68 327 Rebuild Which Heads To Use?

[Steve Z.]

WOULD LIKE TO DO A REBUILD ON A 68 327. trying to get around 350 + or - hp. i have several head combos i could use. i have 487 from 1971, 041 from late 1969,441 from late 1968,or 291 from early 1968? i also have a set of 462 but they are from 1966 with no accessory holes.what would be a good comp ratio to get that hp? i dont care if i have to add octane booster or such.what is a good cam profile for the 400 turbo auto trans? thanks for any info. you guys know your stuff---steve

[Duke W.]

Re: 68 327 Rebuild Which Heads To Use?

Any "big port" head will be okay and the difference between the 1.94/1.5" and 2.02/1.6" valve set is marginal at best. My preference is to retain the 1.94/1.5" set unless the seats have already been cut for the larger set.

Any of those heads (as long as they have at least 1.94/1.50" valves - avoid any '70s vintage truck heads that have 283-sized ports and valves) should do with proper "massaging", which is the key to power. After rework they should flow 220-230 CFM on the inlet side at 0.5" lift, 28" H2O depression and about 170 CFM on the exhaust side at the same conditions. The only way to know if the heads have been properly massaged is the flow test them.

Since you have an auto trans (and likely a 3.08 or 3.36 axle) low end torque is very important, and the amount of cam required to achieve 350 gross HP will not be auto trans friendly, and would be a BIG mistake.

Use an OE replacement cam, and you can retard it four degrees if you want to trade a little low end torque for more top end power and revs.

Erv Myers has a '69 base 350/300 that he so reworked (without any OE cam retard). I've driven it and it's a very nice runner. Flooring the throttle from a dead stop just hazed the tires and the engine pulled strong and linearly to 5500. It was all OE equivalent other than the massaged heads.

Limit true, measured CR to 9.8:1 (which is easily attainable with the OE pistons and proper head gasket selection) if you want to run on pump premium. "Octane booster" is worthless. Go too high on compression and you will have to run race gas or avgas - at least in some proportion, which is a major hassle and not worth the very slight extra torque/power.

If your block is a true '68 version it has large journals, so build it with a base 350 cast crank and 350 rods/pistons, which will easily handle up to 6000 revs as long as they pass Magnaflux inspection. It's an easy upgrade and the increased stroke will make more torque/power through most of the rev range.

Consider that a road engine spends 99.9 percent of its time below 5000 revs. What's important in a road engine is the average power from 2000 to maximum revs - NOT peak power.

With an auto trans you need 90 percent of peak torque at converter stall speed. Otherwise it will be a slug with poor throttle response in normal driving. A big cam requires a high stall speed converter, and then you end up with a SB that will barely get 10 MPH.

There is lots of information in the archives on how to manage an engine restoration to retain OE visual appearance, low end torque, idle characteristics, and overall driveability while increasing maximum power 20-30 percent and extending the maximum power bandwidth by 500-1500 revs.

It's all about the heads!

HEADS! HEADS! HEADS!

Duke

[Steve Z.]

Re: 68 327 Rebuild Which Heads To Use?

what style cam would be advisable? i would like to keep the torque high and dont plan on revving over 5500 to 6000 is the l79 too much? what combo has anyone had good luck with? stick with oe stuff? thanks for your reply,steve

[Joe C.]

Re: 68 327 Rebuild Which Heads To Use?

WOULD LIKE TO DO A REBUILD ON A 68 327. trying to get around 350 + or - hp. i have several head combos i could use. i have 487 from 1971, 041 from late 1969,441 from late 1968,or 291 from early 1968? i also have a set of 462 but they are from 1966 with no accessory holes.what would be a good comp ratio to get that hp? i dont care if i have to add octane booster or such.what is a good cam profile for the 400 turbo auto trans? thanks for any info. you guys know your stuff---steve

I don't advise using any "open chamber" heads, which are "smog" heads with large, 75-76cc chambers. Although they flow marginally better than the closed chamber heads, they will give a slow burn rate, and require a large domed piston of about 12cc in order to give the desired compression ratio.

I advise using a compact chamber, or "closed chamber" head, which, if equipped with 2.02/1.6 valves have chambers of about 67cc. If fitted with 1.94/1.5 valves, the chambers are about 64cc. These flow marginally less than the open chambered heads because the valves are somewhat more shrouded, but the compact chambers will give a fast burn rate and higher compression ratios for more torque across the entire rev range.

The 487 and 441 are both open chamber "smog" heads which I would NOT use.

The 462 head is a good "closed chamber" head, and is the second generation "fuelie" head, after the 461. It has better spark plug placement than the 461, but is not as desirable as the 291 and 041.

The 291 and 041 heads are both closed chamber "performance" heads.The 041's are a better choice, as they were OEM on the '69 Z28, and have accessory holes. They are likely to be more expensive than 291 heads.The 291's were OEM for 67-68 302(Z28)/327/350, but do not have accessory holes.

The 3863151 cam is a good, all around street performance cam with generous torque and good horsepower, which will work well with your auto trans. It was the most sought after cam for 1965-68 SBC because it could be equipped with power steering. This cam should be matched to at least 10:1 compression up to an absolute maximum of 10.5:1 if your engine builder will minimize quench distance in the chambers to .035". I assume that your axle ratio is either 3.08 or 3.36 if it and the trans are original to the car.

In any event, be sure to have your engine builder measure all relevant volumes, and then use a formula, such as:

http://www.bgsoflex.com/cr.html

to calculate static compression ratio.

[Duke W.]

Re: 68 327 Rebuild Which Heads To Use?

what style cam would be advisable? i would like to keep the torque high and dont plan on revving over 5500 to 6000 is the l79 too much? what combo has anyone had good luck with? stick with oe stuff? thanks for your reply,steve

The OE 3896929 or the current GM 14088839 replacement or an aftermarket exact replica. I thought I already said that.

The L-79 cam is not a good match with an auto trans. GM never offered an auto trans with the L-79 engine option.

Massaged big port, small chamber heads with proper compression will yield the necessary low end torque and useable revs to at least 5500 with a 3.48" stroke and about 5800 if you keep the stroke at 3.25". Add 200-300 revs if you retard the OE cam indexing 4 degrees.

Duke

[Tom L.]

Re: 68 327 Rebuild Which Heads To Use?

All these posts are valid but here's my point. Stock car racing is an addictive game. In the division we ran for a while we had to use OEM production heads but were not very limited on machine work. Over the years we used 461 and 492 heads, they were the best we could use. With angle milling, extensive massaging they were able to support the HP numbers you are looking for. However as noted they crack and all that expensive machine work went to the scrap pile. After 15 years I can still hear our engine builder aying, "I wish the @#^%!&* sanctioning body (NASCAR) would let us use cast iron Bowtie heads with no milling or porting. It would be cheaper, more durable and make about the same power."

If you don't care about origionality, new may be a better option and they have the mounting holes. Gook luck!

[Clem Z.]

Re: 68 327 Rebuild Which Heads To Use?

i agree if you are not chasing points use a set of cast iron bow tie heads as these are one of the best SBC heads made by GM. the newer "votex" heads are even better but present a intake bolt up problem.

[John H.]

Re: 68 327 Rebuild Which Heads To Use?

The 041's are a better choice, as they were OEM on the '69 Z28

Joe -

The '69 Z/28 used the 186 heads (with 2.02/1.6 valves). The 041's were used (with 1.94/1.5 valves) on the L-48 (350/300hp).

[Joe C.]

Re: 68 327 Rebuild Which Heads To Use?

Joe -

The '69 Z/28 used the 186 heads (with 2.02/1.6 valves). The 041's were used (with 1.94/1.5 valves) on the L-48 (350/300hp).

You may be right, John, but then these guys are wrong:

http://www.mortec.com/castnum.htm

Were they used on the 1970 Z28?

[John H.]

Re: 68 327 Rebuild Which Heads To Use?

You may be right, John, but then these guys are wrong:

http://www.mortec.com/castnum.htm

Were they used on the 1970 Z28?

Yes, Mortec is wrong (which is not unusual). The 186 heads were used on Z/28's in both '69 (with pressed-in studs and no guide plates) and in '70 (with screw-in studs and guide plates).

[Steve Z.]

Re: 68 327 Rebuild Which Heads To Use?

thanks for all the info guys. it really means alot. are the 041 heads approx 64 or 68cc? wouldnt the 291 heads have accessory holes? they are from march 68. if i used the 041 heads would i have to change from the original stock location of the alternator, etc. i have air cond too but not too concerned about it right now. it can be left off. thanks steve

[John H.]

Re: 68 327 Rebuild Which Heads To Use?

thanks for all the info guys. it really means alot. are the 041 heads approx 64 or 68cc? wouldnt the 291 heads have accessory holes? they are from march 68. if i used the 041 heads would i have to change from the original stock location of the alternator, etc. i have air cond too but not too concerned about it right now. it can be left off. thanks steve

Steve -

The 041, 291, and 186 heads are all 64cc, but only the 041 and 186 heads have accessory holes - those holes didn't appear until the 1969 model year, and the 291's weren't used after 1968.