1969 400 rebuild help - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 06-05-2012, 10:31 PM Thread Starter
 
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1969 400 rebuild help

I'm in the middle of restoring a '69, and am to the point of rebuilding the trans (TH400) and the motor. Which seems to be all numbers matching to the car. This car will probably be driven fairly regularly. At least a couple times a week. So... My question, what would "the experts" here recommend for the motor rebuild? I obviously want the most power possible. But need to keep it on pump gas so it can be driven a lot. I'll take any advice you guys have to give. I have no knowledge as to what is inside the motor at this time. I have had it running, been never driven. (Trans leaking out the front pump) It seemed to be running quite good from what i could tell. The heads (62 heads) have definitely been to a machine shop. (newer style freeze plugs in them) Other than that, it all looks factory. Intake manifold. Rochester carb. Factory exhaust manifolds. I would prefer to still use the same heads. Not go the stroker route. Other than that, tell me what you would do if it was your car looking for the same daily driver mixed with decent power outcome.
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post #2 of 10 (permalink) Old 06-06-2012, 09:05 AM
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I love strokers (and have one) but if you're going to keep the original 62 heads and want to stay inside a budget, then I'd recommend you not build it into a stroker (slight pause here while everyone on the forum regains conscousness )

The reason being, those heads on a stroker motor would put your compression ratio too high for safe running on pump gas without doing other things to the motor to get it "back down".

Beyond that... making power is all about air-flow, so depending on how much budget you have here are things to consider:

* Send the heads off to have them ported by a skilled porter (I like Dave Wilcox at CVMS) - expensive but worth it.

* "More" cam - "best" profile for improvement and also retaining some street manners will be a solid roller. A roller profile will let you get more effective duration "under the curve" without having to go crazy on overlap, and not going crazy on overlap is what will keep you some street manners. Plus a later intake closing event (due to more duration) helps manage dynamic compression/cylinder pressure to avoid detonation. If you do go with a solid roller cam (the old wives tales about frequent adjustments don't really apply today) make sure you use lifters that have positive oiling to the roller axles and don't rely solely on splash from the cam. Also for a solid, install calibrated restrictors in the lifter bore oil feed passages in the block - the solids don't need as much oil as hydraulics do, so the restrictors keep more of the oil where you need it most - on the mains and rods. Your trade off on the cam is going to be the converter and rear gear. If you go "too rowdy" on the cam you'll need a "looser" converter and possibly more rear gear to take advantage of it. That's another reason for a roller and managing that overlap period. A roller profile will tend to be more civilized than a flat-tappet grind of the same lift and duration.

* Clean up and port-match the factory intake to your heads. Also separate the water crossover from the intake, otherwise as soon as you install the intake and tighten up that crossover connector bolt to the timing cover all your port-matching work will go right down the tubes.

* Zero deck the block - improves "quench" and combustion efficiency so you won't have to run as much ignition timing. (Less "negative work" in the motor) This also helps prevent detonation (and nets you a small increase in compression which a 'bigger" cam will like).

* Pistons. With those iron heads and a zero-decked block (assuming a + 0.030 overbore), and stock style flat top pistons, you'll be at approximately 10.5:1 compression. You'll find lots of opinions on this, but mine is that's too much to be guaranteed safe on pump gas. Something like these:
Icon Forged Racing Pistons would put you around 9.7:1. That's still a little on the high side Iin my opinion) but as long as you have "enough" duration in the cam to keep cylinder pressure down (via a "later" intake closing event) you should be ok with 93 octane, a properly jetted carb (lean is very bad), and a good, efficient cooling system. "Safe" would be closer to 9.5:1. You for sure want D-shaped dishes in the pistons, not round ones, otherwise you lose the cylinder "quench" effect and that will make the engine MORE prone to detonation. Another advantage of forged pistons is they're both lighter, and have less friction due to their smaller skirt area.

* Better exhaust. "Best" will be 4-tube headers, but they're also the most pain in terms of fitment and maintenance. (I hear good things about "Mad Dog" headers on both counts and will probably try them myself when my Doug's need replacing). Next step down from there performance-wise will be the reproduction cast-iron "ram air" manifolds. You give up a little in performance, but lose -all- the headaches of headers. For some folks that's a good trade. Install a good quality exhaust system (no larger than 2 1/2" tubes front to back) with an X-crossover and good mufflers.

* Adjustable valve train. Replace the bottleneck studs in those 62's with the 7/16 screw-in studs. They're much stronger. Any cam much above stock is going to need aftermarket springs and a fully adjustable valve train (poly locks) anyway. While you're at it, replace the factory rockers with aluminum full rollers. They're lighter (less mass/stress on the valve train) and the roller bearings mean less frictional losses.

* Get your carb dialed in. Read Cliff Ruggles's book on the subject, also Lars' (member on here) excellent paper.

* Good quality aftermarket forged h-beam rods. Pontiac factory rods are 'the weak link' in the motors. By the time you have a set of factory rods tested and reconditioned for re-use, you'll have spent almost the cost of a good set of rods that you won't have to worry about. Good rods are cheap insurance, especially on a 400 that can wind higher than a 455+.

* For the rest, check out the "Building Your Short Block" chapter in Jim Hand's book: "How to Build Max-Performance Pontiac V8's". Keep in mind most of that is aimed at 455's - your 400 is going to be happy at higher rpm than a 455 for making power and a cam that is "moderate" in a 455 is going to "act bigger" in a 400.

That's my take on it. I'd recommend you also contact Jim Lehart at Central Virginia Machine Central Virginia Machine Service - Home of the Injun Engine!. He's "the man" (he wrote the short block chapter in Jim Hand's book) and will tell you the truth - even if you don't spend money with him. However, if you want someone to 'build it for you', I highly recommend him.

Bear

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post #3 of 10 (permalink) Old 06-06-2012, 09:14 PM Thread Starter
 
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Thanks Bear. I was hoping you'd be the one to respond. I guess i should give you a little more info. 1, I'm a auto tech. So I'll be doing all of the work in house at the shop. And be using our usual machine shop for all of the machine work needed. They've always been good to us, and haven't messed anything up yet. As far as assembly the block, that will all be done by my 68 yr old co-worker who in his prime built motors of all american makes constantly. He's very good! The only things he's uncertain about is what we need to get her to run on pump gas. I love all the info you gave me, to the point that I would like if you could help narrowing it down for me and make my life even easier. Basically, tell me the parts you would use, and I'm gonna buy said parts and use them. I trust your advice. One thing i do wanna add, I live in Phoenix. Very hot desert. Any proven parts you suggest for keeping her running cool, I'll be all over that as well.
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post #4 of 10 (permalink) Old 06-07-2012, 09:59 AM
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Wow, I'm flattered - thanks

Speaking in generalities, being pump gas friendly is about getting the right combination of mixture turbulence (the more the better), cylinder pressure, and heat management in the combustion chamber. You will hear people say (and I'm one of them) that a target of 9.5:1 or less is generally safe for iron heads, 10.3:1 for aluminum heads. Is it possible to run more and do so safely/successfully? Sure - but it requires more thought and also very careful management of the tune up and cooling system. I've got a copy of the Performance Trends Engine Analyzer program here that I use, and if I set it up to model my 461 with it's 9.46:1 compression ratio the prediction I get out of it is extremely close to what the motor actually made on the dyno. If I do nothing more than change the compression from 9.46:1 to 10.5:1 and re-run the simulation, which would almost certainly knock with iron heads, it nets me a whopping 10 HP increase, from 500 to 510. When I was building my engine I made the decision that it just wasn't worth the risk for me to try to push compression to the limit for so small a difference in power.

in general terms, and this is my opinion only - shoot for a dynamic cranking cylinder pressure in the neighborhood of 170 to -maybe- 180 psi to keep the motor in 93 octane territory without having to worry about it too much.

On cooling systems, I post a lot about getting the water pump backing plate clearance right. This is because I saw it make a dramatic difference on how well my cooling system works and it's something that's easy to forget to do. Beyond that, have a good radiator and good fan, clutch, and shroud (if you're using a mechanical fan) all properly installed or good thermostatically controlled electrics.

Cam choice... several things to consider here: what rear gear? will you be running vacuum-boosted power brakes and/or vacuum-operated factory a/c? How do you plan to drive the car? (street cruise, racing, highway) and if it's an automatic, would you consider changing the converter if needed? I really like my cam, but it's a little too rowdy for vacuum accessories even in my 461 so I converted the brakes to a hydroboost system and replaced my factory a/c with an aftermarket unit that doesn't need vacuum. My cam in a 400 would have even more "attitude".

If you're considering sending the heads off to Dave to be ported, he and Jim would be excellent sources for a good cam recommendation. Being willing to share detailed information without me first committing to spend big bucks with him is what sold me on Jim in the first place. I'm sure he'd advise you even if you don't send your heads to him.

Just for grins, I changed my model in Engine Analyzer to be a standard bore 400 and ran it with "my" heads and cam with 9.821:1 compression (what a standard bore 400 would be with those 12cc D-dish pistons if the block was to be zero-decked) It predicted 489 HP at 6000 RPM, 467 lb-ft at 4700 rpm. Theoretical cranking cylinder pressure was 174 PSI, estimated peak idle vacuum was 12" (not enough for brakes). You'd love the torque curve - it was over 450 lb-ft. already by 3500 rpm and didn't drop below 400 until almost 6400. It reached 400 lb-ft between 2900 and 3000. This thing would pull like a freight train. This was with a factory iron intake and 800 cfm QJet.

"My" heads are round-port #722 Ram Air IV's that flow tested 282 CFM at .600 lift. Dave would be able to get that much out of your 62's, maybe more. I'm also running 1.65:1 Scorpion roller rockers.

How's all that sound?

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post #5 of 10 (permalink) Old 06-07-2012, 02:45 PM
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I pretty much agree with Mr. Bear, as he has indeed done his homework, and has also paid his dues with blood, sweat, and cash. I've been driving early GTO's all my life...my first car was a '66 GTO. I've never stopped owning/driving them. I ended up installing 87cc heads on the original 400 in my '67 because the lower end and pistons were in good shape and needed nothing. If I were in your shoes, doing a rebuild, I would install custom dished pistons for a CR of about 9:1, and a camshaft that is designed for flow with lower compression, like the Comp Cams XE series....probably an XE262 or 268. I have experienced this combo with a couple of 389's, and they had tons of power and ran fine on 89 octane fuel. The 389 in my '65 GTO was overhauled by me in 1981, and still only has 50k miles on it.....mainly because it requires race fuel with its stock compression. If you plan on driving it, plan on lowering the CR and choosing the right cam, exhuast, etc. to work well with the combo. Good luck.
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post #6 of 10 (permalink) Old 06-07-2012, 08:32 PM Thread Starter
 
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Again, love hearing everything you just said Bear. As far as the rear gears, I currently am not sure what's in it. Will hopefully find out this weekend when I pull the motor. But even at that, I am more than willing to change gears and run a different converter if needed. I'm very open there. The car is a power disc brake car. So obviously I would prefer not having to change that... But since you've done the homework and can hopefully make it very easy to do, ie. tell me what pump and hydro boost unit you used, I'm not scared to go that route as well. Back to the gearing again, it is an automatic (TH400) and I will mostly be street cruising in it but would like to have the gearing to jump on the freeway and not be a big deal. But again, I'm honestly just gonna take what you tell me to use and probably go for it. If you say it'll work, I'm game to try it.
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post #7 of 10 (permalink) Old 06-16-2012, 01:58 PM Thread Starter
 
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Motor and tranny got pulled last weekend. Tranny is cleaned and will be rebuilt this week. started to pull the motor apart yesterday. Looks like everything is 100% stock to me. I've decided to go the simple route i believe. I will have the heads worked a bit along with the intake manifold. Gonna find D shaped dished pistons and lower to 9.5:1. New rods of course. Put the xe262 cam in it and probably run the repro ram air manifolds. If I do go this route, what do you guys suggest for the rest of the valve train? ie. valve springs, rocker arms, lifters and pushrods? I will for sure be driving this a lot so I would prefer simple but better than stock. No constant adjusting. thanks for any help guys.
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post #8 of 10 (permalink) Old 06-16-2012, 03:16 PM
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At the least, go with 7/16" screw-in rocker studs in place of the factory bottlenecks. Those are known to break at the neck sometimes. That will also mean running some sort of poly-lock instead of the factory rocker nuts to get a fully adjustable valve train. Also a good idea. These days even with solid lifter cams, the notion of having to "constantly adjust them" really doesn't apply any longer. Once, maybe twice a year is plenty and most of the time you'll probably find they don't need any change of adjustment. Might as well go with roller rocker arms too to get the reduced mass and reduced friction. I'm running Scorpions in mine and I like them a lot - USA made. If you decide to go with 1.65's instead of 1.5's, remember that you'll have to open up the pushrod passages in the heads to keep the pushrods from rubbing. That's not the sort of thing you want to discover after you've already got the heads on and torqued down.

For springs, either go with the ones Comp recommends for that cam (COMP Cams: Dual Valve Springs: 1.437" O.D. Outer, .697" I.D. Inner) or with some with equvialent specs. You'll have to have your heads cut on the spring seats in order to arrive at the correct installed height for the springs.
Get yourself some light checking springs and one of those adjustable pushrods so you can mock up the valve train and measure for the correct pushrod length. I used these:
COMP Cams: Low Tension Checking Springs - Pair
COMP Cams: Hi-Tech Checking Pushrod 8.800"-9.800"

That oughta get you started

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post #9 of 10 (permalink) Old 06-17-2012, 09:02 PM
 
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7/16 studs do not require polylocks. often, the stock 7/16 studs like the chevy stock ones will not allow polylocks to hold tension since the ends are not flat. the lock will not hold. But stock rocker nuts in 7/16 are available at any parts store. if you want to use polylocks, then get aftermarket studs set up for those. Must solid lifter cams need to be adjusted, just see instructions given by the cam manufacturers.
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post #10 of 10 (permalink) Old 06-18-2012, 09:16 AM
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Well, if not using a bottleneck stud you sure can't use the 'factory' method of torquing the rocker nut to 20 lb-ft. because there's no shoulder there for the nut to tighten against. Plus if running different rockers, different springs, custom length pushrods that are matched to the cam then all those geometrical relationships are going to be different from stock so you're going to need a way to adjust the rocker pivot height and have it stay where you put it. More than one unfortunate gearhead has learned the lesson that trying to use stock springs, rockers, pushrods, studs, nets, adjustment etc. with an aftermarket cam can get real expensive real quick when they turn the motor over and bend all the pushrods and wipe cam lobes when they drive the springs into coil bind because they can't handle the increased lift.

Finding flat top 7/16 studs isn't hard. Here's some:
ARP Rocker Arm Studs - JEGS

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