Paddiee

I read the thread about swapping from a V6 to V8. I have a few specific questions, though. I got a GM 350 from a '72 Malibu and I have a 700R4 transmission. The engine was rebuilt before I got it and I am putting on a manifold, headers, and cam/lifters; everything else I'm keeping for now. Once I build the engine, I plan on putting it in the car ASAP. Motor mounts I know I need to get. Is there anything else that is mandatory that I get/do for the swap in order for it to work? My car is carbureted already and I scrapped the computer system. I don't care about air con cause it doesn't work anyway. I guess what I'm asking is if it is possible to just bolt the engine right to the trans with new mounts and call it a day.

chevyv8guy

No, u must change it to a v8 700r4 the bellhousing is a different size for the block and you will also need a v8 rad with the upper house on the drivers side, you also need to move the break line(as shown in the picture for v6 to v8 swap) you will also need to change the power steering pump and hoses to v8 ones i think thats all im not quite sure feel free to ask any questions if you run into problems but im pretty sure that is all you need

Paddiee

for the 700r4 i have, when i carbureted the engine, the lock up valve for the trans was something we didn't know about so the clutch packs got burned through on the trans. it was rebuilt or replaced, i'm not sure. but if it is the 700r4 that came with the v6, can i get some kind of adapter plate that mounts it to the engine? i heard the trans will bolt right up; i didn't know there was a different version of the 700r4 for a 6 cylinder. the power steering pump i can get no problem and the radiator in the car is oversized already. if i have any hang ups, i'll be sure to ask. thank you.

camaronewbie

The 700R4's were different between V6 and V8 - the bellhousing is different and a V6 tranny will not bolt to a V8 motor. You can get a different bellhousing to bolt it up. But - not sure if the internals on the tranny's were different as well - everywhere I read states that its not worth it to swap bellhousings and I'm assuming they mean because the V6 700R4 won't handle the V8 power. Everyone always just states it's not worth it and to just get a V8 700R4.

Also note - when tranny shopping - try and get a 1988+ tranny - there were some major improvements made late in 1987 to the 700R4 - there is a write-up in the tech articles about it, and what to look for.

Paddiee

okie dokie...so i've been doing some reading up on the matter and many sources are saying that internals of the TH700R4 on the 6 are the same as the 8. The only consistent thing that is said to be different is the bell housing and for 50 bucks, Summit sells one so BOP engines can mount to a Chevy engine and vise versa. I'll keep digging things up, but so far, many sources are saying that it should work no problem. I don't see why trannys would be different from a 6 to an 8 if an 8 is supposed to be easily switched with a 6. Thank you for the insight, though.

Pillsbry10

iTrader: (1)

they are different because the bolt to different engines... the bell housing is different as you know and the splines on the shaft are well. its really not as easy as to switch as it sounds. you have to change out your front springs as well

same goes with the manual transmissions

Pillsbry10

iTrader: (1)

https://www.thirdgen.org/forums/engi...swap-read.html

pretty sure its all covered in here

chevyv8guy

It will save you alot of headaches and time to just switch the transmissions out trust me if you do all that work the gears in the v6 tranny will not hold up to the power difference of the v8 then you'll end up spending more in the long run

Paddiee

So you're telling me that a 350 will destroy a 700r4 transmission...that makes no sense at all. I already read that article, it doesn't say that the internals won't hold up, it just states that the bell housing is different.

Paddiee

In the Beginning
The 700-R4 was first introduced in the '82 Corvette. On paper, its specs looked pretty good: The trans had lower First and Second gears (3.06 and 1.63, respectively) than other automatics, its lockup torque converter offered potential fuel-mileage gains, and the 0.7 overdrive decreased the overall drive ratio by 30 percent. But the original design was not considered a strong transmission, with failures behind even a mild 350 not uncommon. The trans was so weak that in its original setup, GM deliberately calibrated it to kick out of lockup and high gear under full-throttle, top-end conditions to avoid burning it up. The original versions had only downsized, 27-spline input shafts, one of many possible and common failure points. By 1984, 700-R4s intended for use behind small-block Chevy V-8s began to receive beefy, 30-spline input shafts similar to those found on classic TH350 and TH400 transmissions. From 1984 to 1987, the most failure-prone internal parts, from the ring-gear to the oil-pump housing, were upgraded. An auxiliary valvebody was added in October 1986. Finally, on performance cars like the Corvette, additional internal lubrication improvements permitted the trans to survive in high-gear, full-throttle, top-end conditions. Many of the improvements can be retrofitted into the earlier, weak transmissions, but the 27-spline versions need so many new parts that it's more cost-effective to swap in a later core. However, it is worthwhile to upgrade the later 30-spline versions to Corvette/IROC-level internals, if they're not already so equipped.

chevyv8guy

OK lets try this AGAIN, there are TWO 700r4's one for the v8 and one for the v6, also you CAN NOT change the bell houseing due to the fact it is a solid housing transmission. 700r4's are automatic transmissions unless you have a standard transmission that is the only way you can change the bell housings or the powerglide transmission which again is not a 700r4 SO if you have a standard transmission go ahead and change the bellhouseing but the gears will not hold up but if you have an AUTOMATIC you CAN NOT change the housing because it is a SOLID housing there is nowhere to unbolt the bell housing unless you are cutting it and welding on a new one...which again after all that work put in a v8 700r4,THERE ARE TWO ONE FOR V6 ONE FOR V8 BOTH WITH DIFFERENT BELLHOUSING SIZES...im not talking out my a** i would know this as i work in a machine shop and my dad has been working in a transmission shop for about 22 years

chevyv8guy

http://www.summitracing.com/parts/TCI-230000/
all this does is allow you to mount a chevy engine to a buick olds or pontiac transmission and vise versa, the 2.8l and tranny you have in that car now are both chevy so that adapter plate won't work unless you a putting a pontiac BIG BLOCK 350 in or an olds rocket 350, put if you are putting in a chevy 350 to that v6 chevy 700r4 that plate will not work its only for mounting a different engine to tranny not chevy to chevy..and yes i know all those a gm products but there blocks are mad differently

Paddiee

I'm mounting a chevy v8 to a pontiac trans so for me it will work.

Paddiee

scratch that, you're right. my dad is a machinist so he can fabricate something for it. i'm just in denial that it won't bolt up because this has been a huge project for me.

camaronewbie

Actually, no it won't. Pontiac hasn't made anything since the mid 1970's. You may have a Firebird, but you have a Chevy tranny.

Sorry I mislead you earlier on the swapping of the bellhousing - I was confused between the manual tranny's and the autos - other posts are correct - the bellhousing is solid on a 700R4 and there's no way to swap a bellhousing.

There's no way around it - you are going to have to get a V8 700R4 if you are going to put a V8 into that car.

Paddiee

Damn...well that's disappointing to hear. I apologize for being stubborn and thank you for cluing me in early before I started ripping things apart. Looks like I'm off to a pull yard.

camaronewbie

The V6 is a 60 degree motor (the V shape is a 60 degree angle), a V8 is a 90 degree motor, thus the difference in the bolt patterns on the back of the motor and the bellhousing differences.

Not all V6's are a 60 degree motor, but as far as I know all the 3rd gen V6 motors were 60 degree (2.8 and 3.1). The 4.3 V6 motor was a 90 degree motor and so a V8 could swap in place of a 4.3 without changing trany's I believe - the 4.3 was common on the smaller Blazer SUV's.

For all the trouble of fabbing something (which I've never read of anyone having done it), it would just be so much easier to get a V8 700R4 and call it a day. Around here, you can get them used with 90 day warranty for $500. Worst case scenerio is that it needs a rebuild in a few months, and if you shop around you can get a rebuild for $500 easily - in this bad economy there's got to be several tranny guys out there doing work on the side. I had my 700R4 rebuilt really nice for $500 from a local trany guy - it will now easily handle 500hp.

Paddiee

Yeah mine is a 60 degree. My dad works in a machine shop that makes parts for Boeing so fabricating a plate wouldn't be hard to do for him at all. I got a quote on a V8 700r4 for 300 bucks. It sucks for me on a personal level because my parents got my trans rebuilt for me for graduation this past May and I'd hate to get rid of it. It's got so much sentimental value now. I've got time before I need to get a transmission because we're still building and cleaning the engine.

chevyv8guy

im sorry for being rude about it but it was getting frustrating lol just make sure u get a 700r4 tranny and not a 4l60e(they are pretty much the same tranny) just the 4l60e was made in 95 i believe and it is computer controlled so it wont work with the carb'd engine either just get sometthing prior to 93 and you should be fine

Paddiee

Okay will do. Thank you for the information. If I have any other questions, I'll be sure to ask.