Dynamic compression for 91 octane gas

[69 GTX]

So I'm doing some number crunching for my upcoming 446 cid engine build. I'd like to be able to cruise with 89-91 octane gas. Thant being said I was using the Wallace Dynamic compression calculator. My proposed set up was
4.35 bore
3.75 stroke
6.76 rod
9.25:1
78cc chamber
.04 head gasket
1000 ft alt.
result:
Static compression ratio of 9.25:1.
Effective stroke is 3.55 inches.
Your dynamic compression ratio is 8.61:1 .
Your dynamic cranking pressure is 174.81 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 8.61 :1.


I have read that for 91 oct I should keep it under 170. I'm trying to use the best piston, head to get the best quench possible to help. Do you guys feel this would be to much ?
I know the cam can make a huge difference.

- - - Updated - - -

I'm trying to obtain 550-575 hp. So pushing it a bit.

 

[Jim's Maxie]

So I'm doing some number crunching for my upcoming 446 cid engine build. I'd like to be able to cruise with 89-91 octane gas. Thant being said I was using the Wallace Dynamic compression calculator. My proposed set up was
4.35 bore
3.75 stroke
6.76 rod
9.25:1
78cc chamber
.04 head gasket
1000 ft alt.
result:
Static compression ratio of 9.25:1.
Effective stroke is 3.55 inches.
Your dynamic compression ratio is 8.61:1 .
Your dynamic cranking pressure is 174.81 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 8.61 :1.


I have read that for 91 oct I should keep it under 170. I'm trying to use the best piston, head to get the best quench possible to help. Do you guys feel this would be to much ?
I know the cam can make a huge difference.

- - - Updated - - -

I'm trying to obtain 550-575 hp. So pushing it a bit.

Where did you come up with a .04 head gasket or is that a mistake ?

 

[Jackpot50]

Yea were getting .04 head gasket and I think HP numbers are out of reach, maybe with 93

 

[69 GTX]

My mistake I was using another calculator and it asked for head gasket thickness.
Was going with comp cams 274 roller with 1.6 rockers to get .570 ish lift with .236-240 duration @ 50 (from memory)
Trick flow heads & 6 bbl for starters.

 

[Seventy]

aluminum heads and mid grade pump gas, shoot for 9.5 to 1 static' should be fine. If you have some specific want or needs I would leave the math to the builder, this way if the dyno doesn't show what you want then you have someone responsible, not just a bunch of guys on a web forum...

Now if you just want a 550 hp 440 that is one thing getting it to run good on 89 octane is your obstacle, as you know its going to limit you cr and since this is a street car you are also going to be limited on cam profile..

I say stroke it, that will make it much easier to get 575 on pump gas in a street friendly engine.

I would grab a source stroker kit and a set of their aluminum heads, it will cost you less than a set of trick flows and get you closer to what you want.
TF's are around $2K a stroker kit and set of heads from source is just over $3000 (call them have a package deal made up)... So your build will cost much less going with the source stuff...

 

[69 GTX]

Your right, I was thinking of having IQ52 build it. Was just wondering if I could do it with 440 first. Great input.

 

[lewtot184]

if you plan on much driving and want 89 octane gas and 550-575hp with a stock stroke engine; then i'd lower my horsepower expectations or find a happy dyno.

 

[Seventy]

Your right, I was thinking of having IQ52 build it. Was just wondering if I could do it with 440 first. Great input.

I was just doing the math over the weekend, I have a great block that will clean up far before -30, so I figure build it now because my builder is going to be retiring soon, I have a 1970 Charger R/T that I am going to pro tour, nice A/C automatic, black bucket console plum crazy car NO ROT all there... Its a few projects away BUT I am always collecting stuff for them all...

So I priced..
Source heads and stroker kit $3130
Fel Pro gasket set $45
valley pan $15
Mancini rr main kit $60
Summit windage tray $50
MSD pro billet with 6al, coil, wires, plugs $725
Roller cam, lifters, timing set, rockers, push rods, dist shaft, fuel pump plate, $1200
Intake and msd fuel injection system (normally I would wait to buy this until the car was ready BUT, I want the motor dynoed all done) $2050
So around $8K all built and machined, I already have tons of pans, valve covers, water pumps, intakes, etc..


I am picking up an engine when he gets back from vacation so I am thinking of ordering all this stuff and dropping it off all at once, just havent made up my mind 100% yet... UNLESS someone wants to give me $12K for the car as it sits, Ill throw the block in and they can do it, lol...

But seriously, stroke it for them numbers, and that money, since you were thinking about tf heads figure it this way.. if you already own stock rods and crank...

TF heads $2000
Pistons $600
Rings $100
Bearings $140
crank work $200
new rod bolts $50
Fit pistons to rods install bolts etc $120
balance $300

That comes to around $3500 and if you have a good steel crank and rods they can be sold for $500ish!!! So it doesnt make sense to go any other way. I wont use cast heads unless I am doing a correct engine anymore, Figure it costs $350-500 in labor to clean, check, match, assemble with a comp valve job a nice set of 906's, then buy cheap valves for $120, springs, locks, retainers, seals, another $200 you are into the set of heads for almost as much as a set of source heads and you can sell your old cores.... Just not worth it... same thing with the rotatting assemblies by the time you turn a crank, balance it all, buy the pistons, rings, bearings, bolts, and pay the labor to do it all you can sell your crank and rods and have a stroker for less money....

good luck, I am sure if you go build a roller cam, roller rocker, source head, stroker motor you will be happy with it...

 

[Dennis H]

Man, this is Rocket Science. The 440 in mine is 9.5:1 compression and runs fine on pump 91 **** gas here on the left coast.

 

[69 GTX]

Looks like stroker it is!

 

[67Satty]

I'm running static compression of 9.5:1 and dynamic compression of 8:1 with 91 octane California pump gas and iron heads with no quench, a small duration cam and 34 degrees of total timing. I race it and beat on it in 80-100 degree temps with no detonation.

So I would think you could go higher than 9:5:1 compression with aluminum heads right? When I finally upgrade to aluminum heads, I will run somewhere between 10:1 - 10.5:1 static compression and don't anticipate any issues.

 

[Seventy]

Looks like stroker it is!

Awesome keep us updated...

 

[1wild&crazyguy]

As for having to keeping it under 170psi cranking....thats not true.

I can't even say for certain that the 184 cranking psi [ 8.8 dynamic] i run on 91 octane is the limit either.

 

[mentor70]

if your running aluminum heads, you need compression to make them work properly.

my current 440 build needs around 185-195 psi to be at its best. flat tops and 78 CC chambers.

with proper timing and tuning 91 oct it possible.

my last 496 was 11.6 to 1 with Edelbrock heads, 850 demon, MP mech dist, and a 250 @ .050 Hughes solid cam it runs like a champ in Socal

 

[1wild&crazyguy]

if your running aluminum heads, you need compression to make them work properly.

my current 440 build needs around 185-195 psi to be at its best. flat tops and 78 CC chambers.

with proper timing and tuning 91 oct it possible.

my last 496 was 11.6 to 1 with Edelbrock heads, 850 demon, MP mech dist, and a 250 @ .050 Hughes solid cam it runs like a champ in Socal

Yes indeed, and really any motor i have a hand in i try to get the compression up as high as the octane will allow, it's more power everywhere in the rpm range and helps under the cam range to boot.

I live in socal and the 184 psi cranking 8.8 dynamic i mentioned is with a stroked 10.1 sb 410 with IRON open chamber heads w/quench dome pistons and a [email protected] solid roller, not aluminum heads. I think there are plenty of people/builders leaving a considerable amount of performance on the table.

 

[69 GTX]

Yes I'm trying to get all the free HP I can by running close to the edge (for 91 octane). I feel if I push it a little to much I could always go up to a .060 head gasket or 93 octane. I guess I really need to nail down the cam first to get my intake valve timing first.

 

[MOPOWER871]

STROKE IT, Just got my 496 dynoed,Eddy rpm 84cc heads, Performer rpm intake 850 demon carb, Eagle 4.15 stroker crank, rods,icon 40 over pistons,final compression 9.7:1 crane hydraulic roller cam #HR-230/352-2S-12 with 1.6 rockers, cloye's double roller timing chain, milodon oiling system.ATI damper TTI 2" headers / 3" x pipes exhaust, msd ignition 18 initial 36 total.motor made 536 hp @ 5200 588 tq @ 3600 runs made high 500 toque #'s from 3600 to 5500, great on 93.pump gas gonna try lowering the octane once i get a feel for the old girl so to speak only got 300 miles on her. plenty of grunt for a street car [video=youtube;WjjneSiNKhY]https://www.youtube.com/watch?v=WjjneSiNKhY[/video]

 

[747mopar]

I'm running 9.8:1 on my 456 with cast iron 452s with no issues running 93 octane. I've ran 89 in it but it will ping a bit if loaded at low rpm's.

 

[69 GTX]

Think I'm going with 440, Jim says no problem getting 550 HP with 6bbl & cam I want. So we start the build soon.

 

[451Mopar]

If your using the trick flow heads let us know how they work out.