1978 GP 301 to 400 swap
 

Helping a friend do this swap. Against my better judgement. AS he has a great running 301...
Keeping TH350 in place using most of the usable 301 parts. AKA Timing cover. He has new intake and carb etc..

Anyway, what are the best exhaust manifolds to get. I told him that I refuse to install headers. If he wants them later he is on his own. Anyone have a decent set?

Also any other information you might have would be great.

Thanks,
Dave

Mad Dog makes them is several configurations. Does good work.



Rick

Dave, unless someone's changed the transmission it's a metric 200 tranny, not substantial enough for the 301 let alone a 400. You'll need a better radiator more than likely. The cheapy 3 tube headers fit this swap. RA III manifolds or the logs will work. Dual exhaust is going to require a different or modifying the transmission crossmember. Gear ratio is probably less than optimum unless your going for gas mileage The rest is probably pretty straight forward.

The 400 is about 125-150 lbs. heavier so the front springs may need help if they're marginal already.

Yeah, the tranny is not my worry. He installed a B&M shifter for a TH350, so I have to assume a TH350.

Which chepy headers? Are they easy to install? You know how much I LOVE headers..

These type headers: http://autopartsway.amazonwebstore.c...source=froogle

I think they're easy to install, easier than 4 tubes are. There are probably other brands of 3 tube headers, these are the ones I found right off.

The shifter can also be used on a TH200. To see if he has the 200 (3speed), look to see if it has the word METRIC stamped into the pan. The 200 and 350 have the same shape to the pan, but the 350 one is larger (and is mounted with 1/2 headed bolts) vs 13mm. A 350 will also have a vacuum modulator, the 200 does not. "Full length"Headers stink for a mild street application(IMO).:gag: 3 tube "Shorty headers" shouldn't be too troublesome to install. For manifolds, I would try and use log manifolds for an earlier "A" body car (ones where both exit out toward the back and not the middle). Eventually, the rear end may be a weak point. While he drives it, I would be on the search for a 8.5 unit from a Buick GN or "T" type. Most '78-'87 "A", "A" Special, and "G" cars have a 7.5.:2cents:

i would not use the 301 timing cover. i'm pretty sure if it even fits, it will only fit without a balancer. some low horsepower motors (77-78) had a hub instead of a balancer. way to tell, is those had bolt on timing marks where the good ones have cast on numbers.

Anyone have any radiator suggestions?

A factory replacement "heavy duty" cooling radiator should do fine. It kept a high compression 400 happy in my car when I was street driving it. The 3 tubes "may" fit. The tube that kicks around the starter on the drivers side might touch the firewall. The mad dog headers do fit well. I also think the R.A.R.E long branch manifolds would probably fit as well.

read this: http://gbodyforum.com/viewtopic.php?...header#p142332

OOOOHHHHH...... Looks like I will get log manifolds. The header thing he can worry about later...

For the street I am sure the logs will be more than enough..

THANKS!!!!

I'm running logs on my 85 and easy to set the exhaust up. As far as a radiator I got one out a mid eighties Cutlass that had a 307 Olds with A/C. Three core will work to keep it cool.

Which logs? A-body?

yeah, for ease of fitment and street use, log manifolds are fine, and so are HO manifolds. IMHO...and yes, use like a modine heavy duty radiator for an AC car--3 row with the AC 7 blade fan and a hayden 2747 clutch.

oh, and make sure its a th350 trans, or you will be replacing that 200 metric with one in a short period of time...:)

I asked him yesterday and he assured me that it was a TH350..

Thanks!!

All log manifolds are not created equally.

There were some produced with a significantly larger collector area, but dadgum If I know which ones. I've seen them here, and while they are well off an HO or 4-tubes, it's a good option for a street driven cruiser. You can always go back and change them out when you get a chance.

good point..and i agree..some log manifolds have a larger outlet than others, and i cant remember which ones do offhand either..but that is correct...good ones to use tho are the early 70s ones with the cast in donut and no heat valve.

Mine are from a 400 out of a 73 Grand Prix.

Mine are off of a 400 out of a 73 Grand Prix. A body manifolds will work fine.

I replaced the 301 in my 78' Grand Am with a 76' 400 from a Trans Am. I used the log manifolds from a 77-78 Trans Am despite the 301 manifolds looking like they will fit. Because the 400 is wider, the 301 manifolds keeps the front pipe too close to the brake line, so you need the 400 manifolds. I used the motor mount brackets from the 301 Grand Am engine as they are different than the F-body brackets. My car already had a TH350 but I changed the 7.5 gears from 2:14 to 3:08. I used my 301 radiator and it works just fine....but then again we don't get the heat like you guys get. The 400 I got is from a 4-speed TA so it already had the larger harmonic balancer. I have since replaced the air breather to a drop base 2" type. My car has pictures of the restoration under that Gbody site (I don't know how to post the link) if you want to have a look. BTW, you will love the feel of the 400!