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Offline Bobcat Racer

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Too much compression?!
« on: July 01, 2019, 01:43:10 PM »
Hi Everyone,
A fellow Pinto racer was kind enough to lend me a set of 40mm DCOE Webers and both my current race motor and spare motor have D-port heads that wouldn't work with the intake.  Time to mix and match with the parts I had available.  I took a 78K mile, 8 plug head motor, pulled the head and replaced it with an oval port head shaved .100 with a fresh valve job and a stock Ranger roller cam and followers.  Put it all together on my test stand and it ran very well so I decided to test compression as I keep a sheet on all of the motors I test before going into the car.  It ranged from 205-210 psi per cylinder which shocked me a bit.  My other race motor never showed more than 185-190 psi and the head is shaved .118.  It should be noted that the engine ran quite well on 87 octane pump gas but there was also no load ever placed on the engine.

I'm going to try another compression gauge but did I make an error in having the head milled?  I know the combustion chambers in the 8 plug heads are opened up a bit more than the oval port or 4 plug D-port heads but not enough that it would make the compression that high.  Any help would be greatly appreciated because the race is two months away.

Cheers,
Greg

Offline Wittsend

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Re: Too much compression?!
« Reply #1 on: July 01, 2019, 05:00:32 PM »
There are two measurements of compression:

Static compression is a calculated number regarding cylinder sweep, piston surface volume, how deep the piston is in the cylinder, gasket thickness and combustion chamber size. Flat top pistons make this easier but some even calculate right down to the small gap between the first ring and the cylinder wall.

Dynamic compression factors valve timing as well.

One of the reasons a "Race Engine" gets higher compression is to compensate for longer cam duration and/or overlap.  There are calculators on line that will tell you both types but you do need to know the cam timing, bore and stroke numbers and combustion chamber size.  This will be helpful as there are general guidelines and if your combination is way outside the numbers there is cause for concern.  Otherwise if it works - use it. You may have to increase octane of lower the ignition timing.

Building an engine is a "system" intended to have appropriately matched parts for the purpose.  Sometimes you get fortunate straying (slightly) outside the norm and other times you get undesirable results. If your other engine had a different (performance) cam it may account for the lower compression readings. But not knowing the combustion chamber size differences before and after any milling of either head is an unknown.

Offline 65ShelbyClone

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Re: Too much compression?!
« Reply #2 on: July 03, 2020, 11:48:03 AM »
head shaved .100 with ... a stock Ranger roller cam
There's your "problem."

The Ranger roller (RR) cam is as mild as mild gets and has no overlap so the dynamic compression is much closer to the static ratio. 10.5 or 11:1+ on a RR is probably not going to be happy even on 91.

RR cams are popular roller conversions with us turbo 2.3s because they have practically no overlap. It's also popular to retard them significantly because....the y're a truck cam and nose-over in the low 5000s.
'72 Runabout - 2.3T, T5, MegaSquirt-II, 8", 5-lugs, big brakes.
'68 Mustang - Built roller 302, Toploader, 9", etc.

Offline Wittsend

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Re: Too much compression?!
« Reply #3 on: July 03, 2020, 12:04:18 PM »
 LOL, an original post a year and two days ago. No report back on how the "race in two months" went.

I wonder how "self retarding" the set up is given the large head cut. Something has to compensate for the slack in the timing belt.

Offline 65ShelbyClone

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Re: Too much compression?!
« Reply #4 on: July 03, 2020, 06:29:36 PM »
Yeah, I knew it was old and replied anyway, mainly out of fascination that a "race" engine would be equipped with a stock roller cam.  ???
'72 Runabout - 2.3T, T5, MegaSquirt-II, 8", 5-lugs, big brakes.
'68 Mustang - Built roller 302, Toploader, 9", etc.

Offline pinto_one

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Re: Too much compression?!
« Reply #5 on: July 06, 2020, 01:31:47 PM »
one of the resons I am useing the roller , but you can change the rocker arms from the last year lima , its a diffrent ratio but brings in a tad of lift and a few more degres of duration and I am going to pull in a much advance as I can for lowi end torque , the max RPM will never see over 2700 , it will be swinging a 74 inch wooden propellor , yep it going on a airplane ,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline Wittsend

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Re: Too much compression?!
« Reply #6 on: July 06, 2020, 02:04:54 PM »
I've heard a lot of differing aspects regarding the rocker ratio change. I SOOOooo wanted to take one of each rocker and test them side by side. Virtually ever article I've read is all "talk" and I can't recall anyone giving proof.

 The only thing that changes is the position of the roller as it relates to the ratio. It would have to move closer to the lifter to improve the ratio. BUT, - and this is assuming the stock roller sits directly centered under the high point of the cam (we will call it 6 O'Clock) at full lift, then the greater lift rocker would be inclined towards 5 O'Clock at its full lift. It then becomes a factor of does the greater ratio give equal or greater compensating lift..., or does the high lift occurring at an angle (5 O'Clock)  therefore only be equal or less? I  did a drawing (limited skills) to illustrate the point.

BTW, why a Lima engine in a plane? It is one of the heavier 4 cylinder engines.

Offline pinto_one

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Re: Too much compression?!
« Reply #7 on: July 07, 2020, 08:13:02 AM »
The cam and rocker set up I got from a write up on Routh 66 hot rod high , has a listing for what year cam and rockers , and what changed when you swap parts , Got both of them and also going to check to see if the industral 2.5 cam is any diffrent , ( got one of those also ) as for why the lima engine in a airplane is because they are very reliable and there is one airplane that will work with it , only is was built back in 1928 with the ford model A engine , yep only forty HP on a good day but it worked , not fast but it did work well , many engines were put in that aircraft but I wanted to keep it all ford , (model A engines are getting hard to find ) but I will be useing the 2.5 with the duel plug head so I will have a secondary ign like real aircraft , the ford industral book list the LRG425 at 65 HP @ 2700 rpm so power is enough and the weight of the engine is about the same as the model A engine , just need the low end grunt to swing the prop , as for how lnog it will last , it will out live me , I work at the airport and most of the tugs here have that engine in them , I look on the hour metter (HOBBS) they have over 6 to 7K on them , they overhaul the piston engines in aircraft at 2K some go more but not often ,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline 65ShelbyClone

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Re: Too much compression?!
« Reply #8 on: July 07, 2020, 11:38:45 AM »
The cam and rocker set up I got from a write up on Routh 66 hot rod high

Not that site again....

The 2.3 cam and rocker information on that site is entirely wrong and at this point I would argue entirely responsible for the roller follower "ratio upgrade" myth refusing to die. There is no difference in ratio between early and late roller followers.

https://turboford.org/thread-95-rocker-arm-swap?
'72 Runabout - 2.3T, T5, MegaSquirt-II, 8", 5-lugs, big brakes.
'68 Mustang - Built roller 302, Toploader, 9", etc.

Offline pinto_one

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Re: Too much compression?!
« Reply #9 on: July 07, 2020, 03:56:55 PM »
What ! I thought everything on the internet was true  :o  , but good thing I did not go out and buy thinking they would work , have to double check that mith myself , but still do not know if the industral cam is any better , the head casting is diffrent also , it was made as a duel plug head but the extra hole for the spark plugs are not machined out at all , and has the small valves and valve seats , this one had a propane carb on it , thanks for the info , guess typos always waste time and money when they look to be legit , at least I can run the engine on a test fixture with the prop and swap out the cams to give me max rpm static and find out which one is the best ,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline 65ShelbyClone

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Re: Too much compression?!
« Reply #10 on: July 07, 2020, 07:01:36 PM »
What does the exhaust manifold look like on the industrial engine?
'72 Runabout - 2.3T, T5, MegaSquirt-II, 8", 5-lugs, big brakes.
'68 Mustang - Built roller 302, Toploader, 9", etc.

Offline oldkayaker

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Re: Too much compression?!
« Reply #11 on: July 08, 2020, 04:47:10 AM »
According to the link below, the exhaust manifold looks like a turbo manifold, see pages 27, 28, & 64. 
http://www.rothfam.com/svo/reference/ford%20industrial.pdf
Jerry J - Jupiter, Florida

Offline 65ShelbyClone

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Re: Too much compression?!
« Reply #12 on: July 08, 2020, 01:24:20 PM »
That's why I asked, but it's not clear how many/if any came with the E6 version of the manifold. It looks like the E3 was used into the late '80s on industrial engines well after the cars were shipping with E6s.
Maybe the E3 doesn't crack on a non-turbo engine.  ???
'72 Runabout - 2.3T, T5, MegaSquirt-II, 8", 5-lugs, big brakes.
'68 Mustang - Built roller 302, Toploader, 9", etc.

Offline pinto_one

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Re: Too much compression?!
« Reply #13 on: July 09, 2020, 07:53:40 AM »
yes it does have the turbo exhaust manifold , first thing I noticed when I got the engine , guess this was the best way to go to run the exhaust up or down , the muffler is on top and came out of a lift that had a accident ,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0