cheap power improvements to the 425... - Page 3

7.0,hellyeah · #31 (**permalink**) 11-05-04, 10:35 PM

Best parts ever for the 425, these people are really knowledgable: http://cad500parts.com/newpage1.htm Or go to cad500parts.com, click on complete motors, and in the same place click on the ultimate 425

caddycarlo · #32 (**permalink**) 11-05-04, 11:10 PM

as far as I know there is no drop in header for your car .... I live in the same town as the cad co and know the guy that builds the headers they sell and he has not had a car in house to build a set for yet ..........

abcdefg · #33 (**permalink**) 12-09-04, 11:05 PM

i still havent had my question answered:

By going with a 3x14" air cleaner box and filter, no exhaust (cut it off after it starts to bend into one peice) and a 500/472 intake manifold?

I know doing something that small can make a difference, just having the cat made the car really go better.

Dead Sled · #34 (**permalink**) 05-07-05, 07:55 PM

since so many people have been asking about the 425 i figured I'd shove a big thumb tack through it and stab it into the top of the board

Night Wolf · #35 (**permalink**) 05-07-05, 11:54 PM

Quote:

Originally Posted by abcdefg

i still havent had my question answered:

By going with a 3x14" air cleaner box and filter, no exhaust (cut it off after it starts to bend into one peice) and a 500/472 intake manifold?

I know doing something that small can make a difference, just having the cat made the car really go better.

What are you asking?

When I drained the catalyst beads from my cat. conv. it made a nice difference. the 14" open element Edelbrock air filter also helped a little.

I still have to install the modifed 472 intake manifold and the rebuilt carburator... that will fix my carburator problem and give me more power/fuel economy also....

But the 2.28 open rear end really has to go...

king of the road · #36 (**permalink**) 05-08-05, 07:40 AM

ive thought to rip out the exhaust and the cat and center box,with a 2.5 pipe all the way to the back where ill fix ona muffler, i read somewhere on here as well that removing part of the intake manifold by machining it or whatever way possible will help it breath and to give my carb a overhaul, would fitting bigger jets bring about more bhp?, i know my fuel consumption would rise.

venom242 · #37 (**permalink**) 05-11-05, 08:47 PM

Richer jetting is definitely something to consider. I have heard that these motors were so emissions choked by the factory that they purposely jetted them lean, enough to melt pistons (rumor). If had known about that years ago, I might have rejetted my carb instead of doing my 500 swap.

After my carb was rebuilt by a local shop, my 425 ran like a dog. From that point on, I rebuilt all my own carbs. I highly recommend the Quadrajet book by Doug Roe if you want to know more about them.

Benlomand · #38 (**permalink**) 05-11-05, 09:19 PM

I know a young kid that has a '79 deville, claims that the carb was rebuilt. Says it starts fine but wont run once he takes his foot off the gas. I'm not real keen on auto carbs but my SS on my Harley requires slight adjustment of the idle air screw on order to get it to run after repair. Single barrel though. Is the 4 barrel similar? and if not where can I get some info on how to proceed.

Night Wolf · #39 (**permalink**) 05-11-05, 09:45 PM

Quote:

Originally Posted by venom242

Richer jetting is definitely something to consider. I have heard that these motors were so emissions choked by the factory that they purposely jetted them lean, enough to melt pistons (rumor). If had known about that years ago, I might have rejetted my carb instead of doing my 500 swap.

After my carb was rebuilt by a local shop, my 425 ran like a dog. From that point on, I rebuilt all my own carbs. I highly recommend the Quadrajet book by Doug Roe if you want to know more about them.

The carb on normal 425's are fine.. not leaned out or anything... if the car was equiped for cali. emmissions, then yes, it does have a lean-tuned carb along with other junk...

Night Wolf · #40 (**permalink**) 05-11-05, 09:49 PM

Here is a question I have...

lets say I want to keep my origanal 425 in my '79... no 472/500 swaps...

Is the BlackBird kit from Cad Company a good choice?

for $4,000 you get all the stuff to build up your enigne to get 400hp and 500ft-lbs torque on premium pump gas.

So the question is... for $4,000 can you piece your own engine together and get more power... and still be reliable? and also... for $4,000 would it be betting to buy a 472/500 and build that up?

Just something I am thinking of... a 472/500 would be sweet... but it would require me buying another engine, then letting my 425 sit... when in fact I have an awesome running 90k origanal mile 425 sitting in the car as it is...

Of course there is machine shop work and whatnot, but I was looking at the kit, and that is looking pretty nice...

http://cad500parts.com/newpage1.htm

davesdeville · #41 (**permalink**) 05-11-05, 10:36 PM

For $4000 it would probably be best to go for a 500..

Night Wolf · #42 (**permalink**) 05-12-05, 11:34 PM

Yeah, it would probably be the best bet... and a 500... that would just be cool....

I would just hate to let my faithful 425 sit in the corner because of that... eh, I guess by that time it wont matter much, and I would have a great running 425 is I needed one, maybe a cool swap into a Jeep or something?

This time is long away though... but visions of my '79 pulling some low numbers at the drag strip and beating some unsuspecting sports cars, while surprising everyone is still in my head.... until then I can keep dreaming

Although I gotta say, given what was going on with the gas crisis at the time, the emmissions and all that other stuff, not to mention a 26 year old car that probably isn't as powerful as when it was new.... she really does move, especially from a roll of around 30mph, and this is with a carb that needs to be rebuilt. the 425 has never let me down

just emptied my wallet at the pumps faster then I would like

davesdeville · #43 (**permalink**) 05-13-05, 04:08 PM

Get a propane carb system, a late model 500 and swap the 76cc heads on it for 12.5:1... Propane's cheaper than gas and 12.5:1 is better than 8.5:1 or 10:1.

djcwardog · #44 (**permalink**) 05-21-05, 02:29 PM

I am looking to buy a Deville this summer and the 77-79 cars have my interest, as do the 1980 cars. Both sets have smaller big block engines (425 and 368). If I decide to drop in a 500 (even a junkyard one at first), I'm told that everything bolts across as far as accessories, pulleys, etc. Of course the 1973 and 1975-6 cars also interest me! Tough to choose. 5000 pound car with mongo motor or 4000 pound car with smaller relative of it...

Anyway, for your question, I think I am with you on this. If it were me, and it could very well be this summer, I would want to tweak out the stock 425 (or 368 if I get a 1980 Coupe Deville, that year sure is good looking!) first for not alot of money just to see what it will do. Then if I decide it doesn't do enough, I can go ahead with the 500 option. So - to optimize beathing, first you need to at least port match your intake manifold. If you swap in a 472/500 one check its ports as well. You will not be creating extra work in doing this because you are going to have to remove the manifold anyway to do the one thing that is mandatory for you...

Pitch out that stock cam and put in something like the MTS 3 (for great torque and better mpg) or their MTS-5 or MTS-10, or even a just a stock spec 1973 cam, for better power over what you are getting now. Your stock smogger cam is retarded by design and not at all optimized for much of anything! A new cam with lifters is maybe $200. If you can use your stock rockers and valve springs then you are doing OK. Call MTS and ask them. Cad Co and Potter offer similar stuff as well... Comp Cams lists a few cams for these big block Caddys.

I would also recommend a true dual exhaust system custom bent at your local muffler shop. I like Dynomax Super Turbo mufflers but pick what you want.

Bottom line: short duration/high lift cam, port-matched intake, dual exhaust, and a proper carb setup to go with these mods and you will be at a point where you know whether or not the 425 will do it for you in the long run. If not, pull it and sell on ebay - someone else will want such a carefully prepped motor for their MPG king Caddy! You can then put in a 500.

Night Wolf · #45 (**permalink**) 05-22-05, 12:40 AM

the cam.... I had a BIG discussion about that a little while back, I was very close to getting a #5 seires IIRC from MTS.

I do not want to remove the heads, and the process of replacing the springs, retainers and all the other good stuff was too much then I was willing to do. Plus all the cam will really do, for a near stock 425 atleast, is move the power band around.... which will make it rev higher, but also move the power up... which really isn't what I want with this car, especailly with the 2.28 gears, it bogs from a stop as it is, I don't need to make it worse by cutting more low-end power from the engine.

My 425 is all stock, and once it is warmed up and some of the carb issues are gone, it hauls... I am really happy with it's performance, I mean if you are doing 35mph and floor it, it downshifts into 1st and puts you in the seat until the shift to 2nd at 53mph, then keeps accelerating.... for what it is, the 425 does a great job at moving the car around. Once I do even a few mods (intake/carb etc...) I know it'll be running alot better too....