Compression

General engine tech -- Drag Racing to Circle Track

Moderator: Team

DCal
Expert
Expert
Posts: 769
Joined: Fri Aug 11, 2006 11:37 am
Location: mooresville nc

Re: Compression

Post by DCal »

Sum Ting Wong -- We Tu Hi
User avatar
af2
Guru
Guru
Posts: 7014
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Compression

Post by af2 »

OK one more time checking.
@ .300" 70cc

4.135" x 3.75"

.010" in the hole

.030" x 4.160" Cometic head gasket
You do not have the required permissions to view the files attached to this post.
GURU is only a name.
Adam
CGT
Guru
Guru
Posts: 2063
Joined: Sun May 10, 2009 12:29 pm
Location:

Re: Compression

Post by CGT »

af2 wrote: Wed Jan 22, 2020 11:24 am OK one more time checking.
@ .300" 70cc

4.135" x 3.75"

.010" in the hole

.030" x 4.160" Cometic head gasket
Well, that's coming up to 4cc of dome volume roughly the other way. So that changes things :lol:
Last edited by CGT on Wed Jan 22, 2020 12:02 pm, edited 1 time in total.
David Redszus
Guru
Guru
Posts: 9633
Joined: Tue Nov 27, 2007 9:27 am
Location: Chicago
Contact:

Re: Compression

Post by David Redszus »

LoganD wrote: Wed Jan 22, 2020 9:19 am
mag2555 wrote: Wed Jan 22, 2020 6:16 am Yes,so let me get this straight, your shooting for a 17 to 1 compression on your 403 cid motor?

I am hoping you have more then 4 head bolts per cylinder?
Eh....why is this any different than running 25 psi of boost? As long as it doesn't go lean your peak firing pressure is just going to be similar to that of a boosted engine. Build it accordingly.
An NA engine at SCR of 17.0-1, will produce (at 20deg BTC) 230psi and 760deg F.

Lowering the SCR to 9.0 and running 25 psi boost will produce (at 20 deg BTC) 500psi anf 696deg F.
While the cylinder pressure under boost will be significantly higher, the temperatures will be somewhat similar.
And, if the boosted engine can be fitted with an efficient intercooler, inlet air temperature will be further reduced.

Inlet temperature at the begining of combustion is much more important than is pressure, except that pressure provides an
increase in air density.

We can always adjust boost as needed, but SCR is forever.
User avatar
af2
Guru
Guru
Posts: 7014
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Compression

Post by af2 »

Normally aspirated. Kinsler injection
GURU is only a name.
Adam
User avatar
Stan Weiss
Vendor
Posts: 4801
Joined: Tue Feb 20, 2007 1:31 pm
Location: Philadelphia, PA
Contact:

Re: Compression

Post by Stan Weiss »

af2 wrote: Wed Jan 22, 2020 11:24 am OK one more time checking.
@ .300" 70cc

4.135" x 3.75"

.010" in the hole

.030" x 4.160" Cometic head gasket
@ .300" 70cc means you have no dome volume and 3.98 cc's extra. As 4.135 X 0.3 = 66.018 cc's

15.26:1 does not include any top ring volume.

Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
mag2555
Guru
Guru
Posts: 4585
Joined: Sun Sep 18, 2011 11:31 am
Location: Heading for a bang up with Andromeda as we all are.

Re: Compression

Post by mag2555 »

My line of thought and questioning was in regards poor combustion due to the piston dome, as the combustion process can be very different from a boosted motor running at + 2 or more Atmospheres and NA motor with 17 to 1.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
maxracesoftware
Vendor
Posts: 3627
Joined: Sat Feb 14, 2004 4:04 pm
Location: Abbeville, LA
Contact:

Re: Compression

Post by maxracesoftware »

af2 wrote: Tue Jan 21, 2020 8:05 pm Ok I am lost trying to figure out the static on this new build...... 3.75 stroke 4.135 bore. I have at .375" down 75 cc the head gasket at .040" and the heads 46 cc. I measured down .375 because of the domes. Thanks I have a head ache finding it out I am figuring 17:1 but making sure so I can get a good flow# for the injection set up.
i know you have PipeMax .... so just use the Compression Ratio Calculator in PipeMax v4.50 :)
PipeMax ( Compression Ratio Calculator ) :
Image
MaxRace Software
PipeMax and ET_Analyst for DragRacers
https://www.maxracesoftwares.com
User avatar
af2
Guru
Guru
Posts: 7014
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Compression

Post by af2 »

Thanks Larry and Stan I'll have to look on pipemax. The heads are 46cc.
GURU is only a name.
Adam
travis
Guru
Guru
Posts: 1611
Joined: Sun Mar 15, 2009 5:31 am
Location:

Re: Compression

Post by travis »

I’m coming up with 15.02 compression w/46cc heads
CGT
Guru
Guru
Posts: 2063
Joined: Sun May 10, 2009 12:29 pm
Location:

Re: Compression

Post by CGT »

af2 wrote: Wed Jan 22, 2020 11:24 am OK one more time checking.
@ .300" 70cc

4.135" x 3.75"

.010" in the hole

.030" x 4.160" Cometic head gasket
Do you have a leak? :D Did you figure out where your inconsistency is coming from? I know it can be deceiving from pics, but from looking at the pics its hard to believe that piston doesn't have positive dome volume
travis
Guru
Guru
Posts: 1611
Joined: Sun Mar 15, 2009 5:31 am
Location:

Re: Compression

Post by travis »

Your first set of numbers I came up with 7.5cc effective dome volume...the 2nd set I got 4 cc of dish volume :?
travis
Guru
Guru
Posts: 1611
Joined: Sun Mar 15, 2009 5:31 am
Location:

Re: Compression

Post by travis »

CGT wrote: Wed Jan 22, 2020 3:58 pm
af2 wrote: Wed Jan 22, 2020 11:24 am OK one more time checking.
@ .300" 70cc

4.135" x 3.75"

.010" in the hole

.030" x 4.160" Cometic head gasket
Do you have a leak? :D Did you figure out where your inconsistency is coming from? I know it can be deceiving from pics, but from looking at the pics its hard to believe that piston doesn't have positive dome volume
Exactly what I was thinking. Those pistons look very similar to the +4cc domed pistons we put in a buddy’s 4” bore block.
User avatar
af2
Guru
Guru
Posts: 7014
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Compression

Post by af2 »

CGT wrote: Wed Jan 22, 2020 3:58 pm
af2 wrote: Wed Jan 22, 2020 11:24 am OK one more time checking.
@ .300" 70cc

4.135" x 3.75"

.010" in the hole

.030" x 4.160" Cometic head gasket
Do you have a leak? :D Did you figure out where your inconsistency is coming from? I know it can be deceiving from pics, but from looking at the pics its hard to believe that piston doesn't have positive dome volume
I went to .300" and got the burret better stabilized. Yes I am looking at almost 4 cc dome. Thanks a bunch!

Now how much HP will it make!!!! LOOOOL. So Kidding :lol:
GURU is only a name.
Adam
dannobee
Expert
Expert
Posts: 898
Joined: Mon Nov 04, 2019 9:01 pm
Location:

Re: Compression

Post by dannobee »

Dunno about hp, but the max torque it'll make is 644 lb ft. It's up to you to get it all out. :wink:
Post Reply