7mgte block build help

[Dark Knight 56]

i have a 7mgte with 020 wiseco pistons. there is a spun bearing and im going to send the block to get machined. The pistons were in the car when I purchased it and this is the first time i will be tearing apart the block. Now im not sure if there are rods in the block, but i wouldn't understand why someone would put 020 pistons and not aftermarket rods. Im planning on getting a Master power T70 turbo and i wanna know what are some good ways to build a powerful reliable block. Im looking to stop around 500- 600hp..
I was told about sharp edging the crank?!?!?! Are there aftermarket (lighter) cranks? Other than pistons and rods is there anything else that can be done to the block other than going with a bigger piston?
I didn't spin the bearing and that pisses me off in its own right, but at least i can build this block the right way and know exactly whats in it.
Thanks for all your help & input......

 

[Victor Charlie]

Budget? Goals?

 

[Dark Knight 56]

Budget? Goals?

Budget...ummm not sure. I'm willing to spend the money to do it right. I'm not planning on going into this block again so I wanna do what I can.. I already have the pistons @ 020 & I don't wanna go any bigger. Not sure about what rods are there. Im gonna purchase eagle rods if rods Are needed. I'm trying to build a really powerful, reliable block. I wanna eventually install a t70 turbo.....
My goals are anywhere between 500- 600. But I'd be happy with a 450hp car. I have no clue what that would feel like. This won't be a track car, only a street car. Won't be racing for any $$$ just beating up ricers & any other challengers. All for the fun of a fast, top off, sunny day drive!

 

[Dark Knight 56]

Anybody??

 

[Boosted7M]

as far as the crank goes i havent really found like anything but the stock crank i been told can handle alot of power safely...im in the same boat as you but im building just to build...nothing wrong with my motor now but building another just to have more power :naughty: have you thought about your plans for the head aswell? anything currently done with it? youll have to do that to match the rest of your beefed motor...plus with those numbers you wanna get ittl help alot.

 

[Dark Knight 56]

It already has a stage 1 port & polish. Grinded cams & a 3amgle valve job... Down the road I'll do a full port & polish & titanium valve springs & retainers

 

[Victor Charlie]

The only crank swap I have heard about is a 6M crank, found on early year 7M engines as i understand it. It is supposed to be lighter for a slightly higher redline, and probably a bit more vibration.

Your power goals are a bit beyond the safe range for the stock pistons. The stock rods might take it, but you are in the upper range of what I have heard of people doing with stock rods. I would do the rods if they haven't been done, just to be on the safe side. It depends also on your tune and how much you are pushing the envelope on ignition advance, compression, etc.

I'm pretty sure your plans for the head are more than sufficient for your goals. You need to measure your combustion chamber, measure head and block height, and get numbers on your pistons to get accurate compression ratio numbers. I have just researched this myself, so I'm not speaking from personal knowledge. What I have gathered is that you can get away with stock compression 8.4 and run enough boost to get to 600hp. I'm going with a bit higher compression, because I am aiming for less power but more midrange torque and fuel efficiency. Some people lower compression for high boost, I believe, but I would think you are safe to 600hp without doing this.

Most of the high power builds get the big numbers from high boost, but it's a great idea to rework the motor from the bottom up like you are doing, if you are looking for longevity as well as power.

Here's an excellent build thread that should help. The only thing I wonder at is not regrinding the crank with the rebuild, which I have heard elsewhere is always a worthwhile precaution:

http://www.supramania.com/forums/showthread.php?t=5631

 

[whitemike]

The only crank swap I have heard about is a 6M crank, found on early year 7M engines as i understand it. It is supposed to be lighter for a slightly higher redline, and probably a bit more vibration.

From my research on cranks, I've found that 6m crank is lighter but usually very unbalanced. If you get the 6m crank balanced you should be good to go. If not, stick with the 7m crank. Apparently the earlier model 7M's that had this crank had a +500rpm redline above the ones with the 7m crank.

Again, this is from my research I haven't verified any of it.

-Mike

 

[jdub]

From my research on cranks, I've found that 6m crank is lighter but usually very unbalanced. If you get the 6m crank balanced you should be good to go. If not, stick with the 7m crank. Apparently the earlier model 7M's that had this crank had a +500rpm redline above the ones with the 7m crank.

Again, this is from my research I haven't verified any of it.

-Mike

You guys should really refrain from posting in the tech section unless you are 100% sure. The 6M crank is not "very unbalanced" - it has 2 less counterweights than the 7M and is lighter as a result - that is why it's red line is higher than the 7M crank. It did came on the earlier model cars - most pre '89 and some 90 motors. The 7M is smoother due to the additional counterweights - it can be lightened to weight less and is easily balanced by a competent machinist. IMO the 7M is the more desirable of the two.

 

[IJ.]

6M

7M

Lightened 7M

 

[Dark Knight 56]

Thanks for all the input guys. I might just get the crank reground & leave it otherwise intact...
Reliability is important as well as power.. I'm a just get a set of eagle rods & call it a day

 

[whitemike]

You guys should really refrain from posting in the tech section unless you are 100% sure. The 6M crank is not "very unbalanced" - it has 2 less counterweights than the 7M and is lighter as a result - that is why it's red line is higher than the 7M crank. It did came on the earlier model cars - most pre '89 and some 90 motors. The 7M is smoother due to the additional counterweights - it can be lightened to weight less and is easily balanced by a competent machinist. IMO the 7M is the more desirable of the two.

I didn't think it was a problem if I pointed out that I hadn't verified any of that information- which I did point out.. Sorry.

-Mike

 

[supraguy@aol]

IJ- How much weight was shaved from that 7m crank?

 

[jdub]

I didn't think it was a problem if I pointed out that I hadn't verified any of that information- which I did point out.. Sorry.

-Mike

If it's not verified, then what is the point?

Regardless of whether you point it out or not, this is exactly where "I heard" comes from and increases workload for the moderators...not to mention what it does for the OP's quest for a correct answer.
Do us all a favor and just don't post "I hadn't verified any of that information".

 

[WhtMa71]

The pistons you have might be .020 over, but do you know if they are forged? Chances are, if your block is already bored .020 over, it's going to have to get bored even larger to get the ring gap and piston/wall clearances right. Even a light hone to break the glaze on the cyl. walls can be enough to take it out of spec.
Just wait till you get word from the machine shop. Find out what pistons you're running and they correct clearances recommended for them by the manufacturer and tell your machine shop. They'll tell you if it needs to be further oversized.

 

[suprarich]

OP - You can call me at 330-541-1122 m-f 9am to 4pm and I would be happy to explain eveythng you need to know in great detail.

 

[IJ.]

IJ- How much weight was shaved from that 7m crank?

5>6 Lb's from memory

 

[whitemike]

If it's not verified, then what is the point?

A starting point for the OP's search for the answer? So he can verify it?

 

[figgie]

Folks,

tech secton

facts or don't post.....

 

[whitemike]

Sorry, won't happen again.