Swapping DOHC for 3X00

[jmgtp]

Forgot to mention... I plan on making the 3500 exhaust manifolds work - I'll have to build a custom crossover. Though it looks like some Impalas came with an LX9 and the crossover is the over the trans type, unless I'm mistaken and the Imp motor is a vvt. My engine is from a G6 and the headers available won't work in a W car. They might work if I built a modded xover for them too but I can't justify the cost of the headers expecially if they dont bolt right on.

[jmgtp]

Well, we have already established I'm crazy for pulling a perfectly running LQ1 out of the car so this should be no surprise. My real motivation to pull the heads is because this is essentially a junkyard motor: I want to see the cylinder walls before turning it over, clean the heads, and maybe do some really light head work. What I consider light headwork would be me removing casting flash and that is probably not even worth the effort...?

I suppose I can always change my mind. If I pull the rocker covers off and everything looks clean and sludge free then I may not pull the heads.

According to the power plot GM has on that site it looks like it should be making ~180 ft/lbs at 1000 rpm. That is impressive. I like the overall torque curve, pretty flat. Certainly will be different than the dohc, especially mine since it is modded for top end and lost a bit of low end. Torque is what is really important to a DD. Having some high rev horsepower to back it up just makes it fun when you want it to be.

[IsaacHayes]

Let me first say you are crazy for wanting to take it apart with only 52,000 on the clock.

My engine is somewhere over 220,000 miles, and sounds new. It was a bit noisy once, but that was a worn chain and guide. Now it's like it was when I bought it at 100k. The first part of it's life it was a rental/fleet car. Then it was DD'ed towing a trailer back and forth 60mile round trip until I bought it and then have ever since ran the loving piss out of it. I've never let it warm up in winter, just fired it up, and hammered it in a hurry. It see's 5800 RPM probably at least 10 times a day. Other than the timing chain and intake gaskets (now metal) it has not given me any trouble. I'm surprised the trans has lasted this long too, which I've abused just as much.

Considering I got the car with 100k on the clock and then ran it hard every day in town since then, I think you are CRAZY for wanting to inspect a 52k engine.

If you want reliable, just get the metal LIM gaskets, throw them on, and be DONE WITH IT. That's all you'll have to do to the motor until maybe 160-180k or so when you might want to replace the timing chain.

And 220hp is probably obtainable with a good exhaust and tune. You might need more than 3400 log manifolds for that, the 3500 ones would be better, headers would gain you at least 20hp. Depending on how crippled the stock 3500 tune is you could pick up a lot from the tune if you don't care about emissions.. You will have a big increase in bottom end torque with this motor swap, so if you shift it conservatively, you will have no problem pulling with low RPMs for MPG.

6200rpm is the redline stock. 200hp at 5400 RPM, 220 tq at 3200 RPM.
http://media.gm.com/division/2005_pr...ain/index.html scroll down there is a power plot in PDF format.

The 3.5 even though it's 2 valve, has tons of torque and lots of top end power. I don't think you will be disappointed.

[jmgtp]

Sounds good... pulling the heads is back on the table. I'll use the 3400 headgaskets and the 3500 metal intake gaskets.

I wasn't even sure of the 'stock' 3500 redline. Is it 6000? Where do they peak anyway? I'd love to see a stock or mild modded 3500 dyno plot if anyone has it.

[1QUICKHATCH]

I am using 3400 head gaskets on my 3500 in my alero. they will only work with a stock bore 3500 because the edge of the gasket lines up with the edge of the cyl wall. Should give the 3500 a very slight increase in compression!

I know I'm probably giving up 50-60 horsepower and some revs and that sux to think about.

you are probly giving up 100 lbs and only 1000rpm depending on your tune!


I got 30mpg on the high way in my Alero doing 70mph 90% of the trip. It would probably be better with 2.5" exhaust (or any thing bigger than the stock 2") a larger TB and a tune.

I am using a 3400 plenum right now and 3400 exhaust manifolds on a stock 3400 tune.

[jmgtp]

$150 sounds a lot better than $300.

Autozone has 3400 headgaskets for $44 for both. Then I would need the Felpro metal gasket for the lower intake (think it includes upper intakes as well?) $80 at WOT Tech and then head bolts another $60 I think... So I'm looking at $180-200 in gaskets.

can anyone second that 3400 head gaskets will work? i imagine the only difference is the bore size and the difference between 3400 and 3500 is probably negligible.

[bszopi]

I am pretty sure you can get by with 3400 head gaskets on a 3500. But still look at spending $150+ in gaskets.

[jmgtp]

thats easy enough to get back, just talk to superdave about what he's done...

I know it can be done but that is straying away from my goals of a solid daily driver and will far exceed my budget.

Are 3400 head gaskets the same as the 3500? The WOT-Tech store has a headgasket set for the 3500 for $160 but it looks like the lower intakes included are the plastic ones - meaning I'd also buy the $80 felpro metal gaskets + head bolts ~$30-50 and I'm looking at near $300 in gaskets if I pull the heads off... yikes!

I want to tear the heads off and have it all be fresh and clean. I may consider some really light head work... meaning me just removing casting flash. I don't trust myself enough to reshape anything.

The dohc head gaskets were something like $15 each! Maybe the expensive gasket cost is the falldown of the limited run LX9! I can't find headgaskets listed at the big chain stores for this motor.

My goals right now in order of importance:
-reliability
-fuel efficiency
-performance

What do you guys think a stock LX9 with 2.5" mandrel bent exhaust and maybe a 65mm TB, as well as a good tune should produce? I think 220hp/220tq (crank, not wheels) is in the ballpark. What about mpg in a W car with a getrag 284?

[robertisaar]

Oil pump drive o-ring is a 60V6 issue, not just a DOHC issue. Granted, it is somewhat harder to repair on the DOHC, but that wouldn't cause me to list is as a major issue with the DOHC.

and i thought i was the king of splitting hairs

i'm just saying those are about the only two problems that commonly hit a LQ1, and people swear them off as pieces of shit.

I know I'm probably giving up 50-60 horsepower and some revs and that sux to think about.

thats easy enough to get back, just talk to superdave about what he's done...

[jmgtp]

Just to clear up... I keep up with maintainance on the DOHC, meticulously. It is in great shape. No knocking or ticking and loves 7k rpm. You may think I'm crazy for pulling it - I do. I am pulling a perfectly good running engine out of the car. It hurts me to think the heart of the beast that I've had for so long is going away. I still think it is a great performer, responds well to mods, and can last a long time. I want to keep it and put it in something else someday but I really don't have the space to store it and certainly not the space for a 4th car.

The problem is, that mine is 18 years old and regardless of make, model, engine, whatever - 18yrs is a LONG time for a machine. I think that the fact that my engine still runs perfect, on an all original bottom end is a testament to the dohc and should silence the naysayers.

BUT... it is still 18 years old and anything at all can go wrong. I can spin a bearing tomorrow. I dont think that will happen, but I can't say that it won't. My goal is to build this car to be as reliable as something that is new. So with that, an 18 year old engine is at the top of the list to be replaced. I know I may have said I am "getting my reliability back" and I'm eating those words now. It has had its share of failures but for the most part it has been reliable. Mechanically speaking with regard to just the engine the ONLY thing that has ever broken is a timing belt tensioner and a few lower/upper intake gasket failures. That is it. Never had a bearing, lifter, cam or any other kind of problem. Sure it's been through alterantors but that really isnt the fault of the DOHC. If a timing belt on the DOHC scares you, then you don't belong around cars. It is easy to service timing belt setup.

For me to keep the car I need to KNOW that it will be reliable in the future without question and that is not something I can say with an 18 year old engine.

With the LX9 now in my garage it looks like it is half the size of the DOHC. The big heads, cam carriers and massive manifolds on the dohc really make it look huge. I know I'm probably giving up 50-60 horsepower and some revs and that sux to think about.

[bszopi]

Oil pump drive o-ring is a 60V6 issue, not just a DOHC issue. Granted, it is somewhat harder to repair on the DOHC, but that wouldn't cause me to list is as a major issue with the DOHC.

[pocket-rocket]

I know that's not the case with John though. I've been talking with him for a few years now on here. But yeah, for the most part, you are correct sir.

[robertisaar]

people don't keep up with maintnance on a 3.4 and the belt takes a shit or the oil pump drive seal starts leaking....

i guess that qualifies as unreliable.

[pocket-rocket]

But I am getting back my driveability and reliability and keeping it 60v6.

I dunno... it just confuses me why everyone thinks the DOHC is so unreliable lately. I asked my friend that was over earlier when the last time he heard my car was down and he said never. Maybe I just got the best 2 out of all of them were made because I haven't had many problems with mine despite their age. I just hope you enjoy the 3500 as much as you did the DOHC. I'm not knocking the 3500, it's a great engine (and has an aftermarket).

[jmgtp]

Picked it up this afternoon.

It is pretty dirty. Once it is on a stand I will likely tear it down to the head gaskets. I want to see the shape of the cylinder walls before turning it over. There is a plug in every vacuum, water, intake and exhaust orifice so I feel pretty safe that dirt moisture didn't get in. I'll be disassembling and cleaning the heads too (How much are HG for this engine?).

Mandatory engine dangling from the hoist pic: