1988 Merc 420's
 

Does anyone know what Brand parts they put in the Bottom End of these motors? Im going to be pulling a couple down in the next couple months. I see Crane Gold rockers under the covers, have heard Crane Cams, 800 Holley on Weiand Team G Intake. Rec Port Iron Heads. Anyone know what the stock Compression Ratio is? Thanks! Tim

I believe they are 8.8:1 with trw 2399 pistons gm dimple rods and gm forged cranks

Correct me if Im wrong....the 420hp motors are 496in? If so...would be an aftermarket crank?!

If not..I may just sell the COMPLETE motors? Was planning on Hyd Roller Cam..."better" Intake and Quick Fuel 850 carbs......

I will correct you then. They are 454 cubic inches

420 is a 454, forged crank, 7/16 dimple rods, forged pistons, rectangle port heads, Crane 132561 flat tappet cam, Crane gold rockers, some had Weiand Team G intakes, some had GM intakes, Holley 800 carb, and most had Gil exhaust.

Interesting! Thanks...ya...got the Gil Exhaust.....I may put these motors on the Market ant start from Scratch! Serious! If anyone oyt there is interested....one motor has 120 hours ...other gas 3 hours...yes...3! Have the build sheet from CK Motorsports they charged the previous owner $7K in the re-build...NEW Crank, cam, lifters, etc..... If I can sell these...and they run GREAT! I will start with new Dart Blocks and go NUTS!! hahaha Lets talk!!

WOW! where the heck did I get 496 in my brain??!! lol Probably cuz that is where I am leaning! lol Thanks

what are your horsepower goals? That is a pretty decent foundation to start with depending on your goals.

What is reusable in these motors for a little more power.Also is the components quality enough that you could reuse almost all of the motor on just a stock rebuild even the camshaft if it checked out.

Reason i am thinking is seeing all these older 420s up for sale has me thinking to sell my SBC CMI and tail pipes for 1500 and maybe get another thousand out of my fresh nothing to special 300 horse 355 and buy a 420 to put in my little 19 footer..

Dumping another grand into sbc heads to get 30 horse doesn't add up to me when i could buy a 420 for 3000 and do a simple rebuild for a grand if the motor is in decent shape to begin with and have a base if i wanted to build 500 horse later if I chose to.

For SOME reason...I thought these were 496 in motors?? As the SELLER "Advertised"??!! wont drag him through the mud yet! My "Thinking" was if I had a "good" bottom end....put some $$ in the Top.....600 to 625?? If I start from "scratch"...I can get there EASY....but this is just one of my "toys"....don't want to get crazier than I am.....lol Already bought Konrad Drives to replace the TRS's.....want PERFORMANCE with RELIABILITY!!

Tommy, the crank, rods, and pistons are all good quality parts. Essentially the same quality parts as used in the 500 HP carbed motor. I tore my starboard motor down at 680 hours and the only real problem found was a cracked head. Bores looked good but I didn't measure for taper or concentircity as I was boring it anyhow. The pistons looked perfect, the cam and lifters still looked excellent, it could have been very easily refreshed inexpensively. As a matter of fact, I could have just redone the heads and put it back in service with no worries.

Where you at?? I'll give you 2500 for one of those 420's

Thanks Matt

Just what I was looking for.

I used to run the old 330 in our parsail boats and we would get 4000 hours out of them with no problems if we kept the exhaust replaced After 4 years we would replace them just for the fact that they were saltwater motors and were on borrowed time. But they ran great after being removed, never tore one down as we scrapped them soon as they came out of the bilge.. Figured if these 420 aren't too much wilder than a 330 but with much better parts and had not been ran super hard that they should be a decent motor even after 100s of hours

Good to see that they don't need the heads refreshed at 400 hours like the hp500s

Oh yeah, forgot to mention the 420's were 4 bolt blocks. It is also the perfect compression ratio for a little boost. As a matter of fact, that is essentially what the Hawk 525's were, 420's with 174 blowers on them.

and i will match that for the other one.

TA...your somewhere arounfd holland...Mike and I will even pick them up...no shipping hassles!!!

il drive,you buy the beer!

Actually he is halfway between us, looks like we are meeting for lunch.....

Put a 500 Hp intake and carb on the 420 and it really helps. Also go .060 over if you need new pistons and get 468.

Wannabe

You can just do this to them. :cool-smiley-027:

Stock 420's= 67mph

Mild Thunder modified 420's= 90mph.

Great engines! I did this to mine..[ATTACH=CONFIG]531117[/ATTACH]

NICE! Tell me...what all did you do? Dyno test? I was "told" mine were 496's by the previous owner....of course, he wont return calls or e-mail:mad: Same boat I have! Mine is the red/black version

Good looking mill, Joe!

if i remember correctly the only thing 420 on your engines would be the block&crank.

anychance you could have the 496 425hp motor?? which would be a completely different animal. are you carbed or fuel injection??

I don't think so? These have rec port iron heads, 800 Holley, say 420 on the finned alum valve covers. Will have to tear into one to figure it out, or "try" to get the Build Sheet from CK Motorsports, the port motor has NEW Crank, etc....If they are indeed just 454's...they WILL go back in as 496! Hyd Roller cam, etc...

I did a roller cam and aluminum heads, there's a nice write up in the formula section. I documented everything with photos along the way so might be beneficial for you to check that out.

AWESOME! Im new here...Formula Section?

Dummy me....just had to scroll down farther...lol What is the Title of the Thread? would LOVE to read it!

Flywheel and balancer too! lol

What did you put on your boat for heads, and what did you end up speed wise in your 311. I'm really thinking about upgrading the heads and cam in my 292 w/420's to something better. I know you used the Teague Stage 1 cam, but I don't think you ever specifically mentioned what you did for heads other than they were aluminum.

I used the world products Merlin 3 310's ... Current speed is 74 gps but still dialing it in

Thats a nice speed gain. Are you still spinning the 25 Mirage Plus props?

Yes

I meant to say yes on the 25 pitch, but mine are non plus