Cranking Pressure concern

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SchmidtMotorWorks
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Re: Cranking Pressure concern

Post by SchmidtMotorWorks » Thu Dec 06, 2018 4:31 pm

splitdecision71 wrote:
Thu Dec 06, 2018 3:46 pm
MadBill wrote:
Thu Dec 06, 2018 3:39 pm
Cam King or ?? could provide chapter and verse, but I believe cam cores are supplied drilled and doweled, and occasionally with an unusual LCA or whatever, the grinder will offset the lobes from index to avoid breaking through the hardened surface, leaving it up to the buyer to correct the offset.
I guess that could be likely as Howard's ground this cam and sent it to me. Im going to make a call to Eric and see what he has to say. Thanks for your input.
To add to this point.
If it does turn out that the index is very far off, you may have reason to be concerned that a core that was not well suited for the design was used.
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splitdecision71
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Re: Cranking Pressure concern

Post by splitdecision71 » Thu Dec 06, 2018 4:58 pm

SchmidtMotorWorks wrote:
Thu Dec 06, 2018 4:31 pm
splitdecision71 wrote:
Thu Dec 06, 2018 3:46 pm
MadBill wrote:
Thu Dec 06, 2018 3:39 pm
Cam King or ?? could provide chapter and verse, but I believe cam cores are supplied drilled and doweled, and occasionally with an unusual LCA or whatever, the grinder will offset the lobes from index to avoid breaking through the hardened surface, leaving it up to the buyer to correct the offset.
I guess that could be likely as Howard's ground this cam and sent it to me. Im going to make a call to Eric and see what he has to say. Thanks for your input.
To add to this point.
If it does turn out that the index is very far off, you may have reason to be concerned that a core that was not well suited for the design was used.
Im trying to get ahold of Eric at howard's to see what he can tell me. Thanks for the input.

Keith Morganstein
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Re: Cranking Pressure concern

Post by Keith Morganstein » Thu Dec 06, 2018 5:18 pm

Did you check Valve to Piston clearance?
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splitdecision71
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Re: Cranking Pressure concern

Post by splitdecision71 » Thu Dec 06, 2018 5:31 pm

Keith Morganstein wrote:
Thu Dec 06, 2018 5:18 pm
Did you check Valve to Piston clearance?
Yes, but with another cam that had a lot more lift and duration. I didnt bother with this cam because I knew there would be no issues. Other cam a was way to big and was for 5000 to 9500 rpm.

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Re: Cranking Pressure concern

Post by rewguy » Thu Dec 06, 2018 6:41 pm

Too many variables in the cranking compression to me. We had two separate sbc engines in the same year.

One was 14.25-1 406 sbc with a 280/290@.050 .660/.630 on a 106, installed at 102. Old sportsman iron heads etc. Ran 10.40@129.5 in a 3550 lb full factory interior 66 chevelle. It pumped 240-245 on gauge.

The other was a 14-1 408 with some fairly serious Pro Topline 235 heads. It was 14-1 with a 283/292@.050 on a 106, installed also at 102. Ran 9.69@136.0 best in decent air......only 12 passes total ever at track. 3430 lb 67 camaro, full interior, 260 lb driver etc. It only pumped 165-170 on same gauge.

Same gauge, different batteries and starters, both engines hot with no plugs in, and throttles wide open.

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Re: Cranking Pressure concern

Post by Newold1 » Thu Dec 06, 2018 8:10 pm

Do leak downs with a good setup and listen for the air leaks.
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splitdecision71
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Re: Cranking Pressure concern

Post by splitdecision71 » Thu Dec 06, 2018 9:14 pm

rewguy wrote:
Thu Dec 06, 2018 6:41 pm
Too many variables in the cranking compression to me. We had two separate sbc engines in the same year.

One was 14.25-1 406 sbc with a 280/290@.050 .660/.630 on a 106, installed at 102. Old sportsman iron heads etc. Ran 10.40@129.5 in a 3550 lb full factory interior 66 chevelle. It pumped 240-245 on gauge.

The other was a 14-1 408 with some fairly serious Pro Topline 235 heads. It was 14-1 with a 283/292@.050 on a 106, installed also at 102. Ran 9.69@136.0 best in decent air......only 12 passes total ever at track. 3430 lb 67 camaro, full interior, 260 lb driver etc. It only pumped 165-170 on same gauge.

Same gauge, different batteries and starters, both engines hot with no plugs in, and throttles wide open.
Thanks for your input. New motor is definitely a lot stronger than my iron headed 406 I pulled out. Old motor 5000rpm on stall converter. New motor hit 6000 on stall converter. My old motor was making around 450 to 470. Ran a best of 6.82 @ 99 mph in the 1/8th. I'm going to run another compression test this weekend with a different gauge and see what happens. My goal is low 6s maybe high 5s on new motor. Car weighed 2760 with iron headed motor. Doing a few things to remove some weight so should come in around 2600.

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Re: Cranking Pressure concern

Post by splitdecision71 » Thu Dec 06, 2018 9:15 pm

Newold1 wrote:
Thu Dec 06, 2018 8:10 pm
Do leak downs with a good setup and listen for the air leaks.
Going to run another compression test first with different gauge and then leak down is next. Thank you!

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Re: Cranking Pressure concern

Post by plovett » Fri Dec 07, 2018 5:42 am

splitdecision71 wrote:
Thu Dec 06, 2018 4:18 pm
plovett wrote:
Thu Dec 06, 2018 3:57 pm
You don't have to pull the motor to degree the cam.
Ok thank you. Im going to run out to my buddies tonight where I have the car and run a compression test with a different gauge. I will get back with everyone as soon as I have the results.
I was just wondering why you said in an earlier post that you were going to pull the motor already. I guess you were just being sarcastic. It makes it hard to tell what you really mean. Sorry.

paulie

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Re: Cranking Pressure concern

Post by Caprimaniac » Fri Dec 07, 2018 6:10 am

Newold1 wrote:
Thu Dec 06, 2018 8:10 pm
Do leak downs with a good setup and listen for the air leaks.
X2 and if without any leaks, rings, valves, gaskets, wiki- or whatever- run it!

Ok to do a cam index check and try a different preas gauge- just to eleminate eventual errors.
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splitdecision71
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Re: Cranking Pressure concern

Post by splitdecision71 » Fri Dec 07, 2018 9:56 pm

plovett wrote:
Fri Dec 07, 2018 5:42 am
splitdecision71 wrote:
Thu Dec 06, 2018 4:18 pm
plovett wrote:
Thu Dec 06, 2018 3:57 pm
You don't have to pull the motor to degree the cam.
Ok thank you. Im going to run out to my buddies tonight where I have the car and run a compression test with a different gauge. I will get back with everyone as soon as I have the results.
I was just wondering why you said in an earlier post that you were going to pull the motor already. I guess you were just being sarcastic. It makes it hard to tell what you really mean. Sorry.

paulie
My apologies sir. I was extremely disappointed and my first reaction was to pull it and start all over. I just need to relax and go over a few things first. I'm new at this and this was my first attempt at a big hp motor. Super excited and scared to death of being let down by the results. To be honest I'm being really negative and looking for anything bad! Lol. Thanks for your input.

splitdecision71
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Re: Cranking Pressure concern

Post by splitdecision71 » Fri Dec 07, 2018 9:58 pm

Caprimaniac wrote:
Fri Dec 07, 2018 6:10 am
Newold1 wrote:
Thu Dec 06, 2018 8:10 pm
Do leak downs with a good setup and listen for the air leaks.
X2 and if without any leaks, rings, valves, gaskets, wiki- or whatever- run it!

Ok to do a cam index check and try a different preas gauge- just to eleminate eventual errors.
Thank you! Going to go over a few things then I'm going to send it!

splitdecision71
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Re: Cranking Pressure concern

Post by splitdecision71 » Sat Dec 08, 2018 9:21 pm

Just wanted to say thank you fellas for all the comments. Results from my testing today.
My starter is an old TCI starter from the mid 90s. Compared to my buddies it turns quite a bit slower. That being said with motor up at temp and using a snap on compression gauge all of the cylinders were at 215 to 220 psi. Consider the difference in mine and my buddies starter I would say that was right in line to where it should be. Again thank you all for the info and comments! Have a great rest of your weekend.

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Re: Cranking Pressure concern

Post by MadBill » Sun Dec 09, 2018 12:00 am

The SpeedTalk Collective aces another challenge! \:D/
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Cranking Pressure concern

Post by David Redszus » Mon Dec 10, 2018 12:44 pm

Having faced the question of determining true compression pressure many times over the years, we have found a solution.

We have built an adapter for a pressure sensor that screws into a spark plug hole of a running engine with the pressure signal fed into a data logger. We can now see that compression pressure (both max and min) varies with speed, throttle position and induction flow.

We can also compare multiple cylinder compression pressures at a range of engine speeds.

Since compression pressure contributes to chamber temperature, resulting in variable ignition points, flame propagation and peak pressure locations.

If anyone is interested in more information about this device, let me know.

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