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Old 04-07-2011, 08:01 AM
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TH350 Crossmember-

I am still in the process of gathering all the parts I need, and trying to build on a budget here..from a v6 to a v8 swapping engine and tranny. engine is done and is waiting for the tranny..only thing is ill need a special crossmember to mount the diff tranny. it had a (v6)700r4 so i had to swap it out also. My question is if i could use the existing one but fabricate it or alter it to fit? any suggestions?

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Old 04-07-2011, 11:31 AM
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I found this while surfing, couldn't get the link for the page to work, so I copped it, I hope it helps you.

1. Anything the V6 bolts to, and anything that bolts to the V6, will be different than the V8. Only possible exceptions are AC compressor (but the hoses and brackets will be different), alternator (early V6's were different, and again the brackets & wiring are different anyway), and power steering pump (guess what - the brackets & hoses are different).

2. Emissions-legal is harder and more involved than non-emissions legal.

3. It isn't "easy", "quick", or "simple". But, many of us have done it, so obviously it is possible. Follow general disassembly discipline; take pictures before and during disassembly, label everything as you take it apart, and it will be a lot easier to put back together..

4. A donor car that came from the factory with a V8 is the best way to get all that is needed to do the swap, whether or not you use the engine and/or transmission from the donor car. It's best if the donor is the same model (Camaro or Firebird) as the receptor car. It's also best if the donor car is at least the same year or newer than the receptor car (this is doubly true if the swap is to be emissions-legal). At this point, the simplest answer is, "Everything that's different between the V6 & V8 cars, change it." But, if you insist on knowing more details, keep reading.

5. The V6 rear end is as strong as a V8 rear end, because they are the same design. Only the ratio and/or posi/non-posi are different. Often, the V6 came with a more desirable ratio for performance than the V8's did. If you want posi, a PowerTrax can be installed with common hand tools. See the Tech Articles for beefing up the factory 10-bolt rear end for engines with higher horsepower than factory.

6. You may be able to use the radiator that came in your V6 car if the upper hose connection is on the driver's side and the lower connection is on the passenger side (the 3.1 V6). Otherwise, get a V8 radiator.

7. Forget about using any of the factory-type V6 exhaust on the V8. This is a perfect opportunity to upgrade to headers and high flow cat on back. A good choice for aftermarket exhaust is '86-'90 TPI single cat application headers, cat, and cat-back, even if your swap doesn't match that description. Otherwise, use the donor car pieces.

8. If the transmission you are using didn't come from a 3rd or 4th gen f-body, you're going to need some means of mounting the torque arm. B&M makes a bracket that uses the tail shaft housing mount bolts for a TH350 or TH400. A good upgrade is a cross-member/torque arm kit from our site sponsor Spohn (see sponsor ad on right). The TH700 tail shaft housing can be swapped, so if you have a non-f-body TH700, you can put an f-body housing on it.
Side note: Transmissions from 4.3 liter Chevy V6's will mount to Chevy V8's.
V6 T5 transmissions can be used behind a V8. But, you will need a V8 bell housing, and the input shaft is smaller than V8 T5's - meaning you need a small-spline clutch disk (reports are there is a 10" S10 small spline disk available), and the transmission will be very weak and will not stand up to V8 abuse.

9. If you are doing a computer-controlled swap (which is the only emissions-legal way), the engine control module (ECM) from the V6 won't work without modification. Use a V8 ECM, change the PROM, or have the computer reprogrammed.

10.The V6 tachometer has a different resistance than the V8 tach. You can change the resistor, but it's typically easier to just get a V8 tach.

11. You may be able to modify the engine harness from the V6, but it's usually easier to get a donor harness. The ECM harness will come out in one piece. Remove the plastic fender liner from the passenger side, and you can get access to the pass-through grommet/connector. Unplug it (take off clip from the inside). In the engine compartment, I disconnected and labeled everything that went to the engine, and unbolted sensors that went to the car (again labeling where they came from). Then, the entire harness w/sensors can be lifted out from the car and installed in the receptor car. (Note: The pass-through plug and therefore the pass-through hole on my '82 was smaller than my donor '86. Don't know when it changed, but I believe they're all the same size at least from '86-up. All I had to do was take a file to the '82 hole and enlarge it until the '86 connector fit.)

Part of the harness comes from the driver's side. The engine-specific part will separate from the chassis part so you can install your engine part from your donor.

If you are doing a non-emissions/non-legal swap, you'll typically need ignition power (if you started with external coil, the positive wire to the coil), tach (if so equipped), alternator, oil pressure, coolant temp, and possibly radiator fan wiring. All of these can be used from the existing harness, and since you labeled everything before you started taking it apart, you'll know which ones these are. There may be some length changes required. If your V6 was not carbed, you may need to find or make a switched 12v source if your new engine's carb has an electric choke.

12. The engine mounts are two pieces; one half bolts to the chassis cross-member, the other to the engine. Both are used on other GM Gen I SBC vehicles such as full-size B-bodies, trucks, etc. You can get the engine side new from the factory, but they are expensive. The only part of the chassis side you can get new (that I know of) is the inserts, either factory-type rubber or poly. The chassis half is mounted to the rear-most holes for the V6, and the forward-most for the V8. Getting to the mount nuts inside the cross-member is easiest when the front A-arms are dropped, but figure on using a spring compressor if you go this route (see #14, below). Otherwise, figure on sockets/extension/u-joint/very small hands/lots of time/many colorful words getting to those nuts (check this thread for a possibility in making the job slightly easier (Motor mount installation tip) ). The right/front brake line mounts to the front of the cross member for the V6, right where the V8 mounts need to go. Either use the V8 factory line, or carefully bend the line to the rear of the cross member after the mounts are removed from the V6 position. The p-clamp mount holes are there for the V8 position for this line. Side note: '82-'84 used SAE-type brake fittings, '85-up used metric.

These pictures show the V8 mount and brake line positions on the cross member:
Driver's side

Passenger side

13. If the V6 is fuel injected and you are putting in a carbed V8, the fuel pressure will need to be lowered using a 3-port (with return) adjustable fuel pressure regulator. Or, drop the fuel tank and remove the in-tank electric fuel pump. If you keep the electric pump, be smart and use an oil pressure safety switch. Depending upon the V6, you may have to rewire the in-tank pump when the ECM is disabled. Also, if you eliminate ECM control and have an overdrive auto tranny, you will have to make provision for the torque converter clutch lock-up.

V6 and fuel injected V8 fuel lines go up the driver's side frame all the way to the engine compartment. Factory carbed V8 fuel lines cross from driver's to passenger side in the transmission tunnel. If you're going carbed with a mechanical pump, consider keeping the lines on the driver's side and crossing over on the front of the cross member - it should be a cooler environment than the tranny tunnel and exhaust system. I used rubber hose with a slip-over braid for pressure, just rubber for return, and found some nifty nylon tie wrap anchors that you just push into a 1/4" drilled hole and then strap the tie wrap through it. Nifty. Remember, if you intend to drag race, rules limit the amount of rubber line you can use.

14. Most likely the V6 power steering gear will be fine. Just remove the pressure & return hoses from the gear and attach the V8 parts to it. There are some performance steering gears out there that the V6 probably doesn't have, but your donor car probably doesn't have it, either.

15. If your car has auto tranny and AC, and is intended to be driven on the street, use V8 front springs and sway bar. Otherwise, you'll be bottoming out the suspension regularly.

Last edited by richard stewart 3rd; 04-07-2011 at 11:39 AM.
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