I have finally decided to put an LS7 in my car but still want to take advantage of the basic LS4 external dimensions in order to fit the motor in my engine compartment with the least amount of fabrication to the passenger side shock tower and frameand to do so I have to use the LS4 crankshaft with the 3.622" stroke (the LS7 is a 4" stroke) - all journals are the same. Is the design of the LS7 pistons the same as the LS4 in regard to wrist pin location whereby allowing me to use modified to fit LS4 rods with the shorter stroked crank?Any help would be appreciated. Thankyou

 

you do relise by doing what your saying your going to be Destroking the motor. there fore it will change it some also.

As for the wristpins being the same or not i have no clue but im sure you can get a hold of a machine shop and see if they ahve a speck sheet on both and they might beabel to find it out for you.

or if you have a parts person around there go get one for testing the fitment of it.

 

Mickey: Thank you for your help. And yes, I do know that I would be destroking the motor from 427 to about 392/3. My goal ishigher RPM's andless torque. Just trying to figure out if the rods from the LS4 will work. Thanks again

 

just wanted to make sure ya knew some folks would not have relised this. and i didnt knwo C.I. with them inplace.

I would bet for specks that the dealer might have some on the rods etc..
the biggest thing you would need to know is the radius of the end caps etc.. to make sure they would be the same fit.

matter of fact see if you can find somethign with a rebuild kit for both motors that would include rods. you might beabel to call Northren. i have had great luck with them if i call they will messure it for you sometimes or read specs etc...
I would love for ya to make a jurnal on here of your project so we can follow along with the cars progress. and how ya do things.

 

Mickey: I have been speaking to a GMPP dealer here in town and to be honest their basic knowledge of specs is a bit lack luster to say the least and they have not been much help. I started my research on this project about 2 months ago and have flip flopped around a bit based on the research I have done. I am really trying hard to get answers to questions in this build project before the actual teardown to minimize down time taking notes and having problems solved before I run into them during teardown. I have heard of Northern but do not know where they are at - I will look them up on the internet - thanks for the referral. Currently I am working with a manufacturer on the block adaptor to transmission housing and have resolved that butstill do not have a solution to the input shaft/pilot spacer due to the crankshaft lengths I am dealing with. The engine compartment as you know is tight and adding 3/4" or more of length to the overall dimensions does not help, but a welded shock tower to frame loop to strengthen the notch made for clearance resolved that with the addition of a reinforcing bar from tower to tower. The next problem that I have is the reverse placement of the top half of the intake manifold. Iknow they are two piece but will my top half fit the bottom half of the manifold used on the LS7? Space constraints only permit me to use my setup as it came from the factory there is no way I can use a forward mounted air intake. As you can seeI have alot of work ahead of me. Thank you for allyour input.

 

Mickey: I did forget to mention that I do know that the rods on the LS7 are scalloped to fit the pistons - LS7 pistons are reinforced more so than the LS4 pistons. The LS4 rods are not scallopedand would have to be to fit the LS7 pistons.

 

i dont think that the ls4 pistons are the same as the ls7 i think that the wrist pins are not at the same place (i could be wrong as i never checked in to it personly)
i would think that the only way to do wat you are trying to do is get custom pistons

oh have you thought of geting your crank stroked and keeping your LS4 block you would still have to get custom pistons tho but you could keep the same block and crank so it would be that much easyer
check out http://www.flatlanderracing.com/cran...weldedstrokers
they do what they call a welded stroker it maybe worth looking in to it !

 

I'm just looking for clarification on this a bit myself due to highway laws and experience. Why are you looking to drop torque and add hp?

The reason I ask is because most people are concerned about their acceleration in the 1/4 mile on this board when it comes to modifications. Torque does that.

What you are looking at is going to be a higher top end speed. Don't get me wrong with that engine it will get you up there quick enough but I'm not sure of the usage of the higher top end.

 

88ss408: You are right there is a definite difference in the LS4 & LS7 pistons. I am not entirely sure either at this point but I think the LS7 is reinforced further with some inside webbing of somekind and the LS4 rods will not work with LS7 pistons - LS7 rods are scalloped to fit.As far as wrist pin location goes I am still investigating that. I can'ttell you howhard it is to get reliable information on the LS4 from a dealer, GMPP or GM Tech directly. I called the GM Tech guys today in Flint MI and they actually gave me the number to a company who is putting LS7's in thePontiac Soltice because they were not familiar with what I wanted to do. Those guys are strictly by the book , if it isn't published they really have a tough time assisting in engineering a project with you.

 

04 Intimidator: My logic on keeping my torque down relates directly to what I believe the transmission can handle even after modifications. My research tells me the transmission can be modified to reflect different gear ratios - thereby adjusting my ability to stillhave the car launchwell - and what I lose in torque I can gain in keeping the RPM's up.I believe HP is more manageable with RPM's rather than withstatic torque. But I am always open to suggestions. Thank you