how much more power with a compression bump?

Posted By: mshred

how much more power with a compression bump? - 10/17/11 01:34 AM

Hey guys,

Just curious how with everything else being the same how much more power my engine could pick up with a compression bump from just under 9:1 up to about 10.5:1? The current configuration has the pistons below the deck about .083". So with the new compression I would be zero decked with about .040" quench. Here is a mild run down of the engine...best time is in my sig...guessing at about 320hp at the wheels

1991 360 Roller block
Bone stock bottom end
9:1 compression
RHS heads prepped by Brian at IMM engines
custom ground hydraulic roller from Brian at IMM with specs as follows:

Gross Valve lift with 1.6 rocker arms- 577 int., 569 exh.
Duration at .050�- 230/230
Lobe Separation- 106
Cam installed at 101 Intake Centerline (5 degrees of advance ground into cam)

Topped off with an Eddy air gap, Holley 750HP, 1-5/8's headers, 3" exhaust

So how much more power can I expect to make? If i can get this engine to e/t the car to a high 11 on the motor I would be super happy.

Posted By: MIKES_DUSTER

Re: how much more power with a compression bump? - 10/17/11 01:43 AM

Ive heard every point is about 30hp.

Posted By: 451Mopar

Re: how much more power with a compression bump? - 10/17/11 02:50 AM

Posted By: DaytonaTurbo

Re: how much more power with a compression bump? - 10/17/11 09:37 AM

I think years back one of the mopar mags did a dyno test and saw roughly 4% power increase for a 1.0 increase in compression on a 450hp or so street 440.

Posted By: Crizila

Re: how much more power with a compression bump? - 10/17/11 02:50 PM

I know this doesn't answer your question, but raising compression has deminishing returns. You will get more of a HP return going from 8:1 to 9:1 than from 12:1 to 13:1, etc. I would say the range you are looking at would still have good returns HP wise. To come up with an actual # would be a guess on anyones part IMO.

Posted By: nhramark

Re: how much more power with a compression bump? - 10/17/11 03:11 PM

You need 4 tenths. I'm not sure those pistons alone will get you that much. But with the higher compression plus the ported heads and that big cam, I would say your upgrade should include 1 7/8 headers. that combination might get you into the 11's. The engine will be out of the car already.......

Posted By: Dodgem

Re: how much more power with a compression bump? - 10/17/11 05:51 PM

My opinion 1.5 compression numbers will only gain you 15 to 18 hp. You need 40 to 45. I would bump the compression to 10.5 with a bigger 254/264 ish cam .620/.600 ish lift with 108ish LSA.
Those two things should get you there. A step header 1 5/8 to 1 3/4 might be a great add on without giving up any bottom end. (or 1 7/8??) if you can afford CNC porting that will add even more.

I don't feel a 230 duration cam will get you there.

The better quench of a 0 deck piston should help some more for sure!

Posted By: gregsdart

Re: how much more power with a compression bump? - 10/17/11 06:48 PM

Give Brian a call. He built it, right? Sharp guy.

Posted By: Dunnuck Racing

Re: how much more power with a compression bump? - 10/17/11 07:57 PM

I have a truck/towing build in the truck section I have been working on. It is on my dyno now,a 440 with factory closed chambered heads. When I recieved it,it had KB quench style pistons but was set up with too much quench clearence.
I took the .053 head gaskets out and went to a .020 steel shim gasket to tighten up the quench,that gained me just over a half point of compression.
With the quench fixed and the small bump in compression,it gained roughly 30 hp. The best part was that it really helped the power hang on for a lot longer than before.
Keith

Posted By: polyspheric

Re: how much more power with a compression bump? - 10/17/11 11:36 PM

X2, cam is too small.

Posted By: polyspheric

Re: how much more power with a compression bump? - 10/17/11 11:43 PM

Jennings pointed out 35 years ago that the volume in the squish band does almost nothing - it burns too late, and burns with lower efficiency than the remainder of the chamber volume, which adds to emissions.
That's why the chamber on 452 etc. RB heads is recessed - to get that volume exposed to the flame front at the right time, and reduce emissions.
If you have a 10cc band at .080" now, reducing the band to .040" and 5 cc not only suppresses knock, etc. but also adds 5cc to engine size.

Posted By: Brian Hafliger

Re: how much more power with a compression bump? - 10/18/11 03:23 AM

Quote:

Hey guys,

Just curious how with everything else being the same how much more power my engine could pick up with a compression bump from just under 9:1 up to about 10.5:1? The current configuration has the pistons below the deck about .083". So with the new compression I would be zero decked with about .040" quench. Here is a mild run down of the engine...best time is in my sig...guessing at about 320hp at the wheels

1991 360 Roller block
Bone stock bottom end
9:1 compression
RHS heads prepped by Brian at IMM engines
custom ground hydraulic roller from Brian at IMM with specs as follows:

Gross Valve lift with 1.6 rocker arms- 577 int., 569 exh.
Duration at .050�- 230/230
Lobe Separation- 106
Cam installed at 101 Intake Centerline (5 degrees of advance ground into cam)

Topped off with an Eddy air gap, Holley 750HP, 1-5/8's headers, 3" exhaust

So how much more power can I expect to make? If i can get this engine to e/t the car to a high 11 on the motor I would be super happy.

With Kb 107's at zero deck, if your heads were 62cc that'll be 10.6:1 so I would back the cam up so it's straight up. That will pick up power in the upper end while the compression will pick it up in TQ everywhere.
Then zero lash the rockers and rev it to 6500 and that should be close to where you want to be.
Then work on the chassis...

Posted By: mshred

Re: how much more power with a compression bump? - 10/18/11 04:03 AM

Quote:

Give Brian a call. He built it, right? Sharp guy.

yes, Brian spec'd the heads and cam for me and did an awesome job

This thread was more of me just trying to learn the effects of compression....I know Brian is a busy guy and I didnt want to call him to discuss this since i wasn't sure yet how it all even works (not to mention my schedule has been way to hectic to get a chance to call him during the week).

To everyone who replied, there is alot of good info here, some of it i have and have not heard before

Posted By: mshred

Re: how much more power with a compression bump? - 10/18/11 04:08 AM

Quote:

Quote:

Hey guys,

Just curious how with everything else being the same how much more power my engine could pick up with a compression bump from just under 9:1 up to about 10.5:1? The current configuration has the pistons below the deck about .083". So with the new compression I would be zero decked with about .040" quench. Here is a mild run down of the engine...best time is in my sig...guessing at about 320hp at the wheels

1991 360 Roller block
Bone stock bottom end
9:1 compression
RHS heads prepped by Brian at IMM engines
custom ground hydraulic roller from Brian at IMM with specs as follows:

Gross Valve lift with 1.6 rocker arms- 577 int., 569 exh.
Duration at .050�- 230/230
Lobe Separation- 106
Cam installed at 101 Intake Centerline (5 degrees of advance ground into cam)

Topped off with an Eddy air gap, Holley 750HP, 1-5/8's headers, 3" exhaust

So how much more power can I expect to make? If i can get this engine to e/t the car to a high 11 on the motor I would be super happy.

With Kb 107's at zero deck, if your heads were 62cc that'll be 10.6:1 so I would back the cam up so it's straight up. That will pick up power in the upper end while the compression will pick it up in TQ everywhere.
Then zero lash the rockers and rev it to 6500 and that should be close to where you want to be.
Then work on the chassis...

Hey Brian, I was looking at a forged offerring in pistons, possibly from probe. My biggest thing was with the compression bump and the fact that I would create quench by zero decking and using the appropriate head gasket, how much more power would I make? Im not sure im comfortable taking the stock lifters to 6500rpms considering my prior luck with them this past summer, but I do trust you. I really wouldnt mind getting a different cam ground either if it is the best way...I was going to eventually call you about this, but was just trying to get an idea of what the compression bump would do...Ideally I want to do a stroker, but not sure if its in the cards financially, so just exploring my other options. I would also be spraying the heck outta this thing if i kept it a 360 with forged pistons, so that may change cam stuff up a little

So far the chassis on my car is working pretty good....Reason I don't want to rev the car higher also is because I would need to up my rear gear ratio, and with the 4.10's its already a huge compromise. Only crossing the stripe at 5500rpms in 4th gear with the current combo, so I would definitely have to gear up

Posted By: mshred

Re: how much more power with a compression bump? - 10/18/11 04:11 AM

Quote:

I know this doesn't answer your question, but raising compression has deminishing returns. You will get more of a HP return going from 8:1 to 9:1 than from 12:1 to 13:1, etc. I would say the range you are looking at would still have good returns HP wise. To come up with an actual # would be a guess on anyones part IMO.

this is something I have heard before which is part of why I was asking the question to begin with...wasn't sure how far up on that scale I was with the compression im at right before the increase of cr has diminishing returns

Posted By: mshred

Re: how much more power with a compression bump? - 10/18/11 04:15 AM

Quote:

My opinion 1.5 compression numbers will only gain you 15 to 18 hp. You need 40 to 45. I would bump the compression to 10.5 with a bigger 254/264 ish cam .620/.600 ish lift with 108ish LSA.
Those two things should get you there. A step header 1 5/8 to 1 3/4 might be a great add on without giving up any bottom end. (or 1 7/8??) if you can afford CNC porting that will add even more.

I don't feel a 230 duration cam will get you there.

The better quench of a 0 deck piston should help some more for sure!

As far as cams go, I dont really want to increase duration because I figure im going to have to rev it more? My car is street/strip and im already in need of more gear with my 4.10's and 28" tires, but I drive it to the track, and 2 hours at 3000rpms isnt fun, so i cant really go more...I don't mind getting a totally new cam to work with the setup, and I have no doubts Brian will set me up nice...I just don't want to overcam it..I mean with my current combo things were so simple and the cam was nothing radical yet it worked real well to squeeze every last bit out of my engine.

As far as headers go, I thought the 1-5/8's I have would be good for producing torque, which I thought is what I need considering im using a short stroke low tq motor

I was also hoping that the bump in CR and the quench factor would work well together... I should also look into CNC porting, though im not sure that is offered on the RHS castings?

Posted By: mshred

Re: how much more power with a compression bump? - 10/18/11 04:16 AM

Quote:

I have a truck/towing build in the truck section I have been working on. It is on my dyno now,a 440 with factory closed chambered heads. When I recieved it,it had KB quench style pistons but was set up with too much quench clearence.
I took the .053 head gaskets out and went to a .020 steel shim gasket to tighten up the quench,that gained me just over a half point of compression.
With the quench fixed and the small bump in compression,it gained roughly 30 hp. The best part was that it really helped the power hang on for a lot longer than before.
Keith

Now that is some promising info right there

Posted By: mshred

Re: how much more power with a compression bump? - 10/18/11 04:16 AM

Quote:

http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html

Im going to read this thanks

Posted By: SomeCarGuy

Re: how much more power with a compression bump? - 10/18/11 04:37 AM

You have a solid running engine that takes crap gas. Maybe lighten the car and leave this for the next rebuild?

Posted By: Brian Hafliger

Re: how much more power with a compression bump? - 10/18/11 06:40 AM

If you don't mind changing the cam, we can pick up the power you want with pistons and cam...no problem!

Posted By: RobX4406

Re: how much more power with a compression bump? - 10/18/11 07:18 AM

At 10.6, that cam and RHS's should be enough to get you running 11's. Might be tight on pump swill although your stuff is better than our California sacred goat pee.

Those lifters are good to around 7K... Don't be afraid to twist it, ask Brian. He also knows about another engine, as do you, that ran those lifters and a similar cam. It did OK.

tti Step or 1.75" headers will help some. I wouldn't put 1 7/8" headers on it. If 500hp strokers can't use 1 7/8" tubes effectively, doubt your mill will either.

Work on the front end of the car. There is some more in the 60's. You might try a shorter rear tire on it to get more effective ratio. It's got a 12.10ish in it based on MPH with a better 60' so you aren't that far off your 11 pass.

Keep jetting it up until it slows down, then back it off to highest MPH jetting. I don't think you hit that yet with the old mill, thinking it still had some MPH in it .

Posted By: mshred

Re: how much more power with a compression bump? - 10/19/11 12:55 AM

Quote:

You have a solid running engine that takes crap gas. Maybe lighten the car and leave this for the next rebuild?

I know man, it does run awesome for what it is...but you know how it is, you always want more power...I dont want to have the thing apart to fix it and not do something to make it go a little faster lol

Im hoping that considering how well the car ran now, with just a few small changes it should put me in the 11's

Posted By: mshred

Re: how much more power with a compression bump? - 10/19/11 12:56 AM

Quote:

If you don't mind changing the cam, we can pick up the power you want with pistons and cam...no problem!

Sounds good Brian! Im gonna yank the motor very soon, and then get er to the shop to start pulling it apart and assess the damage. I will be giving you a call in the very near future to discuss some options

Posted By: mshred

Re: how much more power with a compression bump? - 10/19/11 01:04 AM

Quote:

At 10.6, that cam and RHS's should be enough to get you running 11's. Might be tight on pump swill although your stuff is better than our California sacred goat pee.

Those lifters are good to around 7K... Don't be afraid to twist it, ask Brian. He also knows about another engine, as do you, that ran those lifters and a similar cam. It did OK.

tti Step or 1.75" headers will help some. I wouldn't put 1 7/8" headers on it. If 500hp strokers can't use 1 7/8" tubes effectively, doubt your mill will either.

Work on the front end of the car. There is some more in the 60's. You might try a shorter rear tire on it to get more effective ratio. It's got a 12.10ish in it based on MPH with a better 60' so you aren't that far off your 11 pass.

Keep jetting it up until it slows down, then back it off to highest MPH jetting. I don't think you hit that yet with the old mill, thinking it still had some MPH in it .

Hey Rob,

We get up to 94 octane here, so if I run it on that with a compression bump and tight quench im hoping it will pick up some decent power

Not going to lie, im a bit chicken to turn it higher than 6k just because of my previous luck with the stock style lifters earlier in the season...but i can always balls up and try again lol

If I can find a set of cheap 1-3/4's then maybe I will pick them up, but not sure if that will be financially feasible for me at this point. Are the 1-5/8's going to limit me that much? or will they just generally help with low end torque instead of mid-upper range power?

The front end of the car works real well actually, at least from what I can see...Already have the calvert 90/10s in there with /6 t bars. My caltracs are set at zero preload- I was just pondering today what adding preload would do for me

The alignment is setup properly too. I personally think I need more gear with my setup, but like I said its just not possible considering I drive it to the track...and a shorter tire is not in the deck, I like the look of my 28's lol

I try to keep in mind that my best 60's were running out of the groove at a national event, and the rest of them were on no prep nights, so I never really got to see what the car would do fully (I was kicked out of the groove since I have a stick car, told me i rip up the track too much

)

I never did get a chance to jet it up since I never went back to the track with my carb feed line fixed. Im redoing the fuel system over the winter with a good electric pump and new line, so im going to get that sorted out then. I to think I could have jetted up more...my dad even mentioned me trying his 850 from his 440 on my car, though I don't know if it will be too much- he thinks that if we tinkered more with the old setup I could have saw a bottom 12, but obviously that can't happen anymore lol