Team Chevelle banner

1 - 20 of 23 Posts

·
Registered
Joined
·
118 Posts
Discussion Starter #1
Building a 100% street 406. I have a choice between 64 CC and 68 CC heads. I am GUESSING the 68 CC heads are my best choice between the two. What do I use for a piston the will be pump gas friendly. NOT forged please. Should I avoid a dished piston because of the quench?

I have read that with the 68 CC head and a.039 gasket .013 dished piston I would end up with 10.3 compression which seems to high to me, I think flat tops make it 10.9:1 ugh...Thanks for your anticipated help.
 

·
Super Moderator
Joined
·
12,959 Posts
Cast iron head or aluminum ? Stock 400 rod length ? Stock deck hgt ?
 

·
Registered
Joined
·
118 Posts
Discussion Starter #3
Aluminum heads, I think the rods are 5.7. I don't know if it has ever been decked, but I'll guess its stock, I don't have the short block in front of me...
 

·
Super Moderator
Joined
·
12,959 Posts
If you are using 5.7 rods then a Sealed Power H615P will be 9.75 with 68cc and 10.14 with 68cc H616CP bumps it up to 10.4 with the 68cc head. Of course that can or will change depending on deck hgt. I would not be afraid of 10.4 to 1 with the aluminum heads and 93 octane unleaded.
 

·
Registered
Joined
·
1,887 Posts
My 406 last year had 10.8 compression with flat top pistons and Vortec heads that were 68cc's after I opened up the chambers. I ran it on 100 octane though as I do not and cannot hear detonation at WOT to be on the safe side.
 

·
Registered
Joined
·
11,685 Posts
If you are using 5.7 rods then a Sealed Power H615P will be 9.75 with 68cc and 10.14 with 68cc H616CP bumps it up to 10.4 with the 68cc head. Of course that can or will change depending on deck hgt. I would not be afraid of 10.4 to 1 with the aluminum heads and 93 octane unleaded.
I agree. Our average engines were 9.5-1 with iron heads, 10.5-1 with aluminum. If we were looking to push it we’d go 11. Don’t forget piston deck height in your calculations too.
 

·
Premium Member
Joined
·
11,318 Posts
There are some cases and luck where some guys are running 93 with as much as 11.5 to 1 maybe slightly higher, but not many. Everything in the tune is spot on from what I have seen. Ever small detail is examined and looked at though.

Installing a wide band in the headers would be wise choice to monitor AFR would be money wisely spent. You can then tune the tune on the go. Almost impossible to read plugs on pump gas these days.

Studying on subjects such as flame travel, combustion, and etc would be a benefit.

Read Eric Niefert's page on his website. Eric started on pump gas and then made the jump to E85. Might help.

Tech Articles | Horsepower Innovations
 
  • Like
Reactions: Aml383

·
Premium Member
1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
Joined
·
7,784 Posts
I have a 10.7-10.8:1 alum headed 489 that runs fine on non eth 91 & 93 pump gas and is a little out of tune (hadn't been able to get back to the engine shop) but no pinging and starts/runs good, I was under the opinion from reading when you get past 11.5-12:1 with alum heads tune needs to be spot on along with higher octane, I'm also thinking this question would get more answers in the Performance section..?
 

·
Registered
Joined
·
118 Posts
Discussion Starter #9
I picked up the short block last night, 5.7 Eagle Rods and Eagle Crankshaft, It had the Speed proo615cp's as recommended above . Two of the six pistons were cracked. I found out the engine had a supercharger on it which likely explains the piston damage. I am just going to put it back together with new pistons, Hyd roller cam and most likely a set of 68cc 200 runner Skip White NKB heads.

Should I consider either Keith Black pistons with I believe a 22cc dish or the Silvolite dished , I don't have the specs on the silvolite looks like a deep dish [speed pro 13cc dish

I'm thinking I'm leaning towards the speed pro as recommended above but would love you input on anything

Cam is a Howards 100245-10

Has anybody ever used the ultra cheap roller lifters off ebay? 1/4 the price of name brands..[I'm cheap]
 

·
Registered
Joined
·
226 Posts
KB has 18cc dish pistons you could use with 68cc heads, be aware some rebuilder type pistons have reduced compression height to go with assumed deck surfacing
 

·
Premium Member
70 Malibu, Orion silver/black
Joined
·
169 Posts
I'm quite happy with the Speed pro H615cp pistons. That's all I've ran in my motors for 20 years and they're currently in my 406. It's 9.5:1 with 72cc Dart Iron eagle platinum 200's and 9.020 deck. I'm doing a .040 build with forged pistons and aluminum heads now, but that's a different story. I busted a ring land and cracked a skirt once with the Speed pro pistons, but that was my fault (too much timing and too tall a gear). I'd try to keep compression below 10.1:1 with hypereutectic pistons, but that's just this guy's opinion. Those are good pistons.
 

·
Registered
Joined
·
118 Posts
Discussion Starter #12
When trying to calculate compression I get different numbers from different places with the same combo.

I'm set on 68cc headsm block never decked, and the H615cp pistons. I think the head gaskets at .039. Is there a reliable way to figure out what the compression would actually be? I'm guessing 10:1 would be close to perfect, but I would rather it was 9.5:1 than 10.5 :1...
 

·
Premium Member
Joined
·
7,019 Posts

·
Registered
Joined
·
226 Posts
using the UEM pistons calculator it's about 9.8 to 1- if the block is 9.025" and the gasket is 4.2" X .039"
 

·
Super Moderator
Joined
·
12,959 Posts
The Sealed Power piston book that I have says 9.76 with a 68cc head and .025 deck hgt. It is a 12.5cc dish.

I personally prefer the Sealed Power pistons over KB.
 

·
Premium Member
Joined
·
7,019 Posts
I figured 68cc head , 18cc piston 0 deck .04 head gasket. All 3 came out to 9.76.
 

·
Premium Member
70 Malibu, Orion silver/black
Joined
·
169 Posts
With 2 different calculators, I came up with 9.80:1 and 9.78:1. If you know that the block hasn't been decked, then I say run it. It'll do great with that camshaft too and you'll be a happy man.
 

·
Registered
Ryan
Joined
·
182 Posts
When trying to calculate compression I get different numbers from different places with the same combo.

I'm set on 68cc headsm block never decked, and the H615cp pistons. I think the head gaskets at .039. Is there a reliable way to figure out what the compression would actually be? I'm guessing 10:1 would be close to perfect, but I would rather it was 9.5:1 than 10.5 :1...
Just for your peace of mind, I run 11:1 in a 383 (385) on 91 pump with 36 degrees total and have zero issues. I wouldn’t be scared to run 10.5:1. Here’s the combo:

-4.04 flat top pistons
-zero decked block
-0.039 gasket
-64cc head
-Hydro roller on a 108 with 237/243
 

·
Registered
Joined
·
118 Posts
Discussion Starter #19
Thanks for all your help fellas, I ordered roller cam, heads and pistons today. Now all i need is all the pieces parts like head bolts, gaskets pushrods, guide plates, all the tin and on and on.

Why are some of the fel pro had gaskets so expensive? Do I need $50 a pop head gaskets?
 

·
Premium Member
70 Malibu, Orion silver/black
Joined
·
169 Posts
It's really up to you if you need them or not. I'm using Fel pro 1014. It's more of a high performance gasket over their $20 stock rebuild gaskets. You're building a high performance motor. Easy choice if you ask me.
 
1 - 20 of 23 Posts
Top