Little Mouse

Put the pistons in that give you 9.5 comp. your good to go.

63mako

Your good!

breathial

As time goes on, I learn more and more. At the moment, I'm building my first tall-deck stroker motor (to sell to make $$ for another Vette... the family situation forced me to sell my last one).

Combination is as follows:
427 tall-deck BBC, bored .060"
4.5" stroke, 6.7" rods, forged pistons, ARP studs and H-beam rods, internally balanced.
My calculations indicate the TDC will be .020" below the deck height, -3cc valve relief.
I just scored a set of 290 large-oval heads, 2.19/1.88 valves, ported and blended bowls (for $350), ready to run. 106 cc chambers (polished).
With a .039" compressed-thickness head-gasket, I come up with (IIRC) a static compression ratio of 9.8:1.

The intake will be the Dart tall-deck oval-port version. It might kill a little torque, but not in numbers that'll matter for the average rodder...

I am not sure which cam it'll be, but I know that the red-line of the engine will be 5500 RPM, limited both by critical piston speed AND piston-ring acceleration limitations. Also, I'll install a hydraulic flat-tappet cam, avoiding the unnecessary costs of the "sexy" parts, and the decreased reliability which may occur due to the roller-lifter needle-bearings failing.

So I'm probably going to make this an idle-5000 torque GUERRILLA, that'll idle on pump-gas. My estimate is 475HP @5000, and ~600lbs-ft of torque at 3000, with torque exceeding 500 lbs-ft from 2000 to 4500. (Going off memory, here.)

The irony is, I'm using good-quality parts, but not using a water-cooled checkbook to build a monster, which should idle like ANY stock big-block... But pin your eyeballs to the back of your head any time you step on the go-pedal... :-D

As the parts arrive, I'll post pics, on this. A coworker was considering using this exact engine in his '72 roadster. I realized that this would require (probably) solid motor-mounts, block-hugger headers, and a smaller-diameter power-brake booster... But he's since backed out, since his two daughters in college take the lions-share of his $$$...

AWilson

Scott, how's it goin! I came up with 7.55 so I'm not going to worry about it anymore. Thanks.

AWilson

Thanks Mouse, I will.

AWilson

63mako, thanks!

MotorHead

A little info...take it or leave it. It is meant to help not hinder. My aluminum headed 406ci is 11:1CR, DCR is 8.3:1. My quech is .060" and my cranking pressure 230psi across the board. I run 91 octane pump gas ( I can get 94 if I want but don't need it ) and never had any problems

AWilson

I appreciate that MotorHead. It just tells me I will really be in the safe zone because all I want is 9.5:1 CR.

Belgian1979vette

230 ?

MotorHead

Most forum members who have been here for a while know that I don't post BS, things that I have heard, things that I have read, things that sound like they might work etc etc.

I only post things that I have done and seen with my own eyes work.
That way I know I will not give out misinformation to someone who is asking for help and potentially make the situation worse for him / her.

I don't post here to make myself feel better and to show people how smart I am and how much I know ( I save that for my girlfriend )

I post here to help fellow members and enthusiasts figure out what is best for them in regards to anything to do with motors and C3's in general. That is usually the main reason for my posts, other than
occasionally trying ( in vain ) to be a funny boy.

When I said 230 psi yup that just about hit it on the button


These two have today's timestamp on them, the first shows the gauge hooked up to my motor, the second one is down a pound or so because it was sitting a couple of minutes

Belgian1979vette

And no knock ? Are you sure about 8.3, because is seems pretty low compared to that reading.

MotorHead

I built the motor in my basement, I picked all the parts, I blueprinted everything, I can give you measurement specs on everything from main bearing bores to piston to wall clearance off the top of my head, yup pretty sure it's 8.3:1 DCR.

I posted the general specs CR, DCR, quench, and cranking pressure of my motor because I didn't like the way this thread was going. Too many measurements and specs were re-hashes of what is put on the web.

Those with 175psi cranking pressure should try and build a motor with 225psi cranking pressure and actually see if there are any problems rather than stating what was told to them.

Those that are stuck on .040" inch quench should try and find some dyno printouts of the exact same motor with .040" and .060" quench to back up their claims before going on the bandwagon. The general only built 34,000,00,000,000 motors with .060+ quench

And those that are shooting for 7.5DCR are probably leaving allot of power on the table.

I've done it, I've got the proof it works so sorry I just get a little po'ed when I see this stuff, that's enough for me on this one

AWilson

MotorHead,
I appreciate the comments, but I simply don't know enough to go against the consensus. And there is one thing. I want to keep this conservative because I don't want to wreck my matching components. But I truly understand your frustration. Imagine how hard it has been for me trying to do this. Knowing, that I don't know. But have to somehow come up with the right info. Eventually most of the truth seems to come out. Hopefully people don't get tired of answering my dumb questions. I am moving forward, just kinda slowly. All in all I still am very thankful that I have the forum.
Thanks guys!

MotorHead

Don't get me wrong what has been told to you is quite safe and you will have no problems. I wouldn't tell you to run 11:1CR and 8.5DCR either it's more the person that is looking to get the the optimal performance out of a pump gas motor that I am getting at.

Like I said you can run 7.5DCR, and you are OK, but I wouldn't want to go any lower than that because it will run like a dog. There was thread back a month or so ago about a member with a motor that should have been making killer HP and wasn't and as far as I was concerned it was related to low DCR.

So if you shoot for 7.5 and some of you calculations or measurements are a little off then you could end up with a dog. Personally for a mild buildup with a 355ci with iron heads I would shoot for 10:1CR and 8:1 DCR, hey wait a minute I had one of those too, and it ran good, real good, made 300RWHP and 334RWT

63mako

The other side of the coin is: if you shoot for 10.1 CR and 8.1 DCR with iron heads, have no concern about maintaining optimum quench and your calculations or measurements are a little off you will be building another motor sooner than later or looking for a place nearby that sells race fuel.

Especially when his objective is to get better performance but be safe so as not to destroy his correct components. Useable, 68 correct dated parts are getting harder to come by and way more expensive. JMHO

MotorHead

I said he was fine at 7.5cr I said personally ( usually meaning me ) I would shoot for 10:1cr and 8:1DCR I didn't tell him to

I also speak from experience because I have built a 10:1cr and 8:1DCR and had absolutely no probllems with it. I actually feel I can give advice if I have actually done something and it worked

MotorHead

I see you took out "This is a mild buildup ? "

Anyway I don't want to argue, like I said I am here to try and help, simple as that, not stir up anything so if I offended anyone my appologies. I was debating since yesterday whether to say anything and the guy on my left shoulder with the pitchfork won

63mako

Yea, I edited that out. I didn't want to aggravate you.
I am not a rookie. Been doing this for over 30 years, 4 years of collage automotive, 3 years full time at a performance machine shop, raced for over 15 years and have built and helped with more street and race engines than I can count. I have seen more than my share of melted and broken pistons, dropped valves, broken rods ect. and have seen, personally the aftermath of detonation.
We have butted heads on this a few times and probably will again. I know you have built a real nice 406 and run it for a lot of miles with no issues. But your A/F is right on, Your timing and curve is correctly adjusted, Routine valvetrain adjustments and inspection, Great cooling system. ECT. You need all these things to be correct and maintained regularly to achieve these results. For the guy that dials his car in close on build day and just wants a low maintainance, durable street engine with good performance, I think the OP is heading in the right direction. Just to humor me go with .040 quench on the 427 SB.
the guy on my left shoulder with the pitchfork won!

TheSkunkWorks

MotorHead, I'm in the same boat with you, in that I've noodled every detail since the first custom stroke, full-on racing engine I built nearly 3 decades ago. Back in the day, DCR wasn't something I gave much thought to. I knew it existed, tho I didn't know what it was called or what it should be, but I've gone back and found that the static CR / cam combinations of the better street build-ups I've done weren't too far off from these DCR rules of thumb which are coming, more or less, into acceptance. Apparently the cam techs I've paid attention to over the years didn't just fall off the last turnip truck to drive by, tho I wonder about some of them nowadays...

I'm still with you on <7.5:1 DCR leaving a good chunk on the table, particularly with SB's. When deciding to step the cam selection up for my pump gas, solid roller 496 BB, I elected to allow the DCR to fall to about 8:1 to leave some margin for top end cylinder pressures - something I figure I can afford to do since torque certainly won't be lacking. Such reasoning aside, 8.25:1 DCR should be a good target for most alum head hot rod street engines, but mid-high 7's is fine for "milder" builds.

I'm also OK with cranking pressures considerably above what is commonly advised in the popular press, as long as everything is right. It's not that precise of a reference point anyway, so I don't get too caught up in exactly where the needle points, unless it's way off from what I expect. Figure I'll likely see 200psi on the 496...

However, I feel it should be noted that the vast majority of those umpteen-million GM mills with >.060" quench operated no where near the limits of 92 octane gas, and that Mr. Yunick (who knew more about Chevy engines than about anyone who ever lived) found that a good tight quench is indeed important in truly high-performance engines. IMHO, accepting Smokey's case on this matter, until someone of similar stature shows that things have changed, shouldn't necessarily define anyone as unknowledgeable, by whatever means they may have come by it.

No offense taken, and none intended. Just my story and I'm sticking with it...

Belgian1979vette

I think that some of you will have a high speed knock with pressures much over 200 psi that is not audible. I don't say it will destroy your engine but i can't be that good. If the engine comes in its powerband and the filling of the cylinder comes near to optimal (100 %), your compression pressure could even be higher IMO for a very narrow rpm-range. More than likely you have some detonation in that range.

Of coarse with things like open, or load exhaust, mechanical cams etc, it may not be audible but my guess is it will still be there.

I do not think that what they say in the press is all true, but once you go to far, it won't be easy to go back. So maybe it is better to stay conservative even at the expense of some hp and tq