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If a 65 396 was bored to 427 and still used all the stock 396 parts including the 3124 carb would the horsepower be higher , lower , or stay the same ? The reason I asked is a friend removed his original 327 from a FI 64 and built a 350 with the FI on it and it didnt run as good . He thought the FI didnt pump enough fuel for the larger bore .
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Re: 396 / 427 horsepower
Bill,
Personally I have had good results increasing bore to get HP. I am not a stroke guy. In the case of the 327, I did the same removing a rare 327 and built a 350 using the same compression & cam. The 327 was better with the combo.
Many say it's the small journal crank in the 327 vs the large journal in the 350. The RPM seemed to pick up faster in the 327 and rev a bit higher. It was also said that the small journal crank was less weight to turn and would make RPM faster.
My guess is that a 396 bored to 427 would be an improvement in HP and wind up a bit faster due to the bore.
DOM -
Re: 396 / 427 horsepower
I really like the way my 68 327/350 revs, would not consider a 350 CI as a replacement. Did the built high have high compression pistons like 11:1?Comment
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Re: 396 / 427 horsepower
IMO he will pickup a bit more low in torque and maybe 12 to 15 hp at flywheel but I do not feel the difference will be noticeable. A well tuned fresh 396 will stay with the 427 for the most part. 1/4 mile depends on a lot of factors and I really believe that in some cases some motors just run better than others - there are so many factors to consider including balance, blue printing, bearing selection, head and valve train set up, jetting, clutch slippage, rear end ratio, and most of all driver ability. While dynos are valuable, when it comes down to stop light to stop light it for the most part rests with driver experience when you are only talking about 10-20 hp difference.Comment
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Re: 396 / 427 horsepower
Bill------
A Chevrolet 327 and 350 (and a 302, too) have the exact same bore size---4.00". They engines differ only in stroke----3.25" for the 327 and 3.48" for the 350 (and 3.00" for a 302).
If you bored a 396 (4.094" bore size) to 427 (4.25" bore size), you might well end up with unreliably thin cylinder walls. 396 blocks were different than 427 blocks.
One thing to keep in mind: the 1965 L-78 and the 1966 L-72 both used cylinder heads with the exact same combustion chamber volume. They both used steel shim head gaskets of the exact same thickness. So, while the advertised compression ratios of both engines was the same (11.0:1) the actual compression ratio of the 427 had to have been greater.In Appreciation of John HinckleyComment
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In Appreciation of John HinckleyComment
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Re: 396 / 427 horsepower
The dome on 396 L-78 pistons is higher than the dome on 427 L-72 pistons. Both have the same actual compression ratio. The 65 only version of the 962 block has the same internal water jacket spacing as a 427 and will have the same cylinder wall thickness as a 427 when bored to 427. With the same cam, the same heads, and the same stroke, a 427 will make more power than a 396 simply because of the 31 extra cubic inches. That is probably why the early 66 L-72 engines wore 450 hp decals replacing the 396 425hp decals.Comment
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Re: 396 / 427 horsepower
Taylor's Similar Engine Rule:
Two engines, absolutely identical other than stroke, will produce about the same peak power at the same mean piston speed.
That seems simple enough, but "absolutely identical" means exactly that - ABSOLUTELY identical. Of course, one can make the longer stroke engine yield more power by reoptimizing the valve timing, but then the engines are no longer absolutely identical other than stroke.
It's not easy to stroke a 327 to 350, but it is easy to stroke a 350 to 377, which is a 3.75" stroke and 383 CID with a .030" overbore.
So if a 350 CID engine makes 300 SAE gross at 4800, increasing the stroke to 3.75" will still make about 300 HP, but at about 4450. The longer stroke will make more average power over the useable rev range, and a highly tuned short stroke engine will feel less peaky with a longer stroke.
The above does not apply to a larger bore. The larger bore should make more power. It will equal the smaller bore engine at somewhat lower revs, but will continue to climb until the heads choke as indicated by a Mach index of about 0.55.
DukeComment
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Re: 396 / 427 horsepower
The reason Chevrolet came up with the 302 in '67 was to go Trans/Am racing. Engines were limited to 5 liters (305"). They just took a 327 block and put a 283 crankshaft in it. I seem to recall reading at the time that the reason they didn't go the other way (283 block/327 crank) was because of what Domenic mentioned earlier about better revving with the smaller journal crankshaft."When a guy turns 16, he automatically knows everything about cars." - Wally CleaverComment
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Re: 396 / 427 horsepower
Mark------
It's better revving with a shorter stroke, not a smaller journal crankshaft. As a matter of fact, only the 1967 302 used the small journal crankshaft. The 1968-69 302's used the large journal crankshaft.
GM did make an engine with the 283 bore and 327 stroke. It was the 307. This engine was never used for any performance applications, though. Then, in 1976 they came out with an engine with a smaller-than-283 bore and the stroke of a 350, the 305 cid engine. This engine never amounted to much as far as performance goes, either.
Ford also used the 302 cid back in the Trans-Am racing days and it had the same bore and stroke as the Chevrolet 302. They never gave that combination up, though, and used it for their mainstream and performance street V-8's for many, many years.In Appreciation of John HinckleyComment
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Re: 396 / 427 horsepower
Joe,
Misunderstanding, I was talking about 2 separate engines, not converting a 327 to a 350. One was a 1966 Chevy II block that I bought. It was the 350 HP only made for the Chevy II in 1966. The block was cast differently than other 327's at the oil filter.
The other was a 1974 350 that we built the same as the 327, Compression, cam, and same numbered head castings, 461.
Both used the same 18 lb flywheel and were installed in the same vette. The 327 out ran the 350. The 350 was STD bore and the 327 was .040 over. The 327 would wind up faster than the 350. Even though they were in separate blocks the only difference was the larger crank ( large journal) and stroke. The heads, piston domes, cam, were the same.
My point was that, in my opinion, the heavier crank and more stroke didn't seem to help, the 327 was a better engine in that car.
DOMComment
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