10.4 vs 10.25 CR and Piston to Head Clearance

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skinny z
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10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

While it may be sweating the small stuff, it very well may not be. So I'll throw this out there.

I'm into the final assembly as the cam is on it's way and the rest of bits that were eaten up by the previously failed lifter link-bar failure are soon to be ordered.
Engine spec: 357. Aftermarket iron Vortec heads. Jones hydraulic roller. Weisco 4032 forged pistons. Peak HP RPM about 6200.
Car: 3rd gen Camaro. 3600 lbs (w/driver). Automatic. 4000 stall (w/ lockup converter). Slicks.
Drag racing primarily although it'll be driven to and (hopefully) from the track. It'll see some street duty and possibly a few long distance highway cruises but that's secondary. Cam was spec'd accordingly.
94 octane pump gas with is arguably 5-10% ethanol.

Among the last few choices to be made are the piston to head clearance. Previous discussions regarding the safest minimum puts me close at .034" using an .026" gasket. Pistons are .008" down. This puts the SCR at 10.4. The DCR falls in at 8.35:1 for those that might be asking (although I'm well aware that some don't care). ICL for that DCR is 104.
Alternately, I could use an .032 gasket, open up the quench to .040" and drop the compression to 10.25 with the DCR now at 8.24.
FTR, the cam spec was based on 10.4:1.

Would the differences in performance even be measurable? How about with respect to ignition timing? If I have my preferences I'd rather a full and proper timing curve as opposed to having to dial it back to compensate. But this may be a case where I can have both. Which of course is ideal.
The .034" piston to head clearance makes me a little edgy but from most accounts it's a benefit. How much when compared to .008" in the difference I suppose is open to debate. And debated it has been.

Curious as to opinions here. Which way would you go?
Kevin
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by Monza355 »

Run the 0.040” quench. It’s an extra margin for safety but still tight and you’ll never know the difference performance vise
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by F-BIRD'88 »

The amount of air in the tires will make more difference.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by mag2555 »

Your splitting hairs here!

Only if your where running .009" piston to wall clearance and Aluminum Rods would I get concerned about .032"
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by Stan Weiss »

skinny z wrote: Wed May 31, 2023 9:47 am While it may be sweating the small stuff, it very well may not be. So I'll throw this out there.

I'm into the final assembly as the cam is on it's way and the rest of bits that were eaten up by the previously failed lifter link-bar failure are soon to be ordered.
Engine spec: 357. Aftermarket iron Vortec heads. Jones hydraulic roller. Weisco 4032 forged pistons. Peak HP RPM about 6200.
Car: 3rd gen Camaro. 3600 lbs (w/driver). Automatic. 4000 stall (w/ lockup converter). Slicks.
Drag racing primarily although it'll be driven to and (hopefully) from the track. It'll see some street duty and possibly a few long distance highway cruises but that's secondary. Cam was spec'd accordingly.
94 octane pump gas with is arguably 5-10% ethanol.

Among the last few choices to be made are the piston to head clearance. Previous discussions regarding the safest minimum puts me close at .034" using an .026" gasket. Pistons are .008" down. This puts the SCR at 10.4. The DCR falls in at 8.35:1 for those that might be asking (although I'm well aware that some don't care). ICL for that DCR is 104.
Alternately, I could use an .032 gasket, open up the quench to .040" and drop the compression to 10.25 with the DCR now at 8.24.
FTR, the cam spec was based on 10.4:1.

Would the differences in performance even be measurable? How about with respect to ignition timing? If I have my preferences I'd rather a full and proper timing curve as opposed to having to dial it back to compensate. But this may be a case where I can have both. Which of course is ideal.
The .034" piston to head clearance makes me a little edgy but from most accounts it's a benefit. How much when compared to .008" in the difference I suppose is open to debate. And debated it has been.

Curious as to opinions here. Which way would you go?
Kevin,
It depends on how close to the edge you are. Based on your SCR and DCR numbers I get your IVC @ 64 ABDC. Using a 104 ICL I get 280 seat-to-seat. Using this I see less than 4 psi difference in cranking compression between the 2.

Stan

PS - Let me add that all of the calculation were done using a 5.7" rod if you rod length is different those number will change a small amount.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

Stan Weiss wrote: Wed May 31, 2023 12:42 pm
skinny z wrote: Wed May 31, 2023 9:47 am While it may be sweating the small stuff, it very well may not be. So I'll throw this out there.

I'm into the final assembly as the cam is on it's way and the rest of bits that were eaten up by the previously failed lifter link-bar failure are soon to be ordered.
Engine spec: 357. Aftermarket iron Vortec heads. Jones hydraulic roller. Weisco 4032 forged pistons. Peak HP RPM about 6200.
Car: 3rd gen Camaro. 3600 lbs (w/driver). Automatic. 4000 stall (w/ lockup converter). Slicks.
Drag racing primarily although it'll be driven to and (hopefully) from the track. It'll see some street duty and possibly a few long distance highway cruises but that's secondary. Cam was spec'd accordingly.
94 octane pump gas with is arguably 5-10% ethanol.

Among the last few choices to be made are the piston to head clearance. Previous discussions regarding the safest minimum puts me close at .034" using an .026" gasket. Pistons are .008" down. This puts the SCR at 10.4. The DCR falls in at 8.35:1 for those that might be asking (although I'm well aware that some don't care). ICL for that DCR is 104.
Alternately, I could use an .032 gasket, open up the quench to .040" and drop the compression to 10.25 with the DCR now at 8.24.
FTR, the cam spec was based on 10.4:1.

Would the differences in performance even be measurable? How about with respect to ignition timing? If I have my preferences I'd rather a full and proper timing curve as opposed to having to dial it back to compensate. But this may be a case where I can have both. Which of course is ideal.
The .034" piston to head clearance makes me a little edgy but from most accounts it's a benefit. How much when compared to .008" in the difference I suppose is open to debate. And debated it has been.

Curious as to opinions here. Which way would you go?
Kevin,
It depends on how close to the edge you are. Based on your SCR and DCR numbers I get your IVC @ 64 ABDC. Using a 104 ICL I get 280 seat-to-seat. Using this I see less than 4 psi difference in cranking compression between the 2.

Stan
Spot on Stan.
Kevin
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

Monza355 wrote: Wed May 31, 2023 10:06 am Run the 0.040” quench. It’s an extra margin for safety but still tight and you’ll never know the difference performance vise
I'm of the same mind. Thanks.
F-BIRD'88 wrote: Wed May 31, 2023 11:17 am The amount of air in the tires will make more difference.
As I expected. Then there's the question of what tyres? But that's a question for another day.
mag2555 wrote: Wed May 31, 2023 11:45 am Your splitting hairs here!
Only if your where running .009" piston to wall clearance and Aluminum Rods would I get concerned about .032"
Is this to say you have no issues with .032" and a steel rodded, tight piston, low RPM deal?
Do you see any great benefit from tighter vs looser? So to speak.
Kevin
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

Stan Weiss wrote: Wed May 31, 2023 12:42 pm
skinny z wrote: Wed May 31, 2023 9:47 am While it may be sweating the small stuff, it very well may not be. So I'll throw this out there.

I'm into the final assembly as the cam is on it's way and the rest of bits that were eaten up by the previously failed lifter link-bar failure are soon to be ordered.
Engine spec: 357. Aftermarket iron Vortec heads. Jones hydraulic roller. Weisco 4032 forged pistons. Peak HP RPM about 6200.
Car: 3rd gen Camaro. 3600 lbs (w/driver). Automatic. 4000 stall (w/ lockup converter). Slicks.
Drag racing primarily although it'll be driven to and (hopefully) from the track. It'll see some street duty and possibly a few long distance highway cruises but that's secondary. Cam was spec'd accordingly.
94 octane pump gas with is arguably 5-10% ethanol.

Among the last few choices to be made are the piston to head clearance. Previous discussions regarding the safest minimum puts me close at .034" using an .026" gasket. Pistons are .008" down. This puts the SCR at 10.4. The DCR falls in at 8.35:1 for those that might be asking (although I'm well aware that some don't care). ICL for that DCR is 104.
Alternately, I could use an .032 gasket, open up the quench to .040" and drop the compression to 10.25 with the DCR now at 8.24.
FTR, the cam spec was based on 10.4:1.

Would the differences in performance even be measurable? How about with respect to ignition timing? If I have my preferences I'd rather a full and proper timing curve as opposed to having to dial it back to compensate. But this may be a case where I can have both. Which of course is ideal.
The .034" piston to head clearance makes me a little edgy but from most accounts it's a benefit. How much when compared to .008" in the difference I suppose is open to debate. And debated it has been.

Curious as to opinions here. Which way would you go?
Kevin,
It depends on how close to the edge you are. Based on your SCR and DCR numbers I get your IVC @ 64 ABDC. Using a 104 ICL I get 280 seat-to-seat. Using this I see less than 4 psi difference in cranking compression between the 2.

Stan

PS - Let me add that all of the calculation were done using a 5.7" rod if you rod length is different those number will change a small amount.
A follow up to some of my earlier analysis paralysis questions.
Now that I'm all but committed, what's the approach for part throttle? In my conversation with Mike Jones, he wasn't so sure how the 108 LSA and stop and go traffic would play out. Since I don't recall ever being in that situation since I moved to this part of the country we settled on this spec. (Thanks again Mike!).
But, there will be occasions when I'm converter locked at 2500 RPM (rare but I do have to get to and from the track). All else being equal, and air inlet temps in particular, would that 2-4 PSI difference kill any potential to proper ignition timing and subsequent fuel economy? (To and from the track may one day mean a 2500 mile trip one way!).
Kevin
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by lefty o »

as long as you have enough converter that it isnt lugging, id not worry about a 108lsa. i used to daily a 106lsa. for driving to the track, or a weekend toy it wont become onerous.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by F-BIRD'88 »

Your 108 lsa. am is not that hairy.
What you may want to do is control tC lock up manualy or have a override switch... or...
You'd want to avoid driving in OD at low engine rpm reguardless.. The OD only really benefits you at steady long highway speeds... Otherwise its a toy.
Cammed engines by nature want to run at high(er) cruise rpm.
You'll know as soon as you get to driving it axjust as needed..
With overdrive you can gear the hell out of it for drag launch ET. Don't be shy.
I don't see big issues with your combo in that reguard.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

lefty o wrote: Wed May 31, 2023 2:30 pm as long as you have enough converter that it isnt lugging, id not worry about a 108lsa. i used to daily a 106lsa. for driving to the track, or a weekend toy it wont become onerous.
From the previous setup, (before it wasn't), it had excellent street manners. And way more cam than I have now. COMP's 288HR. The converter did an excellent job in street traffic.
With less street now, I expect it'll be indeed be very reasonable.
Last edited by skinny z on Wed May 31, 2023 5:00 pm, edited 1 time in total.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

F-BIRD'88 wrote: Wed May 31, 2023 2:51 pm Your 108 lsa. am is not that hairy.
What you may want to do is control tC lock up manualy or have a override switch... or...
You'd want to avoid driving in OD at low engine rpm reguardless.. The OD only really benefits you at steady long highway speeds... Otherwise its a toy.
Cammed engines by nature want to run at high(er) cruise rpm.
You'll know as soon as you get to driving it axjust as needed..
With overdrive you can gear the hell out of it for drag launch ET. Don't be shy.
I don't see big issues with your combo in that reguard.
I agree on the cam. It's less than previous and that was very tunable.
I've got the converter lockup dialed in. It's in OD only plus a manual switch to disengage should I want to. Very much like driving a 5 speed.
As for drag racing, with the 700R4 1st gear and the 3.73's, it's like a TH350 with a 4.56. Plenty of launch gear I would think. Traction was generally at a premium as the slicks got older.
Looking to better my best 1.70 60'.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by F-BIRD'88 »

Try the Air lift Air bag set.. "drag bags"
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

Already in the playbook Mr. F.
Drag Bags with 15-20 PSI right hand side. Static (5 PSI) left side.
Keeps me drifting out of the lanes towards the trackside pub at TMP (Damned if I can't recall the name).
TMP is home to my best 60'. On McCreary Road Star tires no less.

Speaking of McCreary Road Stars, here's a special video to reminisce by:

https://www.youtube.com/watch?v=0DCt5sagHco
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by F-BIRD'88 »

Ya TMP is not bad. I saw a guy walk right out of his shoes at the start line one day.. ha ha.
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