I’m new to this whole thing and i’m looking for as much info and helpful tips i can get. I plan to swap a ls3 into my 87 iroc this upcoming year. It has a 305 and a 700r4 trans right now. I’m wondering if i would be able to keep the 700r4 and use it with the ls3 and if so what would i need to do upgrade wise to make sure its able to handle the power from the ls3. if you recommend using a different trans all together, what would you recommend and would there be any upgrades needed for that trans to work reliably. That was my main question. However, i need as much help as i can get. What would i need to do fuel system and cooling system wise for this swap to work. I appreciate anything so if you’ve got any other info to help me with this swap i’d be glad to hear about it, thanks.

 

Welcome aboard. Spend some time reading the stickies at the top of the LS swap forum, specifically this, LS Swap Digest. This swap is very popular and is no different than any other LS swap. Most of your questions can be answered with some reading and use of the search function. Should you get hung up or confused, or have a very specific question, post up and folks will be happy to help.

 

First of all welcome to the board, there is a ton of information here. So much that it can be overwhelming when you first start researching. Check out the Stickies at the top of the LTX and LSX. I think everything you are asking is there and much more. There should be plenty of information there to get you started.

https://www.thirdgen.org/forums/ltx-lsx/

The 700-R4 can be made to work but it's not worth it and wouldn't last long behind a LS3. Go with a 4l60e or T56. The 4l60e would probably be the easiest since you are starting with an auto car. If you get one from a reputable builder it will last a long time. The 4l60e will fit nicely in the tunnel and you can get a transmission crossmember to match. I recommend the Holley transmission crossmember since it has clearance for exhaust. There are a lot of options with trans crossmembers and torque arm mounts...each with pros and cons, I think there is a sticky on that too.

The stock cooling system will cool a naturally aspirated LS3 with no issues as long as it's in good condition.

You will need to upgrade the fuel system, you can re-use the stock tank and install a different pump. Or you can get a new tank, pump and sending unit, there are several options. Make sure you do a hot wire kit or upgrade the wiring to handle the extra current that your new fuel pump will require no matter which direction you go on the fuel system.

As far as other stuff goes, I would recommend doing a lot of research on this board to develop a solid plan. Be realistic with your goals for the car and what fits your budget. You will probably want to upgrade the rest of the car to handle the extra power. Brake and suspension upgrades aren't mandatory but it's nice for the handling and braking of the car to be up to par with the the additional power of the LS3. Subframe connectors are highly recommended to reduce chassis flex. Use quality parts for a reliable swap. Be extra mindful of the electrical connections, use the correct method or type of connector for reliability.

There are a lot of us here who would love to follow along with the swap if you start a thread. That is also a good way to ask specific questions with pics. Hope this info helps, good luck with your swap!

 

As you start planning your swap try to NOT to think of it as an engine swap or even a drive train swap but as it applies to the entire car. Think about how it will impact the car from front to back. Adding 200 HP, changing the weight balance , wiring ,fueling, cooling , converter, drive shaft , differential ,exhaust etc. Have a written plan for everything you can think of and you will be less likely to be surprised or discouraged and more likely to enjoy the challenge. Have fun and good luck.

 

^^^^ Yep, this is mostly how we all learn from each other and where the most detailed advice are given.