cheap power improvements to the 425... - Page 5

77deville · #61 (**permalink**) 06-08-05, 01:12 PM

I have similar issues on my 77 deville with stalling when cold, but it runs smooth when warm. The problem cropped up recently when I tuned it up, replacing the fuel filter, etc. Prior to that, I only had a little trouble starting after it sat for a week.

Did you find a solution to this stalling problem?

I haven't begun to tinker with mine yet (only got it 3 weeks ago) so it'd be nice to know what to try first.

Thanks in advance.

Night Wolf · #62 (**permalink**) 06-11-05, 01:53 AM

simply put... rebuild the carburator...

besides the performance and fuel mileage benifit, on a 28 year old car, it would be a good thing to do anyway.... that should get rid of most your driveability issues too...

rdromano · #63 (**permalink**) 07-02-05, 06:44 PM

you said to bolt on some headers.
Who makes headers for the 425? How abot ones that will fit teh FWD Eldo?

N0DIH · #64 (**permalink**) 07-04-05, 03:20 PM

Anyone ever use a 500 cam or 472 cam in a 425? It would be a dirt cheap bigger cam.

The Ape Man · #65 (**permalink**) 07-21-05, 01:50 AM

Quote:

Originally Posted by N0DIH

Anyone ever use a 500 cam or 472 cam in a 425? It would be a dirt cheap bigger cam.

As far as I can tell, the 425 and even the 1980 368 used the same camshaft as the 472/500. GM PN 1486583.

Fleetwood472 · #66 (**permalink**) 08-12-05, 01:29 PM

For you guys that have problems with your 425's stalling on you or hesitating when they are cold I used to have the same problem with my 78 Fleetwood. The carb was rebuilt the engine was fine and I changed the plugs wires, cap, and rotor and it still ran like that. Well I finally found the problem and its very simple to fix. What was happening was my advance weights in my distributer were slightly rusted so when they were cold they would sort of stick together and the car would run like shit for like 5 minutes when it was cold. To fix this you pull the cap off of the distributer then remove the 2 bolts that hold on the rotor and you can see the advance weights first I cleaned them off with WD40 then I oiled them and pulled outward and saw if they would spring back if they would spring back I would repeat the process till they did. Then I put everything back together and the car ran like a champ. Hope this post isnt too old and you guys see this. - Justin

N0DIH · #67 (**permalink**) 08-13-05, 12:13 AM

HEI's had issues with the rotor burning through to the first thing they could arc to, the weights/springs. They took a hit. First sign that something is up is the rust color there. Keep the plugs/wires/cap and rotor in top shape, when the wires and plugs are weak, all the HV has to go somewhere, and the rotor takes the brunt of it. They should always be inspected closely.

WD-40 doesn't last too long, I would recommend some white lithium grease on the pins for the weights. They do wear, and will get oblong causing timing to get more erratic.

Glad you brought it up Justin, the HEI is an awesome distributor, and well maintained, will be a solid performer for almost any car, street or race!

Always inspect closely the cap and rotor wear. The rotor for burn through, and the cap for the HV arc to be stuck in one spot, that is a sign the mechanical or vacuum advance is not functioning properly. Always check the index of the cap too, if the HV arc is to one end of the cap contact, and never moves, (ECM cars are far more suceptable to this), and it is starting to arc off the end of the contact, the cap may need to be indexed. I did a post on how to in the Cad 4.9L/4.5L/4.1L section sometime back. It really improved the idle/low rpm drivability in my 85 Cutlass Olds 350 (was a 307) and the CCC computer system.

I have a "trick" good HEI mod (uses only factory GM parts) that really helps the starting and idle/off idle drivability in the HEI for high compression cars. If anyone is interested, let me know. It really works well with a non ECM HEI. Low compression cars it can help as well.

The Ape Man · #68 (**permalink**) 08-13-05, 12:44 PM

When the distributor machanical advance gets stuck on these engines the culpret is not the weights and pivots. The binding occurs between the long shaft which is attached to the weight's hub whose other end goes all the way to the cam drive pinion and the outer hub on the top of the distributor who's inner diameter is only slightly larger than the shaft that it centers on. Hope this makes sense. The point is that the proper fix is to pull the distributor and clean everything then reassemble with lubricant that will keep working. I usually just take the fast route and bathe the hub with WD-40 while working it back and fourth. Most times this works. I then spray a little fast drying solvent like brake parts cleaner into the distributor to get rid of all the stuff. When taking the quick route it will be necessary to keep an eye on the thing as it will get stuck again sometime. Dunno if any other GM products ever had this problem. Maybe the Cad distributors were built with tighter tolerances and it resulted in binding.

abcdefg · #69 (**permalink**) 08-26-05, 05:18 AM

Are you people trying to make me insane, with that familar sounding cad exhaust gurgle, and speedometer ripping from one side to the other video footage? Im still crusing around in a 1.6L diesel car

... If anyone cares to know, my 0-55 time on it was 20 seconds. I was going to do the 0-60, but it was taking waay to long so I just said screw it and stopped the watch. Also, I passed someone in it. Myes... 45hp to the ground, hit 65mph while doing it.

Im going into the airforce, and if it all works out for me, I should have some spending cash when I get back. Guess what im doing when I get back?

Latley I have been thinking of swapping in a cummings turbo diesel engine and trans into the '77 CDV. You know, save on gas and enjoy the 600Ft-Lbs of torque. But, I think id rather swap in a build up 500CI.

If the rest of you havent grabbed all of the 500CI engines out of the junkyard, then as soon as I can, I will certainly mash the go pedal on my diesel car up to spokane and rip out a 500CI or two, and bring them home on a trailer.

Btw, on ebay, there was a pre-hotrodded cad engine bored out to 514 inches for $6,000. Yeah, pricey, but it was shiney. They also had a blower to fit it for around $3,000. But, it was one of those real monstor sized blowers. That would really crap on my whole "keep it looking stock" agenda of mine.

These cadillac engines are wonderfull things. Hopefully, 4 years from now, gasoline wont be much over $3.00 per gallon.

eldoradoprime · #70 (**permalink**) 08-27-05, 12:08 PM

on my 78 coupe to get some more snot out of it....i ripped out the resonators and put a straight pipe with a flowmaster , i ran a good air filter and the A/C never worked so we took the pump off the the top end and fiddled with the belt arrangement...seemed to work rather well from what i recall

Night Wolf · #71 (**permalink**) 08-29-05, 03:31 AM

So if someone is going to swap the intake manifold...

lets just say they want to pull the heads and throw a cam, new lifters and springs in it...

while the heads are off, it would only make sens eto do some work on the heads.... right? then if so, what work?

If the object was to keep costs down, then would you even bother? yeah a valve job may help, but on an engine you don't plan on keeping that long? what about shave the heads slightly for boost in compresson? or is it the same idea?

Or if he heads were gonna get pulled, not even bother and just stick to the cam/lifters/springs etc... ?

BluEyes · #72 (**permalink**) 08-29-05, 04:12 PM

If you're not going to keep the engine that long, I'd leave the heads alone. They do not have to come off to swap intakes, so just leave them be.
IF you were to do headwork though, I'd have a bowl blend done, install larger valves, shave the heads, and then re-work the rest of the runners slightly (in that order) Have a pro do the headwork though unless you know what you're doing - it is easy to lose power with badly done headwork! This all gets real expensive real fast though, so might be best to save the $$$ for a motor you plan to keep around awhile.
Also, with a new cam, keep in mind to not go too big on stock compression. You'll end up killing your lowend. I really wouldn't go a step or two above stock without adding significantly to the comression. Follow the cam-makers reccomendations for cam selection and you should be safe.

Night Wolf · #73 (**permalink**) 08-29-05, 10:26 PM

yeah, I would have a shop do all the work.

It is just my "half way there, do it all" thinking... I will be installing a modifed 472 intake manifold and figured since I am there, see how much it is to do more... but I really think I'd be getting into more then I would like with the 425.

really, I am just trying to get a little more pep from the beast, the main purpose of the 425 though is to just be a reliable engine to move the car around until I drop a 500 in it... years from now... that also means that when the car comes to FL with me, the 425 will be powering it, I wouldn't second guess taking it to FL tomorrow, I know i'll do it, I just want to keep it that way and keep costs down also.

Night Wolf · #74 (**permalink**) 09-16-05, 09:13 AM

In case anyone is wondering, the stock 425 in a stock 1979 Sedan DeVille with 91,000 miles is good for a 17.5s @78mph in the 1/4 mi.

Chrome · #75 (**permalink**) 09-16-05, 12:51 PM

Quote:

Originally Posted by N0DIH

I have a "trick" good HEI mod (uses only factory GM parts) that really helps the starting and idle/off idle drivability in the HEI for high compression cars. If anyone is interested, let me know. It really works well with a non ECM HEI. Low compression cars it can help as well.

I haven't seen anybody ask yet, so what is this trick?

Thanks