I have a 75 Caddy (500ci) with twin, stock Grand National turbos. It has a stock bottom end, so they meet the need for now.

https://www.theturboforums.com/smf/index.php?topic=127787.msg1260008

I'm working on a forged bottom end for the motor and want to upgrade the turbo's when it goes in.

I currently have one Precesion TE60 with a .63 A/R exhaust housing. I called Precesion to order a mate for this turbo, but they thought these turbo's would be too small for my power goal of 800-900 rwhp. They reccomended a pair of 65 - 67mm billet turbo's.

I'm sure they would be ideal, but I started looking at the Master Power T-70's as a cheaper alternative but have a couple hesitations.

1. The rep at Precesion felt a 70mm turbo was too big for my set up. I've seen smaller CID engines running twin 70's succesfully, so would like other opinion's.

2. I was told that they only offer either .68 or .96 A/R exhaust housings (T4) but see .81 listed on their site as "coming soon". .68 seems small, and .96 seems large for twins. Should I wait for the .81 to come out or would one of the current housings match up?

Any help is greatly appreciated

 

A 500 caddy has a 4.304 stroke, so giving up a little bit of spool-up and going with .96 housings is a good trade off to me. You are going to need a pretty good sized set of turbine housings for an engine that big, and then base the compressors off of how much power you want to make. Looking around on Masterpower's site, a couple of T64s with Q-Trim T4 1.00 exhaust housings might be able to handle your power goals and the exhaust flow coming out of that thing.

 

I think you'll be fine with a pair of 70mm MP's with the 68 housing. Reason being that you probably aren't going to spin it to hard and the .68 would spool pretty quick and be a riot to drive in town. If this is your hooligan car or your street/strip toy - I would go with a pair of 70's with the .68 housing. Will be a riot to drive! Gotta think you're talking of feeding each 70mm turbo with an equivalent of 250 cubes.... Mustangs with the 4.6/281ci motors don't get all choked up with the .68 unless they are spinning em pretty good or making up over 500 at the tire.... Not a turbo guru by any means but I think you'd have a TQ monster and a handful with the smaller ones.