[Scubasteve95]

I'm building a 455 with 11.4 to 1 compression my engine guy is confident I'll be able to run standard pump gas which around here is 91 octane but he's a race guy and I drive mine as a daily I do get into it every now and again at the local track but I think I'm going to have issues with the 91 octane on a Tri-State Cruise.
Here's a rundown of what I'm building:

1974 455 block decked to .005
1.5 harland sharp roller rockers
3/8 trick flow pushrods
74cc KRE D-port heads as cast 260cfm
Sealed power forged .030 pistons+6.7 / 4.1815 bore
Shot peened OEM crank
Shot peened OEM connecting rods 4.210
Cometic MLS head gasket .040
Comp cams evolution hydraulic lifters
Comp cams thumper roller cam 51-602-11
Holley Sniper EFI 800cfm

[Dragncar]

Ditch the cast rods (Molnar) and the pistons.
Both will hold you back.

[Scubasteve95]

lets get out of the other guys post,
not concerned with the rods or pistons( which have a 1/16 ring) they have done well for me over the last 8 yrs I'm concerned about the detonation on 91 octane with the high compression , some say with the new KRE heads it wont be an issue with the new camber and cam i have i don't have a calc to figure all that out i want to get ever once of power i can out of her and still pull up to the pump( cake and eat it to deal) just thought i would put it out there.

[Scubasteve95]

approx 190-195

Originally Posted by PunchT37

Nothing is absolute. What one can get away with "up north", won`t fly down here in the heat and close to sea level.

not sure who said absolute but if your talking about the 1 point he was only generalizing saying aluminum can handle more then iron

[PunchT37]

Originally Posted by Scubasteve95

approx 190-195




not sure who said absolute but if your talking about the 1 point he was only generalizing saying aluminum can handle more then iron

You asked about 11.4 and 91 octane. Some folks say yes, no problem. And, they probably have done it. I say, it depends a lot on where one is located.

Run 11.4 on cast or aluminum heads down here, on 91 octane, and you`re asking for problems.

The absolute wording came from advise that one can get.

[Jay S]

I noticed too that this new combination is getting the new evolution comp lifters. Those have only been out less than a year. So have you even ran that big thumper cam? Do you know what it will be like driving a cam with 95* of overlap?

I don’t think I can carry that much beer.

[steve25]

A big factor here besides the cylinder pressure you end up with is getting the Exh heat out in terms of having your motor survie on the edge of having too much compression for fuels you may be forced to run.

Are you running headers, or Exh manifolds.?

To keep info correct here, your cast Rods C to C is not 4.210", that's your cranks stroke.
The Rods C to c is 6.625.

These days with out of the box heads that can make over 500 hp I consider aftermarket Rods in motors with 4…210" strokes or larger a very smart way to go, especially seeing that you have to rebalance the motor for those Pistons anyway.

I can't think of a worse sonarero then a new build with cast Rods in it detonating from having too much compression.

Unless your a well experienced top notch tuner Your crusin for a bruisin with that set up!

Do be one of those guys that post back here in a year and a half with a ventilated block story to tell!

[ta man]

It is certainly doable..I'm at 10.8 to 1 with 190 cranking compression..and I can use 89 octane. WIth your build I think a different cam would have been a better choice.

[Scubasteve95]

there was a place in Trenton n.j. around the shop that does my drive shafts but the guy passed away its to bad he was a good dude and an encyclopedia on legs, had great stories too

[72projectbird]

Had a 455 with 205psi cranking compression. Was a .060 over block with forged pistons and rods, with ported #62 heads, an old Holley 850DP and a simple HEI ignition system. I didn't know if it was zero decked or not, so knowing the exact compression was up in the air. It was between 11.5 and 12.0 depending on how much was removed from the block.

Shaker455 helped dial it in. It ran on 93 pump.

[PunchT37]

It better not fall out of tune at all.


I have a 463 with Dave`s fast burn chambers. 72cc round port Eddys. 20cc Ross dish piston. It`s at 10.3 static with a 246/253 on 112 cam degreed at 107.5. Last I checked, it`s at 175-180 cranking pressure. I don`t have detonation BUT, it will run on sometimes in the summer down here. This is with 93 octane.


That will give you a clue.

[PAUL K]

I would never build an engine like yours and expect to run safely on 91 octane. Your heads won't support a cam that would let that happen. Your rod and piston choice wouldn't support the RPM the correct cam would need to operate.

I have no idea what the specs are on that cam but my guess is someone is thinking the extra exhaust duration is going to kill off cylinder pressure. That only works on a lawn mower while your pulling the rope. It's the intake valve closing point which has the most control over cylinder pressure and the Thumper cams close that valve earlier than normal and help build cylinder pressure.

[Jay S]

I assume with that bigger thumper cam a single plane intake and headers are in the plans.

I think the thumper cam with it’s 107 LSA is going the have to much mid range power (too high VE’s thru peak tq) for what you are wanting to do. It will be packing to much power in to narrow of a RPM range, and the heads won’t flow enough to spread the power out to make it work better. They don’t spread the power out as much as a ported 300+ cfm head, the extra head flow spreads the power band out more and makes it quite a bit easier to run more compression. I would want the compression to be more in the mid 10s with a good quench and that thumper cam and OTB D port head combo.

The last production run of speed pro 455 pistons appeared to have the compression height adjust down so they generally are .025” to .030” below the deck. If that is what you have, it takes some milling to get them to zero deck. The compression height was lower almost .020” from an older piston. If you don’t deck the block with the last version of those 455 pistons the compression will end up in the high 10s. But it needs a good quench to run that much compression. Something to else keep in mind. Not sure when the change was made. Can’t assume anything anymore though. Lol

[Scubasteve95]

SMH...
come on dude.
when someone says last forever do you take that as it will? what he ment was they will be fine.
when someone say hey nice car look at the size of the wheels there on steroids.. are they? why are you so angry and have to be right? I'm not here to debate you or argue with you ,since your first post you've done nothing but snipe. other people are giving me input and there experience not jabs enough already your dog is bigger then mine is that what you wanted to hear?i know you have been here a long time and have people here so go troll them.

here is your 1/16 second ring

[Dragncar]

Originally Posted by Scubasteve95

SMH...
come on dude.
when someone says last forever do you take that as it will? what he ment was they will be fine.
when someone say hey nice car look at the size of the wheels there on steroids.. are they? why are you so angry and have to be right? I'm not here to debate you or argue with you ,since your first post you've done nothing but snipe. other people are giving me input and there experience not jabs enough already your dog is bigger then mine is that what you wanted to hear?i know you have been here a long time and have people here so go troll them.

here is your 1/16 second ring

You came here asking for help. So I ran a TRW 455 for about 30 years and pushed it about as far as I could at 9-1 CR. Got down in the 10s. Now just built a 11.5-1 engine with aluminum heads so there is a comparison to what you are trying to do. Only I have safety margin on top of safety margin and even that is no guarantee of anything.
Post #4 is trying to tell you, and post #5, and post #7, post # 8( might want to listen to him) and post #9.
Its like you are trying to build a engine with a glass jaw and the price could be a hole through the side of your block.
Engines are very expensive and PMD blocks are not made anymore. Not to mention your time which plays into this.
A safety margin should be a part of any street-strip build and all it would take is a bad batch of gas with what you are trying to do and its all over.
Cast rods should not be a part of any semi serious build.
I have a 455 block out in my garage and I picked it up from a kid who tried to race it at our track. Kept the RPM low and had a smaller cam than yours.
I told him the same thing, ditch the cast rods. He did not take the advice and stacked the bearings when those cast rods egg shaped.
He was about 2 seconds from snapping that rod and ruining the block. The crank is junk.
Not sure where you get the angry part of what I am trying to say. I can be blunt, its not personal.
The 1/16 ring comment was mostly about being able to get a good ring pack and TRW pistons-pins are heavy. And you are slinging them on cast rods. That 1/16 2nd ring is not helping your situation.

People here are just trying to advise you not to build a potential ping monster with cast rods.
Good luck with your build.

[Jay S]

Paul treed me, I didn’t see his comments before I commented. My thought’s are pretty similar to his. I did not mention the cylinder pressure that cam is going to pump if it ended up at 11.4 SCR, my guess is 215 lbs.


A local guy had the next size smaller thumper in his 400 (406 cid) with round port 72 cc E heads, RPM intake and RA manifolds. His compression was in the mid 10s, I think it did run ok on 91 octane. It didn’t run that well though, I had a chance to buy it but passed since it was a 557 block. I think it made 350 HP to the wheels in his 4 speed 67 GTO. He was not happy with it, he sold it and built a stroker motor with KRE heads. I think he would have been a lot happier with it if not for the poor cam choice.

[PAUL K]

Originally Posted by Jay S

Paul treed me.

That's because I typed that response before my morning coffee.

[djustice]

It seems like we have a very similar shortblock assembly, i have 73 455 casting with a 455 "N" crank with stock cast rods and arp bolts. and sealed power/speed-pro/trw L2359 .060

When i changed heads to 85cc edelbrock heads i measuerd piston deckheigth and found it to be 0.001 in the hole. i can not 100% confirm if the block has ever been 0-decked before but deck stampings where clearly visible, if that is any indicator of decking or not.

[Scubasteve95]

Thanks for all the input I was coming up with the same info with the few calculators I was able to find online.I will definitely post back after I get this done. it's more like a rebuild I'm changing the heads over to the KRE everything else I've been using for 8 years at 10.75 to 1 with single plane intake, headers and 3in exhaust going to go with a .051 gasket bring it down to 11:1 I'd like to go 060 but I can't get them for about a month. Last time I had it on the dyno I had 355hp and 450tq to the rear wheels

[77 TRASHCAN]

Originally Posted by djustice

It seems like we have a very similar shortblock assembly, i have 73 455 casting with a 455 "N" crank with stock cast rods and arp bolts. and sealed power/speed-pro/trw L2359 .060

When i changed heads to 85cc edelbrock heads i measuerd piston deckheigth and found it to be 0.001 in the hole. i can not 100% confirm if the block has ever been 0-decked before but deck stampings where clearly visible, if that is any indicator of decking or not.

I have ZERO experiences building 455's, BUT
I've read here, seemingly more than once...Cliff mentioned that those pistons specifically are usually ONLY about .005 in the hole, with little room to get to zero, IF block needs much taken off. Of ourse that can be adjusted with head gaskets...
Cliff???