Max cranking psig, DCR for pump gas?
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Max cranking psig, DCR for pump gas?
Asking for a friend: He built a 1980 iron block, alu head 4 cyl engine for street. Unknown SCR, possibly in the 10.5 range. Lame stock cam, possibly off timing, could be advanced.
Cranking compression is 210psig, cold. Worried about detonation w pump gas.
What should i tell him?
Cranking compression is 210psig, cold. Worried about detonation w pump gas.
What should i tell him?
Re: Max cranking psig, DCR for pump gas?
Cold air intake, sub 180 thermostat, premium fuel, listen for knock.
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Re: Max cranking psig, DCR for pump gas?
I would be worried on pump gas. Not to start a flame war, but I do pay attention to cranking compression. If it has a lot of cranking compression, it is an indicator that it may detonate. And while it may not detonate on a cool fall day, what about a hot humid summer day?Nut124 wrote: ↑Mon Nov 14, 2022 9:59 pm Asking for a friend: He built a 1980 iron block, alu head 4 cyl engine for street. Unknown SCR, possibly in the 10.5 range. Lame stock cam, possibly off timing, could be advanced.
Cranking compression is 210psig, cold. Worried about detonation w pump gas.
What should i tell him?
I use performance trends engine program; it will generate a timing curve and tell you if detonation can be a problem. Usually what it tells me is that in the middle rpm range is where it may be an issue. So, by delaying the advance you can sneak under the wire. I use the generated timing curve as a starting point, it is usually pretty close. Since distributor machines are not common anymore, you can have someone hold the throttle at 500 rpm increments and then graph out the curve with a timing light. Change springs and weights until it matches what you want. And if it has vacuum advance hook to ported vacuum not manifold vacuum.
Re: Max cranking psig, DCR for pump gas?
If you run the numbers thru a cranking compression calculator, does it show a similar result?
Has it been verified with another gauge?
FWIW, I used to have a 1995 dohc neon. The cranking pressure spec was like 180-200....... and that’s what it had.
Has it been verified with another gauge?
FWIW, I used to have a 1995 dohc neon. The cranking pressure spec was like 180-200....... and that’s what it had.
Last edited by PRH on Tue Nov 15, 2022 10:11 am, edited 1 time in total.
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Re: Max cranking psig, DCR for pump gas?
What is the bore, stroke and rod length of his engine? What the specs on this lame stock cam? Also at what elevation is he?Nut124 wrote: ↑Mon Nov 14, 2022 9:59 pm Asking for a friend: He built a 1980 iron block, alu head 4 cyl engine for street. Unknown SCR, possibly in the 10.5 range. Lame stock cam, possibly off timing, could be advanced.
Cranking compression is 210psig, cold. Worried about detonation w pump gas.
What should i tell him?
Stan
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http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
Re: Max cranking psig, DCR for pump gas?
The aluminum head may allow him to sneak by. With an iron head on a 100-degree day on an uphill pull at cruise RPM, probably not.
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Re: Max cranking psig, DCR for pump gas?
I can't see how a any street motor made in 1980 could have been intended to pump even 190 with how automotive computer control was still taking baby steps back then.
I would wager a bet that the Cam is out of proper time.
I would wager a bet that the Cam is out of proper time.
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!
Re: Max cranking psig, DCR for pump gas?
Thanks for the replies.
Bore: 84mm, stroke: 90mm, rod c/c: 145mm.
He put in domed pistons and an early head with a smaller chambers.
Bore: 84mm, stroke: 90mm, rod c/c: 145mm.
He put in domed pistons and an early head with a smaller chambers.
Re: Max cranking psig, DCR for pump gas?
You could tell your friend not to mix blindly 1600/2000 TC ignition parts.
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Re: Max cranking psig, DCR for pump gas?
Engines with identical CCP @ 165 psi and DCR @ 8.04:1 can have completely different tunes, especially as to when the torque curve begins.
1. high static CR + late intake valve closure: 12.00:1 CR, IVC 82 degrees ABDC; torque will be low for quite a while
2. mild static CR + early intake valve closure: 9.00:1 CR, IVC 47 degrees ABDC, torque will rise immediately above idle
1. high static CR + late intake valve closure: 12.00:1 CR, IVC 82 degrees ABDC; torque will be low for quite a while
2. mild static CR + early intake valve closure: 9.00:1 CR, IVC 47 degrees ABDC, torque will rise immediately above idle
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Re: Max cranking psig, DCR for pump gas?
What is a rough idea of the stock cam specs?
Stan
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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
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
Re: Max cranking psig, DCR for pump gas?
Stan, thanks for that interesting graph.
That 66 ABDC IVC seems just about right for the stock cam.
He could retard the intake cam one tooth, which is 17 crank degrees for 83 IVC, which is what some hotter street cams run about.
Any chance I could ge the same chart for my engine?
Same bore, 84mm. Stroke: 79.2mm, Roc C/C: 136mm, cranking compression 185psig.
That 66 ABDC IVC seems just about right for the stock cam.
He could retard the intake cam one tooth, which is 17 crank degrees for 83 IVC, which is what some hotter street cams run about.
Any chance I could ge the same chart for my engine?
Same bore, 84mm. Stroke: 79.2mm, Roc C/C: 136mm, cranking compression 185psig.
Re: Max cranking psig, DCR for pump gas?
Understood. What do you think that would do other than lower dynamic CR? The stock cam has a pretty short duration, in the 250 deg seat to seat range.