GTOguy

I'm running speed pro (Sealed Power) forged pistons in my '65 GTO (since 1981), '67 GTO (since 1988) and '61 Corvette (since who know's when). Old school technology and heavy compared to the latest fancy stuff, but tough as nails and dependable. I haven't opened up the '65 in 38 years, and it still runs great. The '67 has almost 90,000 miles on the rebuild and doesn't use oil. The '61 is due for a refresh due to worn rings. I like forged Speed Pro pistons, personally. The cast 'hypertectronic' and the teflon coated ones, etc. I have no use for.

ohpoppy

modern day speed pro's are made in india. They are value priced pistons unlike what you have. Forged are best but I'm not 100% convinced these are great pistons. The lower price is great but suspicious. I read good reviews on them..

the hyper pistons are priced right but not as durable as forged. do I need the strength of the forged, probably not I'm learning.

I was told modern day hydraulic lifters are superior to what we knew back in the day. There is no high rpm float or failure. Thzt's what the sales people say anyway. I remember having a blanket over a beautiful paint job while I mess with a hot squirting oily mess. I used to hate that job. even with clips it would spill over and hit the exhaust manifold and smoke. Every time I drop a hydraulic lifter in I remember those days. hmm

vmaxpwc

My engine builder, Kent at K&S in Tulsa, found the .020 over pistons. The engine bores were right on the boarderline. We first considered oversized rings but when he found the pistons we decided to just hone it to .020 over and put in the new pistons.

Cam was a speed pro 30/30 replacement with edge orifice lifters and springs. Used my original (circle) rocker arms with lock nuts and new pushrods. Just a clean up valve job without new seats in original heads. I run 100 low lead fuel. The engine only had 61k original miles and had never been apart. This is from memory.


Also ran motor for an hour on dyno to break it in and check power level.

SWCDuke

Unless you measured deck clearance before you disassembled the block no compression ratio calculator on the planet will give accurate results. Deck clearance is the biggest variable in the compression ratio calculation. This is all explained in my article that I previously recommended you search for and read. Better shops have tools to measure deck height of a bare block and from there you can compute deck clearance and make accurate compression ratio calculations.

Unless you plan on serious racing, hypereutectic pistons are fine and less expensive than forged. Follow my CR recommendations for your available fuel octane and you'll be fine.

Duke

ohpoppy

the hyper and forged pistons I mentioned are the same price.. Duke, which would you choose?

deck clearance is impossible for me to determine since I got the block disassembled. summit used ,003 as a figure. the block has not been decked so likely the compression will likely be slight greater I believe.

cv67

pistons can be anywhere from .025 to .050 down the hole
The indian hypers are cheap stuff but they cost hardly anything either
If you arent revving it to the moon and your tune is good you are fine.

Investing 200 in an 02 sensor kit can give yo upiece of mind...no timing by ear either lol

SWCDuke

My specific recommendation is the Keith Black KB157 hypereutectic. I believe it is manufactured in the USA. Do a Web search.

As I said previously, good machine shops have tooling to measure deck height of a bare block. Then using nominal rod length and piston compression height you can compute deck clearance of the assembled engine and use that and the other necessary measurements to accurately compute CR. This is all explained in my compression ratio article.

Did you read it???

Duke

ohpoppy

I haven't the patience to search those old threads but I will call the machine shop, he's old school and may know. I like the look of the pistons you recommend. the indian ones are not hyper, they are forged. Duke, you seem like a smart guy.. are you quite sure the forged ones aren't the right choice?? the K black ones come with a floating pin which I prefer. I don't trust myself with a propane torch and icecubes! I was going to pay the machineshop to place the pins.

back in the 70's I adjusted FI porsches and alfas with a in the tailpipe o2 sensor. Over the last few years I've contemplated I should find one somewhere for this car. I didn't realize a daash mounted one existed. i should have known.. thanks for that info. Its seems to me adjusting that rochester with a mixture gauge would be simple if the rochester is ok. That guy in Carlisle pa rebuilt it 20 years ago so it should be ok.

jim lockwood

If you want to get a wide band, air/fuel gauge, buy equipment from Innovate Motorsports. And once you have it, contact me. I'll be glad to instruct you on what to do to calibrate your Rochester FI and the order in which to do it.

Jim

ohpoppy

thats a great offer Jim.. I will. it will take some time before I get there though. thanks

ghostrider20

Why .030 over? Is that what it needs to be bored to clean it up? Will .020 work? It would be well worth your time to read the dissertation SWCDuke authored on my rebuild. All the parts, sources, etc are there.

ghostrider20

I used the speedpro L-xxx forged stock replacement piston, .020 over. Sent the piston to Aries to have Them bored and cut for floating pins and spiro locks. Used Crower sportsman bushed rods.

ghostrider20

https://www.corvetteforum.com/forums...27-lt-1-a.html

ohpoppy

I read the post..
by the way.. not sure it will be ,30 over, it was a guess.. will know when he does it. block appears to be low mileage at a glance

question about deck height.. I thought if they are straight all is fine, didn't realize there can be variations. My block is stamped on the deck FI #'s. Decking it risks losing the #'s and ruining the value of the car. I suppose it could be decked and #'s could be restamped but then its a fraud.

I know so little.. When I was young I worked mostly on Porsches , but they were newer stock motors that just required a turned crank valve job and pistons. Porsche had jugs so cylinders were just replaced. My personal cars had big block I used to race but they were newer factory builds with mild modifications.


I just read a post in this regard and I understand it better now.. I'll see what he says and maybe decide to run it "slightly off" or maybe he can leave the number area alone.

63 fuellie

I think what fuel you are going to run is the key here. I found ethanol fuels don't idle well in the warm weather with the Rodchester unit so I run 1/2 110 and 1/2 high test and its ok, straight 110 would be better but expensive. I used 11 1/2 domed pistons and comp cams solid lifter cam to be as close to original as possible. If I need to run that fuel for the fuelie unit anyway why not run the bigger pistons
On a side note I was at a cruise night this summer with my old hot rodding buddys and they asked how did I get my car to sound just like they used to, I said that's what its supposed to sound like

ghostrider20

You don’t want to deck the block, just measure it and find out where it’s at. IIRC 9.25” is nominal. Don’t let your machine shop guy engineer your build.

SWCDuke

Nominal deck height is 9.025". The nominal sum of crank throw radius (1.625"), nominal rod center to center length (5.700') and nominal piston compression height (1.675") is 9.000", so nominal deck deck clearance is .025".

The biggest variable is deck height. As the broach tools wear, it increases. I've seen decks up to .015" high and .010" side to side variation. This is why deck clearance must be measured to accurately achieve a target compression ratio. Otherwise you're just guessing.

The best time to measure deck clearance is before the block is disassembled. Each cylinder should be measured to determine if there is any slope (usually it's not enough to be of concern). Then the new deck clearance can be determined using values for the new parts. Some replacement pistons like KBs have slightly higher compression height than OE.

If the left deck is higher than the right it can be machined down to equal the right side without consequence because the machine work is not visible once the head is installed. The right deck should not be touched to preserve the original stamped data and broach marks. Another alternative is to use different thickness head gaskets side to side to make up for any variation in side to side deck deck. This will help equalize SCR on all eight cylinders. I like to keep max variation to no more than 0.1 and 0.05 is preferred.

The above is why I am always harping about PLANNING and doing a FORENSIC TEARDOWN if you want a truly precision engine that maximizes performance and doesn't detonate. Just tearing down the engine and sending everything to the machine shop is a recipe for disaster and there are many horror stories on the Web. The final outcome will be directly proportional to your planning and forensic teardown effort, but all too many guys completely ignore this.

Duke

cv67

you CAN deck blocks these days, plenty of places can send yours out and have the block CNC w/a program to save the almighty #
QMP racing in Chatsworth Ca is one

Compression is what makes your engine work the way its supposed to..Id pick a cheap forged piece over the best hyper.
OE hypers are better grade than what we can buy. if you tune yours with an 02 sensor and it dont run hot then maybe but why worry?Its very little money for lots of piece of mind.

Yrs ago the mentality was to drop compression, not. We have efficient heads even a double hump look alike (tfs 175) build it right.

SWCDuke

Yes, but "11:1" engines often were dropped to 8.5-9:1, which was foolish.

Most 11:1 engines were closer to 10.5 when they left the engine plant, and modern pump gas is a couple of points below the best sixties premiums (93 PON ~ 97-98 RON). That's why I recommend no more than 10.5 with the LT-1 cam and 10.3 with the L-79 cam with . 0.1 reduction for each point reduction in PON. A couple of tens can mean the difference between detonation, which will require a lazy spark advance map with less than the 38-39 ideal total WOT advance and an engine that will tolerate an aggressive spark advance map that will yield maximum torque bandwidth.

Words like "built it right" are worthless BS. It's all in the details and experience.

Duke

MikeM

There are thousands and thousands of engines out there that were rebuilt and didn't go through all that rig a ma roll you describe and they perform perfectly for mahy tens of thousands of miles. Maybe not perfectly but very acceptable.

All that "perfection" just adds to probably double the cost of a rebuild, and is totally unnecessary for the avereage enthusiast on this forum. Paying attention to what the engine looks like when you take it apart goes a long ways toward whats needed for a decent rebuild that lasts a long time.

But you can do it your way.