Help! Rockers and Push Rod Question

[eoseitz]

Hi. I have a 1974 Corvette that had an engine swap. I know I'm about to get flamed when I say the type of engine, but it came in the car. It is a 1978 LM1 out of a Camaro. I've heard plenty of people tell me to buy a crate engine and not to build this. I don't have the money to buy a crate engine and I'm only looking for around 300-350 horsepower. I've bought a new set of stainless steel headers and I'm about to buy a set of aluminum heads. I'll put a link to the heads below. My question is, will I need new push rods and and rocker arms? I know my current rockers have a 1.5:1 ratio. I've heard I'll get better performance if I move up to some with a 1.6:1. What would you guys do? Also, my new heads have guide plates for the push rods. Do I have to get hardened steel or will my stock ones work? Thanks for any help.

Chevy SBC 350 220cc 64cc Straight Complete Aluminum Cylinder Heads 600 Lift | eBay

 

[KANE]

Hi. I have a 1974 Corvette that had an engine swap. I know I'm about to get flamed when I say the type of engine, but it came in the car. It is a 1978 LM1 out of a Camaro. I've heard plenty of people tell me to buy a crate engine and not to build this. I don't have the money to buy a crate engine and I'm only looking for around 300-350 horsepower. I've bought a new set of stainless steel headers and I'm about to buy a set of aluminum heads. I'll put a link to the heads below. My question is, will I need new push rods and and rocker arms? I know my current rockers have a 1.5:1 ratio. I've heard I'll get better performance if I move up to some with a 1.6:1. What would you guys do? Also, my new heads have guide plates for the push rods. Do I have to get hardened steel or will my stock ones work? Thanks for any help.

Chevy SBC 350 220cc 64cc Straight Complete Aluminum Cylinder Heads 600 Lift | eBay

If it were me... I would swap out the cam and go with a set of iron Vortec heads and a Vortec intake.

Aluminum is good, but I think Vortecs are better when I'm not sure who made those heads.


If money is a concern- I'd just go with Vortec heads and an intake.

Jegs has them for $619 for two heads...
Chevrolet Performance 12558060, Chevrolet Performance Small Block Chevy Cast Iron Vortec Cylinder Heads | Chevrolet Performance


EDIT:
What size cam do you have? Is it the .390/.410 cam? If so, you'll need a lot more cam than that to get the horsepower numbers you are looking for.

 

[eoseitz01]

Probably the stock cam


Sent from my iPhone using Tapatalk

 

[KANE]

If you have the LM-1 350... you would have about 170hp @ 3800rpm and 270lbs-ft of torque at @ 2400. Which would make sense with that cam, if you have the stock .390/.410 spec cam I've read about.

FYI- I sourced the specs for that engine here...
1978 Camaro data - Statistics, facts, decoding, figures & reference information

Moving from 170hp to 330-ish is a big jump. Totally possible though- with the right cam, heads, intake, and fuel delivery system. Vortec heads, intake, and a cam would be the best bang for the buck.

Not being a downer here, but if you have an engine that was built in the 70s, I'm not sure it will hold up to what amounts to a 160hp increase if your target is 330hp. I would do a compression test to see first. If it all checked out- then maybe I'd consider swapping the cam and heads. If the compression was low... yeah, could be valve seals... or could be rings. Rings and wear would make me think twice about a significant upgrade in power. Just my $.02 though.

 

[eoseitz01]

The engine was rebuilt before I bought the car. It's had roughly 2k miles put on it since then. What kind of hp gain would you estimate without putting in a new cam? Assuming it's stock. I was told a mild cam may have been put in it.


Sent from my iPhone using Tapatalk

 

[KANE]

What kind of hp gain would you estimate without putting in a new cam?

Wow... that's a good question. Lots of variables here.

Some folks have seen between 20-40hp on Vortec heads alone.


But that's an internet estimate from people that heard from someone who did XYZ ten years ago...


I am pretty sure you'll need a cam to get close to your 330-400hp number.

 

[Peer81]

Hello,

To begin simple. How much do you know about how an engine works internally and how torque (and horsepower) is made in relation to the different components in that engine?

Second. What kind of an engine are you looking for as a result when all the mods are done? Torque engine, high rev horsepower etc etc?

Third. Did you choose the heads yourself and by what standards? (For example the 220cc intake runner?)

I have no problem explaining things but i need to know at what technical level you're at.

Greetings Peter

 

[Tom Bryant]

Without knowing what cam is in the engine and what pistons were used in the rebuild choosing a head is just guessing and hoping they work out like you want. Those aluminum heads are way too big for a stock or mild cam and a dished piston, which would be your standard rebuild piston for that engine. A 195cc intake runner or even a 180 cc, with a fairly aggressive cam matched to the compression ratio and the intended rpm range would be better. Too big of a runner will bog down the engine if the other components are not well matched to the heads.

Does the guy you bought it from have the paperwork for the rebuild?

Yes you need hardened pushrods with guide plates. Rocker arm ratio depends on camshaft, rpm range and valve to piston clearance. You may need custom length pushrods too but you won't know that until you mock up the build.

Bottom line is you are going to have to match the components to obtain your goal and a properly specced camshaft is the heart of the project.

 

[kpic]

Hi. I have a 1974 Corvette that had an engine swap. I know I'm about to get flamed when I say the type of engine, but it came in the car. It is a 1978 LM1 out of a Camaro. I've heard plenty of people tell me to buy a crate engine and not to build this. I don't have the money to buy a crate engine and I'm only looking for around 300-350 horsepower. I've bought a new set of stainless steel headers and I'm about to buy a set of aluminum heads. I'll put a link to the heads below. My question is, will I need new push rods and and rocker arms? I know my current rockers have a 1.5:1 ratio. I've heard I'll get better performance if I move up to some with a 1.6:1. What would you guys do? Also, my new heads have guide plates for the push rods. Do I have to get hardened steel or will my stock ones work? Thanks for any help.

Chevy SBC 350 220cc 64cc Straight Complete Aluminum Cylinder Heads 600 Lift | eBay

There isn't any sense putting heads set up for .600 lift on that engine.

You really need to know what components are in the engine before you can possibly know what you need to do to get the 300-350 RWHP.

Second Generation Z28 Engines - LM1 Specifications

 

[Hib Halverson]

Probably the stock cam


Sent from my iPhone using Tapatalk

Don't buy those heads.

Way too large a port volume for a stock cam.

Probably too small a chamber volume for an LM1-based engine running on pump gas.

Way too low a price, too. They're gotta be made in China by coolies working in slavery. With Chinese heads at 650 bucks fully-assembled you'll get what you paid for.

You'd be better off if you changed the camshaft to a nice little hydraulic roller, had your existing heads ported and fitted with bigger valves then added an Edelbrock Performer manifold.

No matter what you may think on seeing crap like that on eBay, when it comes to building high-performance engine, there are no free (nor even cheap) lunches.