Offset Grinding 292 Inline 6 Crank

[enigma57]

Have a question regarding offset grinding crank journals......

I have one of the 1963 forged steel 6 counterweight cranks for my 292 inline 6 build. Also have one of the later model nodular iron cranks with 12 counterweights.

The long stroke 292 6's are prone to harmonics issues at engine speeds above 5,500 RPMs. So I have been thinking about offset grinding the crank journals to destroke it a bit. Stock stroke is 4.120" and journals are 2.1", same dia. as 350 V8, only the inline 6 rod has a wider big end (1.030" versus 0.940" for small block V8 rods).

I have heard of these cranks being offset ground for the short deck 230/250 blocks using 5.7" 230/250 inline 6 rods which have 2.000" dia. journals same as a 283 or 327 V8, but as with the 292, wider on the big end.

However, I am interested in offset grinding the throws to fit some used Carillo NASCAR type rods that utilize smaller 1.850" journals. I have seen them with big end widths varying from 0.820" or 0.900", but none as wide as the big end of the stock inline 6 rod.

The reason I am considering offset grinding the rods for smaller 1.850" dia. bearings is that I would like to destroke the 4.120" stroke crankshaft to 3.875" and also reduce the counterweight dia. to lighten it. Is this doable or would you advise against it? Engine will go in my mostly street driven '57 Chevy which will be run at the track from time to time mainly for tuning.

Thanks,

Harry

[KnightEngines]

You won't have enough metal removed for a cheek to run rod guided, you'd have to run piston guided.
Can be done, I've done it to use rb30 rods in an l20b.
Pistons need a full skirt & the inside flanks of the pin bores machined flat, then make up spacers to locate the rod in the piston, can't remember side clearance I used, but I'll dig it up for you if you go down that path.
You need to add extra oiling holes for the small end & pin bores (preferabley forced pin oiling) as you're taking away one of the main entry points for lube onto the pins, pins also need to be run a little looser for the same reason.
You need to run tight on the big end clearance, .0018" or so & the crank journals & rod big ends need to be accurately sized - tolerance of a tenth, no more.
Rod bearing life will be shorter, but still within the realms of reasonable if you get it right.

[jed]

If you are turning it less than 6500 rpm leave it alone and put the biggest diameter and heaviest harmonic balancer
On it u can find. Or if u have a good crankshaft shop have the snout built up to BBC size and use a BBC balancer.

[Truckedup]

Is this a street engine? How much time will it spend over 5500 RPM?....In my opinion, a N/A street engine with 300 cubic inches can not afford to loose any displacement..I don't know what power goals you have in mind but it if it's one HP per cube the engine should do that at 5500 rpm if modified properly...Otherwise, forced induction..

[Norris Marshall]

going the direction of destroking, 1/4 inch, combined with your total journal size reduction is going to move the oil hole in the rod journal quite a bit, might want to model or draw that out to see where the oil hole ends up.

[PackardV8]

If you are turning it less than 6500 rpm leave it alone and put the biggest diameter and heaviest harmonic balancer
On it u can find. Or if u have a good crankshaft shop have the snout built up to BBC size and use a BBC balancer.

Is this a street engine? How much time will it spend over 5500 RPM?....In my opinion, a N/A street engine with 300 cubic inches can not afford to loose any displacement..I don't know what power goals you have in mind but it if it's one HP per cube the engine should do that at 5500 rpm if modified properly...Otherwise, forced induction..

X3 - as we're occasionally prone to overthinking here, it's good to have others to talk us back from the ledge.

jack viens

[inline6]

I would also be concerned with the cross section you may lose by going to a smaller Diameter. The overlap between the main bearing diameter and the rod bearing diameter. That section may be smaller then what you had to begin with that will weaken the crankshaft. Sorry dont have access to CAD at the moment otherwise I would have modeled it.

[enigma57]

You won't have enough metal removed for a cheek to run rod guided, you'd have to run piston guided.
Can be done, I've done it to use rb30 rods in an l20b.
Pistons need a full skirt & the inside flanks of the pin bores machined flat, then make up spacers to locate the rod in the piston, can't remember side clearance I used, but I'll dig it up for you if you go down that path.
You need to add extra oiling holes for the small end & pin bores (preferabley forced pin oiling) as you're taking away one of the main entry points for lube onto the pins, pins also need to be run a little looser for the same reason.
You need to run tight on the big end clearance, .0018" or so & the crank journals & rod big ends need to be accurately sized - tolerance of a tenth, no more.
Rod bearing life will be shorter, but still within the realms of reasonable if you get it right.

going the direction of destroking, 1/4 inch, combined with your total journal size reduction is going to move the oil hole in the rod journal quite a bit, might want to model or draw that out to see where the oil hole ends up.

I would also be concerned with the cross section you may lose by going to a smaller Diameter. The overlap between the main bearing diameter and the rod bearing diameter. That section may be smaller then what you had to begin with that will weaken the crankshaft. Sorry dont have access to CAD at the moment otherwise I would have modeled it.

If you are turning it less than 6500 rpm leave it alone and put the biggest diameter and heaviest harmonic balancer
On it u can find. Or if u have a good crankshaft shop have the snout built up to BBC size and use a BBC balancer.

Is this a street engine? How much time will it spend over 5500 RPM?....In my opinion, a N/A street engine with 300 cubic inches can not afford to loose any displacement..I don't know what power goals you have in mind but it if it's one HP per cube the engine should do that at 5500 rpm if modified properly...Otherwise, forced induction..

X3 - as we're occasionally prone to overthinking here, it's good to have others to talk us back from the ledge.

jack vines

First of all...... Thanks to all here for your thoughts on this. Points well taken by all and much appreciated.

Yes, this is a street engine, Tony. And yes, I'm an old guy (71). But I still enjoy locking out overdrive and going through the gears every now and again. And as Jack so correctly noted, I do tend to overthink things at times. Just my nature.

The point of destroking from 4.120" to 3.875" was to minimize the harmonics issues the long stroke, tall deck 292 inline 6 engines are prone to when run at sustained engine speeds of 5,500 RPMs or more. When you spin that 31" long 73 lb. crank at those engine speeds factoring in the heavy rod/piston combo, long stroke and distances between firing pulses, etc...... The forces at play tend to wreak havoc inside these engines. And the longer the stroke, the more it wants to self destruct. So my plan was to destroke a bit, lighten the reciprocating parts substantially and run the best torsional dampner setup I can afford. Figured a square engine (3.875" bore X 3.875" stroke) with a 0.040" overbore = just a fraction less than 280 cu. in. and would allow her to rev a bit.

However, I see now that offset grinding the rod journals from 2.10" dia. down to 1.850" in order to accomplish this creates more issues (oiling and longevity related) than it solves in this instance.

So I will go back to my original plan and build the 292 with 0.040" overbore and I'll lighten both the rotating and reciprocating parts, use the best torsional dampner setup I can afford. And balance the bejavvers out of it, of course. Will use just enough cam to support the engine to self imposed redline of 5,000 RPMs to keep it together. Build it for torque and gear it to run about 2,100 RPMs cruising in high gear overdrive at 70 MPH.

16 years ago, a friend gave me a copy of Dyno2003 to play around with. I don't believe these computer programs are necessarily right on the money, but do feel they can be useful in predicting the comparative results of changes made to a given engine combo. So I used it to compare predicted results for my 292 engine using 2 different cams I designed using Isky solid lifter flat tappet lobes and flow numbers for a Sissel lump ported head with 1.94" / 1.60" valves.

Cam #1 has a nice power band, but needs to spin up to 6,000 RPMs to make full power. Used Isky ZM-89 lobe for both intake and exhaust and tried several LSA, ICA & ECA variations. I found best results with a single pattern cam having 244 degrees duration @ 0.050", ground on 107 deg. LSA with 106 deg. ICA and 108 deg. ECA and 64 deg. overlap. The 194/230/250/292 inline 6's run 1.7 rockers, so valve lift with this lobe worked out to 0.544".

Cam #2 (this is the cam I will run) makes the 292 into a stump puller with max. power between 4,500 and 5,000 RPMs. Used Isky S-50 E4 intake lobe and S-99+10 exhaust lobe, again experimenting with several LSA, ICA & ECA variations. Found best results with 210 deg. intake and 216 deg. exh. duration @ 0.050", ground on 108 deg. LSA with 108 deg. ICA and 108 deg. ECA and 42 deg. overlap. With 1.7 rockers,valve lift is 0.481" for both intake and exhaust.

The interesting thing when comparing these 2 cams (same engine specs except Cam #1 required higher comp. ratio (10:1) whilst Cam #2 required 9.4:1 for correct DCR)......

Cam #1 with 244 deg. duration@ 0.050", 107 deg. LSA and 0.544" valve lift when compared with Cam #2 having 210 deg. / 216 deg. duration @ 0.050" and 0.481" valve lift ...... Made 325 HP @ 5,500 - 6,000 RPMs and 338 ft./lb. TQ @ 4,500 RPMs. Not too shabby for a 292 inline 6 in street tune running through a full length muffled exhaust system. But compared to the milder Cam #2, was down 20 HP and 50 ft./lb. TQ @ 2,000 RPMs and did not make equal HP and TQ to Cam #2 until reaching 4,000 RPMs.

And whilst the milder 210 deg. / 216 deg. cam 'only' made 270 HP @ 4,500 - 5,000 RPMs and 335 ft./lb. TQ @3,500 RPMs (down by 55 HP and 3 ft./lb.TQ at peak)...... If you average all HP and TQ readings from 2,000 RPMs to each cam's respective peak HP and TQ reading...... The milder cam averaged 25 less HP, but 15 more ft./lb. TQ than did the 244 degree cam....... At between 1,000 and 1,500 fewer RPMs.

In fact, the milder cam had the flattest torque curve I have ever seen...... Made a minimum 318 ft./lb. TQ from 2,000 RPMs through 4,500 RPMs with peak TQ of 335 ft./lb. @ 3,500 RPMs. At least according to this old dyno program. So I will run Cam #1 and gear the car accordingly. Interestingly, this cam worked out pretty close to the old Isky E-4 grind from the mid-'50s except with higher valve lift due to the 1.7 rocker ratio (one lobe is actually from the old E-4).

Will let you know how it works out. Should be a torquey little 6- banger.

Best regards to all,

Harry

[Truckedup]

Harry, sounds like you have a plan......I built a few old Chevy 261 inline 6's then did the 302 GMC inline 6 and put it in the tin can 37 Chevy PU...The GMC has only 4 main bearings with a nearly 80 lbs crank I did a little head work, SBC valves but no real porting.A custom short duration high lift tight lash cam from the late Lazer Cams.....A home made header and single 4 barrel 400 cfm AFB..Once tuned up it made about 225 HP at about 4500 rpm and 300 or so ft lbs of torque across the rpm range...It would rev freely to 5000 rpm...In the 2900 pound truck it was quite snotty, geared for 70 mph at 2100 mph with a 5 speed OD manual..The flat torque curve was great for pulling hills but it lacked something..that would be the building of power with RPM that makes it feel fast through the gears. Done again I would try for a higher torque peak..,Just my experience and opinion ....

[Dan Timberlake]

Pete Hagenbuch, the Mopar development engineer, did some interviews over at allpar.
He was pretty enthusiastic about the slant six. The development of the "Super six" is an interesting story.
I figure the exhaust he describes in such glowing terms might be worth a try on any inline 6.

https://www.allpar.com/corporate/bios/h ... rview.html

"Well, the first and most important thing was the carburetor; it had 2 holes in it. Oh, there is so much you can do, Dave, that doesn’t even show. We messed around with the spark advance schedules and did a super calibration job on the carburetor. We had a low restriction air cleaner. Improved exhaust system, still single of course. I wanted in the worst kind of way to have a twin exhaust system because, man, will that do wonders for a six. You put one, two and three, and four, five and six together and you run ‘em down about 6 or 8 feet and bring them together in one tailpipe and you've added great huge gobs of output."

[strokersix]

I am running a 292 12 weight crank destroked to 4.062, 2.0 crankpins, clearanced for Crower 6.0 rods and lightweight JE pistons in a 250 block with a modified small block Streetdampr. Manual trans with heavy flywheel in a street car. Just a point of reference for you.

[enigma57]

Thanks for your comments, strokersix. This inline 6 build will be a learning experience for me.

Sounds like a stout 292 you have there. I was using my old 292 tall deck block to mock up front motor mounts a while back and found a crack and a couple cylinders that won't clean up with a reasonable overbore. Have considered dropping my 292 crank into a 230 or 250 low deck block mainly due to hood clearance issues. I will be running Weber downdraught carbs on a modified sidedraught intake, so height of carbs and air cleaners may be an issue in my '57. Don't want to butcher the hood if I do't have to.

Have you had any issues with piston wear or with cylinder walls/ring seal with your setup?

Rod angularity running a long stroke crank with short rods in a low deck block is a concern for me. I built a small block V8 stroker some years back. 4.00" stroke crank with 5.850" rods. Wiseco did my pistons and they were concerned about ring placement, so did not go longer on the rods. Oil rings ended up in wrist pin area anyway and I wasn't real crazy about that.

How far did you cut your crank counterweights down for lightening and piston skirt clearance? What have you found to work best regarding torsional dampner? I have been considering adapting a smallblock Fluidamper. Are the mechanical type any better?

Thanks,

Harry

[enigma57]

Pete Hagenbuch, the Mopar development engineer, did some interviews over at allpar.
He was pretty enthusiastic about the slant six. The development of the "Super six" is an interesting story.
I figure the exhaust he describes in such glowing terms might be worth a try on any inline 6.

https://www.allpar.com/corporate/bios/h ... rview.html

"Well, the first and most important thing was the carburetor; it had 2 holes in it. Oh, there is so much you can do, Dave, that doesn’t even show. We messed around with the spark advance schedules and did a super calibration job on the carburetor. We had a low restriction air cleaner. Improved exhaust system, still single of course. I wanted in the worst kind of way to have a twin exhaust system because, man, will that do wonders for a six. You put one, two and three, and four, five and six together and you run ‘em down about 6 or 8 feet and bring them together in one tailpipe and you've added great huge gobs of output."

Thanks, Dan! That was an interesting read. Especially so, as my daily driver was a 1962 Dodge Lancer for a number of years. Only reluctantly parted with it after a back operation left me unable to get down into a small, low car such as that. Loved the Lancer. It was all original except for the exhaust. The original 170 exhaust manifold had a crack in it so I went to the wrecking yard and pulled one from a '76 'Super Six'. The 2bbl intake was already gone or I would have got it, as well.

The exhaust manifold from the '76 225 'Super Six' engine was identical to the original exhaust manifold on my 1962 170 slant 6 engine except that it had a larger outlet flange which took 2-1/4" exhaust tubing instead of the little 1-7/8" head pipe my car was originally fitted with.

When I removed it from the '76, I hack sawed through the original 400 series stainless steel head pipe about 3" below the attaching flange. Other than the enlarged exhaust outlet, the '76 manifold was a direct replacement for my original manifold. So much so that my original intake and 1bbl carb fit right up when I put it back together. The original exhaust system was getting pretty rusty by then (1992, the car was 30 years old at that point). So I took it to a buddy who ran a muffler shop and had them install a complete 2-1/2" single exhaust system along with a new turbo muffler. 2/1/2" tubing is a nice fit when slipped over 2-1/4". I had them slip the new 2-1/2" tubing over the 2-1/4"about an inch and weld it up.

The exhaust for the 292 I am building will begin with split manifolds as was discussed in the slant 6 article you posted. I have a pair of Tom Langdon's split exhaust castings. They place exhaust from cylinders 1, 2 ,& 3 together and 4, 5 & 6 together. Outlets are designed for 2-bolt flange with 2-1/4" outlets. The ones I have had the bolt holes drilled off center. Too close to drill and tap new holes. So I picked up a couple 1" thick heat risers for big block Gutted the butterfly and shaft, brazed them to the Langdon castings and now have dual 2-1/2 " 3-bolt flanges. Planning on running 2-1/2" duals and a short H-type balance pipe. Or might join them together and run a single 3" exhaust. I remember Randy Brzezinski stressing the need to bring the pipes on circle track cars together into a large single exhaust. Of course, those are V8s. Would inline 6 firing order work well with both pipes joined downstream or are V8 exhaust impulses a different thing altogether in that regard?

Best regards,

Harry

-

[enigma57]

Harry, sounds like you have a plan......I built a few old Chevy 261 inline 6's then did the 302 GMC inline 6 and put it in the tin can 37 Chevy PU...The GMC has only 4 main bearings with a nearly 80 lbs crank I did a little head work, SBC valves but no real porting.A custom short duration high lift tight lash cam from the late Lazer Cams.....A home made header and single 4 barrel 400 cfm AFB..Once tuned up it made about 225 HP at about 4500 rpm and 300 or so ft lbs of torque across the rpm range...It would rev freely to 5000 rpm...In the 2900 pound truck it was quite snotty, geared for 70 mph at 2100 mph with a 5 speed OD manual..The flat torque curve was great for pulling hills but it lacked something..that would be the building of power with RPM that makes it feel fast through the gears. Done again I would try for a higher torque peak..,Just my experience and opinion ....

Tony, sounds like you built your truck with many of the same ideas I have for my '57 sedan as far as gearing and engine setup. Regarding the GMC 302 having only 4 mains versus the 194 / 230 / 250 / 292 series engines having 7 mains...... I believe the 302 Jimmy block and head are much heavier (thicker) castings than the thinwall castings used by GM for the later inline 6's and that is why they are at the very least just as reliable when modified for greater power (at levels not requiring a stud girdle for the mains).

After I read your post, I thought about what you said regarding the tradeoff (pros and cons of each) between building a stump puller with a nearly flat torque curve from off idle through 4,500 RPMs...... And an engine such as we are both more familiar with that requires winding out through the gears to get up into a higher, much narrower powerband.

So I fired up the old 2003 computer dyno program today and input my engine specs. Ran them with both cams again as I did earlier to compare one against the other...... The torquey 210 / 216 degree solid lifter cam and the higher winding 244 degree solid lifter cam. Only change being the cams and bumping compression from 9.4 to 10.0 for the hotter cam (would have gone to 10.5 comp. with the hotter cam, but I' concerned about running that much squeeze with what passes for pump gas now of days).

As before, my 292 with the milder 210 / 216 degree cam had a nearly flat torque curve from 2,000 RPMs through 4,500 RPMs with peak TQ at 3,500 RPMs and peak HP at 4,500 to 5,000 RPMs (500 RPM flat plateau at those revs before dropping off)......

Whilst the hotter 244 degree cam did not reach peak TQ until 4,000 to 4,500 RPMs (500 RPM flat plateau at those revs, before dropping off) and peak HP until 5,500 RPMs. And as before, the 244 degree cam was down 20 HP and 50 ft./lb. TQ @ 2,000 RPMs and did not 'catch up' (make equal HP and TQ to the milder 210 / 216 degree cam) until reaching 4,000 RPMs. The result being a much narrower powerband between 4,000 and 6,000 RPMs with peak TQ and peak HP reached 1,000 RPMs higher than the milder 210 / 216 degree cam.

In short, 6,000 RPMs being the point at which harmonics are said to become the 800 lb. gorilla for these engines when running unmodified OEM rotating and reciprocating parts)...... I designed the 210 / 216 degree solid lifter cam having 0.481" lift to get all the power I could from this 292 inline 6 from off idle through 5,000 RPMs redline by using the least duration and lift that would take the 292 to a 'safe' self imposed redline...... 1,000 RPMs below the engine speed at which the destructive harmonics issues these tall deck, long stroke 292's are so noted for when running unmodified OEM reciprocating parts...... Resulting over time in broken cranks, flywheel retention issues, cracked main webs and other assorted mechanical mayhem (depending upon what lets go first).

I had previously found that with my particular lump ported 292 engine specs...... Cams smaller than the mild 210 / 216 degree solid lifter grind left a lot of power on the table...... Whilst cams larger than the 210 / 216 degree cam resulted in diminishing returns...... Requiring (in my view) a disproportionate increase in both duration and lift to justify any additional power gained.

So the 244 degree cam, I designed with just the opposite in mind from the 210 / 216 degree cam. The question in my mind being...... For a naturally aspirated lump ported 292 in a road car running on pump gas...... Putting driveability, mileage and idle quality on the back burner...... How much added duration, and lift can be put to good use in a road car to raise the powerband enough to take the 292 engine within a hair's breadth of self destruction at sustained RPMs when running unmodified OEM rotating and reciprocating parts...... And with what results?

In other words...... For my 292 inline 6...... When comparing the 210 / 216 degree cam to the 244 degree cam...... What are the net gains and losses realized by increasing duration @ 0.050" by 34 degrees, overlap by 22 degrees and valve lift by 0.063"?

Well, the 210 / 216 cam's broad power band from off idle through 5,000 RPMs was compressed into a narrow span of 2,000 RPMs (4,000 to 6,000 RPMs) with the 244 degree cam. Peak HP and peak TQ were raised by only 1,000 RPMs. Overall, the 244 degree cam made consistently less power below 4,000 RPMs...... At 2,000 RPMs for instance, being down by 20 HP and 50 ft./lb. TQ.

Final results measured from 2,000 RPMs to the points at which each cam's respective peak HP and TQ readings were reached...... The 244 degree cam was up by 55 HP and 3 ft./lb. TQ overall.

However...... On balance...... If you average all HP and TQ readings from 2,000 RPMs to each cam's respective peak HP and TQ reading...... The milder 210 / 216 degree cam averaged 25 less HP overall, but averaged 15 more ft./lb. TQ than did the 244 degree cam. So from the standpoint of what I would want from a 292 in my '57 Chevy sedan (its a road car, not a race car)...... I believe the milder 210 / 216 degree cam should do all I need it to do even when towing a boat or small trailer.

Tony, how is your twin engine motorcycle coming along? Have you had it on the salt yet?

Best regards,

Harry

[Truckedup]

Well, I think you know the what you want.........Good......The dual engine Triumph made a few passes at Maine the summer before last..It ran near 150 MPH but had a random flooding issue on one carb than cut speed.Front engine lost oil pressure due to failed seal that wasn't supposed to fail.I was not there to fix it....No damage but he parked it and set a few records on the single engine bike...I fixed the problems but since then the bike has been on display in his bar...Every year is supposed to be Bonneville but it's a 5000 mile round trip and no one wants to drive that far...