looking for a 9:1 piston 454

[76zimmer]

We're looking to get 9.0-9.5 true compression ratio.
454 +.030, 119cc 781 heads, .039 (?) gasket.
Looking for a forged piston at a decent price, something off the shelf.

 

[4X4HIGH]

You also need to know what the deck height is. The piston could be as much as .030" down the bore when at TDC.

I also recommend you have someone CC at least one chamber of the heads to verify the actually CC's because i have seen them vary from 125-115 CC's

 

[76zimmer]

I'll have him do that Scott. Its a standard deck height 9.8 block. My machinist wants to try to go with SRP pistons if possible. I don't want to get into a custom piston though.

 

[4X4HIGH]

Are the heads rebuilt yet? I highly recommend having a chamber CC'd after they have been rebuilt to get as close as possible with your C/R you're looking for. You need to know how far down the bore that piston sits when it is at TDC and then you'll need to know the pin height of THAT piston so the math can be figured out for a different piston.

 

[76zimmer]

Let me see if I follow you Scott....the old piston needs to be measured down in the bore for reference of piston to deck height, and to reference the deck to pin distance? Those #'s will be used to get the new piston right. Am I following you here?
I'll talk to my head guy about cc's on the heads. I don't think he has started on the machining yet for the bigger valves, so that will have to be done first, along with the bowl work right?
That will give a basis for measuring the finished cc's, which needs to be done to come up with the formula for the new pistons.
I'll talk to the block machinist too, to pick his brain a little more. I'm sure he knows what he's doing, but I'm not sure I follow him entirely. He did say he was starting to look at some pistons in the 9:1 range though. I don't think I want to go any higher than that, for fuel quality sake.

 

[4X4HIGH]

Let me see if I follow you Scott....the old piston needs to be measured down in the bore for reference of piston to deck height, and to reference the deck to pin distance? Those #'s will be used to get the new piston right. Am I following you here?
I'll talk to my head guy about cc's on the heads. I don't think he has started on the machining yet for the bigger valves, so that will have to be done first, along with the bowl work right?
That will give a basis for measuring the finished cc's, which needs to be done to come up with the formula for the new pistons.
I'll talk to the block machinist too, to pick his brain a little more. I'm sure he knows what he's doing, but I'm not sure I follow him entirely. He did say he was starting to look at some pistons in the 9:1 range though. I don't think I want to go any higher than that, for fuel quality sake.

Yep, you're following along with me now. For the most part a flattop piston with a 3cc valve relief should put you as close as you're going to get without doing some expensive stuff.

The large valve install WILL change the CC's of the chamber so that definately MUST be done before you have him CC the chamber(s).

 

[4X4HIGH]

I just did some quick math and IF you zero deck the block, get the chambers down to 113, use a flattop piston with 3cc valve relief, and .039" gasket thickness you're still only at 8.512:1. If you don't plan to deck the block a realistic figure for deck height would be .025" down the bore on the piston and then your C/R would only be 8.175:1 with all else being the same.

I based this number off of a KB forged piston with 3cc valve relief (piston #IC780)

 

[Russellk30]

I have a few quick recommendations that you might not be interested in because of cost, but they are both practical and reliable.

It looks like you are trying to get higher compression ratio without sacrificing driveability or reliability. Stay with flat top pistons. They are less prone to detonation than domed pistons because the heat spreads across the piston face more evenly leaving less hot spots.

Install a stroker kit. This will give you higher displacement, more power, higher compression, and it will lower the RPM of the peak power numbers by a couple hundred RPM.

or..

Buy aftermarket heads with a lower combustion chamber volume. You can find them down to 100cc, which would put you right between the compression ratios you are looking for, all without changing anything else. Edlebrock makes a set that size. Another thing you have to worry about is detonation. A big block that sees heavy loads with iron heads and 9.5:1 compression could have detonation problems. Aluminum heads effectively increase detonation resistance by one compression point and could easily handle 9.5:1.

If you do stay with the Iron heads, you might want to get a thermostat with a lower opening point and a high volume water pump. Maybe even an oil cooler.

As far a forged pistons go, unless you are planning on abusing your engine, or making gobs of power with forced induction or nitrous, there is absolutely nothing wring with a decent set of hypereutectic cast pitons. Many forged pistons have a low silicon content and therefor expand much more when heating up. Hypereutectic pistons are built with smaller clearances, so you get less blow-by and better efficiency. For forged pistons, there is more clearance between the cylinder wall and the piston at start up, and because of this you may hear piston slap at start up. If you do go with forged, you should look for a type that is designed to expand little through warm up.

 

[76zimmer]

This is great stuff guys, I do want to go with forged pistons...we are going to stud the bottom for "possible" power adders in the future, perhaps nitrous. I want to have that capability.
He is going to line hone the caps with the change to studs.
I'm used to forged pistons, my Vette has had em forever in it, and I don't have any issues with how they act. For now we are just using a single carb.
I have a good magged crank, and rods, so don't really want to throw money at a stroker kit. I'm going over budget on this as is, but dont' want to have to open it up again in the future. I do not want to get into running race fuel to get more compression, thats why I want to stay at 9.0-9.5:1.
Is 9.5 to high for even premium (93 octane)? Thats about the best at pump fuel we have regularly around here.
I will call my head guy today, to see about the CC's, and then try to call my machinist tonight.

Thanks Scott, and Russell. I'm thankful for your experience, and input.

 

[Russellk30]

Since plan on running nitrous in the future, or at least installing a longer duration camshaft than stock, you should be fine with 9.5 compression. A camshaft with a longer duration/valve overlap will lower the dynamic compression making 9.5 static compression more manageable. With a stock cam and iron heads, 9.5 is about as far as I would push the engine even with higher octane gas. Using domed pistons to achieve the desire compression ratio would also lower detonation resistance.

You might ask your machinist about milling the heads too, and/or buying a thinner head gasket. Both would increase the CR.

 

[76zimmer]

we will be running a soild flat tappet 4/7 swap with 236/242 duration @ .050, and .568.578 lift. That should bleed a little off huh?

 

[Russellk30]

Yeah, that's a pretty big cam. You'll be fine. If you are looking for forged pistons and you haven't tried this yet, type big block chevy forged pistons site:craigslist.org into google so you can search all craigslist regions at once. Also under search options, choose the past week option so you don't get hundreds of expired ads.