I know Jason A has discussed this before but just wanted to revisit it. The Montero SOHC 3.0 V6 sits at approx 150 HP while the Diamate 3.0 SOHC output is 175 HP. How is this extra 25 HP achieved exactly?

The reason I'm curious is my wife's 89's engine was replaced by some previous owner with what appears to be a diamante engine. I've came to this conclusion due to the valve cover configuration(matches diamante in 6G72 rebuild manual) as well as the timming belt cover (which I've since resored to the Montero correct cover). The Timing sprockets are cast not stamped so I know its not a crysler mini van variant. from looking at the rebuild manual there's an supposed to be an H code on the cams of the Diamante and a G on the Montero Cams. I guess I should of looked for that when I changed the Valve cover gaskets <img src="/forums/images/graemlins/lol.gif" alt="" /> The Distibuter, intake and exhaust are Montero correct of course and the engine runs very well and seems curiously peppy. Should I be running premium gas in this engine if its diamante? Change in timming? I guess this requires further investigation on my part.

Diamante compression ratio is 10 to 1 so I assume that is where the majority of power increase comes from..Reading up on the Diamante shows a fuel requirement of 87 octane so I should be good to go running regular unleaded.

Nope.... the increase of 1.1 CR yields only 5HP:

Bowling & Grippo CR/HP Calculator

The main difference is in the camshaft grind.... plus it's also likely that ignition timing is a little closer to the curve for best power. I don't think I'd run 87 octane in a 10:1 engine, but all engines react differently.

Here's the FSM that covers the 6G72 SOHC 12v and DOHC 24v variants in the Diamante and Montero, including the differences in the SOHC FWD and RWD engines. Note the difference in valve timing between the SOHC FWD and SOHC RWD cams:

6G72

Frank

Frank, Yea that was the FSM I was scoping out when I realized the valve cover/timing cover config was identical to the diamante. The alternator brace shown in the FSM near the bottom of the engine was also there(with nothing connected) which I removed when I did a timming belt job to the engine I got curious. Frank in your opinion do you think the 89 ECU will be able to adjust to the diamante configured engine to take advantage of the HP potential? I've been running 89 ocane maybe I should make the switch to premium till I know for sure. Do you know exactly wher on the cam this designation mark is? Thanks..

I don't know, but my instincts say "No". The '89 Montero ECU has a very conservative ignition timing curve.... and the curve is based on the valve timing of the Montero heads. A change in valve timing can require a change in ignition timing to make maximum power, but I suppose if the difference isn't too great, ignition timing might not be a huge issue relative to valve timing and the '89 Montero ECU ignition curve MIGHT allow you to run 10:1 CR on regular grade gas without damage, but it's a guess at best.

The injectors appear to be the same flow rating. The Montero injector is a B210H and the Diamante is an N210H - both are 210cc/min but there are 2 questions:

1) The injectors may have different impedance values which would not work unless the correct injector was paired with the ECU.... not a big deal as long as you're aware of it when replacement time comes.... the Nippon-Denso manufacturer's number is cast into the injector, but in the case of the Montero's B210H, the Denso number is actually INP-051. The Montero injectors are high impedance.... don't know whether the Diamante injectors are high or low impedance and I've looked in several reference places, but can't find anything on them. I did see in another reference that there are 2 injectors used in the SOHC Diamante engines: '92-'93 uses MD156760, '94-'96 uses MD189023..... neither are the same as the '89 Montero's MD111421. If you want to solve that riddle, you can pull an injector electrical connector and measure resistance across the 2 terminals..... high = 10-16 ohms, low = 1.7-3.0 ohms.

2) Even if the injectors have the same impedance, the two computers may have a different pulse width programmed into the processor for similar load and rpm metrics - particularly since the HP is different..... more HP at a given rpm and load requires more fuel, so for the same size injector, the pulse width needs to be longer in order to feed the HP need. Could the o2 sensor trim enough to make up the difference???? Dunno.

I don't think you can figure out anything by looking at the cams unless you put them on a degree wheel.

Why don't you remove the ECU from under the passenger side dash and see what number is on the ECU case? That might tell you a lot.

If Charlie is reading this, maybe he'll chime in - he knows the Mitsu engine variants pretty well.

Frank

Yea whoever did the swap was sloppy as they switched over the Montero Alternator bracket and intake as required, but didnt bother to swap the montero valve covers or timming belt cover. Probably just a sloppy job which is kinda good in a way because if they did a good job I would not be the wiser. If they swapped the intake from the montero over I'm thinking that most likely the original montero injectors were used but I'll do the resistance check to see for sure. Most likely what I'm looking at is a Diamante long block intalled with all the Montero externals including ECU. Just trying to confirm to ensure I'm doing the right things. So your saying the cam designation mark talked about in the FSM of "H" or "G" is not visible with the cam installed? Yea I was thinking Old Colt may have some insight as well.

The casting markings are located so you can see them when installed - but there are so many marks, I don't know if you can make sense of it all. Here are Chrysler mini-van cams - there are more marks than what you can see in the pictures:



One cam is marked in various places with 22/1/A/K/F. The other is marked with B/F/K/20/3.

"K" sounds like it could be the designation for Chrysler, but I'm not sure.

If you know what to look for, I guess you can figure it out. I think I'd want a Montero cam for comparison.

Note that if the block contains the 10:1 pistons, it's probably an interference engine - so be careful.

Frank

I'm looking at a diamate engine,,,see a post yesterday,,,,
Would a good machine shop have a book that gives different part numbers and specs to tell the difference in the cams.
I was gonna grab the dia engine , mainly for the heads ,,but I don't want them if they are gonna give me peak torque at a higher rpm.

Torque peak would be different. As an example, here's the Montero/Raider compared to a 3000GT SOHC 12v:

Montero/Raider
143 HP @ 5000 rpms / 168 lb-ft @ 2500 rpms

3000GT SOHC 12v
164 HP @ 5500 rpms / 185 lb-ft @ 4500 rpms

I'd guess the Diamante specs to be similar to the 3000GT.

Frank

What are the internal differences between the 2 to get this power out of what would appear to be an identical engine? Compression ratio? Stroke? Injectors?