low compression

[moper]

I put together a '73 with 7?K miles on it 440 back in 1991. I pulled it, pulled the heads, de-carboned the chambers, lapped the valves, cleaned up the piston tops, installed a windage tray, an HV pump, new timing set, a set of MP "hemi" springs, and a Crane H302-2 cam. With an iron 6bbl and 1 3/4 tube cheapie headers, it ran for two years, hit 6500 many times, and went a best of 12.4 @ 104, on pump unleaded in my 70 cuda. In an A body, that same engine would run closer to 12.10s, and that was with 3.91s and a 2200 convertor. A real convertor, a set of 4.30s, and slicks, and I'd bet I could get a similar car into the 11s.

If anyone's got a running engine, I'll do my part...lol

 

[RustyRatRod]

Don't ask me. I aint going down this road again.

Think! If your overhauling it, then why not HI comp slugs? It aint cheap anymore.

I'm out of this convo.

Wasn't trying to cause a problem. It just was not clear to *me* so I asked, that's all.

 

[cudaboy 67]

im keenly watching this, runnin a 440 now and am stoney broke. no one round here with mopar so id win my regional class even if didnt turn up lol

 

[bad440]

Oh lookie here, prime example;

Answer, because some people simply do not have the money to do a full and total rebuild. Isn't that what the low compresion question is about Moper?

With this statment alone, you shove the person with no money into a corner and make fun of him as being a cripple and shouldnt bother trying to have fun and make power with his engine.

I guess, "Broke/low income guys should not apply/subscribe to adding extra power to there engines."

Is the new answer, "If ya can't afford to rebuild the MoPar, go run a cheap *** Chevy?"

i represent that broke /low income group,and the basics apply:cam intake,ex.,will make more power,but moper is right you wont keep a low(to me low is below 9 to 1)comp.if you can help it.and it limits you tremendously.bet you can't make that 400 with stock heads only cam and etc run quicker than 12.00 and those engines had about 7.8 to one comp 75 up.and chevies cost $$$ to go fast too.and break easy....
oh yeah i forgot IN an a body.the 12.00 thing.

 

[IQ52]

So i was sitting here and had a thought:
What kind of BB mopar can be built with low compression to handle pump gas and make some big hp-naturally aspirated, no NOS etc...? Any ideas or tried and true methods?

New here, but the original question seems pretty simple. Not knowing the exact defination of "low compression", I offer two examples.

1) 8.0:1 compression, 383, stock forged crank, stock rods, .040" overbore cast pistons, ported 906 heads, single 4bbl, 524 HP.

2) 9.7:1 compression, 451 (oh my, another one?) forged 440 crank, H-beam rods, forged pistons, ported 906 heads, single 4bbl, 694 HP.

Nothing spectacular. The 383 could have been run on 85 octane, though we tested it on 91 octane, as we did the 451.

Dad told me there are three secrets to building horsepower. The first two are cylinder heads and the third and most important is cylinder heads. I think a big horsepower discussion must include something other than stock cylinderheads as a stock BB mopar head is going to limit you generally to the 450 HP range.

So, as a general rule, pick an engine size 383-440, run low compression (8.0-9.5:1), use a stock head and figure some 450 HP maximum.

By-the-by, there's nothing wrong with stobbin' a big cam, headers, intake and carb on your stock shortblock and and stock heads and havin' some fun. Might not run real efficient but it will make more power and still be FUN.

 

[bOb shingler]

the generally accepted rule on "low compression" is under 10-1 ratio.

 

[jamesdart]

those numbers sound almost unbelievable.

 

[ibleedmoparts]

That was my original intent with this thread "low compression" , seems everybody generally agrees < 10 is low...main reason i started this was to have fun and talk shop about budget builds or even high $$ builds that can make HP and run off the pump...i still think it would be fun to have a low compression shootout...thanks for everyones inputs thus far, i look forward to reading more

 

[IQ52]

That was my original intent with this thread "low compression" , seems everybody generally agrees < 10 is low...main reason i started this was to have fun and talk shop about budget builds or even high $$ builds that can make HP and run off the pump...i still think it would be fun to have a low compression shootout...thanks for everyones inputs thus far, i look forward to reading more

"high $$ builds that can make HP and run off the pump...."? Not low compression? Well....

Here is the same 451 shortblock as above with ported Edelbrock Performer RPM heads (340+ cfm) @ 11.7:1 compression running on 91 octane Chevron Supreme, Erson Custom Solid Roller 276/280 @ .050" .816"/.816" lift, Indy Single Plane, 1140 cfm Pro-Systems Dominator.

Yes, it does say 786.9 HP at 7,200 RPM. This little engine made 500 lb-ft of torque from 3,500 rpm to where we shut it off at 7,600 rpm. Drove it around on the street, just filled it up at any premium pump, some fun!

Small potatoes. If they will comment, there are people out there that can make some unreal power with big motors (600ci+) on pump gas.

So were you looking for "low compression", "pump gas" or "low compression-pump gas" builds? I'm still not clear on that now.

 

[moper]

They are looking for low comression, not the ability to run pump gas.... That's where I was confused (and beaten up for...lol) too.
I'll also add, the street engine that is low compression will be sluggish unless the other components of the package (meaning gear and convertor) are matched to take advantage of the higher rpm nature of the power. A friend's stock eliminator engine was also low (blueprinted factory) compression, all stock parts except the duration and lobe shape of the hydraulic cam. It made 485hp 10 yrs ago. But, it made it from 6500-7400rpm. The car was a stick with 5.57 gears. That's why I say it's much more about the whole car, than just the engine, when we talk a low compression package.

 

[Rice Nuker]

Sounds pretty fun. Low budget stock parts. I would run those early bb heads for more compression. I think they are clsed chamber.

 

[green1]

We got the 440 back from Dvorack, and in a Charger, all it does is smoke tires, 3.55 posi.93 octane.

The engine is 9.0 cr, 750 eddy, iron heads.Msd. You can't get Dan's tricks out of him, but going down there 4 times, I think he slipped up and told. You can barely hear the cam rump, but I think he bought a cam with a little more duration than stock, (don't ever ask him to compare a cam to the several purples, lol), with a very fast ramp, fooling the engine into thinking it had more duration after idle. And he claims he found a grind that tricked the engine into thinking it had 3" exhaust.
As far as lift? secret, I can't get it out of Dan, And can't get my bud, the owner, to pressure him for the cam card. We haven't even gone full throttle yet, car in 2nd (forte 727 3000 stall), and all over the place; his street-crappy asphalt. I told him those BFG 's wouldn't hold it, lol.
Full exhaust to rear,2.5.

I think the trick is good heads, and the cam, for low compression. I think he messaged the heads pretty good, I know he installed bigger valves.

He told my buddy, before he agreed to the price, that this thing will jump forward, at the lightest throttle. And it does, if you can get traction; No winding up to get in the powerband; it goes off idle.

 

[Doosterfy]

Seems like this same debate keeps coming up. I would use a 440 for the cubes. To keep costs down (that is the idea right?) I would look for some 383 heads with closed chambers to try and raise the comp. as much as I could. See if the heads could be cleaned up without going crazy on them. Use a flat hyd cam with Rhodes lifters, maybe a Comp Cams 292 Magnum for example, use a performer RPM or a Torker II with 750 to 850 carb. Freshen up the short block of course. Its not going to make huge power but I'd estimate maybe up tp 450 hp. I've posted before that I did things like this with GM engines and got decent results but I'm still new to Mopar so I havent tried it. Remeber though engines like this usually don't last.

 

[jamesdart]

ive heard from more than one guy the closed chamber heads do not work on the smogger engines with the piston way down in the hole. you dont get the benefits from the closed chamber unless you are close to zero deck, all they got was real bad detonation. that doesnt really make a bunch of sense since the low po 383s that came with the closed chamber heads had the pistons pretty far down too. i also knew one guy that put larger valves and ported a set of 516 heads switching from similarly prepped 906 heads and he actually slowed down a little.
this is just things ive heard. i have a pile of BB heads here and i do have a set of 516s but ive always been leary of dumping a bunch of cash into them.

 

[RustyRatRod]

For this particular discussion, my take on "low compression" was whatever the engine has from the factory, not as much as you can get away with on pump gas. Rumblefish, I am beginning to see you r aggrevation. lol

 

[IQ52]

So i was sitting here and had a thought:
What kind of BB mopar can be built with low compression to handle pump gas and make some big hp-naturally aspirated, no NOS etc...? Any ideas or tried and true methods?

I just wonder if this would be worth attempting to build/research and run on a dyno...i like to think about "what could be"

See thats what im talkin about-499hp on pump gas...what do you guys think max compression would be for 91 octane?

I don't seem to have found a maximum compression yet. Just two weeks ago we tried 11.9:1. With iron heads and 500 ci it made 742 HP. There was what appeared to be ring flutter above 6,400 rpm, blowby got bad and power dropped off. Was it the 91 octane fuel?

Thats really the idea, more power, less octane, ANY pump...i think it would be a really good build

I would be willing to give it a shot...best HP so i can run low octane gas...

Real point of my initial post was to see if anyone had a good, low compression, pump gas, good HP combo. I think a "smog" shootout would be loads of fun in the future if no one cheated. Plus in my opinion it emphasizes budget build and makes you use your noggin on how to get the most outta a boat anchor

That was my original intent with this thread "low compression" , seems everybody generally agrees < 10 is low...main reason i started this was to have fun and talk shop about budget builds or even high $$ builds that can make HP and run off the pump...i still think it would be fun to have a low compression shootout...thanks for everyones inputs thus far, i look forward to reading more

Maybe it's best to try to understand the intent of the original poster and keep to his idea of the thread. There seems to be some flexability there and he seems to be open to slight interpretation variations.

 

[IQ52]

ive heard from more than one guy the closed chamber heads do not work on the smogger engines with the piston way down in the hole. you dont get the benefits from the closed chamber unless you are close to zero deck, all they got was real bad detonation. that doesnt really make a bunch of sense since the low po 383s that came with the closed chamber heads had the pistons pretty far down too. i also knew one guy that put larger valves and ported a set of 516 heads switching from similarly prepped 906 heads and he actually slowed down a little.
this is just things ive heard. i have a pile of BB heads here and i do have a set of 516s but ive always been leary of dumping a bunch of cash into them.

The 516 is just not a performance head when compared to the 906. They may look the same to most people but there is a BIG difference. If you have a choice to go with the flow of a good set of 906s or the compression of the 516, "go with the flow" every time. Even the small chamber BB 915 can't flow as well as the 906 and I've tried real hard to figure out why.

 

[RustyRatRod]

According to Mopar Muscle, the 906 is a regular passenger car head. The 452 actually beat it out in a couple places. If the 906 was so great, how come Chrysler put them on 383 2bbls in station wagons? I agree the 516 isn't a performance head. Chrysler actually only made one HP head for the big block besides the Max Wedge and that was the 1967 915 head.

 

[ibleedmoparts]

As everyone has noticed this "low compression" business is open to interpretation- this was my original train of thought/intent

1) Build a low compression big block( low compression due to high octane restrictions and issues caused by not running high enough octane gas)

2) Have fun and see what parts combinations folks put together to create some good HP out of a solid pump gas motor

3) The more budget minded, the better

This was more of a fun thing trying to get great minds and mechanics together, maybe that cleared up my intent as it may have been missed

i look forward to getting everyones ideas together and doing this. If I had a dyno it would make combo building of this nature a blast

 

[IQ52]

Stroker,

This thread gettin' off course?

These are the reasons, I say what I say, about the 516, 906, 915 and now the 452 heads. We have ported and tested them. I don't know what anyone else gets, but these are flow results I pulled from some of our tests. These are not the best results we have gotten except for test (3) the 915 heads. The upper lift flow gaps between the 452 and 906 heads is typical in our fully ported heads.

1) As a standard from our bench, a box stock Edelbrock Performer RPM 440 head
2) Ported 452 2.19 intake
3) Ported 915 2.25 intake
4) ported 906 2.25 intake
5) ported 516 we tested them once, we now throw them away and use something else

-----------(1)-----------(2)-----------(3)----------(4)

.100".......73 cfm..........90 cfm...........87 cfm.........91 cfm
.200.........146...............166..............157..............165
.300.........209...............218..............212..............219
.400.........254...............255..............253..............272
.500.........276...............278..............285..............299
.600.........287...............288..............309..............325
.700.........291...............294..............321..............335
.800.........000...............000..............327..............339

I guess if we're gunna continue this line we oughta find an applicable thread or start one.

 

[green1]

Ring flutter- install 1/16" rings, 1st and 2nd. Streetable. with mahle

 

[RustyRatRod]

Stroker,

This thread gettin' off course?

These are the reasons, I say what I say, about the 516, 906, 915 and now the 452 heads. We have ported and tested them. I don't know what anyone else gets, but these are flow results I pulled from some of our tests. These are not the best results we have gotten except for test (3) the 915 heads. The upper lift flow gaps between the 452 and 906 heads is typical in our fully ported heads.

1) As a standard from our bench, a box stock Edelbrock Performer RPM 440 head
2) Ported 452 2.19 intake
3) Ported 915 2.25 intake
4) ported 906 2.25 intake
5) ported 516 we tested them once, we now throw them away and use something else

-----------(1)-----------(2)-----------(3)----------(4)

.100".......73 cfm..........90 cfm...........87 cfm.........91 cfm
.200.........146...............166..............157..............165
.300.........209...............218..............212..............219
.400.........254...............255..............253..............272
.500.........276...............278..............285..............299
.600.........287...............288..............309..............325
.700.........291...............294..............321..............335
.800.........000...............000..............327..............339

I guess if we're gunna continue this line we oughta find an applicable thread or start one.

That's kinda what I was sayin. Your input is welcome here, believe me. Knowing you from the MM forums, this place needs you. You're a sharp tack for sure. But "MY" thinkin on this thread was factory low compression....as in 8.2 and probably lower. lol But it's gone so astray now.....start up anerdun if you want. I'll jump in.

 

[IQ52]

Stroker,

You are right, 8.2:1 is low compression. But you can do respectable things with it as you well know.

My son bought his wife a 71 Scamp. He took the stock 318 bottom end, pulled some old 2.02/1.60 valves out of the trash can, installed them in the 318 heads with some bowl work, shoved a Comp 270S in the cam tunnel and used some 273 rocker arms and pushrods to hold the lifters down. Had a $20 aluminum single plane put under a $30 Edelbrock 600 cfm Performer. It sounds like a big block, makes 320 HP and turns heads where ever it goes. Pulls right off idle and feels like it will never quit winding. Uses 85 octane. Anyone can feel like they own a race car even on 8.2:1.

 

[ibleedmoparts]

Stroker,

You are right, 8.2:1 is low compression. But you can do respectable things with it as you well know.

My son bought his wife a 71 Scamp. He took the stock 318 bottom end, pulled some old 2.02/1.60 valves out of the trash can, installed them in the 318 heads with some bowl work, shoved a Comp 270S in the cam tunnel and used some 273 rocker arms and pushrods to hold the lifters down. Had a $20 aluminum single plane put under a $30 Edelbrock 600 cfm Performer. It sounds like a big block, makes 320 HP and turns heads where ever it goes. Pulls right off idle and feels like it will never quit winding. Uses 85 octane. Anyone can feel like they own a race even on 8.2:1.

IQ-
This is what im talkin about! budget builds, good hp, and LOW octane!!!! That comment right there hit the nail on the head

Floyd

 

[67 prostreet gt]

go with what im doing, a 500 cube stroker, 440 block, indy heads, intake, quick fuel carb, should make around 570 with 10.75 to 1 compression, it all matters on the cam, used to know someone who always said, " cams make the engine, not the engine makes the cam" crazy i know but the man was a genius with a 413 max wedge