Hot Rod Forum banner
1 - 20 of 157 Posts

·
Registered
Joined
·
706 Posts
Discussion Starter · #1 ·
Hello! I have started numerous threads in the past and have always been helped. Im hoping to return the favor to someone like me, in the future. (Even though you can find this build type countless times on countless sites all the frick over the place)

Going to try and post the best pictures as well as price throughout the whole thing.

First step is buying different pistons for my 1986 STOCK rebuilt short block.
Then looking for a roller cam, spider, bones, etc roller train components.

Probably going to use H345CP spreed pro pistons. Im shooting for 9:1 compression. I dont have them yet but I have 400 set back for a set of 64cc vortec heads.

I spent 425$ on the short block and 50$ on a gasket set.
 

Attachments

·
Registered
Joined
·
17,613 Posts
I don't understand why you would buy a completed short block and then want to begin changing parts, but hey, whatever.

Pay attention to the compression height of the pistons you plan to buy. Stock CH for a 350 Chevy is 1.560", but rebuilder pistons have a shorter CH (1.540") to compensate for shortening the deck height of the block. The shorter CH will make it more difficult to achieve a tight squish. Hang just the tip of one jaw of a dial caliper into the top of the pin bore and the other jaw at the crown just above the top ring. A 1.560" CH piston will measure 1.096"/1.097".
 

·
Banned
Joined
·
9,993 Posts
When you buy your pistons I'd buy a set that is close as you can get to the same weight as the ones you have, then balance them to match the pistons already in the block. It'll save you from having to rebalance it.
 

·
Registered
Joined
·
706 Posts
Discussion Starter · #5 · (Edited)
I don't understand why you would buy a completed short block and then want to begin changing parts, but hey, whatever.

As this is my first build... I'm sure this wont be the first inefficient move I make.
I screwed up and jumped the gun on this deal. Now im hoping I will beable to install the new pistons myself? I assume I need to take the old piston/rod combo and have a shop switch the pistons?

Also I believe the H345CP speed pro hyper piston is a standard compression height piston.
 

·
Banned
Joined
·
9,993 Posts
I don't understand why you would buy a completed short block and then want to begin changing parts, but hey, whatever.

As this is my first build... I'm sure this wont be the first inefficient move I make.
I screwed up and jumped the gun on this deal. Now im hoping I will beable to install the new pistons myself? I assume I need to take the old piston/rod combo and have a shop switch the pistons?

Also I believe the H345CP speed pro hyper piston is a standard compression height piston.
they should be the correct height if they haven't changed anything.

As for weight matching you can do it yourself with a gram scale, or have a shop do it. you'll need to compare the specs before you buy though between your current piston and your next one- word of caution speedpro hyper pistons tend to be HEAVY. A set of very gently used stokc LT1 pistons may be better (they're hypers made by Mahle and lighter- but they have a metric ring pack).
 

·
Registered
Joined
·
706 Posts
Discussion Starter · #7 ·
they should be the correct height if they haven't changed anything.

As for weight matching you can do it yourself with a gram scale, or have a shop do it. you'll need to compare the specs before you buy though between your current piston and your next one- word of caution speedpro hyper pistons tend to be HEAVY. A set of very gently used stokc LT1 pistons may be better (they're hypers made by Mahle and lighter- but they have a metric ring pack).
So the LT1 pistons are a direct swap as any other piston? Is there a particular year of camaro? 1992 camaro pistons?
 

·
Banned
Joined
·
9,993 Posts
So the LT1 pistons are a direct swap as any other piston? Is there a particular year of camaro? 1992 camaro pistons?
any LT1 piston will work, you will need to get the correct rings though, and will have to check balance on everything again. You can try buying them from a yard but you can also watch local ads, craigslist, ebay, etc.
 

·
Registered
Joined
·
706 Posts
Discussion Starter · #9 ·
From the pictues it looks like your block has new pistons in it. What is the purpose for the change? With 64 cc heads looks to me like your going to be close to 9.5 to 1 and use larger gasket if need be. Correct me if im wrong but arent the 4 valve flat pistons +5 cc right?


I wish those were 4valve relief flat tops but they are stock style dish...
 

·
Proud LOSER
Joined
·
2,185 Posts
From the pictues it looks like your block has new pistons in it. What is the purpose for the change? With 64 cc heads looks to me like your going to be close to 9.5 to 1 and use larger gasket if need be. Correct me if im wrong but arent the 4 valve flat pistons +5 cc right?


I wish those were 4valve relief flat tops but they are stock style dish...
Yah, I have those same same...factory small dish piston...um.....am I missing a page here? I can spew the same stuff you have all heard about a solid fun budget combo...but will refrain till later.....your welcome.
What's the purpose? What's the budget? What's the platform?
Maybe I missed it somewhere?
 

·
Registered
Joined
·
706 Posts
Discussion Starter · #11 ·
The pistons have 423Np stamped on them. Probably a rebuilder piston. Like i said i jumped the gun on this deal and bought the thing before i did research on the pistons.

Looks like I would be lucky to have 8:1 compression with these pistons and probably wouldnt even have that.

I dont want to build a dog of an engine i want good quench and strong compression. I have been looking at H345CP speed pro hyper pistons, they state 9:25 compression with a 64cc head.

Now I am wondering about my rods, I know they have been "resized". Does that mean I should NOT be looking for a piston designed for a 5.7 rod?

I cant seem to find a weight spec on either one of these pistons and I know about balancing issues....
 

·
Registered
Joined
·
706 Posts
Discussion Starter · #12 ·
Dont fix the block fix the part you do not have already. First off with 64 cc you will have more than 8:1 you should be able to buy heads in 58cc.

When i run my 350 numbers with 64 cc heads i get much diferent numbers.
United Engine & Machine Co. Incorporated

Check this site. Off the top of my head the stroke for 350 is 3.48 with gasket of 4.063 min and .043 thick with .025 deck and +5 cc dish i get 9.7:1 unless your dish is even more than 5 cc. You will need to actually measure i think once you run all the numbers you can rasie the compression with thin copper gaskets if need be but try to aovid it. Also gas is **** these days better to stay safe. 10:1 on iron heads is pushing it.


???? I am under the impression that the pistons in my short block are around -33cc maybe more becuse they sit lower in the hole "rebuilder piston"
 

·
Registered
Joined
·
706 Posts
Discussion Starter · #13 ·
:/ ill check block decking prices tmrw.. Your right and I should just leave the stupid thing alone. I am just upset about the quality of piston and worried about quench/compression. Ill just leave it alone though.
 

·
Proud LOSER
Joined
·
2,185 Posts
well I was only hoping for 350hp at best so that makes me feel better.
If your only looking for 350 reliable HP, and are on a beer budget.....find some 416 heads, spend some time, not money,time, porting them at home.....add 1094 felpro headgaskets, a used performer rpm or knock off equivilant, Holley 750, small 268 cam, long tube headers.....and a recurved Hei. This can be easily accomplished with the current short block you have. And likely for under 750$ on top of what you have already invested. It will be dead reliable, make the number your looking for, and give you a great feeling of accomplishment. And its fun when your buddies laugh at your budget build until they ride in it......there.,,,,,,I waited as long as I could.....sorry.
 

·
Registered
Joined
·
706 Posts
Discussion Starter · #17 ·
specs im reading sais 8:1 compression with these pistons under a 64cc. Im sure thats without a head gasket and a zero deck too lol. Im willing to spit out the 200-250 for a roller camshaft. I might just try and sell this block though. I need to sleep on it.
 

·
Registered
Joined
·
454 Posts
The 423np pistons are Speed Pro cast dished pistons. According to the Speed Pro electronic catalog they are 1.54 compression height "rebuilder pistons", with a .100" dish, 10cc dish/valve reliefs.

I don't see a H345CP piston listed.

The H345ACP is a hypereutectic flat top 4 valve relief piston with 1.548" compression height, so it's still .012" shorter compression height than the standard 1.560", but not as bad as most of the rebuilder pistons. The piston dome volume is 6.88cc, and the weight is 545 grams.

The H345NCP is a hypereutectic flat top 4 valve relief piston, full 1.56" compression height, 5cc dome volume, weight 546 grams.

You already have the short block with basically the factory piston style except for the shorter compression height. Either use it as is, or as suggested, disassemble it and have the block decked. Figuring you now have about .045" "in the hole", use a Fel Pro #1094 shim head gasket .015" thick, that will give you a .060" quench. With vortec 64cc heads you will still be about 9.4:1 static compression ratio, the same as the '96 thru 2000 vortec truck engines, and the same as the GM Performance Parts 350HO 350 cubic inch 330 HP crate engine and the CT350 350 cubic inch 350 HP circle track crate engine. These engines both use a very mild hydraulic flat tappet cam with .435"/.460" lift, 212*/222* duration at .050" lift, 112* lobe spacing angle. Even a very mild roller cam will improve these figures so you can reach your 350 HP goal.
 

·
Proud LOSER
Joined
·
2,185 Posts
ive been looking for vortec heads and a roller cam but are the heads you are suggesting 58cc? Still worried about compression figuring i should get the smallest chamber possible. I like vortecs flow numbers though..
Yep, before you get to stressed out about your pistons, search 416 heads, try and wade through the garbage from people who hate them, and have yet never used them, or used them wrong.....the more time you put in, the more you will get out. Find F-bird 88 posts, he knows what he is talking about.....yes, they are 58cc, yes, they CAN flow more then enough to meet your goals....and then some.....and people almost give them away.....mine were given to me free, my neighbour has a set for sale, 40$.....they are out there...with 1094 shim style gasket your compression will be there. I have a stone stock short block, my pistons look just like yours, I have a porting kit I bought, a small compressor, and a die grinder....assorted length carbide cutters.....and about 40hrs into them. Small lunati barebones cam, under 100$, I had a perfomre Intake, and a stock qjet card....it pulls....hard...very....on a gtech dashboard dyno it traps 112mph, factor in 5mph optimism....and I'm still around 107mph in the quarter......the math says 367hp......yah yah, its not a track.......I get that.....trust me...the math is close.....the motor works.....800$, from top to bottom....sees 6000rpm daily....gets decent mileage, sounds good, and has been reliable as hell.....look into it.......you will enjoy it.
 

·
Registered
Joined
·
1,684 Posts
Here is a website with the pistons that you have in your block. Federal Mogul Pistons 423NP - SummitRacing.com. Like was said the compression height is 1.540. 9.025-1.740-5.700-1.540=8.960. The piston would be .065 down in the block if the deck height is 9.025". Here is a website with the pistons H345CP that you want to buy. Sealed Power Hypereutectic Flat Top 4 Valve Reliefs Piston Std Size | Northern Auto Parts. The comp ht. is 1.548. 9.025-1.740-5.700-1.548=8.988 The piston would be .037 down in the block. With the new pistons in the block and a .015 compressed thickness head gasket with 64cc heads would have a static compression ratio of 9.669 and a quench of .052. If I had to make a decision like this I would get my measurement from the center line of the crank to the top of the deck. Then you can figure what comp. ht pistons you need. You can figure the compressed head gasket thickness and quench.
 
1 - 20 of 157 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top