace setters headers i bought them from Jet hot some of my buddy's with camaros gave me 2 thumbs up?Still be a world of diffrent from the stock stuff right?

 

pics

 

If the heads are stock '74 pieces, they probably have 74cc chambers since that was the beginning of the smog era, which will kill the compression which also kills HP, you may want to look at upgrading the heads also.

 

I do have a open air cleaner the K@N Xstream set yup. Thanks

 

I would start there. Replace that cam with just about any other cam you can find.

The heads are equally poor. If you have already put some money into them, now would be a good time to minimize the losses. Sell them to somebody who needs some good stock heads "with a little extra". They are worthless for performance.

If you put that all together with that combo, you will be setting yourself up for disapointment.

 

i agree with lijonwell but, i think you could get buy with just an aftermarket cam like a comp cams xe256 and still maintain a much better than stock 305 power output.

 

When you say profromance what do you guys mean?I am really looking for something with about 300ish hp that it nothing crazy something better then that Lg4. I only paid $1200 for the engine it is a 355 lt better then that 305 155hp way more reliable this engine has totaly been rebulit with 0 miles on it. I talked with a couple guys around here and they are pretty good with engines they said that cam is not the best but its not that ....... bad the cam was in a kit with all the parts the paper work said with the lifter and other stuff in the kit they used to rebulid the engine with it would be 350hp. Thanks for all your input after i get it broken in i'll dyno it so i'll know for sure.

 

The heads themselves are smog heads, with larger CC's than the 305 heads and will drop the CR to around 8-8.25:1 which kills HP. I really don't think that you will get 300hp out of the heads/cam that you are going to run.

 

The 155 HP of the LG4 and the "350" HP the shop is talking about are apples and oranges.

The 155 is a "net" flywheel horsepower rating, meaning as-installed in the engine compartment - all exhaust as would be installed in the car attached, air cleaner installed, engine driving the water pump, fuel pump, alternator, etc.

The "350" HP is a "gross" flywheel horsepower rating. They use long tube headers without mufflers, a velocity stack on the carb instead of an air cleaner, electric water pump, no alternator, fuel supplied by the facility - basically, the engine doesn't have to "run" anything in order to support itself. It's an unrealistic rating used primarily for marketing and bench racing.

If you dyno the car after break-in (assuming you're not talking about removing the engine to have it put on an engine dyno), you'll be running it on a chassis dyno. Results vary greatly, but at least it is a measurement of how much power actually makes it to the wheels. A 350 GFWHP engine often produces less than 250 on a chassis dyno, but it may be 250 on one system and 275 on another.

 

I was looking at the vin number of the car the engine came out of this is what i found dose that big valve heads mean anything?

Z28 Verification: The 5th digit of the VIN will read "T". Period.
Total Production: 13,802
Engine: Includes special 350 CID, 245 hp V8. Four-bolt main bearing caps, forged steel crank, impact extruded aluminum pistons, heat treated & shot peened connecting rods "big valve" cylinder heads with high speed valve train. Cast aluminum rocker covers with internal galleries. Hydraulic lifters cam & cast iron intake with EGR. Rochester Quadrajet. 17-quart cooling system with 18" 7 blade flex fan. Oil pan windage tray and high speed crankshaft damper. Dual Exhaust pipe system. Same setup as 1973, HEI (high-energy ignition) introduced in mid-year (January 74). Special dual snorkle air cleaner with chrome lid. 245@5200

 

sounds like the bottom end is definetly up for the task, that's a good start.

As for big valve cylinder heads that doesn't realy mean anything to me, what i consider a big valve could be completely different than what they considder big valves.

Most likely they have 1.94/1.50 valving.

Anyways with 8.25 compression your not going to be able to go with a very big cam at all..... Best bet is to find some later model heads like some 081s or 083s or something like that.

With iron heads you can run as much as 10 to 1 compression or even a little higher on premium fuel and if your going n/a i'd run 9.5 or higher myself...

 

To change the heads would you have to pull the motor how hard is it?

 

You do not need to pull the motor to swap heads. Not really that hard to do. You'll need to buy new head gaskets and intake manifold gaskets, probably valve cover too unless you have rubber ones and are carefull at removing them or have steel impregnated ones, which I doubt. Terms of time, fairly easily done in a weekend if you're a slow worker. Just my .02.

Gilley's86