'76 F250 Turbo Build

pmuller9 said:
The DCR number is strictly a reference number we use to determine the 300 sixes tendency towards detonation and it also has relevance to the cranking compression.
We developed a DCR range for the 300 six based on engine build history using the .006" intake lobe closing point.
Any other lobe lift point is meaningless as far as detonation is concerned for the 300 six.

The Cam card I posted shows a .006" (advertised) duration of 268 degrees and a 114 degree LSA.
The .050" intake opening at -5 degrees and closing at 35 indicates the cam is to be installed 4 degrees advanced with the intake lobe center at 110 degrees ATDC.
That puts the .006" closing point at 268/2 + 110 -180 or 64 degrees ABDC.
All timing events are on the card using a little math.

So you would use 64 in the calculator to figure DCR.

The DCR should calculate as 6.6

The Felpro 1024 head gasket has a bore of 4.18 and a .039 compressed thickness.
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Got it, this is based on historical data. That makes a lot more sense.

Also I don't have much experience in this realm, so I didn't know that advertised duration was equivalent to "duration at 0.006 lift". Thanks for clarifying that.

As it turns out, the GFM calculator might have an error in a formula somewhere. Putting in all the above values with a valve close at 64° and piston volume of 30cc, it turned back a DCR of 5.85 and not 6.6. This is a good lesson in putting trust in online calculators when you can't see the math working. After going through all the hand calcs, I arrived at the same 6.6 DCR

Piston math.jpg

The two numbers I calculated was 18.9 CC to get a DCR of 7.25, and 30.8 to get a DCR of 6.6. Pmuller, you are saying 6.6 would end up being a good way to go on this build? I can calculate theoretical bests, but I'll trust your empirical recommendations.
 
jgavac said:
The two numbers I calculated was 18.9 CC to get a DCR of 7.25, and 30.8 to get a DCR of 6.6. Pmuller, you are saying 6.6 would end up being a good way to go on this build? I can calculate theoretical bests, but I'll trust your empirical recommendations.
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Great job on the math.
You could have also used the Law of Sines with the inside angle of 116 degrees (180-64) to get the 5.257" side but it's not any shorter in steps.

If you could cool the intake charge back to ambient after compressing it with a turbocharger then the standard range for DCR would hold true.
Street driven intercoolers are less than 100% efficient so the compressed intake charge is still above ambient and we take at least a 1/2 point of DCR away for a safety margin.

This is the calculator I like to use.
Just enter the actual .006" intake closing point at the last entry.

Compression Ratio Calculator

ENTER YOUR DATA CALCULATED DATA Cylinder Head Volume (cc) Cylinder Head Vol (cubic in.) Piston Head Volume (cc) Piston Head Vol (cubic in.) Gasket Thickness (in.) Swept Volume (cubic in.) Gasket Bore (in.) T.D.C. Volume (cubic in.) Cylinder Bore Diam
uempistons.com uempistons.com
 
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On a completely unrelated topic, I picked up a cam sync sensor for a 2001 3.0 V6 after reading up on modifying one to work. After some comparison to an old distributor, the only thing that doesn't look like it will work is the slightly smaller diameter housing (calipers are still on the way, so I don't have exact numbers... Roughly 5/16").

The drive gear on the sync was smaller, 14 teeth instead 16, but the shaft diameter and pin locations are the same.
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There's a significant difference in length from the mounting face, with the shaft collar on the sensor being much longer
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But, the oil pump drive shaft slides in to the same overall depth on the sensor as it does on the dizzy, so I'm thinking it shouldn't be a problem.
20210420_194121.jpg

I haven't been able to check fitment with the engine and won't be able to for a while, but I think it'll work.
 
Quick update; I got autotec pistons on order from Racetec last week, it'll be about an 8 week turnaround time on those. I'll share my order sheet soon to make sure I got my info correct.

--
Also came home from work yesterday to find my Crower cam and lifters had arrived! I didn't get a shipping notification so I didn't realize it was done
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That's about all I got for now. Mostly playing the waiting game for the rods and pistons
 
jgavac said:
Quick update; I got autotec pistons on order from Racetec last week, it'll be about an 8 week turnaround time on those. I'll share my order sheet soon to make sure I got my info correct.
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I would like to see the Racetec piston order sheet.
 
The Piston order sheet looks good.

The connecting rod's small end is offset so we usually put 1.100" for the small end width.
They will probably figure that out when they see it is for a BBC rod.
I also specify "No piston pin offset" in Notes section.

Have you talked with Randy?
 
I'm curious if you got anything figured out with the cam synchronizer? But also stoked for you moving forward with your project. Considering a similar build later for my 91 4x4.
 
benchracer said:
how much lighter are BBC rods and Autotec pistons than stock parts?
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These particular BBC rods weigh 732 grams and an untouched stock rod weighs around 720 grams.
Stock piston and pin weigh around 820 grams. These pistons will weigh somewhere over 600 grams.
My Autotec pistons and pin weighed 574 grams but these pistons will have heavier pins and longer skirts.
 
Very nice! Do those rods come chamfered on bothe sides of the big end?
 
CRIG said:
I'm curious if you got anything figured out with the cam synchronizer? But also stoked for you moving forward with your project. Considering a similar build later for my 91 4x4.
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Sorry I didn't get back to ya earlier. Nothing really new to report on the cam sync, I haven't test fit it in my running motor yet, and my block is at the machine shop.

Be sure to share all the good deets if you build something similar!
 
Not much news at the moment, my pistons made it out of engineering this week so I should see them within a couple weeks per Racetec.

In a brief departure from the section/topic, just wanted to share a pic from what I've been up to in the meantime. Went on a 550 mile trip on dirt thru Eastern WA with my 76 and a bone stock 300 out of an 81 truck 💪
20210707_112946.jpg

Won't share any more to keep the thread on brand and the mods happy 😉
 
Sorry for lack of activity, it's been a busy few months outside of this build.

Now that I've got the big items in, I'm taking everything to my machine shop later today so they can get moving on the project. Originally, I was planning to do most of the engine assembly myself and just have the shop do the machining. As this project has evolved a bit and I have more money tied into components, I'm thinking I'll have the shop assemble the bottom end at minimum. I've never built an engine in this detail before, so there's a lot of tools and resources I don't have. I'd rather not grenade this engine because I messed up something during assembly, so I'll leave the rotating components to the pros. Maybe on the next build I'll do more myself, I just really don't want to mess this one up.

Anyway, here's a trunk full of beautiful parts
20210725_162041.jpg
 
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