Tom454

I posted this on the C2 section... but didn't get many responses... so I'm re-posting here-

My own 66 327 passed away a few weeks ago while I was testing a Holley carb for another forum member... some of the cam lobes wiped and the dist drive gear (on the cam) self destructed.

Anyhow... I measured one of the best intake lobes and it came out at .282. With .016 approximated wear, this would end up at .298 which is the 3277/350 GM 3863151 327/350 cam lift of .447 using 1.5 rockers. I have owned the car since 1975, so I am pretty sure it is a 327/350 cam although I did not install it originally. I re-ringed the block around 1983, but I am not the original engine builder.

Here's my question: rather than going with the COMP CAMS 12-106-3 (=3863151 222 duration, .447 lift), I am thinking of using the 12-211-2 which is a little bit stiffer at 224, .470

The engine is a T0IIIMK (67 Camaro?) piece (3903352) with 194 heads #3890462 64cc with pressed in 3/8 studs, standard bore, fly cut valve reliefs, forged crank.

Has anyone used the COMP CAMS 12-211-2 (270H) with pressed in studs and stock GM 327/350 valve springs?

I am only fixing this so I can move it around while I build another engine for the car. I know pressed in studs are the way to go, but if I can get away with it for now, I just want to get the car mobile and I need input from someone who may have tried this combo. Normally I would just machine the heads for screw in studs but I want to try to slip by on this one since it's my own engine and I'll be dumping the engine in about 6 months.

If I can expect the studs to pull out with 1.5 GM rockers and GM springs, then I will just step back to the COMP CAMS 12-106-3.

Anyone have real world experience with the 270H and pressed in studs? (I can "guess".... I really need to hear of actual experience.)

Thanks-
Tom

68shark

Ganey is the best to answer this....if he doesn't see this, may want to post on C3 section. I think the High Energy series, or the stock 151 cam are both fine with stock springs and pressed in studs, which would have been "factory" on your engine. I think either cam choice would be fine. If you went with one of the Extreme Energy Series you would have to upgrade the springs. Given your plans for the engine are short term, I think I'd go with the stock 151 cam (which is a nice cam anyway!) and be done with it. My .02.
By the way, even the Extreme Energy series doesn't call for screw in studs, although my heads have them anyway.

63Banshee

I wouldn’t sweat the studs. I would change the springs if the motor has significant mileage. If you are running stock exhaust manifolds I’d rethink using a 270H. Too much intake for efficient scavenging with manifolds.

Ganey

Well I haven't & wouldn't. The short answer to anyone other than an engine builder like Tom454 thinking about this is don't. At least change springs. You might want to try one step down to 268H which have seen turn 6000 w/ stock springs & pressed studs w/ 1.52 rockers & over 100k.

:cheers:

63Banshee

Wouldn’t a stock (new) spring be sufficient for a .470” lift cam considering that the stock 350 HP spring handled a .460” lift? This is assuming that the 270H cam has a .470” lift as stated. For that matter, the 300 HP spring should handle it as well because Chevy used the same spring for 300 and 350 HP motors.

No doubt I would change springs with any higher lift cam change if the current springs have 10K+ miles on them.

I thought of one thing while driving home that I left out, spring pressure. Shouldn’t come into play considering the difference in cams we are talking about, but definitely an important concern when changing cam profiles.


[Modified by 63Banshee, 5:22 PM 1/8/2002]

68shark

Comp Cams website lists the 981.16 spring for even their version of the 151 cam. Agree changing springs would be smart no matter what the choice. Still think that as Tom has short term only plans for the engine, that I'd be inclined to put the stock 151 cam in.

mountainmotor

68shark has a good point about short term and cost.Competition Products has Elgin"10 grinds available" cams,lifters,springs ,seals,locks and assembly lube for $114.00

Ganey

Dave

The max. safe lift is .460 w/ stock springs, which is what a 268H has w/ 1.52.

Expect Tom who builds Chevy engines is aware of what he is asking that is why he said:
"Anyone have real world experience with the 270H and pressed in studs? (I can "guess".... I really need to hear of actual experience.)"

63Banshee

I’m not labeling you incorrect, but it contradicts information I have from a prominent Chevy engine builder. I’ll go back and check my correspondence I had with him a few months ago. We may have been talking about '68 327s only, I don't remember exactly.

Is there documentation that you know of verifying this?

Yeah, that's why I didn't mention that the rocker arm slots are sometimes shorter on lower performance motors and it's something to watch for... I figured he'd know that.

:cheers:
L8r,
DJ

Tom454

Thanks for all the comments...

I'll clear a few things up-

RE: Springs- they are undoubtedly shot & weak. I'm not replacing them because I would have to pull the heads.
I feel it's easier to pull the heads than mess around with them on the engine.
I'm trying to get this car out of my way... no time for that. I have another more critical project on-going.
I have the engine out of my wifes car, and she wants it back ASAP. Who woulda known.

RE: Slotted rockers- yes.. I am aware of that issue. Also aware of coil bind and valve clearance issues.
I have solutions in mind for all of those if they become an issue.

The reference guides I use have:

327/300HP
Lobe lift- .2658
closed spring pressure- 78-86 @ 1.66
open pressure- 170-178 @ 1.26
installed height- 1-21/32

326/350 HP:
Lobe lift- .2981 (higher)
closed spring pressure- 78-86 @ 1.66 (same)
open pressure- 180-185 @ 1.21 (higher, but compressed more)
installed height- 1-21/32 (same)

Notice that the open pressures are at different heights- so the springs are probably the same, but the 350 springs were probably "selected out" to meet the spec. This is common in manufacturing... to measure a products stats and throw similar pieces in the same bucket, rather than relying on a higher degree of quality control. They even used to do this when they manufactured transistors.


Rule of thum is that if you are installing springs that generate 40-50 more lbs of pressure than stock, then switch to screw in studs.

I was hoping someone had actually tried this (270H) combo so I could just slap the 270H in. Although I am "dumping" the engine, I will probably drop it in my truck, so I thought I would try the cam for kicks. I didn't want to rely on a rule of thum, so that is why I posted the question.
On any one elses engine, I would just machine the heads and install studs. Since it's my own, I can be "Bubba for a day".

I just measured the installed height and it is 1-24/32 which does not match the OEM spec of 1-21/32.
3/32 is a significant difference, so there is another issue.

I know the valves are not sunk because I did the machine work myself back when I re-ringed the engine.
When I found out the heads were 194's I decided not to spend any extra time or money on it, and I just slapped it back together as is (new rings, honed, new bearings, 3 angle valve job). Never even bothered to check installed height at that time.

Since it has been running for about 15 years with the 327/350 cam, I'll just leave it alone and drop the 12-106-3 (327/350) in it, as suggested by a few.
The weak springs will be fine as long as I don't beat on it while moving it around. I can change those easier when I have the engine on a stand.

Summit suggested their K1102 so I can use a "stock" distributor gear, but I don't like the specs on the K1102... they are weaker than the 12-106-3.
The car has sidepipes and stock exhaust manifolds, but the packings in the sidepipes have been gone since I bought the car back around 1975... so it is essentially running straight pipes.

Thanks again for all the suggestions.

Tom