6G74 help?

[Toasty]

There really isn't anything wrong with the DOHC other than normal maintenance needs to be done correctly and on time, they went to SOHC because Americans don't want to take care of Japanese cars (it will run forever attitude). The SOHC i think is a little better in the low end of things (around town and on the trail) but falls flat when you're trying to get on it out on the highway. Then the DOHC is way better on the highway and in town if you have a heavy foot, the DOHC really shines on steep grades on the highway.

I personally like the SOHC+good gearing

 

[IncorpoRatedX]

DOHC systems sound more complex...did they break? Why would they revert to SOHC?

My fuel is usually the cheap stuff (in the truck). Next time I'm in the mountains I'll fill w/premium...can you put a number on what sort of hp/tq change to expect?

switching back and forth from low to high grade fuel will do nothing.

The ECU develops long term fuel trims and by changing suddenly the computer wont just automatically bump up the horse power, it knows you've been treating it like **** and feeding it low grade fuel so it will keep the timing at a save level for low grade octane even if it has high grade fuel in it.

This thread is over as far as im concerned, if you're not running premium in your truck 24/7, you're the reason the truck is underpowered, that and the fact that it's a SOHC. Go reset the ecu, put in premium and drive it like that for a month. You should see a minor increase in power, but one thing I noted after buying trucks that were ran on 87 (continued to run 87 until i had a weekend to do a reset, fill with premium and drive a few hundred miles) was that the fuel economy went up by running higher grade fuel, the engine had to work less to make the same power so it became more efficient.

 

[SoCalMonty]

You won't see more than a few HP and a few lbs of tq between 87 and 93 octane. A performance engine (read: probably a boosted engine) will be able to maximize the higher octane, but an N/A truck engine probably wouldn't.

Additionally, though I don't have my owner's manual handy, I looked up specs for my 1995 SR and according to what I saw online, the factory recommended fuel is regular unleaded (87 octane). This would suggest the fuel and ignition maps aren't optimized for 91-93 octane fuel.

In other words, it would be barely enough for even the most sensitive of dyno-butts to feel, and if it's a big difference, then there's probably another reason for it (carbon deposits).

https://www.youtube.com/watch?v=gQghB4asSnI&feature=youtube_gdata_player

 

[SoCalMonty]

DOHC systems sound more complex...did they break? Why would they revert to SOHC?

My fuel is usually the cheap stuff (in the truck). Next time I'm in the mountains I'll fill w/premium...can you put a number on what sort of hp/tq change to expect?

In many cases, it's cost. The dohc engine is more expensive to produce, and when they realized they could get nearly equal power from a less expensive cylinder head, they went to the cheaper engine.

 

[IncorpoRatedX]

You won't see more than a few HP and a few lbs of tq between 87 and 93 octane. A performance engine (read: probably a boosted engine) will be able to maximize the higher octane, but an N/A truck engine probably wouldn't.

Additionally, though I don't have my owner's manual handy, I looked up specs for my 1995 SR and according to what I saw online, the factory recommended fuel is regular unleaded (87 octane). This would suggest the fuel and ignition maps aren't optimized for 91-93 octane fuel.

In other words, it would be barely enough for even the most sensitive of dyno-butts to feel, and if it's a big difference, then there's probably another reason for it (carbon deposits).

https://www.youtube.com/watch?v=gQghB4asSnI&feature=youtube_gdata_player

I guess i've got one sensitive butt

really though, a tuned butt will know the difference between full timing advance and minimal. I've tuned enough of the turbo mitsu engines to know the feeling of timing not being where it should. Though the manual says 87 is fine, i guarantee it's pulling timing on 87, turbo cars will do this much worse than NA cars, but there's no way the truck is getting full timing advance on 87 octane without the knock sensor feeling some ping and pulling the timing back.

 

[dookie]

This thread is over as far as im concerned, if you're not running premium in your truck 24/7, you're the reason the truck is underpowered.

That's awfully dramatic. I have no doubt that the ECU tweaks the timing, but I tend to agree with...

You won't see more than a few HP and a few lbs of tq between 87 and 93 octane. A performance engine (read: probably a boosted engine) will be able to maximize the higher octane, but an N/A truck engine probably wouldn't.

I have noticed the mileage improvement you mention, very slight & no ECU reset apparently required. I did not feel a difference in performance. Owners manual states 91 min recommended, 87 acceptable.

So seriously, no US-legal headers? How long should the main cat last (will it plug to the point of performance hit before it throws a code)?

 

[off-roader]

I run 87 nearly 99% of the time and I don't believe I have a power issue so I don't believe running 91 to be any kind of a magic bullet here. I suspect either A) you have real tech issues with your engine... or B) your expectations on the performance for this rig are miss-set.

What kind of other vehicles do you drive/have driven? If you're expecting to behave like a car or even some of the later model (read lighter and more powerful) SUV's, then you're expectations one power are probably miss-set.

 

[Mudrunner]

The best way to baseline your expectations is to drive others. I have the 3.5l in my 01 Sport and I have no problems even at around 90 finding more power. So maybe find another 01 like yours and drive it. See if it feels any different to know if yours has issues or not.

 

[IncorpoRatedX]

I run 87 nearly 99% of the time and I don't believe I have a power issue so I don't believe running 91 to be any kind of a magic bullet here. I suspect either A) you have real tech issues with your engine... or B) your expectations on the performance for this rig are miss-set.

What kind of other vehicles do you drive/have driven? If you're expecting to behave like a car or even some of the later model (read lighter and more powerful) SUV's, then you're expectations one power are probably miss-set.

91? that's mid grade, i was referencing 93-95 octane

 

[Clem]

91? that's mid grade, i was referencing 93-95 octane

Out here in California at the average pump we get 87 low, 89 mid, 91 high grade.

HTH,

Clem

 

[SoCalMonty]

91? that's mid grade, i was referencing 93-95 octane

91 is premium in CA. It was 92 up until 10 years ago or so.

 

[Mudrunner]

I was going to say most places in the west 91 is high with 89 being mid. I know the midwest has higher ratings. And people in Utah suffer even worse they 85 85 89...

 

[SoCalMonty]

I was going to say most places in the west 91 is high with 89 being mid. I know the midwest has higher ratings. And people in Utah suffer even worse they 85 85 89...

You don't need as much octane at higher altitudes. That's why you'll see 85 in Utah, Colorado, etc.

 

[MonteroLTD]

So why are the earlier ones quicker? They would have had the same 4s tranny, no? Lighter? How was the DOHC output & when was it in use? I'd hope a low-revving truck V6 would be more torque oriented...my Japanese rev fix comes from the Miata and TSX. And I definitely don't like the shift program on the 4s...it bails out of 1st before you're through the intersection (unless you paste it) and then holds 2nd FOREVER.

Gen 2 and 3 transmissions are not the same.

 

[dookie]

Gen 2 and 3 transmissions are not the same.

Even the 4s (which I have)? I know the 5s electronic one (in your LTD) is unique to the gen3.