420a rebuild questions

[eclipsetuner23]

Okay so i think i bent a valve cause i have a knock! Now should i rebuild the entire engine so i can boost to about 300 hp? or should i just rebuild the heads to boost and get 300 hp?

 

[brassc2007]

the stock bottom end will not hold 300hp if you are looking to get that out a a 420a then you need to go with a forged bottom end and 8.5:1 or so, our compression is n/a and should be in the 9s or 10s and that wont work well with a turbo setup. Alot of people do good with the stock cams so you could put new valves, springs, and retainers in with a port and polish job on the head.

 

[brassc2007]

and are you sure you bent a valve does it run normally just make a sound and what type of sound is it is it a deep sound or like say a tink tink sound

 

[eclipsetuner23]

its a light tink tink sound not deep! and it runs perfect but slow acceleration from 2000 to 4000 rpms.

 

[99RedGs]

its a light tink tink sound not deep! and it runs perfect but slow acceleration from 2000 to 4000 rpms.

That is because it isn't exactly a powerful motor. You don't need to do anything to the head to reach 300hp. It has been seen up to 500hp in stock form. You should be able to hit 250whp on a stock bottom end depending on what you use for tuning and fuel. Most people say safe boost is from 8-10psi, but there have been people at 12 or so as well. Of course this all depends on the turbo you are using, but for the average turbo used in boosting the 420a 8-10psi is where you will probably be at.

 

[eclipsetuner23]

so i can stay with stock internals and hit 250hp?! and what about the slight knocking? what do i do to diagnose the problem and how to go about fixing it? i dont want to assume its one thing and replace that part and find out its another prob.

 

[Diablopaintball]

hey man i just got done rebuilding my 420 but before i had that same slight knock.... ended up being a rod bearing, and it spun on me over the summer. i suggest putting your car up on a lift and taking off the oil pan. Check each rod bearing for a little bit of play and also check for some metal particles in your oil pan

 

[toxicity883]

A light tick is usually a stuck lifter, try seafoaming your car

 

[eclipsetuner23]

Well i'm pulling my engine next week, i'm just gonna start doing my build now! But i still wanna know what it is and learn to fix it! so thanks for the info fellas i appreciate it a lot.

 

[Locke]

Bouncing vacuum readings is indicative of a damaged valve.

 

[eclipsetuner23]

how do i check vaccuum readings?

 

[#40Fan]

Go to a local parts store and get a vacuum gauge. Pull a vacuum line off of the manifold and hook the gauge up to it. Start the car and watch the need. Even post a video of it if you could.

 

[eclipsetuner23]

I will add video when i do this! i will be doing this work come Monday when my parts store is opened.

But which vacuum hose would be a good one to use? and what is gonna happen when i get it hooked up, what do i look for? thanks

 

[#40Fan]

Any of the hoses that are on the manifold, like the brake booster, PCV, etc.