[69Farburd]

It has developed a bearing knock, so at the least I am going to have to drop the pan. I'm debating on whether I should go ahead and pull the motor and do some other improvements. I have been pretty happy with it the way it is. I do have to put 2 1/2 gallons of 108 racing fuel in with a tank of 93, but I don't drive it that much so it's not a major issue. It is a 68 428 with the big valve #16 heads in a 69 Firebird convertible with 66 tripower, 200-4r trans and 3:55 gears. The engine is bored .30 over, has Erson cam TQ30H with 310/310 adv dur, 226/226 lobe lift, .493/.493 valve lift, and lobe sep 11 +4 with dual valve springs, stock pistons, push rods and rockers, long branch manifolds with 2 1/2 inch exhaust. It has AC and power brakes, so I need to keep some vacuum. What would you suggest? Zero decking? Different cam? Dished pistons? I would appreciate all ideas.

[steve25]

I would pull the motor out first off.
Even if its just the start of a rod knock, chances are that the rod has gone somewhat out of round on the big end and stuffing in new bearings will only serve to hold off the restart of the knocking for a short while.
Rod knocks with the cast rods progress to total rod failure real fast!
I do not belive in re-sizing cast rods that have gone out of round even if they mag out OK.

[screamingchief]

I'd rebuild it with some KB/Icon #KB892 pistons and some of Ace's forged rods,zero deck the short block,then sell or trade the #16 heads for some 6X-4's,mill those to at least 89cc's or so,and use some +.100" longer valves in these for more lift clearance,and then run a nice 230ish/112°+4 custom ground hydraulic roller cam in it.

Then you can run straight pump gas,and still have plenty of ummmppphhh to get-r-done.

Should also pull plenty of vacuum for power brakes too.



Bret P.

[J_JAMNIK]

I agree on dumping off the #16s. Had them on my 68 YE block and although the power was great, the constant gas mixing was a real drag.

[getmygoat]

You definitely need to pull the motor, forget about some half-a$$ bearing replacement - that is if you could even get the oil pan off the car with the motor in - and then replace the bearings - wow - can't imagine.

You don't need to get rid of the heads. If you are trading out the pistons anyway, you can put a dish in them - about 20 cc will usually get your compression to around 9:1.

[screamingchief]

Agree that dished pistons are an option if keeping the #16 heads is an important part of the plan,but remember that the dished 4" stroke pistons like that will almost certainly be custom order pieces,so they'll surely cost a bit more,and there is often a bit of "lead time" to actually get such in your hands.

There are pros & cons to either way of addressing the CR situation,that choice really boils down to personal preference often.

There are other reasons I'd opt for the 6X-4 heads here,but those too are mostly personal preference related as well,so I wont bother ya'll with those.

FWIW

Bret P.

[Leftyarmstrong]

Great trans/rear end setup. Save some pesos. Pull that motor, tear it down, message that block, get the pieces for lower compression (whichever way these guys suggest they really know what they are talking about). Assemble. Install. Gofast on pump gas. Smile.

[69Farburd]

Thanks for all the advice. I have decided to pull the motor and do it right. Scream, I would like to hear your other reasons for opting for 6X-4 heads. It seems that it would be less expensive to get dished pistons. Does using a hydraulic cam mean I could use stock lifters? Where can I purchase the parts you recommended? I'm probably off base here, but it seems that if I zero deck the block and add dished pistons, the two changes would offset each other? Are making these changes going to cause me to lose power? I always thought that more compression = more power.

[77 TRASHCAN]

Far,
Zero decking is really a good thing for any Pontiac, regardless of the compression ratio.

The combustion process is improved quite a bit by doing this, it has to do with effecient one direction flame travel, and using (and mixing) as much of the air/gasoline mixture as possible.

The cam Bret is referring to is, a hydraulic roller cam, it takes hydraulic roller lifters, not a stock type part. This type of cam has good performance advantages, and none of the potential headaches, a stock type flat tappet cam can have

The 6X-4 heads IMO, are a great way to go for a 4" stroke engine. The compression ratio will be around 9.3-9.5:1 w/ flat top pistons. 6X-4 heads have harder seats, can perform quite well (as many others can) AND they are pretty plentiful...

I think a 4" stroke engine w/ 6X-4 heads is a great build, don't know of any, just another good combo that would make a good street engine...

I'm glad you pulled the engine out when it just started knocking, I'd hate to see a scrap 428...

[screamingchief]

Originally Posted by 69Farburd

Scream, I would like to hear your other reasons for opting for 6X-4 heads.

Hardened exhaust seats,better spark plug selection,easy to upgrade for more lift,just more "potential" in a couple of areas.

Plus I like the option to run the later model timing covers,brackets,and pulleys on my engines.

Nothing too major,like I said personal preference mostly.

Anyhow...

FYI most all the 4" stroke pistons come with a small dish to them as SOP.

The TRW forgings did,as do the KB/Icon forgings (10cc).

There are reasons I like the KB/Icon forgings too,besides being off the shelf pieces that are cost competitive,they're also lighter,and they come with lighter pins,better ring package,better raw material,drilled ring oiling vs. slot ring oiling,and better valve relief locations and pin heights for less deck height problems.

Cams,honestly there are a multitude of choices there,flat tappet & roller.

The hydraulic roller just buys one some "peace of mind" and a bit more "latitude" with regards to the cams "sizing" choices.

But there are plenty of sound flat tappet cam choices out there as well.

I did'nt mention any solid cams because it did'nt sound like you were the sorta fella looking for maximum yeild from the cam choice.

The basic outline I gave would be a pretty common one if you went around and asked most known pontiac engine builders what would be a good HP build for a 428.

Though same as here,I'm sure some would say custom dish the pistons and use the current #16 heads,and others might suggest the head change for use with the readily available "off the shelf" piston choices.

The only "complication" to the 6X-4 head change will be the exhaust crossover area on the passenger side head with the 66 tri-power intake.

But that's NBD really,and fairly easily dealt with.

HTH

Bret P.

[69Farburd]

You've given me a lot to think about. I guess the main question in my mind is what combo is going to make the car go fastest? I don't go to the track much, but want to be fast when I do. But it does need to be streetable. I guess it is hard to get the best of both worlds. Does more compression mean more hourspower? If it does, would I be better off just zero decking the block, runing the combo I have with a possible cam change and continue adding race fuel to my gas?

[beargfr]

Changing nothing else, raising (or lowering) compression by .5 is only going to make a difference of about 7 or 8 horsepower, if that. Compared to the headaches of mixing fuel and having to worry about detonation, my personal opinion is that for a street motor it's not worth it to try to push the limits on compression. For a max-effort race motor where you're looking for every advantage you can get and running race gas, you bet, but on the street - for me - the risk and headache isn't worth the small HP difference. Of course, everyone's free to make their own choices.

Bear

[screamingchief]

Originally Posted by 69Farburd

You've given me a lot to think about. I guess the main question in my mind is what combo is going to make the car go fastest? I don't go to the track much, but want to be fast when I do. But it does need to be streetable. I guess it is hard to get the best of both worlds. Does more compression mean more hourspower? If it does, would I be better off just zero decking the block, runing the combo I have with a possible cam change and continue adding race fuel to my gas?

Well,if you think about this,a large part of the reason your where you are right now is due to the fact that this motor very well may have damaged the rod bearings due to detonation,this despite your best efforts via mixing fuels to try and account for any CR issues.

So to use a lame cliche',how's that working for you?

If a combo like I described is'nt "enough" power,then there are simple ways to address that,the first being adding more headflow via porting the iron heads or better flowing aftermarket aluminum heads or such.

But a well built unported iron head 428 with good tuning should easily be able to make 425 hp no sweat,even @ 9.5:1 cr.

And with the slight CR drop,you also wont have to be super conservative with the timing curve either.

The zero decking often adds roughly like .25 to .5 a point of CR depending on how far down the pistons were to begin with.

So in some respects your just compensating for that by either adding more dish or a bigger chamber.

But what I'm saying is I would drop it just a bit more to make it more pump gas friendly and eliminate the need to mix fuels,and then make up for that slight loss in those other changes like using a better cam and more aggressive tuning and maybe more headflow & such.

But the choice is yours.

Good luck with it.

Bret P.

[Old Goat Racer]

I've seen two engines destroyed by "mixing" gas. The first was mine, the second I bought that way. I never mix gas anymore and I lower the compression if it's on the street. But that's just me.

[69Farburd]

Thanks Bret. That was the kind of information I was looking for. I am leaning towards going with the suggestions you made in your first post, and looking for some 6x-4 heads. Do you want to make me a grocery list of everything I am gong to need, and where to purchase them?

[lust4speed]

Originally Posted by screamingchief

...So to use a lame cliche',how's that working for you?..

That was funny

...but so to the point. Dropping from 10:1 to 9:1 compression looses less than 2% according to the old H.O. graph (also on Wallace website) -- and that's if you're running the proper fuel for 10:1.

For an engine putting out 300 rear wheel horsepower that would be less than a 6 horsepower loss. If timing has to be reduced from 36° to 28° to allow the engine to live, you might drop 5% or more (15+ horsepower).

[grivera]

Originally Posted by old goat racer

I've seen two engines destroyed by "mixing" gas. The first was mine, the second I bought that way. I never mix gas anymore and I lower the compression if it's on the street. But that's just me.

Please explain.

[69Farburd]

My wife is getting on me about te amount of money I have been spending on this car. Could someone give me an estimate of the cost involved with the following?

Get a set of 6x-4 heads and have them milled. Would I be able to use my existing rods and pistons with them?

Install dished pistons.

Install a hydraulic roller cam.

Zero deck the block.

Bret, what is the complication with exhaust crossover area on the passenger side head?

Again, thanks everyone for the advice.

[chiphead]

Costs from my build and various research I've done:

Basic headwork: $250-500+ depending on starting condition of heads

KB Dished pistons for 4" stroke: est $450 + machine work

HR Cam: $700-1200 (overkill for your app)

Zero deck: $150-250 (very worth it)

Forged rods: $350-600

The tripower intake won't cover the later head's exhaust crossover, so you get a big exhaust leak at the x-over. Usually requires filling the heads with aluminum or making block-off plates.

To be honest, You're gonna need the 6X-4s, the forged pistons, good rods and the zero decking for any iron-head combo. Fixing this 428 is gonna cost a couple grand any way you slice it, because it's knocking. The rods are junk, and the pistons may be damaged. I would use forged rods for sure. How is it bored .030" over with stock pistons, as the original post states?

Worst-case you're gonna have to throw everything but the crank in the trash for a decent build.

I do agree that mixing the race gas won't work. You can't get the octane consistent from batch to batch unless you keep a log, so it will eventually beat out the rod bearings.

[lust4speed]

Rule #1: Keep the wife in the dark on the costs. Parked next to me a few years ago was a woman driving her husband's truck with a new top of the line lift kit and very trick Fox shocks. I was researching lift kits for my truck so I asked her where they purchased the kit. She gave me the shop name and volunteered that her husband got a great deal - $800 installed. I upheld the man-code and went on my way. The front shocks alone were $,1200 each at the time and he had two per side. He was happy, the wife was happy.

Just another thought on your engine, the spun rod bearing could have been hammered by detonation or by exceeding the safe operating range of the stock rods and rod bolts. You will find that a good set of rods won't be much more expensive than putting the band-aid repair on your current rods even if they are salvageable. I would suspect that the ring lands on the original pistons are also hammered or broken, and the pistons will need replacing. A set of the new style D-cut dished pistons (@24 cc) would work great with the 16's and bring the compression ratio down to around 9.2:1. It's the old pay-me-now-or-pay-me-later. You will save money in the future on not buying race gas and by avoiding the next repair when the fuel mixing fails.

It's good to shop price on similar parts, but don't shop price on machine work - pick someone that has been recommended by several people. The guys doing it for less either know what their work is work or they plan add-ons to get the price up after the parts are dropped off.