suggestions for 1968/9 400 rebuild

I just got a call back from the machine shop saying my GS 400 engine cleaned up and checked out OK and is ready for the rebuild (+0.020). I will be reusing the crank and valves and connecting rods (I think), all else will be replaced. I want to rebuild it to basically a stock engine, but would add a little performance if it was a small increase in price. I am trying to keep costs down. I am looking for recommendations for a set up and a supplier or manufacturer of parts. The machinist was surprised at the cost of the rebuild parts he came across so I told him I would post here for some more info. Thanks

 

http://www.v8buick.com/index.php?th...rted-stage-1-heads-machine-shop-fresh.321558/

I have this for sale, have a couple people thinking about it. But pic the cam of your choosing and should have anything from a nice warmed over stk rebuild, or one like we ran and have a pretty good street/strip car. The custom grind cam even though it only had about .500 lift had enough overlap that to run power brakes might be an issue, but feel it was a perfect cam for that setup

 

Don't just go with a .020" over bore because it's the least you can go!
Your spending hard earned money on new bigger Pistons and bore size to get back good ring seal and if going .030" over allows you to run a ring size that will just drop in without any gapping that may have been needed with only being .020" over , then you will have far better ring seal and ring life at .030" over

 

I've bored several 400's to standard 430" bore size.

 

Camshaft selection, distributor recurving, and carburetor rebuild/recurve are going to be the best low-cost improvements you can make. To make real power increases you need more head flow, or more compression, both of which cost $$$. Most of the "off the shelf" pistons out there are probably going to lose compression compared to your stock '68-'69 stuff- I'd pick what you want for pistons very very carefully.

The absolute bottom line in Buick speed parts is TA Performance. Their website is not great- what you want to do is get a paper catalog, or download a PDF of the paper catalog from the website. They have lots of flashy stuff like AL heads and what not... but they also have a good stock of just the ordinary junk that 10 years ago you could get at a parts store, and now you can't. Gaskets, pushrods, fasteners... you name it, they sell it.

If your machinist is a Chevy guy... he is just going to be shocked by prices throughout this rebuild. Buick parts just cost too much, it's something you have to either accept, or get out of the brand.

 

Even a low cost , but well executed bowl porting job with get enough added flow to make 400 HP out of a 9.5 motor with a 228 @.050" Cam

 

My machinist says he can get cast pistons and the rebuild will be a 9.5:1. I believe it was originally a 10.25:1. He said a car wont run well on today's gas at 10.25, and 9.5 is the way to go. Is he correct? I was not expecting to drop compression. BTW I asked to have it rebuilt as a more or less stock condition driver.

Stampy - Good advice. any particular suggestions for pistons? Cam?

 

Not many aftermarket choices for BBB 400 pistons these days for a 3 model years engine.

If you can get away with not boring the block and just re-honing it you can re-use your cleaned factory pistons if there isn't to much wear in the bores.

Or another way to be able to re-use your pistons is to have them coated;

A NEW CLASS OF COATINGS
INTRODUCING APC™ ABRADABLE POWDER COATING™

• Reduce Clearances & Improve Efficiency
• Thickness 0.0007" - 0.020"+ (18µ-500µ+)
• Build it Tight - Wears in for a long term fit
• Self-Lubricated
• Maintains Oil Film
• Low Friction
• Scuff Protection
• Tolerates Foreign Particles
• Proven in OEM and Race Applications

http://www.line2linecoatings.com/

The last time I checked it cost IIRC $40 a piston to have them coated so $240 for a set. The machine shop I have my machine work done by have used the coating for some of his high end customers and has heard back that they love the coating and will definitely use it again. IIRC I think one guy when the same combo was re-dynoed with the now coated pistons he said there was a 20 HP increase with the coating being the only change! This was a high HP turbo build I think the output was in the 950 HP range so with an engine with half that output isn't going to gain as much maybe an extra 5 HP and plus you get to re-use something that you can't buy anymore!

I would hazard to guess that if your engine was rated @ 10.25:1 it actually would have about 9.4 to 9.9:1 if everything is measured. Plus if you don't have the deck milled and you use the felpro composite gaskets that are .020" thicker you will lower your compression ratio by .3 to .5 of a point making it even more pump gas friendly. You can't get anymore stock condition driver than re-using the original pistons coated if they are still in good enough condition for that process that is.

If you want it more like the factory built it to be then just have a minimum square deck cleanup making both sides the same and use the felpro composites and the amount removed from the deck the composite gaskets extra .020" will make that up. This will help maintain valve train geometry and enable you to re-use the factory pushrods as long as your shop doesn't sink the valves in to far which would push the tips up to high.

If you go with the "9.5:1 replacement pistons" I suspect that your engine won't run as good as it did before this rebuild. Unless you spring for a set of customizable forged piston and ring kit like the AutoTecs that are $649 vs the $240 plus the cost of a set of rings if you get the originals coated.(who says that the engine can only be original once?) GL



Derek

 

I got lucky on eBay about 10 years ago, and found a set of NOS Sealed Power 2362P pistons. They were produced for 1 year only(?) as a direct replacement for 1970 455 pistons, and they match the advertised factory 1970 10:1 compression ratio. All other off-the-shelf ~$300 455 pistons I have seen are the deep dish, 8.5:1 style. With resized rods and a fat head gasket I am at about 9.7:1, which is really as good as you can hope for on a half-assed, minimal-amount-of-machining build like mine. I am sure if there exists an equivalently magical solution for the 400, it is equivalently hard to come by, unfortunately.

I personally don't have any experience with piston coatings, but that does seem like an appealing route to try to avoid the expense and compression loss of aftermarket pistons.

You can have your machinist deck your block to bring compression back up with the off the shelf pistons, but it ends up being a huge cut (0.050" or more). With that big of a cut the heads start getting too far apart, and the intake doesn't fit right anymore. That problem can be managed... but it's a problem.

The least frustrating 10:1 route is probably to get custom pistons. Call TA Performance or Tri Shield performance, and I am sure they can set you up with the right thing. It will be $$$ though...

I think that with the right cam, distributor, and carburetor, you'll make more power than you did before, even if you end up losing some compression. The whole aftermarket piston situation is a nightmare, and for a stock rebuild you probably shouldn't get stressed about it.

For a camshaft, I'd called TA Performance and talk to Mike or Tim. For your application I bet they will recommend TA-112, maybe TA-212 if you can actually keep the compression up like your machinist claims. You can read about TA's cams in their catalog, page 60 or so- it's pretty educational.

For the distributor, I'd go read Larry's timing thread in the Buick FAQ section, if you haven't already. If you can make your distributor deliver the timing curve he describes, you'll be pretty well off. If not, there's people on the board who recurve them. I am running a Pertronix Ignitor III in my distributor that seems to make the car run a lot better than it did on points, but that is a pretty controversial 'upgrade' around here. You'd have to read up on it and make up your own mind. I like it because it's pretty stealth, compared to something like an MSD box.

 

We found 10.25 cast pistons, as well as 9.5 in .20 and .30 over The machinist says 10.25 will not run well on today's fuel, and being cast, he would not recommend. So, I can get either, any opinions? You guys out there that are running original 400 configurations - do you have detonation problems with modern fuels?

Also, he said the coating option mentioned in the reply above would not work because the ring lands on the old pistons are too worn.

Thanks again for your replies.

 

Many "replacement" pistons have been deliberately sabotaged in terms of pin height. The piston industry calls this "destroking" the piston. Of course, it has nothing at all to do with crankshaft stroke. The pin height is moved upwards in the piston, so that the piston doesn't go as far "up" in the bore.

This reduces compression, but also destroys the cylinder turbulence created by "quench" or "squish". The result is even worse ping at the lower compression, reduced power, and reduced fuel economy.

Then we have the problems inherent in using a thick head gasket where the factory used a thin steel shim. Same problems as with using "destroked" pistons: reduced power, increased detonation, reduced fuel economy.

BE CAREFUL about your selection of pistons, as well as your head gasket. You will probably end up cutting material off of the block to compensate for the head gasket. That can be OK, as the block is probably not square to the crank main bearing saddles anyway. IF the machinist centers the block from the main saddles, and "square-decks" the block, you'll have a better engine when finished. The only question is HOW MUCH to remove from the two decks: Only enough to get them "true", enough to fully compensate for the increase in head gasket thickness, or enough to get the pistons to the top of the bores.

 

You can get pistons from tri-shield with the 2 inch pin height. T/A has them also.

 

Hello again,
I had to put the rebuild on hold, worked on the chassis, but am back at it again. I have been in touch with a few of you, so thanks for the information so far.

Regarding this stock rebuild, I am looking for cast pistons and a cam combination. My car is a factory 4 speed, with positraction (dont know the ratio). I would like this to be a driver that can run on pump gas.

I am reading conflicting information regarding piston compression. The original is advertised at 10.25:1, and TA has a set of 10:1 that they want to match to their 212 cam. Most folks are saying that 10:1 compression really wont be the case, when a new and thicker gasket is used, and only a touch to the deck. However, my rebuilder is cautioning me about 10:1 pistons because of detonation.

Does anyone have any experience with a specific set up and source for piston and cam like this? I was hoping to use cast to keep costs down, and I wont be hard on the engine.

Thanks,
Joe

 

Two truths you may not want to hear about compression ratios:
1--The "factory compression ratio" is BS. It is advertising hype, just like some inflated (or deflated) HP ratings.
2--Change anything in the short block or heads, and the compression ratio is an unknown quantity until you measure EVERYTHING. Factory ratings "assumed" a lower deck than they ever built on a production line. Most modern head gaskets are thicker than factory. Any surfacing of the block or heads changes the compression ratio. "10:1 pistons" are only "10:1 pistons" in the otherwise same engine as what they were designed for.
Granted, for a ballpark number, you don't really need to measure EVERYTHING. Head gaskets should be sold with a defined compressed thickness. (Blue Fel-Pros are 0.041, IIRC.) Your piston supplier should be able to give a dish volume. But you DO need to measure deck height (how far the piston is in the hole at TDC.) And, if any work was done to the heads, combustion chamber cc's. Put all of that in the online calculator Larry posted.
Nick

 

I would bore it to std. 430. I think someone makes forged 430 pistons. My 68 400 block sonic checked thick enough to go 0.060 over 430