Rebuilding my correct 283/230hp. What size cam can I put in and still have it judged for Duntov? Any other tricks to hide but look stock? Any suggestions, thank you.
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Re: ci engine rebuid, Bigger Cam
One area is precision machine work, clearances, balancing, the whole area often defined as blueprinting. There are a lot of items such as cylinder bore finish, piston ring selection, cast vs. hypereutectic pistons, it goes on and on. If it will be assembled by an engine builder, pick that person very carefully, then tell them all the details. Actually, a good engine builder should be asking you a lot of questions, providing explanations and answering questions. If you're looking for a little more power, even with a stock cam, you can have some minor port work done on the heads - typically called something like bowl blending or minor street/strip porting. A precision multi-angle valve job is also a good idea. I would assume it needs to sound like a 283/230, so be sure the builder knows that a lumpy sounding cam is a no-no. Also, if the block has the correct stamping on the deck surface, make sure it is known how critical this is - a lot of machine shops will do a clean-up cut on the deck surfaces as part of a machine work package.
Roger
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Re: ci engine rebuid, Bigger Cam
Bill...
Consider installing Hardened seats and stainless steel valves if the engine has not been prepared for today's fuels.Comment
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Re: ci engine rebuid, Bigger Cam
Bill,
There are at least two camshafts that I would suggest. The first is a Crane HMV260-2 and the second is a Comp Cams XE250H-10. What you want is a cam with no more than 265 degrees of advertized duration for the intake valves. For your application, I prefer a lobe separation angle of 112 degrees or more (which the Crane cam has). Both cams increase the maximum valve lift without noticeably increasing duration and overlap(key to maintaining a smooth idle). Keep your compression ratio below 9.5:1 as these cams close the intake valves a little sooner than the factory cam to produce more cylinder pressure. You will want to use their recommended springs as these cams produce higher valve train acceleration and require a slightly higher valve seat pressure (105 lbs.). The result will be an increase in low and mid-range torque and a corresponding increase in HP. Combined with a mild pocket porting on your cylinder heads, you will also get a slight increase in maximum HP. I have the Crane cam in a 327/300 and really like it. FYI - Chevy High Performance had several articles on the 283 in their September 1999 issue.
PeteComment
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Re: ci engine rebuid, Bigger Cam
Bill -
"Duntov" requires Performance Verification, and a "bigger cam" will become obvious during that test, and result in total P.V. failure. You can do lots of nice internal things to improve performance and pass a P.V., but a "big cam" isn't one of them.Comment
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Re: ci engine rebuid, Bigger Cam
If you are going for a Duntov award use the original type cam. If you go with an aftermarket cam that doesn't idle butter smooth at 500, you will fail your PV and kiss a Duntov award goodby until you swap back to a stock spec cam. Do it right the first time, so you don't have to change the cam after you flunk a PV.
Though the OE cam is no longer available, repros of the late 327/300 HP cam are, and this cam is essentially the same as original. For reference the GM part number is 3896929.
You do not need hardened valve seats and the risk of having them installed is not worth the potential benefit. You can pocket port/port match the heads/manifold and do a three angle valve job, which will not be detectable in judging, but it will improve top end power about 5 percent and not affect idle quality.
Have the original rods magnafluxed or just buy new late design small bearing rods, which is probably cheaper when you add up the cost of magnaflux, new bolts, and resizing. The early small bearing rods are weak. The later design that went into production in the '66-'67 time frame are stonger and more fatigue resistant.
Beyond this use all OE or OE equivalent parts - no hot rod parts.
DukeComment
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early rods...
Duke: Were same rods used in both base and SHP 283s? I never thought to change rods when I "revised" my 230 with SHP guts. (did however get them resized/bolts...) Recipe for disaster or leave well enough alone?
Thank you,
KarlComment
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Re: ci engine rebuid, Bigger Cam
Duke, How easy is it to determine a 66-67 small journal rod from an earlier version? Is it a case of having to see both designs side by side to determine the difference? DougComment
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Re: early rods...
The SB rods from the late fifties carried over to early 327s. With the 327's longer stroke and especially at SHP rev levels, they were weak. Failures were not common on street cars, but plenty of racers (both drag and road) holed blocks with them. The failures were fatigue related, so it was more common on engines that had a lot of high rev time.
In the medium performance 283/230 they should not be a problem, so don't worry about it, but I would still recommend to anyone rebuilding a 283 or small bearing 327 to replace early design rods with new ones of the later design while the engine is apart as cheap insurance.
The weak part of these early rods is at the bolt seat where the rod has what is essentially a notch. This is where they typically fail. The later design small bearing rod has a little hump of metal added on the sides (new forging dies) that increases the section thickness at this point for improved durability.
For medium performance engines I recommend new later design rods. For mechanical lifter SHP engines, especially if you plan to rev them frequently to or near their 6500 redline, I recommend Crower Sportsman rods. These will make the bottom end essentially bulletproof on a SHP engine as long as the bearings never get oil-starved.
Crower Sportsmans are reasonably priced and weight about the same as the OE rods. One thing to always consider with aftermarket rods is weight. Some are considerably heavier than OE, and I recommend avoiding them. These engines don't need a heavy rod - just a rod with better design geometry with the same total mass of material.
DukeComment
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Re: ci engine rebuid, Bigger Cam
When you look at the two side by the change is obvious. The area of concern is adjacent to the bolt seat. The later version small bearing rods have a hump of metal added on each side near the bolt seat that increases the local section thickness for improved durability.
I don't have any laying around, but if anyone has examples of each, a photo would be worth the proverbial thousand words.
This is only an issue with the small bearing rods. As far as I know, the later large bearing rods are fine, and some SHP engines received upgraded versions.
My Cosworth Vega has a rod similar to the small bearing SB rod. The basic forging and finished dimensions are shared with the 140 Vega and 250 I-6 rods. This rod has a bit wider bottom end than the SB rods, so there is more material in the vicinity of the bolt seats, and the CV rods were heat treated to a higher hardness - similar to the "pink" rods on SHP 350s. Of the few CV rod failures I've looked into, they all appeared to have been initiated by a seized bearing due to oil starvation.
DukeComment
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Re: ci engine rebuid, Bigger Cam
Thank you to all who responded. I probally will stick with everything stock and use a 327/300hp cam, so no questions can be asked.Comment
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Re: ci engine rebuid, Bigger Cam
The Crane cam idles extremely smoothly at 500 rpms and produces 20 inches of vacuum. Having worked with factory stock low hp 283's and 327's for many years, I cannot tell the difference in idle quality between the factory cam and the Crane HVM260-2 grind. I can't personally vouch the Comp Cams cam but it has similar, but slightly more aggressive lobe profiles with less advertized intake duration (250). To summarize, there are aftermarket camshafts available that can provide increased torque without sacrificing idle quality.
PeteComment
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