How's the gas mileage with a TH400 and that high of a rear end gear? That's one of the areas I haven't come to terms with in my Pontiac 455 build. I'd like to keep the TH400 for cost purposes, but OD would be a huge plus too. I'd like something that can do ok driving across the country and still have decent acceleration.
Gas mileage is livable at 16-17 highway (75 MPH AC on etc) and at 8.5:1 compression it runs great on regular grade gas. I put 4000 miles on it on a trip back to Illinois back in May and was very pleased with the gearing going down the interstate.
I went with the TH400 primarily for reliability, although I’ll admit cost was a factor also. Building a 700 R4 or a 200 4R to hold 500 ft lbs of torque going thru it is possible, but I have read of too many guys still burning up high dollar rebuilds at that torque level. Personally If I ever do add an overdrive it would probably be a GearVendor (in spite of the transmission tunnel work that would be needed).
Acceleration is good (it’s not too hard to get sideways leaving a stop sign quickly LOL). A deeper gear would be a lot of fun but with doing mostly highway driving the 2.75 is a good compromise without an OD.
Out here the Interstate speed limit is 75 and most of our secondary roads are 65 (and honestly most people, myself included, drive at least 5 mph above that). When I’m back in IL with the 65 MPH interstates and 55 MPH secondary roads I feel like I’m crawling. If I lived back there I would probably have gone with a 3.00- 3.25 gear.
".....are the seats you have in there two drivers side seats out of a bench....."
Yep. My preference has always been low back bucket seats without headrests like found in the 60s cars but that supply is getting pretty dried up. I figured what the heck one day and set the seat from the Monte (which is 6 way power by the way) and the original seat from the El Camino in it and liked the way it looked.
The fact that I had them and the tracks dropped right into the existing brackets was just an added plus.
Gas mileage is livable at 16-17 highway (75 MPH AC on etc) and at 8.5:1 compression it runs great on regular grade gas.
I went with the TH400 primarily for reliability, although I’ll admit cost was a factor also. Building a 700 R4 or a 200 4R to hold 500 ft lbs of torque going thru it is possible, but I have read of too many guys still burning up high dollar rebuilds at that torque level. Personally If I ever do add an overdrive it would probably be a GearVendor (in spite of the transmission tunnel work that would be needed).
Acceleration is good (it’s not too hard to get sideways leaving a stop sign quickly LOL). A deeper gear would be a lot of fun but with doing mostly highway driving the 2.75 is a good compromise without an OD.
Out here the Interstate speed limit is 75 and most of our secondary roads are 65 (and honestly most people, myself included, drive about 5 mph above that). When I’m back in IL with the 65 MPH interstates and 55 MPH secondary roads I feel like I’m crawling. If I lived back there I would probably have gone with a 3.00- 3.25 gear.
I'm usually doing about 70-75 on the expressway too....we drive a little faster/crazier than the rest of IL up here :lol:
I guess the down side of torque is the potential to break things but it makes for a fun car anyway. The machinist that's building my engine is really pushing me to go with a TH400 (not to mention he builds them too) and a 3.08 gear. We'll see in the end I suppose.
Mike I am impressed with the mileage you get. Thats all most of the new big SUVs or pickups get. Mine got 17.0 on one tank and 16.8 on another on an interstate trip where we traveled almost exclusively 72 - 75mph. And mine had the much lighter more efficient 200-4R with working lock-up converter and a taller final drive ratio of 2.29. Mine also had more compression which is efficiency but on the flip side it had more cam which I'm sure didn't help the mileage. The thing I want to see is what yours runs in the quarter mile in its current trim & tune. I am not so much interested in the et as it has a lot to do with traction which might be an issue with an Elky but more so the mph.
Vern I really think the mileage has a lot to do with how I built the engine, which is to say resisting the temptation to do any major deviations from stock.
I spent a lot of time reading over any real dyno results I could find on different 500 builds and one thing that struck me was that any of the typical add-ons especially intake manifolds and cams while increasing HP numbers ended up moving the torque peak to higher RPM ranges and in the case of adding just an Edelbrock intake with no other changes actually led to a net loss in torque (but slightly higher HP numbers). The Cam I’m using (MTS 5) is actually pretty close to a stock 73 El Dorado. Basically from what I was seeing is that Cadillac pretty much got right as far as building the most torque in the 2000-2500 RPM range. From that point it was just gearing and tire size to put the truck at 75 MPH in that RPM range.
At some point I may take it to the local strip in this configuration, but not without changing tires to something that’s shorter and a lot stickier. Even then it’s not necessarily of “.... traction which might be an issue ....”, but rather how big of an issue it will be.
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