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im curious about the differences between the base model 327 and the higher output 327s. All i know is that the 365 and 375 models got the solid lift cam compared to the hydro cam for the lower ends. what else is different? heads? intake? are the rods and crank the same throughout all 327s? etc? my main interest is the reason for the higher redline. my first thought is that the higher ouputs can pull to 6500 because the cam allows that kind of breathing while the 300 horse just doesnt have the components to suck enough air to get past 5000?
Many different combinations of pistons, heads, valves, cams and intakes made the differences (increased compression and breathing improvements), and all '62-'67 327 cranks were forgings. There were basically four different C2 SB cams - the "431" was the base hydraulic cam from '62-'66 (replaced by the "929" starting in '67 and used through '79 and in '81), the "151" hydraulic cam (used in the 327/350 from '65 through '68), the "097" Duntov solid-lifter cam (used in '63 for the L-76 and L-84), and the "346" ("30-30") solid-lifter cam, used in '64 and '65 for the L-76 and L-84. Interestingly enough, ALL SB's used the same valve springs, regardless of cam usage. :thumbs:
ok thats all good to know. i shouldve clarified my question better. id really like to know about the quality of the components. so comparing the 300 horse to the 365 horse in 65 for example, are any of the pieces used of lesser quality? or are the pieces just a little more concervative? meaning are the rods, pistons and crank made of a weaker material? like cast vs forged?
SHP/FI engines use forged pistons versus cast on the 300 HP. Also, SHP/FI cranks have a special surface hardening treatment known at "Tufftriding". All use the same rod, but the early versions are weak, and can crack/break at the bolt head seat. Beginning in '67 a new rod went into production that added a little more metal to this area, which made them much more durable.
Some SHP/FI engines also had slightly better exhaust valve material.
With the exception of the early rods the overall quality of design, materials, and manufacturing on all 327s is top notch. With the late rods or a set or Crower Sportsmans these engines are just about indestructible.
thanks Duke! thats all precisely what I wanted to know! when you say early rods were weak but in 67 they got stronger, your saying all 327 rods through 66s were weak? confused by your use of the word "early" which would indicate to me a 63 to 64 model year, but it seems your saying all but the very last year had weaker rods?
(was C2Vert, figured out his old password and got his old user name back!)
All 327 engines used 2 bolt main bearing caps. All lo comp pistons were cast. All hi comp pistons were forged. I am FAIRLY sure that: all 327 connecting rods were the same, all 250/300 HP engines used cast cranks, all others used forged cranks, cranks with larger journals were used beginning in 1966.
250 and 300 HP engines had hydraulic lifters and 10.5:1 (advertised) compression ratio, standard oil pump, mild timing map, 4 quart pan, cast iron intake, 6" harmonic balancer, steel valve covers, and dual snorkel air cleaner. 250 HP had Carter WFCB carburetor, and 2" exhaust manifolds. 300 HP had Carter AFB carburetor (66-67 had Holley) and 2 1/2" exhaust manifolds (2" with Powerglide 63-65 and all 66-67). 63-64 250 HP engines used 1.4" intake and 1.94" exhausts. All other small blocks 63-67 used 1.5"/ 2.02" heads.
All 340/350/360/365/375 HP engines used finned valve covers, 1.5"/2.02" heads, special water pumps with internal/external bypasses, and 8" finned balancers. These were all designated "SHP", except the 350HP. Power steering was not available with any SHP engine because of oil pan clearance issues. All used peripheral inlet air cleaners of 3 designs (except 360/375 HP). For 1963, the 340 was identical to the 360(fuelly), except for the induction system. For 64-65, the 365 was identical to the 375(fuelly), except for the induction system. 1963 340/360HP engines had 11.25:1 compression, all others had 11.0:1. All these engines: used 2 1/2" exhaust manifolds in 63-65, and 2" in 66-67; used a 5 quart pan, except the 350HP which used a 4 quart; used a high pressure oil pump, except the 350HP which used a standard; used aluminum intake manifolds; used an oil pan baffle, except the 350HP. The 350 HP used hydraulic lifters, all others (SHP) used solid lifters. 1963 SHP engines (340/360) used the "Duntov" cam, while 64-65 SHP engines (365/375) used the "30-30" cam. The 1963 340HP engine used the same Carter AFB as the 300HP with manual trans. 64-65 365, and 65 350 all used Holley 2818 carburetor. 66-67 350 used same Holley as the 300HP. All 350HP engines had milder timing maps than the SHP engines.
There were other differences with the various exhaust manifiods based on options ordered, but I covered the major differences. Same goes for distributors (K66), pulleys and belts(C60, N40, etc.)
The reason for the higher rev limit on the hi horse engines is MAINLY because of the solid lifters, which delay valve float.; they are also built stronger as you can see from the above.
excellent post 65tb. even more then i was asking, but all i wanted to know! thanks a bunch, learning more all the time with this good info that is preparing me for a purchase in the upcoming months. thanks again
The improved small bearing rod that went into production in '67 is 3864881, and as far as I know they are still available. I would buy a set of these rods or equivalent aftermarket replacements or aftermarket racing rods such as the Crower Sportsman for all earlier 327s, espcially SHP/FI, and as far as I know this rod will also work on 265 and 283 SBs.
The early rods should be okay on a medium performance engine (redline 5500 or less) as long as they pass a magnaflux inspection, but given the price of inspecting a set of rods, a new set of 3864881s or equivalents might be cheaper.
The 881s are identifiable by a little hump of metal adjacent to the bolt seats on each side of the rod. This feature is missing from the earlier rods, and it's clear by visual inspection that the 881s are stronger in this area. It was not unusual for the early rods to crack and break at this point in engines that were run hard.
A magnaflux inspection revealed that the #7 rod on my '63 L-76 was badly cracked in this location when I took it down for a rebuild at 115K miles. I don't think it would have take many more excursions to 6500 revs for it to have broken.
Good luck Ross. I'm kinda partial to the 340/365 SHP crowd. After all, these are really user friendly fuel cars with beautiful chrome air cleaners instead of ugly ductwork, and marginally less (ADVERTISED!!!??) horsepower.
Ya gotta remember, it was all a numbers game back then, a la 430 HP L88's and ZL1's. Chevrolet also rated the L71 (1967 427 3x2bbl) @435 HP, while the L72 (1966 427 4bbl)was rated at only @425HP(some early ones were rated 450-but they were mechanically the same). Most people would agree that the 4bbl design is superior to the 3x2system, and delivers higher flowrates using the Holley 4150 (780CFM) carburetor. After all, you don't see them running "3 deuces" on Grand National stockers.
Thanks. That 's one of the 3 items I wasn't certain of--so 1968 and not mid '66. Strange that the larger journals were not introduced in 1967 like the beefed up rods that Duke mentions. Lots of guys were breaking stuff, and GM was scrambling to find the fix. They shoulda done all this engineering in 64-65, when the most potent 327's were produced. After that, we all know that the horsepower wars strictly concentrated on keeping the MKIV engine's ADVERTISED horsepower competitive with Chrysler's hemi, and Ford's 427.
Any facts or speculation as to why they finally started using 4 bolt mains on the later mousemotors.
this is turning out to be quite an informative thread. all very good stuff that will help me when im looking at cars. one of the cars that i checked into and finally decided to pass up had a 350 in it instead of a 327 and that was a big reason why. not sure why but i really want a 327, even though most of the pieces are similar if not the same. really appreciate the good rod ratio the 327 has.
Strange that the larger journals were not introduced in 1967 like the beefed up rods that Duke mentions.
The only reason the journal sizes were increased was to restore lost journal overlap when the stroke was increased to 3.48" from 3.25". Journal overlap is critical to crankshaft stiffness. It had nothing to do with a need to increase bearing size as there was no need. The small bearings can easily take the loading. The '67 350 was the first SB to use the large journals/bearings, and the '68 302, 307, and 327 went to large journals/bearings just to standarize on bearings for production. F5000 builders from the seventies generally preferred the small journal cranks because they reduced internal engine friction for more brake horsepower, and since those engine only had a 3" stroke, the small bearing journals provided sufficient overlap for adequate crankshaft stiffness.
The early rods were the only weakness on the SBs before 1967. The '67 rods are the best of the small journal lot, and the large journal rods are all good. I'm talking about an OEM high performance engine for street use or production racing. Building a SB-based racing engine with much higher revs and power is a different story, and that's why the aftermarket started making better rods.
I am not familiar with the term "bearing overlap", but I suspect it has something to do with the ratio of stroke-to-throw bearing size.
Since the stroke was not increased until the advent of the 350 in 1969, then why was the journal size increased in 1968--the last year of 327 production.
It's JOURNAL OVERLAP, not bearing overlap, and as I said previously, it is an important parameter for crankshaft stiffness, and a small change in overlap can have a significant impact on overall stiffness in both bending and torsion. You statement indicates you probably have an intutitive understanding of what it is.
The first 3.48" stroke 350 with the large journals was available in the Camaro in 1967. As I said previously, the entire small block line was changed to the large journal configuration in 1968 to standardize on bearings used in production. This included all '68 Corvette 327 configurations.
Now as an exercise, compute the journal overlap for a 1.625" throw (327) with 2.30" mains and 2.0" rod journals. Then compute the overlap with a 1.74" (350) throw and both 2.30/2.00" journals and the production 2.45"/2.10" journals. Post your answers (and anyone else who wants to give it a shot) and I'll grade your results. ;)
Hint: The formula for journal overlap is main journal radius plus rod journal radius minus crank throw radius , however, you can use diameters - one-half the quantity main plus rod minus stroke.
using your formula,
the 350cid 1.740 crank throw 2.45 main 2.1 rod has a journal overlap of 0.710
the 350cid 1.740 crank throw 2.30 main 2.0 rod has a journal overlap of 0.560
the 327cid 1.625 crank throw 2.30 mian 2.0 rod has a journal overlap of 0.675
so, how does journal overlap affect engine durability?
On the topic of weaker small block rods in the earlier production 327's, that's exactly what happened in my case to my '64 engine, though the rod failure was in a slightly different location than the area Duke describes. The rod had snapped in half across the beam section whereupon the "nub" portion still attached to the crank smacked the side of the block rendering it INSTANT JUNK .. .. The truth was revealed upon oil pan removal. There was this BIG crack .. ! .. Sure hated to lose that original block.
After teardown the remaining rods were magnafluxed. There were two other rods that were found to be cracked, also.