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To build bottom end, or not to build bottom end?

Stephen Shaw

Stephen Shaw

New member
So I had these big plans to rebuild my motor, but due to recent events I'm now broke and i'm looking to get my GP on the road as cheap as possible, and as soon as possible.

So the engine itself has 220,000 KMs (136,701 Miles), I was going to put all new bearings and piston rings in, but keep the orginal pistons and connecting rods.

Parts that I already purchased, and that I plan on putting in:
XP Cam/Valve springs/modified retainers/valve seals
timing chain/dampener
ARP Head studs

My thoughts are, if a spin a bearing, i'll take the engine out and find one with lowers KMs to put my cam and stuff in. If a pistion or connecting rod goes, it would have went anyways because they would still be the orginal ones.

I still have to pay $500 to have the car tuned too.

What are your thoughts? Are these bottom ends good for high miles?
 


Usually our bottom ends never take a dump until they've been messed with or attempted to be swapped. You should be fine.
 
If you have the knowledge, patience, and tools to check clearences and dimensions, then by all means re-build the bottom end, if not, find a REPUTABLE machine shop that is up to the task. If that is not a viable option than find a good-used factory short/long block and go from that as a starting point for an engine build.
 
^ This

The bottom end is not "magical or cursed" on the 3800, the only reason they would fail after a rebuild is ignorance. It's just like every other engine... if you don't know what you are doing, have someone who does do the work. I say have a GOOD machine shop work the block. If you are doing head studs, have them do a torque plate hone.

Sent from my Droid
 


Raven Autosports (James) is doing it. You guys probably know his car, the Cavalier with the turbo 3800. I'm located in Nova Scotia, Canada.
 
you shouldnt really ever need to tune a 3800 car beyond just flashing some garbage on it that makes it run right..... 500 for a tune is easily the worst way to spend money on your car.
 
Quicksilver is right. End of the day, the 3800 was built by someone on an assembly line. GM follows strict guidlines regarding torque specs & oiclearences. Thee 3800 is a very reliable engine because of this. And it shouldn't be a surprise that they are not reliable when these details are overlooked. Also, the variation of rod weight can be extremely wide. I found out that 1 of my l32 rods weighed 14.9 grams more than another (from the same engine). 14 grams of unbalanced weight at 6000 rpm is at least 600 pounds of crank flexing force from that 1 rod alone. This explains why some 3800's are fine being revved to 7k rpm, and some break at 6300. It is important to balance any 3800 that will be used with a big cam at high rpm. GM obviously didn't pay close attention to the balance, probably because they used pretty beefy parts in thier supercharged applications and they were intended to handle boost, but not necessarily high rpm's.

Tricky little bastards I tell you.
 


And no, dyno tunes are for goobers.

Street tuning or nothing. All a dyno is good for is for maximizing gains on a setup with AWESOMECOOLNUMBERSSS.

You don't go WOT everywhere, so tune your car on the street like it should be. In all sorts of situations. In every gear, at multitudes of different speeds.

darkhorizon said:
you shouldnt really ever need to tune a 3800 car beyond just flashing some garbage on it that makes it run right..... 500 for a tune is easily the worst way to spend money on your car.
Click to expand...

You never cease to amaze me.
 
well what do you REALLY do here?

Bump the maf around a little, bump the timing around a little, change the shift points and line pressure.

Not exactly $500 worth of work.

Tunes don't really do much with a 3800.

Its not like you can add 10* of timing and pickup power, or lean it out a point or two and pickup power, or increase boost targets and pickup power.

Its just not in the cards.
 
matt5112 said:
well what do you REALLY do here?

Bump the maf around a little, bump the timing around a little, change the shift points and line pressure.

Not exactly $500 worth of work.

Tunes don't really do much with a 3800.

Its not like you can add 10* of timing and pickup power, or lean it out a point or two and pickup power, or increase boost targets and pickup power.

Its just not in the cards.
Click to expand...

I picked up power from having all those parameters adjusted.
 
How much were these parameters adjust by? What sort of tune did you have beforehand?

Just looking at your mod list, you'd need a tune because you've stuck injectors in there with no known calibration (which are also of an ancient design, worse than the factory injectors), and a larger TB which some claim to have tuning issues with. Larger MAF also requires adjustments.

So I wouldn't doubt it was running pig rich or way too lean.

Tuning isn't magical. Get fuel and spark in order and you're done.

Feel like I'm repeating myself.
 
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The maf and injectors were dialed in upon completion of my cam install. Then my car was running pig rich with an afr in the mid 10's, so a full point was taken away along with bumping the timing a few degrees and the car suddenly felt like it picked up a good amount of power. I'm doing heads and an IC this winter, so I am assuming I will be in need of a better tune come then.
 


What you described is pretty basic tuning, nothing special.

If your tune was done correctly the first time, the intercooler shouldn't change anything.

Perhaps you'll need fuel a little sooner with the smaller pulley though.

But that doesn't constitute the phrase "better", just more accurate for your modifications.
 
So, wait...why are you rebuilding your motor? The way I'm understanding this thread, it's running fine. Correct?
 
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