Hello and thankyou for allowing me to join the forum. I was given my grandfathers 75 Grand Prix after he had passed. Ive had the car for 3 years now and want to start some upgrades and give her some much needed tlc.

Edited May 3, 20224 yr by Thomas75gp
Made it shorter

Sorry to hear about your grandpa. Good it’s kept in the family 👍

Whats the plans for GP? 

I really want to do an engine rebuild. The engine doesnt knock or smoke. Wondering what would be appropriate fun hp. also thinking about maybe a 4l80 swap or 700r4 for some more gears that would be able to handle the weight and torque if i could  even find a bellhousing adaptor and was hoping to find some info on that here if anyone has done it. All of which i am planning to do this winter but for now mainly wheels and tires, looking for opinions on a little wider tire/wheel then stock 225 and a guage cluster swap. i believe there are 76 or 77's that have a cluster that have the four center guages with readings for engine oil, voltage, coolant temp instead of warning lights. 

Edited May 3, 20224 yr by Thomas75gp

Welcome to FP !

You could go with an adaptor kit and a TH700R4, or you could find TH200-4R overdrive transmission that will bolt directly to your Pontiac engine without an adaptor kit. You will have to shorten your driveshaft a couple of inches either way and move your transmission crossmember a couple of inches since the 200 and 700 case is slight longer than the TH350 or TH400 case. 

IF you go with the 4L60/4L80, you may have to beat/cut-and-weld-up the transmission tunnel to make room for the much bigger transmission.  Plus you will have to add an electronic transmission controller, in addition to altering your driveshaft and moving your crossmember. While these are great transmissions, this is much more expensive transmission swap in my opinion. I'd stay with the 200/700 option. No controller and less fabrication means more money for bling elsewhere.

You have a J model Grand Prix. That was the base model for the Grand Prix in 1975 - hence the idiot lights. If you can find a dash from a SJ (Sport) or LJ (Luxury), you should be able to find the gauge package you're looking for instead of the idiot lights, even for 1975. Look online in eBay, Hemmings.com, Facebook Marketplace, craigslist, and your local swap meets. I know there are several active Pontiac and GTO clubs in Minnesnowta. Look for their car shows or go to the bigger car shows and swap meets in the state. 

I would recommend getting a tool to measure your wheel wells and wheel offset before purchasing new tires and wheels, or talking to someone at your local discount tire dealership and letting them measure it up for you. The last thing you want is tire rub or cutting your new tires on the fender lip. Ask me how I know? LOL!

 

I forgot the 4l80s had a tcm and i do agree they are massive. I have found a few lj and sj clusters for sale on ebay before. This car has not been on my mind for a while so i feel better about about this project. i think i will try and see where or when some classic car meet/swaps are happening or even pontiac ones. Thankyou for being helpful, just the information/ opinion i was looking for!

I forgot to mention that if you get the gauges, you will also need to switch sending units/sensors on the motor as well. So expect to do some wiring changes too, to go with the cluster upgrade.

Edited May 4, 20224 yr by Frosty

Welcome to the site.  Great Pontiac to work with there.