? on calculating dcr and quench
Thread Starter
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
? on calculating dcr and quench
i'm trying to get the quench close to .045 but with my 58 cc alum heads i can't figure out how to do it without my dcr being in the high 8s.
i have a 350
4.bore
3.48 stroke
.022 deck ht.
58cc heads
5.7 rods cam intake closing 63 abdc with 1.5 rockers. i have 1.6 so i don't know how much that will affect it.
to get the quench right i need a .023 head gasket.
i found a .026 gasket but that puts me at 10.96 comp.
Clevite Engine Parts
5746
Clevite Nitroseal Cylinder Head Gaskets
Summit Racing Part Number
CLE-5746
Bore (in)4.125 in.
Gasket MaterialNitroseal
Compressed Thickness (in)
0.026 in.
Lock WireNo
would that run on 93 oct pump. i'm running alum heads. but with my cams int closing at 63 abdc i think my dynamic comp is almost 9:1 isn't that to much for 93 oct. if i use a thicker head gasket to lower the static comp i loose my quench. ?
i have a 350
4.bore
3.48 stroke
.022 deck ht.
58cc heads
5.7 rods cam intake closing 63 abdc with 1.5 rockers. i have 1.6 so i don't know how much that will affect it.
to get the quench right i need a .023 head gasket.
i found a .026 gasket but that puts me at 10.96 comp.
Clevite Engine Parts
5746
Clevite Nitroseal Cylinder Head Gaskets
Summit Racing Part Number
CLE-5746
Bore (in)4.125 in.
Gasket MaterialNitroseal
Compressed Thickness (in)
0.026 in.
Lock WireNo
would that run on 93 oct pump. i'm running alum heads. but with my cams int closing at 63 abdc i think my dynamic comp is almost 9:1 isn't that to much for 93 oct. if i use a thicker head gasket to lower the static comp i loose my quench. ?
Last edited by GS977; Jun 5, 2011 at 03:24 PM.
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What actual cam is it? What are the actual heads? Induction? Gearing and trans? RPM range? Cooling system and intended temps?
The reason I ask this is because while DCR IS a real thing and what we're all dealing with, how efficient the combo is has a huge bearing on how it will actually perform on pump gas.
With REALLY good heads and only 9.0 compression ratio...the old Busch roundy round motors would get the cylinder REALLY full as RPM climbed and you had better have serious race gas in the tank.
DCR calculators are neat to play with, but there are a LOT of variables that you need to take into account besides the intake closing point to know if it will run in YOUR car.
JIM
The reason I ask this is because while DCR IS a real thing and what we're all dealing with, how efficient the combo is has a huge bearing on how it will actually perform on pump gas.
With REALLY good heads and only 9.0 compression ratio...the old Busch roundy round motors would get the cylinder REALLY full as RPM climbed and you had better have serious race gas in the tank.
DCR calculators are neat to play with, but there are a LOT of variables that you need to take into account besides the intake closing point to know if it will run in YOUR car.
JIM
Le Mans Master
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From: Graceland in a Not Correctly Restored Stingray
What Jim is talking about is exactly why I refer to DCR calculated from intake valve closing as being strictly "theoretical DCR". There really ought to be a sliding scale by which to go when taking "DCR" into account, as the wilder an engine the more margin typically ought to be left IMCO.
FWIW, true DCR in a running engine is CR*VE% at a given RPM. VE% in a healthy breather can apparently exceed 100%, which could actually put true DCR at more than static CR.
As well as what cam, how much advance are you figuring on? In addition to selecting a bigger cam, you can always lower theoretical DCR by retarding it. Then again, with ~11:1 with any decent head/cam combo you're already likely to produce some critical cylinder pressures on top end for 93. Hope you haven't painted yourself into a CR corner.
FWIW, true DCR in a running engine is CR*VE% at a given RPM. VE% in a healthy breather can apparently exceed 100%, which could actually put true DCR at more than static CR.
As well as what cam, how much advance are you figuring on? In addition to selecting a bigger cam, you can always lower theoretical DCR by retarding it. Then again, with ~11:1 with any decent head/cam combo you're already likely to produce some critical cylinder pressures on top end for 93. Hope you haven't painted yourself into a CR corner.
Thread Starter
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
jim my new cam is this one from comp cams
http://www.compcams.com/Company/CC/c...?csid=107&sb=2
my intake is an edel perf rpm. my pistons are the forged trw 464664 flat top with a single trough. my heads are the weak link, 89 corvette 113s. 700r4 trans 1800 stall, 3.73 or 3.55 gears coming next. it always ran @170 before with the isky 270 mega.
i have 96 c4 dual electric fans and a 160 thermostat.
with the felpro 1010 head gaskets i had before my static comp was 10.96 i ran 38 total timing and it never pinged. no signs of det when i pulled it apart the other day. i think it need more dur on the ex side with the weak heads. plus the isky has to be from the 80s. i think this new cam should help it a little. and i thought if i could get the quench down it would also help.
what do you think jim.
thanks!!!
http://www.compcams.com/Company/CC/c...?csid=107&sb=2
my intake is an edel perf rpm. my pistons are the forged trw 464664 flat top with a single trough. my heads are the weak link, 89 corvette 113s. 700r4 trans 1800 stall, 3.73 or 3.55 gears coming next. it always ran @170 before with the isky 270 mega.
i have 96 c4 dual electric fans and a 160 thermostat.
with the felpro 1010 head gaskets i had before my static comp was 10.96 i ran 38 total timing and it never pinged. no signs of det when i pulled it apart the other day. i think it need more dur on the ex side with the weak heads. plus the isky has to be from the 80s. i think this new cam should help it a little. and i thought if i could get the quench down it would also help.
what do you think jim.
thanks!!!
Thread Starter
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
so much to learn. i did a leakdown and comp test right before i pulled the motor out and they were all 150 psi except 2 were153psi and i had 100 psi going in and the other gauge stayed at 100 psi. so the motor is in good shape. i just didn't like the old single pattern technology from the isky.thanks for the help guys. i've been reading for hours and hours trying to learn as much as i can.
another thing, can i open the chambers up on my 113 heads to lower the comp. i cc'd them last night and got 56 cc's
they were just surfaced and had a 3 angle vj. if i had @64 cc head it would help alot i think.
Last edited by GS977; Jun 5, 2011 at 09:19 PM.
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The old Isky Mega Cams are not slouches. They typically measure a little *bigger* than they are advertised and run well. Single pattern cams have their place and can do well. The Comp Thumpr's are on a slightly tighter LSA and with the much larger duration numbers you're going to pick up a lot of overlap...so be prepared for that. Street manners are going to be a little thumpier for sure especially in a 350.
You could open the chambers surely a little..but probably no need to. Those heads weren't really a *fast burn* design..so not much to hurt...but if it will handle the compression no need to lower it.
The heads are still where the power is and some good port work would pay off definitely. I'd do some work on the heads.
JIM
You could open the chambers surely a little..but probably no need to. Those heads weren't really a *fast burn* design..so not much to hurt...but if it will handle the compression no need to lower it.
The heads are still where the power is and some good port work would pay off definitely. I'd do some work on the heads.
JIM
Thread Starter
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
jim do you think i should just go back with the fp 1010 gasket .039 comp thick 10.96 static cr and for get about quench. or do you think i can get by with a thinner gasket. will the overlap bleed off cylinder pressure enough to use a thinner gasket?
thanks!!!!!
thanks!!!!!
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
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I'd still shoot for tight quench. Overlap doesn't affect compression though it is often repeated that it does. The valves are both open during overlap so no compression is occuring. It's the intake closing point that does it. It just so happens that bigger cams usually end up with more overlap unless you juggle the LSA around...so people assume it's the overlap...when it's not. Overlap is just a by product of the lobes and the LSA.
That 11+ compression is going to be pretty tight but is doable. Just build for mid range grunt like an LT-1 motor.
JIM
That 11+ compression is going to be pretty tight but is doable. Just build for mid range grunt like an LT-1 motor.
JIM
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Le Mans Master
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From: Las Vegas - Just stop perpetuating myths please.
New cam have more duration?
If u can trust your compression test then 150psi is faily low for a performance engine - more like a smog motor. So to 50 dollar question is: does/will the new cam have more duration or less.
My goodwrech 350 had 180 psi with my last performance cam - no detonation problems in 100 degree weather using regular gas.
If u have only 150psi then either u have a really big cam or your c.r. may be off somewhat.
What i'm saying is in your new planned cam has the same or more duration i wouldn't worry with only 150psi cylinder pressure.
Good luck,
cardo0
My goodwrech 350 had 180 psi with my last performance cam - no detonation problems in 100 degree weather using regular gas.
If u have only 150psi then either u have a really big cam or your c.r. may be off somewhat.
What i'm saying is in your new planned cam has the same or more duration i wouldn't worry with only 150psi cylinder pressure.
Good luck,
cardo0
Thread Starter
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
jackson, i saw the GM .028 GASKET on summit. i found 3, one was .026 and the other 2 are .028 .
thanks.
cardo, i don't have much faith in my comp tester. at first it was going to @ 200psi and dropping to zero as soon as i stoped cranking. i couldn't see where it maxed out at cause i was in the car. so i changed the (sp) schrader valve on my tester and this one would go to 150 -153 and stop on every cyl. so i tryed another schrader valve on one cyl and it only went to 140psi. dam sears comp tester.
my leakdown tester is a mac tools brand so i trust it.
thanks.
cardo, i don't have much faith in my comp tester. at first it was going to @ 200psi and dropping to zero as soon as i stoped cranking. i couldn't see where it maxed out at cause i was in the car. so i changed the (sp) schrader valve on my tester and this one would go to 150 -153 and stop on every cyl. so i tryed another schrader valve on one cyl and it only went to 140psi. dam sears comp tester.
my leakdown tester is a mac tools brand so i trust it.
