1978 Oldsmobile Omega

I will be planning out the build on my Oldsmobile 350 it had the stock #8 heads, I purchased a set of #6 heads that I will be cleaning up for the motor, my cam and lifter kit will be a comp hydr. Roller, the cam is 0.505 lift, I have not chose rockers but they will be roller or roller tip, pistons will be 0.030 it will have a solid spark system which I have not chosen, and high volume pumps, topped off with Edelbrock 750 cfm and a performer intake, headers of course. What sort of hp and torque can I expect also what should my crank gear timing be, zero, advanced or retarted? Also, my rear end is a 3.08 posi.

Also, going from the #8 heads to #6 heads, what would the difference in hp and torque be on its own theoretically?

cutlassefi

Will you be installing larger valves?
I wouldn't use the regular Performer, I'd use the RPM. I'd also put a bit more lift in it as well as the full roller rockers vs the roller tip. You may also want to think about changing the gear to a 3.42 or similar.
Just the head swap alone should be worth about 20-25hp. Total resulting hp should be in the mid to upper 300's depending on cam and head work.


Hope this helps.

brownbomber77

Also on the roller tip rockers...not worth it. The pivot ***** DO gall rocker pivot if you don't have enough ZDDP in the oil...at least that's the way it's been in a '77 350 with #4 heads as well as a Ford 302 and 351 with the same rockers. They might work with a stock cam, but anything over .490 valve lift and an upgraded spring (don't remember the pressure), in my experience, has galled at the pivot point with conventional oil.

1978 Oldsmobile Omega

Hey there, I really appreciate the insight, I was leaning towards full roller but I was exploring to find a more cost efficient option, but I guess you have to do it right to get the most out of the parts.

1978 Oldsmobile Omega

Hey thanks for the help, after more assurance, I'm going to go full roller rockers, and I was told by a gentlemen selling ring and pinions at an auto flea market that I couldn't just change the gears and leave in my current posi, so I think at least for now and until I Finnish the car, I will need to stick with My current gears. Would you happen to have any tips on spark plugs and a solid affordable distributor for my application?

billmerbach

Go for the best get them Bosch x4 or something platinums

jag1886

I don't think there is any difference in the heads depending if you are having porting done, it just depends on what compression you are trying achieve as to which set of heads will make it come out right, there are multiple piston designs to choose from. You have to do all the math before starting.

1978 Oldsmobile Omega

Although you have some point to doing the math I don't see your proof, as compression dropped through the years, so did hp and torque, the combustion chamber on the stock #8 was 79, the #6 are 64 with rather large valves. The number 8 heads are for either a driver or an anchor, but compression is what is strived for, and the #6 heads have great compression and with everything else being cleaned and redone makes the heads an extremely desirable head, those heads paired with a good forged piston are an extremely solid combination, there is an extreme difference in heads, as stated earlier, an increase of 20-25 horsepower, that is mountains above no difference.

1978 Oldsmobile Omega

From a great source 442.com
6 '70 350 64cc 403859 W-31's had larger 2.000 intakes. '69
W-31's?
8 '73 - '76 350 79cc 411929 Smog heads. Have huge bb-sized 79cc
chambers yielding poor compression
ratios without extremes of compensation.

cutlassefi

The #6 heads will be closer to 68cc, not 64. But either way they will be an improvement. However I'd seriously consider installing larger intakes.

brownbomber77

Pretty sure this man ^^^^^ has never steered anyone wrong regarding Olds stuff. You're paying for the valve job anyway, 8 2.072 intake valves plus the job will be menial compared to the cost of the entire build and worth every penny in the end.

olds 307 and 403

I picked up a set of #6 heads with 2"/1.625" valves, port work, filled crossovers and milled to 55cc. With the Magnum 280 cam with 14cc pistons, it went 12.70's in the quarter, according to the previous owner.

1978 Oldsmobile Omega

I think I will look into the larger valves, a lot of the head work will be done by me, but I surely won't be doing the valves, but do I only need to do the intake valves?

Smitty275

Put in good valves. Don't waste money on stock style replacements. Use a swirl polished intake and exhaust valve such as those offered by Milodon. Approximately $200 for all 16. Have the head of the exhaust valve turned to 1.625. While not the cheapest way to go its not the most expensive and the valves are very high grade.

jag1886

Since you have been reading way to much propaganda just do what you want. I was just saying for a good street engine that can use todays gas with no problems. #8's work fine with a set of flat tops 0 decked and a thin head gasket and they have larger exhaust valves than other heads, if you port them they work fine.

1978 Oldsmobile Omega

I am looking for a good performance, more that the fine driver, with specs like given before, high 300's in hp, making the earlier heads the choice, the proof is in the motor stats year by year and the earlier heads are known to be the desirable heads for just that.

johnnyjaws

u haven't said nothing about ur pistons. other than boreing the cyclinder to 30 over u need to get rid of those low compression pistons u have in the motor

1978 Oldsmobile Omega

I have a bare block right now, those pistons will not be returning, and they were nice and black. I am certain on forged for my new ones, and believe I am going with a flat top, I'm not building a racer but the flat forged will sure be enough.

VinMichael

Personally I swapped #5 for #8. I have not driven it yet but put a lot of miles on the #5 heads. I don't trust the exhaust valve seats on those old heads. Though #5s having soft seats is supposedly propaganda according to some on this board! I am interested to see how to motor feels compared to when it had #5s.

Surprised to hear the huge jump in hp as stated by cutlassefi.

1978 Oldsmobile Omega

I am no expert, but I think your performance will either be the same or a little better if there are a lot of miles on those, the buildup over time will cause restrictions especially in airflow and of course general wear will hurt them. But I think if it was looked at with restored sets of heads, you would see the large difference in compression and power

DoubleV

If you're going to use flat top pistons then the #6 heads will make your CR higher than I think you want. If you used flat tops with #8 heads then your CR would be right about where you're going to want it to be at.

The problem with using earlier 330-350 heads on mild street builds is there are no over the counter forged pistons ( that I'm aware of ) that would provide you with an ideal CR ( say around low 9's ). This is why the big chambered #8 heads are actually a good thing. AFAIK, the #8's will flow just as good as the earlier heads if you port the exhaust sides.

So in summary, if you want to use your #6 heads, then you need a dished piston to keep your CR from being too high.

1978 Oldsmobile Omega

So I could use a relief set like offered by probe, but if I was to have a higher compression, what would be the outcome of a flat top and the #6 heads.

DoubleV

You gotta plug all the numbers into a compression ratio calculator and figure it all out.

1978 Oldsmobile Omega

I am not quite sure I did it right, I got 5.62:1

DoubleV

No, you did not do something right. Post the numbers you used and the calculator.

olds 307 and 403

The #8 heads just need an hour or two with the grinder just under the valve, a lip blocking the bowl. The actual bowl is better than a J, 3A, 4A or 5A exhaust port. Expect 10.25 to 10.5 to 1 with #6 heads.

holiday88

Compression calculator.

http://www.summitracing.com/expertad...ion-calculator

1978 Oldsmobile Omega

That is the calculator I used, but I used the wrong stroke, where would I find that? Also, I'm new to a lot of this, what is everyone's opinion on the compression ratio around 10.25-10.5

holiday88

3.385 stroke. I like to stick closer to 9/9.5 to 1 compression on the street. Depends how much you like paying for fuel.

1978 Oldsmobile Omega

I got 10.62:1 with relief pistons...Obviously a little high.. Very high, so if I have to use forged flats I should use the #8 heads. But for a strip-like motor I would want something like the #6 heads.

holiday88

I'm going to be building a similar motor so I've plugged the numbers in few times for myself. A lot of unknown info on your motor, but I still get 9.5 to 1 on an estimate. You should be close. I would take a minimal amount of material off the block deck to square it up and resurface the the heads if they need it and use a .040 thou thick gasket. Should keep the compression more reasonable. I used a 5.8cc dish piston, 68cc head, .015 deck clearance for my calculation. With a flat top you should be a little over 10 to 1.

Fun71

Keep in mind that the earlier year horsepower/torque numbers were, well, fictitious. The early GROSS rating system yielded higher numbers than the later NET rating system, and from what I have read there was a lot of cheating on those early numbers, so the production engines didn't actually have the power that the test engines had.

For an example on the difference in power in the rating methods, my '71 Owners manual shows the 350-4bbl engine rated as 260 hp GROSS and 200 hp NET (71 was the transition year between the GROSS and NET so they published both). Same engine but 60 hp difference just from the rating method.

1978 Oldsmobile Omega

I just keep getting the wrong numbers, so I think I am just going to put thought into my pistons and connecting rods and use the #6 heads.

DoubleV

Like I mentioned before, post the numbers you're punching into the calculator.

You can get 'streetable' compression and use your #6 heads. You just need a piston with a small dish. Problem is, there aren't any available. The reason why the #8 heads are being suggested is because they work great with easily available forged flat tops.

jag1886

I can tell you that I also change a set of brand new fully built #5 heads on a brand new engine for a fully built and ported set of #8 heads (the machine shop spent 2 days porting them not a 2 hours), I only have a butt dyno but there is no difference in performance even loosing a point in compression (this is only around town I haven't been out on the road yet), I think part of this is due to being able to running full timing now instead of pulled back timing with the #5's.
From all the info I have read there is really not much difference in any of the Olds SB heads other than chamber sizes so use what makes things come out right and do some port and runner work.

olds 307 and 403

A knowledgeable porter would only need a couple of hours to improve the number 8 heads. Directly under the valve, just removing the ridge in the bowl has to be huge gains. Just get them to add the 2" or 2.072" intake and remove the bowl ridge with a bowl hog. The #8 heads already have the right size exhaust valve. The factory just horribly restricted the opening below the valve, after that, it is a decent port. Two days with a valve job, porting and guide work would be about right.

1978 Oldsmobile Omega

Well the person selling me the heads decided to back out of the deal, I really didn't want to do a lot of porting work or have a lot done i just don't have the time or the money for a good job. I think while I Finnish my car I will look out for an improvement, and hopefully some big block heads, I understand that I can make the 8s better but there are better heads out there, I would really like to play with a set of big block heads

DoubleV

Why are you so against using the #8 heads? Heck, you already have a set too.

76olds

I have a set of #8's on my 76.... I had no idea they could be worked so well. Good info !!!! guys.

1978 Oldsmobile Omega

Well honestly this is the only place I have heard good things about them. Because I am taking the time to build the motor I have no problem waiting to find a 6,7 or big block head, I like the larger valves and same or better flow and a good CC with compensation. I think just about every engine builder I have read comments from has said what sorts or heads and tricks to use, not one has wanted to be near the 8s, also it's just cool that you can put any head almost on it.