My guess - 40 to 50HP Caveat: with appropriate fuel- not pump gas or alcohol

 

NOT EVEN CLOSE--MAYBE 20




JOE SHERMAN RACING

 

Yeah, 20 additional HP at the very most - probably less.

 

And I would think the tuning window would be smaller and less forgiving.

 

Maybe 20 providing the dome is shaped correctly.Bill C.

 

15.5

540.748 Cubic Inches @ 6800 RPM with 110.00 % Volumetric Efficiency PerCent

Required Intake Flow between 382.7 CFM and 406.2 CFM at 28 Inches
Required Exhaust Flow between 266.8 CFM and 299.4 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 884.6 920.9 939.1 957.3
Peak Torque Lbs-Ft 756.1 787.2 802.7 818.3



14.5

540.748 Cubic Inches @ 6800 RPM with 110.00 % Volumetric Efficiency PerCent

Required Intake Flow between 382.7 CFM and 406.2 CFM at 28 Inches
Required Exhaust Flow between 266.8 CFM and 299.4 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 873.3 909.3 927.2 945.2
Peak Torque Lbs-Ft 746.5 777.2 792.6 807.9


Roughed some numbers into pipemax.

 

Maybe 2% increase... maybe

 

Yep all depends on head being used and piston dome used. Could be a loss too depending on Flame propagation. More timing pushing against pressure. 40 CC chamber vers. 119 CC chamber.

 

A good rule of thumb that we've come up with is about 7% of your displacement per point of compression. 548 x .07 = 38.36 hp.

 

Please explain as i've always used the general 20hp up to 13 to 1 and 15Hp after 13? Most here say maybe 20, yet your about double? I figured you'd found something the other don't have, care to expand on what is is?

38+Hp for going a point would be nice gains is this case.

 

The power gain per point of compression is a diminishing return, the higher the compression gets. The gain from 12:1 to 13:1 is higher then the gain from 13:1 to 14:1. This is due to not only the efficiency of the fuel, but the power it takes to compress the air/fuel mixture.
Depending on fuel, you're only going to see a 10-15hp gain at peak, but peak torque will be up about 20lbs.

 

The power gain per point of compression is a diminishing return, the higher the compression gets. The gain from 12:1 to 13:1 is higher then the gain from 13:1 to 14:1.

Yep

 

Before an after...1/2 point of compression, no other changes, from 11:1, to 11.5:1. 93 octane pump gas 572 with my heads and intake, Straub solid roller.

 

Looks like the AF liked it as well which may have accounted for some of the increase, that's crazy

 

Getting the mains line honed, cyl. torque plate honed with the correct finish, the piston to head clearance correct as well as the right ring package might add up to more than the compression increase.

 

You're right. I have a reputable shop in my area performing the machine work for me so I'm not concerned with that. We're changing the pistons and I have my choice of compression. It actually had 13:1 before so I figured it won't cost anymore to squeeze a little more power out of it.

 

Back before the internet in the mid 80's I read an article about the 1985 Nascar IROC series engines. They were trying to keep the top speeds down from regular Nascar speeds. They built the engines 358ci with real basic as cast intakes and stock 390 Holley carbs. They used a pretty mild (for racing) solid lifter flat tapped cams.

The cars were too fast so they dropped the compression from 12.5 to 9.5, a full 3 points with the pistons. Same quench, same weight etc. No other changes. They figured they would lose 40 horses or so. The engines only lost 12 horsepower. Four horsepower per point average.

They ended up changing the cams and some other stuff to get them down slow enough for their intended purpose of testing the drivers skills against each other.

 

On a high VE engine, removing compression by removing the dome can let the engine breath even better and the VE goes even higher making up for some of the lost compression. And if you think about it makes the cyl. "bigger".

 

A certain combo only "wants" a certain range in compression. As we can see from Foxwell's post, that engine is obviously more efficient with .5 point in compression increase but that's not a general rule IMO. It all depends.

 

A certain combo only "wants" a certain range in compression. As we can see from Foxwell's post, that engine is obviously more efficient with .5 point in compression increase but that's not a general rule IMO. It all depends.[/QUOTE]

 

Compression doesn't matter? Well on a drag car...if you don't have pop it won't pull when it's lugged down 1 to 1 in high gear. That's a fact.

 

Not sure I agree with that. Lot of very good running pump gas combinations out there.

 

Before you start believing higher compression does not matter. You should look at prostock and procomp engines. Seems as though they think differently as in general those compressions seems to be ris'in!

In this case we seem to be talking about a 548ci BBC race engine and it's probably going to be machined, clearanced, balanced and assembled as such so any free horsepower there from changes are nominal.

In this case it sounds like the effort and cost of the additional compression is easy and minor, so go for it! Run the right fuel, optomize the cam and heads for the added compression and I think Foxwell and I are closer to the marked increase. Why, let's say this 548 makes a conservative 950HP on 14.0 to 1. This is not a street engine this is a race engine. With just a +2 to 4% increase we have added a minimum of 20-40 HP and most of us know a well planned 548BBC at 14 to 1 on the fuel required will make easily over 950HP. Just do the math, 20HP max is selling short in my humble opinion. " Just build it right and it will come!"

 

My rule of 7% isn't going to apply to every engine. No one rule in this business applies to every engine. It's always going to be application and combination specific. The 7% has come from a lot of years of engine building experience from other builders and shops over the years. It seems to be a good "average" of what you can expect.

 

I'm sure the bigger the camshaft the more it matters.

 

i went from 15.2:1 to 15.85:1 on a 440" and gained 10hp

 

These high effort drag racing builds you guys do seem to make about 20% more power than pump gas deals. I attribute that to 4-5 more points of compression you guys run. Though your cams are probably bigger too.

 

Looks like others are following this subject too:

http://www.chevelles.com/forums/13-...ums/13-performance/1000770-whats-half-point-compression-worth.html#post10085650

 

And here's my response to your same BS there:
Do you have any personal experience to share, or does everything you know come from the internet or your legendary, record setting, record holding, imaginary racing friends?
There wasn't anything inefficient or lacking in the combination. It didn't NEED anything. It responded nicely to the half point of compression. That's all there is to it. Why, could be a thousand reasons. It wasn't exactly a turd before...
You really want to compare an unlimited budget and R&D Cup engine to a home built pump gas street car motor and expect the same results? LOL...
Keep trying John. Keep trying.

 

Here you go again. YES I have some experience with these thing. NOT my stuff, but 3 engine I help with.

360 inline SB Ford. Torched a gasket, surfaced head, raised comp by .6, put back together, Same dyno, gained 11Hp, raised peak power 1 or 200 RPM. 886Hp before 897Hp after Konigshofer Racing Engines built

360 18 deg SB chevy. After we seen what the Ford above did, change to shinner gasket. It made a bit less, 7 Hp from the gasket change and 1/2 point. 911Hp and up to 918Hp. BES/Moroso built

3rd one will keep on the back burner. 750+ pumpgas SB Chevy. Built by Extreme in Ny.

I do know NOT own these motors, and neither do YOU. My crew chief does. I travel and crew on his N.A 10.5 car. So I would say since I was there during build, dyno and seen on-track performance, I have some experience as seeing results.

 

I agree with NPS nova 100%,

There is much more to an over simplified "formula" to estimate compression ratio power increase or decrease. There are many, many factors that will go into a "power increase" equation.
Camshaft timing, bore size, dome size (flame front), fuel used, 1 point CR increase (from 7:1 to 8:1, or 15:1 to 16:1). Many other factors that I have not listed also.
To simply come out with an over simplified equation - and the defend it? lol because you are a big time engine builder with lots of experience?
Calling NPS nova's response as BS, because he doesnt agree with you? You are the engine God now? Your theories are FACT? really? lets get back to reality.

Nothing against you or your shop - you have done some very impressive builds - but stop and think before calling anyones experiences or theories BS because they don't fall in line with your theories. Yes, your equation is a THEORY - not fact!

 

Thanks CANADA. It's more then that. Like I said, we have different ideas on engine things. This mostly stems from Team Chevelle when I was started questioning Scott and Chris about a couple thing. Scott wasn't too bad, but Chris just outright lied. Weather it was the 4600+, 427 '69 Impala, or the dyno where the oil pressure drops as RPM rises on dyno.

Scott is right in one part. I have NEVER built an engine and only changed compression! Again I personally think once you change compression the rest of combo could take advantage of more as well. I have 5 "good" friends and have learned plenty from them and their experiences while racing WITH them and helping them. I do call out people if I don't know or think there B?S or making a false statement. NOT to be a dick, but maybe learn something new.

Thought maybe Scott found something NEW that we have missed? So I asked, That's all!:-Daw

 

Scott, no "personal agenda's" here.

Now I'm SURE you and Chris DO have one!!! Look back, I simple asked how "most" on here have stated and posted "around" 20Hp/point, yet I simply asked for you to expand on you rule-of-thumb? You did, BUT then BUT then turned it personal with the "your dumb hicks" and "not as smart as you" comments!!!!!

So i merely stated that if "most" of this industry on here see's about the returns that you do, maybe "something" in the engine liked the compression, or could have been lacking without it. YOU didn't build this engine either, you did heads and intake.

Scott, most here are pretty knowledgeable. IF they're not, they come on and get some education and hopefully some help to go in the right direction. So with that said, if say a mild enthusiast, has say a Vortec Pro, Pump Gas BBc motor that makes X amount of power, here might think/look into changing that combo from pumpgas to 15-1 and think he can pick up another 150Hp from that change alone.

Like Chris said in his OLD SCHOOL BBC 427 cam thread, he promised them 630 to 640HP, but it made 671Hp. Would it be better to aire on the low side of 15-20 per point as most have stated, then be over optimistic at 7% if engine size and not get the results!!

 

any other information on current combination ?

HP, RPM cam specs ?

 

14.8 to 1


499.665 Cubic Inches @ 9450 RPM with 122.00 % Volumetric Efficiency PerCent

Required Intake Flow between 558.5 CFM and 595.0 CFM at 28 Inches
Required Exhaust Flow between 342.9 CFM and 399.7 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 1327.6 1382.2 1409.5 1436.8
Peak Torque Lbs-Ft 796.4 829.2 845.6 862.0


11 to 1

499.665 Cubic Inches @ 9450 RPM with 122.00 % Volumetric Efficiency PerCent

Required Intake Flow between 558.5 CFM and 595.0 CFM at 28 Inches
Required Exhaust Flow between 342.9 CFM and 399.7 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 1251.6 1303.1 1328.9 1354.6
Peak Torque Lbs-Ft 750.9 781.8 797.2 812.6


OLD PONTIAC PRO STOCK.....

1436 - 1354 = 82/3.8 = 22 avg. as per pipemax old version

 

482 Ford FE 14 to 1 CR

482.334 Cubic Inches @ 6500 RPM with 106.00 % Volumetric Efficiency PerCent

Required Intake Flow between 311.0 CFM and 329.3 CFM at 28 Inches
Required Exhaust Flow between 222.1 CFM and 247.4 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 697.1 725.8 740.1 754.5
Peak Torque Lbs-Ft 624.5 650.1 663.0 675.8



482 Ford FE 11 T0 1 CR

482.334 Cubic Inches @ 6500 RPM with 106.00 % Volumetric Efficiency PerCent

Required Intake Flow between 311.0 CFM and 329.3 CFM at 28 Inches
Required Exhaust Flow between 222.1 CFM and 247.4 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 661.1 688.3 701.9 715.4
Peak Torque Lbs-Ft 592.2 616.5 628.7 640.9


754 - 715 = 39/3 = 13 avg. as per pipemax 3.7