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Old 01-11-2004, 08:08 PM   #1 (permalink)
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Default Let's talk about the n/a 6G72 and its capabilities...

I figured this thread was a little too technical for the other parts of the forum, so I decided to post this in the Technical section. Anyways, I hope Gatecrasher agrees

I've been toying with the idea of rebuilding my engine over the summer, especially since it is burning oil quite profusely lately (valve seals are a big problem in these engines). So let's talk about these engines and the different things I could do to it:

First of all, to build these engines up can be very costly. With everything I'm wanting to do, it could cost me well over $3500 to fund this. That's why I'm very interested in finding out which parts are necessary and which parts are not. The list I have going for my engine is:

11:1 compression pistons, 3rd gen lifters, crower rods, ss valves, high tension valve springs, and later some hard-weld cams.

Now time for some questions:

1) Are new rods really that necessary if I decided to build a good street/strip motor? My rods are already forged out of the factory (my car is a 93), but am I taking a risk at throwing a rod if I don't upgrade them since they have 125k miles on them already?

2) Would it really be worth it to give this engine an overbore? In other words, would the extra .05 liters of displacement give me a decent gain?

3) What do you guys think about taking this engines high-reving capabilities to a new level? With some high tension valve springs, 3rd gen lifters, and other work done, do you think this engine could handle 8000 rpm safely?

4) One thing I really need to learn about is the concept of oversized intake and exhaust valves. Which ones should be bigger? I've only seen intake valves bigger than exhaust, but 3Sx also offers bigger exhaust valves than intake? What significance does the size of the valves have on the performance?

5) What parts of the engine yield the biggest gain?

6) What are some parts that aren't really necessary for high performance?

I'm really wanting to learn as much as I can about building up our engine to squeeze the most out of it as I can while keeping it streetable. Any answers/comments would be greatly appreciated.
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Old 01-11-2004, 09:36 PM   #2 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

I don't know. A lot of what you're proposing is pretty broad and has been discussed in some way in other places.

However, the search engine seems to be giving folks some problems lately, so I figure I'll just let this go for right now. It's not like we're swamped with posts anyway. I'll just leave it up to everyone else to choose if they want to discuss it or not. We also don't have any NA discussion in here, so hopefully this will touch something off.

I can say this much about the increased compression and overbore. I watched Eric Bowden dyno his car in Ocean City last year. He's got 11:1 pistons, a slight overbore (3.1?) and a few other things. He got about 167 to the wheels. Part of that probably had to do with tuning, but it just goes to show a pile of parts alone does not a powerful car make Your gains are really going to come from tuning and breathing improvements rather than any particular part(s).
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Old 01-11-2004, 09:59 PM   #3 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

Do not rebuild you motor. If you want power reliability and a everyday driver. Just buy a Jspec TT motor. The motor will drop right in and a few modifications and an ECU and your good to go (much faster than you could NA). Talk to some of the guys on the board that have either done conversions or swaps and you will learn fast. The best way to go as far as the 6g72 is TT. Even if you just leave a stock TT motor in you will surpass anything you could do to the motor NA (power and efficiency wise). You will be upset if you spend all this money rebuilding an NA and then loose to someone who did a conversion or swap (very upset). If performance is the key then your chances of beating a TT 6g72 with an NA 6g72 without using nos are slim to none. Look at how much money you have to spend and then search for a Jspec TT. Look at the costs involved in doing a swap vs rebuilding and make your choice. I had this debate about 6 months back and decided to just sell my NA and get a TT. The only thing I miss about my NA was the exhaust I had. I can fix that later when I put the same set up on my TT. Either way it is your money. My suggestion is get the most for your money and to me that is a TT motor. Same gas mileage and way more power. Talk to SLguy. He lives in my neighborhood and has an ATX with a TT conversion. Very quick car and he has no complaints. PM him and ask him questions about his car because it is an everyday driver. I am not sure, but I think the site for the jspec is Mr j's motors or something like that. Good look, and again do not rebuild. Start over with more (go FI). You won't regret it.
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Old 01-11-2004, 11:05 PM   #4 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

Gatecrasher - thanks for keeping this up for a bit. I tried searching for things like this but as you said, the search engine is being crappy right now.

KD - nice to hear from you again. Nice Stealth btw. As for your suggestion, that is another one of my options. My mind is fairly open right now. I wanted to either build up my current n/a engine or get a TT motor with the turbos and hook it up. I talk to Paul (SLguy) a lot and he can walk me through it if I ever decide to do the conversion.

But my original questions still remain. I'd like to know as much as I can about how changing the stats on the internals will affect its performance.
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Old 01-11-2004, 11:16 PM   #5 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

167 to the wheels? Was this an ATX or MTX? I thought we put down about that much to the wheels stock. I've seen dyno's around 200 fwhp with cams and a stock bottom end with a few bolt-ons. As far as adding power, I'm going the nitrous route with stock internals. I'm building the fuel system to handle a 150 shot and monitoring it all with a datalogger. The kit is already on its way. Also getting the WebCams race welds, 3sx frontpipe, and headers when they come out. I plan on getting a dyno session in B-Ham once i get all that on. Maybe I can break the 200 fwhp mark off the bottle.
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Old 01-11-2004, 11:19 PM   #6 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

Kibwe, thanks for the contribution, but I'd really prefer to keep these posts technical in nature. We all know the opinions on turbo vs NA and that whole debate. It's been beaten to death far more times than I like to remember. Maybe he just wants to build his car for the challenge of doing so. It wouldn't be the first time.


Let's keep it on-topic, ok?

Quote:
167 to the wheels? Was this an ATX or MTX?
MTX. ~167 to the wheels. We were all surprised. He really needs some engine management work and some breathing work.
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Old 01-11-2004, 11:34 PM   #7 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

Yes I agree that the hp number is rather depressing. I figured Eric would be putting out ~200 with his mods.

Gatecrasher - you guessed right. I wanted to do it for the challenge. When I saw what times WICKEDDREW pulled with his few mods (14.1 w/o nitrous) I was very suprised (although he is a great driver). The thing is, nobody has ever built these motors up enough to say whether higher times can be achieved or not, so obviously people are going to say "just go tt." It would probably be easier that way, but something tells me that these n/a engines have a lot of potential.

Since my first post was pretty broad, let me rephrase. The big reason for this thread is to enlighten me on what the best combinations to make a well-build n/a engine are. What would the best specs be to squeeze the most horsepower out of this engine while still keeping some reliability and driveability? And if I decided to do a rebuild, do you think I'd need to replace my pistons and rods, even if they seem okay?
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Old 01-12-2004, 03:23 AM   #8 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

something big has to be wrong with eric's car. i mean no disrespect but 167 is truly pathetic. he has a dohc correct?


i'm sorry, i don't consider myself a big gearhead as of yet, but perhaps as stated above someone will one day experiment with some higher revs/shifted powerbands. reading about custom camshafts and cam gears made me kinda wonder about what power we could get up top if someone was willing to explore some new ground.

my dyno runs from like a year and a half ago (94 3000gt base, ~90k miles, good compression, intake, 3sx pulley, flywheel) showed a fairly flat torque curve until around 5000rpms and a very sharp hp curve, falling at 5800. maybe we could move our peak ratings up in rpms. of course i'm talking about a higher compression ratio also. i just can't believe that eric's car only put down 167fwhp.

of course, don't make fun of me b/c i'm def. not qualified or learned enough to really contribute to this discussion...
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Old 01-12-2004, 06:44 PM   #9 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

Well, I am planning on going the N/A plus nitrous way. And as Gatecrasher said I am doing it just for the challenge of it. Now lets look at the options that a person like me (or Tyler) has. First as Kibwe Walker said you can go the easy way and TT the car. The next option is to build the car with the 6G72 and build the motor as you have sugested Tyler. I personaly would not go to the trouble of getting the Rods, I just do not see a point in it. I would rather have the spare money and a nice set of shot-peened (sp)* factory forged rods. On the third gen lifter issue if I do not ever do another thing to my car but keep it I will still put these in my motor just becuase of the fact that noises coming from any motor in any car I have really bothers me. Overbore for sure, even if it is small just to clean things up. The pistons for sure need to be forged in my opinion, even more so if you are going to spray it. The compression ratio is really up to you. If you are going for only motor then I would go 11:1 But if you are going to be "Chemicaly Asperated" Then I would not go over the factory 10:1 just for safety and life of the motor. On the high-reving issue I will not coment because I do not know anything about stuff like that, my car will never go over 7,000 RPMs. IF you are going to get serious then I think that a set of heads and cams will make or break a motor's HP. If staying with the 3.0 or 3.1 I would go with a set ported heads(not hogged out) and 1mm bigger on intake and exhaust valves. I can not say what kind of cam profile I would use, I need a cam selection program to play around with a bit to get everything right. Another option you have is the stroker kit that is avaliable to make your motor a 3.3 liter I think, there is a thread in this section about it so I won't make any coments on it. Now for my fav. option and the way that I will be going. I am planing on using the 6G74 3.5 DOHC motor out of a Montero. I have been trying to research the motor but there is not much on it. I am hoping that the crank is forged and I would say that the rods are more then likely fogred. I am going to do a rebuild of the short block with stock parts and a set of custom pistions. I will be going with 9.5:1 comperssion. The heads will be only the best, since the motor will be for nitrous then I will do as much exhaust work as possible and over sized valves. The cams will be a custom grind that I will work out with a selection program. The motor will be the most importent aspect of my car, thee will not be that many bolt ons just good old fashion "Hot Rodding" I will pair the motor with a set of long tube headers (even if I have to build them my self) and a MAFT for flow and tuning. I also take pride in the fact that I probably have one of the most advanced nitrous systems of the 3S world. I have full 6an fuel line off the filter to the rails along with a NX plate nitrous system (inbetween the upper and lower intake plenium) that can supoort up to a 300 shot. Along with this I have a dry kit that will be going on the car for the first stage right before the TB. I will leave off the dry kit which will be a 75 shot then hit the big shot ( probably a 150 ) at about the 330 line. This is the reason I am going with 9:1 compression so it will handle all the cylinder pressure. I am sorry to ramble on about my hopes and dreams but maybe it will help a bit. All in all I belive that the key to builing to 6G7x motor line if ou are really serious about it is the flow. If you are looking for just a good motor that is mild then I would build a stock shot block with a set of forged 10:1 pistions and a set of "Stage Two" type heads and a decent cam profile. Then put a 100 shot on top of it. Sorry for any spelling errors.
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Old 01-12-2004, 06:59 PM   #10 (permalink)
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Default Re: Let's talk about the n/a 6G72 and its capabilities...

Some good words there. I was thinking about doing a little bit of nitrous injection with the motor. So how about this:

Keep the stock rods and pistons. Port the heads and get 1mm oversized valves on both intake and exhaust, high rev valve springs, and hard weld cams.

I hear that our heads flow very well as it is and there is no point in porting them, but they would have to be ported to allow for bigger valves, right?

The only thing with talking about this is that we have never actually done it. If we could get someone to even halfway build the motor up and see what happens, people wouldn't be so skeptical.

I know a motor like this would never come close to dynoing like a TT motor, but if there was a way that we could adjust our power curve in order for it to have a more constant amount of horsepower, then we could see very nice track numbers.
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