Building 3.4. Part deux. What pistons for 9.5-10 compression?

[f85gtron]

If I go with a larger cam, I'll need higher compression, according to the cam specs (crane 272, or 260 w/1.6 rockers).  The 3.4 comes with 9 cr already. The block i have out at the machinists is getting a .030 over bore, so I'll need pistons. I've read that getting dohc pistons will provide the 9.5 i think i need, but will it be too much for the crap gas blends that are readily available?  Remember, it's going to be a spirited daily driver, not a track car.......on a budget.

[Raydar]

The DOHC pistons are reputed to provide 10:1 compression.
Here's a build thread from Pennocks. Doesn't say much more about it than that.
http://www.fiero.nl/forum/Forum2/HTML/122475.html

I ran stock (not sure if oversize, since it was a rebuild) pistons with my 272. I was able to run regular unleaded, with at least 10 - 12 degrees initial advance. I did run the cam a few degrees retarded, relative to the crank, however. I'm not sure how that plays into it. The same engine, before the porting and cam change, would ping with the stock cam, on anything other than premium unleaded.

[Raydar]

Just thought of this...
If you want to, send a message to Freddy Clark on my FB list. He probably did one of the first 3.4s I've ever seen. He ran DOHC pistons in his. It was well documented, but the web pages died.
He turboed his, too, which ended up leading to it's demise. (Too much boost, looking for those last few hundredths of a second, at the drags.)

[f85gtron]

Thanks Raydar,
Here's what I've done:
Went with regular pistons, @ 9.5-10cr (closer to 10 because the deck is shaved too)
Went with the 260crane cam and 1.6 rockers....(that way, i can remove the rockers if i find a suitable small turbo, which turbo is not an option with the 272 cam).
I figured it'd be better to be safe than sorry.
Any pointers on assembly? 
Any tips on valve springs?

[Roger]

Lightly chamfer, use a thread chaser and then vacuumn out all bolt holes and passages.

[f85gtron]

Thanks Roger.
Good tip. I forgot all about that. I would have remembered after ringing off a bolt head though.

[Raydar]

I've never heard anything bad about the 260. Pretty sure it's the same cam that came in the GM HT3.4 crate motor. The lift numbers are identical.
I forget which springs I used. I think I took the Summit recommendation, but I'm not sure.  I'll have to poke around. The main thing I was looking for (at first) was something that would work with the 272, that would allow me to not have to modify the heads for spring height. But that was not to be.
 
FWIW, I really liked  the Comp Cams 1.52 roller tip rockers. They are cast, instead of stamped like the stockers. And they're waaaaay cheaper than the full roller rockers.
Keep in mind that changing to 1.6 rockers will get you the same lift numbers as the 272. Strange how that works out. I was surprised.

[f85gtron]

That's the effect I was shooting for, 260+1.6rockers = 272.  The spring recommendation is the same part no. for both cams.
Got the block back from the machine shop and the cam bearings they installed are scratched. They said that's normal because of the way they're installed and that they normally ream off the large flash then put a cam in with cutting fluid and turn it a few revolutions to make sure nothing catches. They said because the bearings are sooo soft, they break right in even with scratches and gouges. It makes sense, but should I worry about it?

[Raydar]

I've seen cam bearings scratched before. Didn't cause any issues.
You said they recommended the same springs for the 272. Did they mention any clearance issues?
I really would encourage you to measure the installed height and the compressed height with your particular combination, to make sure nothing will bind. (Of course, they may have come up with some different springs in the 10+ years since I built mine. Back then, .454/.480 was an issue.)

[GTRS Fiero]

So...what happened?

[f85gtron]

It must have broken in ok. I've run it in run for the hills, from Augusta, ga to Memphis, tn 3 round trips.  No wipes yet. I pulled the valve covers while changing injectors and oiling looks good and even. I'm thinking if things where not right, they would have shown themselves in the first 1k miles?  Anyone with experience or a story to tell please chime in!

[Raydar]

Most people I've heard of that had problems, had them fairly quickly.
I never had any problems with mine, for the entire time I owned it.
The guy who bought it from me drove it for a while, then resold it to someone else. THAT person had a valve spring to break, after driving it for a while. I don't know what became of it after that.

[GTRS Fiero]

Wasn't that the Grooms build that had problems, anyway?  Didn't TFF do the R&R?

[Roger]

Springs flex and mechanical motion are transformed into heat. They also set up a harmonic vibration. The same goes for push rods. The spring diameter, width, height and both end seats must be equal. The spring seats must be perfectly flat. To tell the truth, if you were to drop a valve spring onto a hard surface it is then an odd looking paperweight. Deformations and scratches of any kind will be where the spring will eventually fail. Subjecting a valve spring to a different tension that what it was designed for by going from a worn 1.52 to a new 1.6 lift ratio is like taking an old person not used to running and putting them in a marathon. Something is going to give. Some of this may sound extreme but anyone who says they did it without any problems just haven't yet run out of luck.

[Raydar]

Wasn't that the Grooms build that had problems, anyway?  Didn't TFF do the R&R?

The Grooms build blew a head gasket, due to a broken head bolt. TFF did do the R & R.
Once that was fixed, I drove it for a while, and then took it back down to a short block. That's when I built it back up with all the hot rod pieces, including a different pair of heads, that I sent off to be "worked", prior to the build.

The springs that were installed on the ported heads (It was one of those springs that broke, later on) were installed fresh with the 272 cam and 1.52 rockers. They never were run with 1.6s.
I did run 1.6s for a while, but that was earlier - on the Grooms "stock" rebuild, after I got it back from TFF.