View Full Version : 425 budget engine build

08-07-11, 04:54 AM
hey fellas... i have a 79 coupe with the original 425....

if you had 1500$ to make youre 425 as powerful as possible what would you guys reccomend i do?

i want an msd ignition, but i have never installed one before, what parts will i need to buy to have my multiple spark discharge? are all gm distributors the same?

someone told me that the best intake i should put on a mildly built 425 is off of an early 70s 500c.i. is this true?

i definatly want to change the cam, what cam should i buy? i dont know much about cam specs.

i have more time than money to spend on my motor.

im already really happy with the power it puts out, and its bone stock, but PLEASE help me pump it out the max for my budget....

im open to all suggestions...

08-11-11, 04:00 PM
The first thing to realize is that 425 and any Cadillac engine has lots of vaccuum lines and vaccuum motors running all over. Correct vaccuum leaks and ensure vaccum motors are operating properly. Then go back throught the tune-up proceedure. When the vacuum controls are working properly, and the lines are in good condition, you'll be surprised how much better the engine will perform.
The intake on the 425 is of single plane design. Some people prefer the dual plane manifold used on the 472 and some 500's. The HEI is about the best offering you will find for GM's offering for the engine. The MSD system may be an improvement, but you would have to find someone with experience in this matter.
You have to realize that you have an engine and drive train combination that relies on low end torque to move the weight and give fairly good gas mileage at highway speeds. If you try to change the performance curve witha more agressive cam, you may be disappointed with what you get. You may want to install a new timing chain to ensure proper crank/cam timing and get rid of that nylon gear on the cam.

08-14-11, 09:40 AM
I think a msd ignition is always a good idea as long as you go with a hei also. You will notice a big difference. I would try and find someone that has some experence with them locally first. They can be a pain and I know I got so frustrated with mine that I was ready to break it then my brother told me I was an idiot and fixed the one wire I had wrong and it ran great.
I do not know much about the intakes but I did the intake mod to my stock 472 intake and it was pretty easy to do. That would be a good way to save some money.
I am not the best with cam specs but when I did mine i ordered it from MTS at 500cid.com. I talked to them for awhile and then helped me get what I wanted and got the most out of my money.

08-15-11, 12:02 AM
If I had a limited budget this is what I would do.. Change the timing chain and gears with a cloyes brand.. The cloyes good one that costs about $100. They have 3 keyways... One is -4 degrees, one is 0 degrees or straight up and one is +4 degrees.. If I kept the stock cam I would use the +4 degree key... I would get a 68-70 intake manifold and cut out the center.. Then I would get a set of 500-472 rwd exhaust manifolds and have dual exhaust put on... If you can find a 94-96 fleetwood RWD cross member, it will make putting on duals eazier.. I had to drill two holes to put that crossmember on my 81...I would not spend my money on a MSD... I would just get a good module and coil and keep everything else stock..

08-15-11, 01:52 AM
hey drmenard,

would u mind explaining more about the cloyes brand timing chain? what does the +4 degree key do? it repositions the location of the cam? im confused what its supposed to do.

08-15-11, 01:55 AM
should i buy this exhaust manifold?

08-16-11, 06:02 PM
By using the +4 keyway it would open and close your valves 4 crank degrees sooner..This will get back some of the power that is lost in the stock cam that have late timing...Plus stock cam gears were coated with plastic to run quiet.. but after many years the plastic gets brittle and breaks off, making way too much play and a good chance of jumping a tooth...
The exhaust manifolds are ok if not cracked.. But I would not pay that much ... maybe $40... $50 tops... there should be plenty of good ones at that price...

08-17-11, 02:16 AM
so where do i buy this "keyway" timing set? i cant just go down to my neighborhood parts store and buy this, can i?

08-17-11, 10:14 PM
This is one place to find it..

08-17-11, 10:26 PM
When replacing the cam gear you must be very careful that the bolts that hold it on are not too long ... they must not stick out past the back side of the cam..Many motors have been damaged by mixing up and using bolts that are just the smallest bit too long ... the bolts that are in there should be fine, but new bolts must not be too long....

08-22-11, 10:31 PM
If I had 1500 to spend on a 425, I would buy a 500 and freshen it up.

08-22-11, 10:45 PM
i know a lot of ppl say to get a 500.... but i like my little 425, i hear that theyre lighter, and know its a solid motor, my engine will fire up with the slightest tap of the starter.... besides my 425 has good power. if i floor it off of the line it will burn rubber through the entire intersection. i just wanna fine tune my baby....

my motor+car has 24k original miles thats another reason i wanna keep it.

do u still think a 500 is a better choice?

09-21-11, 04:45 AM
my motor+car has 24k original miles thats another reason i wanna keep it.

do u still think a 500 is a better choice?

It depends, You might be happy with the 425, a good tune up, dual exhaust and a cam.

This shouldn't cost near 1500.

But, if this doesn't do the trick for ya, the money would be best spent on the 500.

I think it was Shelby who said,"No replacement for displacement."