Building another 350 for a friend and found some interesting things on teardown. Engine had a rebuild in the past but had low compression. Cam was a Comp 260. The pistons were 657P at .030" over. Actual measured spec for this piston are 26.5 cc dish. comp height 1.794. I know the block deck was not cut and don't believe the heads were either. pistons were down the hole .111 on the right bank and .104 on the left. The heads CC'd at 60.5 for the right head and 58.5 for the left. Actual compression worked out to 7.2 on the right bank and 7.4 on the left. So much for the stock rating. I swapped the head numbers left to right and that would then be 7.3 for each side. I'm using the Autotech dished pistons without cutting the block.(saving the stamped numbers) Will cut the heads .030" and should end up with 9.4. Crower level 3 cam.
Thanks Steve for the information. Very useful and helpful! How'd that camshaft look (wear) and how many miles were on it when you tore it down? Gary
P.S. -- is it any wonder why the factory engines leave something to be desired? It's not the camshafts people... Who do you know who builds an engine for performance and uses stock components, but decides to blueprint and properly match compression? Who would know just how much more efficient and powerful that engine is compared to the factory engine that preceded it? Who indeed... Gary
Don't know how many miles were on the rebuild. Other than some carbon on the pistons they look pretty new. Cam looks fine.
whats the max rpm of that cam at the strip? whats shift points? I would like to try this cam also in a mild setup but with 3.90 or 4.10 gears 26 in tire.
deplete? if you didn't use the .020 gasket you will have dropped compression . you gain alittle for overbore. deck heads .060 and measure cc of head,measure depth of piston below deck and get .050 shorter pushrods from TA. if specs come out to my estimates you could have about 8.91 comp. I am doing this exact setup with porting heads and custom shorty headers
So on this topic what is the actual stock compression height? I hear from some it's 1.81, others say 1.875. I'll be measuring mine but I'm still curious.
stock piston is rated 1.805 . if crank wasn't quite indexed and rebuilt rods you can loose some compression depth. there are no pistons I know of for buick 350 rated at 1.875 compression height. 1.855 are autotec and silvolite hyperutectic. 340p are 1.830 rated
This is where I'm so confused because TA is listing 1.875 as stock compression height. Not trying to get off track here just wanted some clarity. It seems there are plenty of piston options out there to reduce the need of milling heads or decking the block. Even more so if you want to stay with dished pistons. With autotech pistons since you can specify compression height without additional charge it's easier to get a desired compression ratio without some of the hassle of milling heads changing pushrod length and making sure the intake side of the heads are milled.
Stock compression height is 1.8. I went with the Autotec dished for this build at 1.85. No deck cut and slight head cut to get to 9.4. The level 3 cam will rev to 5800, maybe more, but becomes sluggish after 5200. Curse of the dual plane intake. I have my trans set to shift at 5200. The RPM drops right into the meat of the torque curve.
This sounds exactly like my '68 stock cammed 350...but with a few less ponies and 3x the life expectancy. :grin: Also corresponds exactly with the dynometer program's power curves of stock ('68) vs Crower level 3 camshafts in identical engines with properly matched DCR's (for each cam). Gary
What's probably more important is where is the actual deck height and how much variance did it have from engine to engine and year to year. Book says it's 10.187, but I've been reading that you need to add .020-.030 to this, and this was before the info in this thread. The listed compression height may have been what was put on paper from the old books ages ago when the pistons used then are no longer available now. All aftermarket pistons put their compression height lower than the factory pistons so as to give leeway for decking and head shaving. Gary
Do you think this cam will work well enough in a 8.8 compression engine? Just yanked a set of heads off a 71 engine to port and possibly bigger valves and thinking about shaving .060-.070 off heads and using this can at 4 degrees advance with 3.90 gears. This is just a for the season race engine.
