Need advice for the 400 in my 69 GS. I'm wanting to keep this motor as it is the original #'s matching block & heads. The car has 82k miles that i believe to be correct. It is showing some blowby, & i have decided i want to pull it and build it up strong. What is the most realistic HP/torque build i can hope to achieve with this motor? The trans is a TH400 with 3:42 gears. Not sure what kind of stall it has. Budget is about 3K. Should i stroke it out, or would i be better off having port work done to the heads? I will also, most probably be going with an Edelbrock performer intake so that i can still use the stock air assembly. The original carb is not with the car, though i am looking for one. Would i be better off locating a correct q-jet for this motor (currently has a 68 GS350 q-jet on it)? Or, what kind would give me the best bang for my buck? Any help would be great! Thanks!:beer
I too have the original in mine and just went through the drill. Your budget is going to restrict you a bit, stroking it will eat up way to much money, you can probably build a 400hp relible engine with your budget if all your cores are in good shape and your skilled enough to do the assembly on your own, (if not build in another $1200-$1500 for shop assy and some limited dyno testing), don't take that part for granted though, it's likely that at least one of your heads is cracked as the original 400 heads are very prone to cracking on the top under the valve covers. Your timing cover will also be another big question mark, as will crank and rods. If your staying at or under 400hp there are quality cast pistons available but if you want to go higher then you'll need to go forged. I'm into my engine for about $4200 including headers, it's a 9 to 1 cast piston engine that with the new cam (old one flatted a lobe) will probably push 380hp as it made 330hp with the much smaller (flatted lobe) cam. I had two cracked heads, a severly pitted cylinder wall that required boring to 430, and a trashed timing cover, all the valves needed to be replaced and as of tonight so do the rockershafts (ok another $250). Probably the single largest bolt on bang for the buck will be headers. Good Luck
Re: 400 motor Thanks for replying Rob. I am planning on an Edelbrock performer intake. I am also planning TA headers. Not sure if i'm going with 3" mandrel or 2 1/2". I've been looking @ a Poston GS-113A cam since the car has 3:42 gears and A/C. What kind of pistons do you think? Rods? Just trying to get as many different views as possible. Thanks!
Thanks, Len. Your're right. I will probably go over budget, but doesn't everyone?:laugh: Don't get me wrong. I'm not going to be cheap and dirty about this, just looking for different senarios on how to achieve the best results. I was looking @ trying to stay in the range of 400-425HP and 475-500lbs/tq. Another question i have is, is that i want to run this on 93 octane. I know i need to have hardened valves & guides put in, but how, or will, that affect my compression ratio? You say your running 9 to 1's. I was hoping to keep the 10.25 to 1. What am i into there?o No:
Re: more info Rob, ALL recommendations are appreciated!:beer So, you think i could keep the 10.25 to 1 and just harden every thing up? Trying to stay away from booster if i can, but if not, oh well. What about the carb and fuel pump? Stock q-jet or go aftermarket? Been looking @ King Demons. Any experience with those? If i move up to stage 1 valves, what about the fuel pump? Did that cam sing well? What kind of mufflers did you use? I've heard good things about DynoMax.
Hi Rick You are starting very close to where I did 4 years ago. My '68 was showing pretty bad blowby and power was down. I found a junkyard 455 core and rebuilt it. Part of the reason was that forged 400 pistons were custom only and pricier than 455 slugs. The other reason was that it is pretty hard to compensate for the 55 cid you give up with the 400 and the 455 bore is larger allowing stage 1 valves to breathe. I found some used iron stage 1 heads for $500, put in the sealed Power forged pistons and GSCA club cam. With a Q-Jet, iron exhaust manifolds, stock intake, the car is now running low 13's on street radials. Total cost was pretty close to your $3k number. Don't forget all of the stuff you want to do to the rest of the car - you'll sink $15k into that thing if you're not careful. My numbers block is in a crate in the garage. The heads were mismatched on the motor - 1 '68 400 casting, 1 '70 455! Strange coincidence - my car also came with a '68 350 Q-jet on it! The transmission and rear are also yanked and piled up in the corner. It would still be possible to do a complete resto on the car with those parts. I can go out and have my fun in the meantime.
"my car also came with a '68 350 Q-jet on it! " John, Your car makes the fifth 68 GS400 I've seen or heard of with the GS350 Q-jet (both of mine had the GS350 carb and both appeared to be original installations), I'm beginning to think that either the factory had a surplus of these and just put them on 400's, or the crossreference documentation is wrong. I've yet to find one 68 GS400 that came with the proper numbered carb, the only ones that I've heard of are where guy's have went out and found the correct numbered carb and installed it.
'68 carbs Thanks for letting me know that Len. I always figured that the previous owner must have exchanged the carb at some point. I'd like to tabletop a 455 carb against a 350 to see if the references I've seen are actually incorrect. Do you suppose that the General actually installed all of those carbs on the wrong engines?
You know guys, i've been wondering the same thing. I talked with a guy out of MA the other day, & he told me that in the 20 yrs he's been collecting various carbs, he has only found 5 or six of the GS400 carbs (#7029242). He was telling me he thinks that most of these carbs wound up on the 430 motors. o No: My chassis manual states the only difference between the 350 & 400 carb are the metering rod size. I know trying to find one of these part #'s is a bear.I'm finding people with them but they want $500.00-$600.00/rebuilt & replated. Then, you have to pay close to $200.00 to have it modified.:eek2: That's why i'm looking into a aftermarket carb. Any advice on the King Demon? I see alot of chevy guys using them around here, & they brag em up. As far as sinking 15K into the car, i'm sure all of us have tried very hard to stay within a certain budget & blown right by it. It's all about having fun with the ride & not going bankrupt in the process!:Brow: I laid out a goal of no more than $11K for the car. Hopefully, by the time i get to that point, the car should be to my satisfaction. Not going for concourse yet. Just want a car that when i pull up to a light, I see every head turned toward it & follow!:Brow:
I'm certainly glad to find this forum and this thread as i am currently building a 69GS400 covertible motor. Block is currently undergoing sonic testing to see if we can bore to 430 specs. Both heads were cracked everything else seems OK so far. Regarding cracked heads... i now have some 8-10 small block and 400 heads that have cracked. Some were pulled off cars with no significant performance problems. I've hung on to them over the years thinking that someone might perfect a way to weld these. I'm willing to donate some small blockheads to anyone who thinks they have a technique. All my contacts say they can't be reliably repaired (and i could really use the space and make the recycling man happy at the same time). As for the replacement heads, i have a good set of 430 heads in the shop now. And the TA aluminum babies were certainly tempting...... I look forward to tapping the wisdon of this forum and note that ICAC-MAN is very nearby. .....will post more as we decide on pistons, oiling modifications, cams, etc wlund
If the cracks are on the top of the head over the water passages (most common area) then they can be repaired, but not by welding. There's a pretty widely used technique that my local shop calls "stitching", where you install threaded tapered plugs one right over half of the one next to it, then grind, and peen them down. This method eliminates the problems of Heat Affected Zone damage that often occurs when welding cast. One of my heads has this repair and doesn't leak a bit. If the cracks are in the combustion chamber then I would consider them scrap. Cost about $75 to have a 1" crack repaired.
And I guess I should explain that my user name is LCAC (Landing Craft Air Cushion i.e. Navy Hovercraft) Man, lower case makes it appear as an I. Where are you at?
400 Rick - My 2 cents - You will be very happy with a switch to a big block carb. The 350 carb will give you a rough idle and some flat spots. I know this is true for the 455 and assume it will also be true on a 400. A nicely setup 455 Q-jet carb is not very expensive (see John Osborne) and is great on the street. A 750cfm (69?-70 & very common) should work well on a 400 or you could go to the 800cfm found on 71-74 cars. If you are going racing, the other carbs can be better for all out HP. Also, installing hardened seats in some heads is risky as the water jacket is very close and you can punch through. And as Rob said, it is not really necessary. - Bill
LCAC-MAN, Sorry for botching your name and thanks for the advice on head repairs! I'm located in Poway Ca. just down the road from Camp Pendleton. I have several GS cars and a few large buicks. I'm currently doing a frame-off on a 69 GS400 convertible. I just got the numbers matching block back from being sonic tested before reboring to 430 specs (it tested ok). The block needs to be re-surfaced due to some gasket erosion which will take of the serial numbers....anybody know any alternatives besides re-stamping (or just giving up...)? I will be doing some of the oil gallery modifications shown in Steve Dove's book (enlarge main gallery, 5/8 pickup, ensure main bearing oil holes are matched, etc) I haven't made my final choices on compression, cam exhaust but i'm thinking of 10.2:1, Postion intake, TA shory headers and either a stage 1 cam or something like a TA112. The car will be street driven only. I would appreciate any experiences to share on the oil mods and the performance selections. I will advise as the block mods and machine operations proceed.
The biggest oil bottleneck is the short piece of passageway that is up the oil sender hole in the block. If you look at it and think about how oil flows thru all the passageways, you'll see what I mean. My only regret is that I didn't drill it bigger. I only went as large as I could without having to retap the sender hole. Now I wish I had. There's also a tech article on this at buickperformance.com, under tech articles (of course). Lots of good tech articles on that site, with digital pics.
