Hi all, I'm in the midst of tearing down a 225 from a John Deere to put in my 1972 Fargo 1/2 ton pickup. The goal of this venture is to get the best fuel economy I can. The #2 cylinder seems like it will need to be cleaned up so the engine will be going off to a machine shop once I figure out all the machining I want done. I'm hoping to raise the compression ratio and possibly put in larger valves.

This has left me wondering what compression ratio I should be aiming for.

It's my understanding that a higher compression ratio will achieve better fuel economy, but the higher octane gas required for higher compression engines costs more... I could back off the ignition timing to lower the cylinder pressures, thus allowing myself to use lower octane fuel, although I'd expect that to lead to a less efficient result. I guess I'm wondering if there's an optimal compression ratio that would net me the best "$/Litre : Litre/100km" ratio.

I'm hoping to be pretty thorough with the assembly and tuning of this engine, so I'll be porting the heads, smoothing out any protrusions that could become "hot spots", tuning to the best ignition curve I can, and selecting a camshaft that would work best (which leads me into another question).

I'm not all too familiar with camshaft numbers, the research I've done leads me to think I should be getting a cam that has good low/midrange torque, thus minimal valve overlap and relatively large lift? Duration I'm guessing would be limited by the LSA/valve overlap? Any suggestions on camshafts would be appreciated. I'll need to figure out which cam I want before I'm able to determine how much I need to get milled to achieve the right dynamic compression ratio.

The intended use of this truck is a road trip rig, maybe a camping setup in a low-profile bed cap. It's a 2wd single cab with an 8' box. I plan on lowering it and doing some aerodynamic additions to reduce drag. It's a basic truck, no P/B, no P/S, no A/C. I'd like to put 2.9 gears in it (which should get me around 1600RPM @ 110km/h with 29" tires). I'll be putting an A-833OD behind it. I also hope to put on an aussiespeed hurricane 2bbl intake, headers into a short 3" single exhaust, and a 300CFM Holley 2bbl carb.

I'm new to all of this, this will be the first engine I build, so any advice is greatly appreciated ◡̈ Thank you all in advance!

Camshaft: Dutra RV10RDP, Oregon Cams grind № 2106R.

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Too many people who were born on third base actually believe they've hit a triple.

I posted here in this topic last night and it doesn't show up now...
Don't know why.
Anyway on the rear end gear I don't think I'd use the 2.9 if I was also running OD. Ive had that gear in a few vehicles before there ever was an OD option from Dodge and for what you're wanting it seems like a perfect gear without OD.
Running the engine too low of an rpm causing it to lug isn't good for economy either.....
I had a 97 jeep Wrangler with the 4.0 inline 6 and a 5 speed, the 5th was OD. It didn't like OD when I had the same 235/75-15 tires as many (if not most) people run on a D100/150 until I was at 44-60+ and at that only if I was running pretty steady speed and flat ground. Otherwise I found myself in 4th alot. It was worse about not liking the OD while I had the 31/10.50-15s on it for a while.

I have an 85 D150 with a slant (currently under "construction") with a slant 6 and 3.21 gears. It's currently a 3 speed auto (727) and I'm wondering whether to leave it or to put in the a 500 or the a833od that is have in the shed. I know that 3.21 with the 833OD was a popular setup back when these trucks were plentiful on the roads, that would be the least I would want with an OD.
And then/6 is even less CID than the 4.0 albeit not by a lot.
I've had a couple of those 4.0s with 3.55s and that seemed about perfect.

While I was driving my 85 it didn't seem bad with the 727 and the 3.21 gears, wasn't too "buzzy" like a typical inline 6 gets when revved too high. Though I didn't drive that one enough long distance before I tore it apart to see how it would be for power and efficiency "before". I just went thru that /6 (actually built a different one for it and dropped it in). Along the way I shaved the block and head 0.100" between them and ended up exactly at published spec. Many here will agree with me about the/6 not actually measuring up to that as manufactured. Most are at least a 1/2 point down on compression as built by the factory even with the original 0.020 steel shim head gasket. Considering that every available aftermarket head gasket is thicker and most rebuilder grade pistons sit lower in the cylinder at TDC than the originals did. You need to machine the block and/or head at least enough to compensate for the difference in head gasket thickness just to keep status quo. I wasn't happy about that as rebuilt my pistons are as deep on the hole after a 0.030 block shave and rebuilder grade pistons as it was stock and all original.
Without the block shave I would have been 0.210" in the hole... Not good for performance and mileage for sure

Original question was compression ratio and camshaft suggestions for a slant in a truck with a two barrel intake and 3 inch exhaust.

For the cam:
Seconded.

For the compression ratio: I would target 8:1 DYNAMIC compression. This calculation takes more measuring and math, but is a better way to calculate compression.

RE: Rear gears an overdrive.

I have a 1995 Ford full size van. It has 3.55 rear gears, an overdrive automatic transmission, and a 351W. 3.55 gears are the numerically lowest gearset i would ever consider using with an overdrive transmission. I wish the van had numerically higher rear gears, like something in the low to mid 4s. On the highway the engine in my van turns around 1500-1800 RPM in the 60-70 MPH range. But as soon as I come to an incline the engine kicks down out of OD or stays in OD and lugs the motor.

I also have a 1976 D100 with a 225, 727, and 3.9 rear gear. That engine spins around 3200 RPM at 70 MPH. OD would drop RPMs down around 2400 RPM at the same speed.

Most street engines make better power in the 2100-2700 RPM band than they do down around 1300-1500. You will get better fuel economy and performance if the engine can operate in its power band.

This is all a long way of says that I also don't recommend an OD tranmission with 2.9 gears unless you live somewhere totally flat and don't haul or tow anything.

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Casually looking for a Clifford hyperpak intake for cheap.

Thanks all for the input. the RV10RDP seems like a great choice. From the math I've done, 0.070 should be milled off the deck and head to get to an 8:1 DCR with a felpro gasket, does that seem correct?. I discovered an old thread where Doc suggested 8:1 DCR for 87 octane, so that should suit my goal very well.

In terms of rear gearing, I'm hoping to run ~31" tires (something like 245/55R20 on 20" Ram spare steelies). After redoing the math, 2.9 would give me 1,470rpm@66mph (wow yeah, that's way too low). 3.2 should give me 1,600rpm@66mph. 3.55 should then give me 1,800rpm@66. I think the truck came standard with 3.55s so I'll be able to see how it performs and switch it up from there if needed. I'm targeting 66mph because most highways here in Canada are 100km/h(60mph) speed limit, so cruising at 110km/h(66mph) seems pretty reasonable.

You won't want any less than 3.55 for sure. 3.91 work really nice too.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Not sure on the mill amount. To be sure you're gonna have to mock it up with one of the pistons you're gonna use, put it and the crank in the block and run the piston all the way to TDC and measure where the piston is in the hole at that point and then figure out how much to shave.
Also need to "cc" the head before you start to tell how much to mill. I did the 70 thou off the head and 30 thou off the block for a total of 100-thou of metal dust and ended up exactly at 8.4:1 CR (static)! Which is published spec for CR on a/6 I was a lil disappointed but by then I had everything reassembled and so I settled .. while at the same time knowing that had I not done the machine work that I did do, I'd have been somewhere around 7.6:1! So I guess I'm glad I did "that" much at least.
My build is a 74 block, '77 "peanut plug" head with SI oversized valves, ported, flow bench tested, ported exhaust manifold with the outlet opened up to a true 2-1/4" (I started out at 1-7/8" outlet diameter) standard cast silvolite pistons, 0.020 over, an Oregon #819 cam and a cast iron super 6 intake with a genuine NOS Carter BBD meant for a 75-77 318 with "heavy duty" emissions (which back then meant an engine had minimal emissions on it)
So far I only have a couple of hours of break in time on my engine.
Had I done as I said above in this post id have taken another 40 thou or so off of the block while the machine shop had it... My application is very much like yours a 1/2 ton long bed 2wd truck that I plan on being a daily driver in good weather, and every day is almost like a small road trip as work is a 70 mile round trip.
Im currently using a 319k mile 360 Durango for that purpose.

Don has got it right about measuring the deck height at TDC and the head cc's before you can decide how much to mill. However, if you want to do it quick and dirty and not worry so much about the exact CR, then 0.070" will probably get you pretty close. Just consider that you might end up at 7.5:1, depending on how they set up the motor initially. Sometimes the industrial/truck 225s had really low CR. That 2106 RDP cam should work well for you.

Lou

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Home of Slant6-powered fun machines since 1988

I've finally got the block stripped, those three seized pistons were a serious pain to get out. I tried to clean up the bores with a stone hone but there's still rather significant texturing, it'll be going to get machined after I get the time to figure out all the compression ratio math. The swather this engine came from had an advertised horsepower of 55 so I wouldn't be surprised if there were differences in compression ratio compared to automotive variants, though that low number may just be the product of the camshaft, governor, and tuning.

In terms of CCing the heads, wouldn't existing head warpage make it difficult to calculate the volume of each combustion chamber after the head gets milled? Would that difference be so minor that it wouldn't matter or is there a method to remove some material from the chambers that end up being smaller as to balance everything out? Additionally, is there an easy way to figure out how much should be milled off of the head vs the block? The math seems pretty easy for removing material from the block seeing as how its a constant dimension. The head however has different angles and such, which makes calculating the amount of material to take off tricky. Any tips on how to do this? Also is there a limit to how much can be taken out of either surface? General engine rebuilding question: I've heard of people saying to bring the new pistons I plan on installing to the machine shop so they can match them better to the bore, but how should I know how much oversize I need to go before the block gets rebored? I'm hoping to go 0.020 oversize to take off as little material as possible, but there's a groove that I'm worried is deeper than that.

For anyone curious, the block casting numbers are 2806830-7, 2722 BH, AAWJ. I believe that makes it a block with additional bracing. I know I'm not going to even get close to enough power to break a crank or block, but its nice to know I've got a strong block

Head warpage will not affect head cc measurement in any meaningful way, as long as the surface is not crusted up. Shaving head small amounts will remove just slightly less than when doing the block but you are right the block is more reliable. You do not need to hit exact numbers to get a close CR measurement, and a few tenths either way will not affect performance noticeably.

I doubt you will get away with 3.42" bore. I would go straight for 3.44" or 3.46", but the machine shop should rough bore it before you buy the pistons.. 3.46" is not a big overbore on a Slant.

Lou

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Home of Slant6-powered fun machines since 1988

Wasn't it close to 1cc for each .006 milled of a head? (roughly of course)

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Yes, that is about right, until you get to about 0.080"-0.100" off, then it starts being more like 0.007-0.008" per cc.

Lou

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Home of Slant6-powered fun machines since 1988

'The swather this engine came'

being a non automotive engine it would be interesting to know if it has a shot peened crank and exhaust valve seat inserts.

if the crank is shot peened it will have a uniform dimpled surface
the machine shop can tell if the valve seats have inserts


' 0.020 oversize to take off as little material as possible, but there's a groove that I'm worried is deeper than that.'

because the bore on a slant six head is so small there is a lot of valve shrouding caused by the cylinder wall being close to the valve head. Going .040 over size really helps that. You can also clear the valve side in the combustion chamber, the bigger .040 bore gives a bit more room to work there.

also be advised the oversized Silvolite pistons have a reduced compression height when compared to stock pistons. They do that so the increase in diameter does not increase static compression, however stock slants are woefully short of compression to begin with. An easy way to compare compression heights on two similar pistons is to insert a piston pin so it bridges the two pistons, then set them on a very flat surface like a pane of glass. Observe if one piston is setting short of the glass.

I always want the replacement pistons in hand prior to doing final bore sizing or milling for compression.
Lastly you know that the replacement head gaskets are much thicker than stock-shim head gaskets. about .030 of the compression increase milling goes to compensating for the thicker head gasket.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

A good site to address the gearing is tremec's official website. It lets you input your trans gear ratios, tire height, and final drive. Next you pick an engine rpm and it will calculate the vehicle speed in each gear. This helps match your desired cruise RPM with expected driving speeds.

https://tremec.com/aftermarket/resource ... alculator/

I have spent a lot of time comparing gear ratios for my own T5 build and anything less than 3.9 final drive would be less than ideal for that trans.

Yup I got burned by the shorter replacement pistons thing. Had no idea til I measured once my short block was already back together. I took a wild ass guess as to how much to mill the block and with 0.030 off the block deck my pistons are still 0.180 down
... With an additional 0.070 off the head my engine measured out exactly 8.4:1 when done. Exactly blueprint spec. I was hoping at the time that with making 0.100" of cast iron dust by milling that it would get me to 9:1 or even slightly more. Goes to show how dismal it would have been if id have just bolted it together without any milling.