olds 425 compression ratio?
November 13th, 2014, 06:09 PM
#1
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olds 425 compression ratio?
Hi guys, I have a 68 cutlass that's been sitting awhile. Im trying to get it back on the road soon! ok, so I have a olds 425 that I pulled out of it. its all torn apart and ive done some research. its from a 1965. theres numbers on the block - 386525A and it has "A" Heads. I have 2 questions. are the "A" heads as good as "C"? and what is the compression on this engine? I pulled the engine beause I broke 2 pistons, so I was about to buy 2 from kanter.com but they only have the 10.25:1 pistons. im worried I have the 10.50:1 pistons. is there a way to tell the compression on this engine? or do I just need to buy all 8 brand new?
Any help is appreciated! thank!
Any help is appreciated! thank!
November 13th, 2014, 06:16 PM
#2
A heads are good because they dont have the AIR bumps in the exhaust ports but require special rocker arm assemblys. I do not think there was a 10.5 CR 425 offered in 1965. You prob have 10.25 CR. This would be a piston with a slight dish on top.
November 13th, 2014, 06:33 PM
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November 13th, 2014, 09:14 PM
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From the books
Hot Rod's Complete Book of Engines (#1)(1965) shows four 425 engines: 300HP@4400; 310@4400; 360@4800; 370@4800. They are shown as 9.0 CR with a 2bbl; 10.25 with a 2bbl; 10.25 with a 4bbl; and 10.5 with a 4bbl.
The Olds parts book for 1965 shows three piston types for the 425: "low compression", "high compression", and "ultra-high compression". It appears that the ultra-high compression was standard on the Starfire & Jetstar 1, and optional on the 98 & Delta 88.
Nowhere can I find dimensions on the piston dishes. Pictures in the service manuals suggest a very subtle difference between the 10.25 & 10.5 pistons; very hard to distinguish. Your photo could be either. The only difference I can see is a "ring" in the center of the dish on the 10.5. The center of the dish on the 10.25 is smooth. Probably more of the 10.25 were sold.
Perhaps Kanter could provide a dimension. Otherwise just order what you need, and compare to yours when they arrive. The worst that could happen is that you'll have to order 6 more.
The Olds parts book for 1965 shows three piston types for the 425: "low compression", "high compression", and "ultra-high compression". It appears that the ultra-high compression was standard on the Starfire & Jetstar 1, and optional on the 98 & Delta 88.
Nowhere can I find dimensions on the piston dishes. Pictures in the service manuals suggest a very subtle difference between the 10.25 & 10.5 pistons; very hard to distinguish. Your photo could be either. The only difference I can see is a "ring" in the center of the dish on the 10.5. The center of the dish on the 10.25 is smooth. Probably more of the 10.25 were sold.
Perhaps Kanter could provide a dimension. Otherwise just order what you need, and compare to yours when they arrive. The worst that could happen is that you'll have to order 6 more.
November 14th, 2014, 04:32 PM
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I got mine off eBay, from falcon global. They had new, 10.25 pistons listed, and discovered that what they had were low-compression. So they had 10.25 pistons made for me by Egge.
Can't get much better than that.
I do remember looking at Kanter, but it seems like they only had low compression. This was at least a year ago, though, maybe two by now.
Can't get much better than that.
I do remember looking at Kanter, but it seems like they only had low compression. This was at least a year ago, though, maybe two by now.
November 14th, 2014, 05:04 PM
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i also have another question i cant really find an answer for my specific motor. im thinking of using a 284/296 -.541/.544 camshaft. will stock springs and rocker arms be able to handle that? or would i need to but 1.7 ratio rocker arms and new springs to match?
November 14th, 2014, 09:22 PM
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You'll need new springs and probably rockers - having just gone through this with A heads, plan on replacing the studs, and get rockers made for Olds. After some trial and tribulation, I ended up with Harlan Sharp 1.7, new springs and studs, and can just barely still get off-the-shelf pushrods to fit. Might not have the same difficulty with 1.6 rockers.
The problem with the stock studs is that the machined edge where a roller rocker sits is both too high and too wide, and it ended up being easier just replacing them for 30-odd dollars than trying to make them work. Also, some valve guide seals won't work with that setup.
The problem with the stock studs is that the machined edge where a roller rocker sits is both too high and too wide, and it ended up being easier just replacing them for 30-odd dollars than trying to make them work. Also, some valve guide seals won't work with that setup.
November 14th, 2014, 09:32 PM
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You should always get matching springs for the cam. You don't NEED 1.7 ratio rockers; 1.6 should work as long as they can accommodate the lift. I don't think factory 1.6 rockers can handle over .500" lift but aftermarket long-slot or adjustable rockers can.
November 15th, 2014, 11:12 AM
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http://www.summitracing.com/parts/cca-17044-16/reviews/
so do you think something like this would work? and would stock heads even be able to handle that camshaft? i feel it may be to big of a cam. (this is my first engine build)
so do you think something like this would work? and would stock heads even be able to handle that camshaft? i feel it may be to big of a cam. (this is my first engine build)
November 15th, 2014, 01:56 PM
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I would go with Harland Sharps. Those Ford-compatible rockers are the same as (or very similar to) the rockers I first tried. Although they will work with Olds heads, the geometry is slightly different. In order to use them, I would have had to get custom length pushrods, as the stock ones were at or near the maximum standard length, and the Ford rockers ended up needing slightly longer pushrods. I suspect this is a worse problem with the 45-degree A block and A heads, as others have used the Ford rockers with no problems.
Save yourself some headaches; get Harland Sharps, replace the studs, and use a pushrod length tester like this one.
What I finally ended up with was Harland Sharp S5107 rockers, Comp Cams guide plates, Crower short rocker nuts to fit under stock height valve covers, and Crower studs.
The springs I used were Comp Cams 995-16, but you'll need to make sure the springs you use are correct for your cam specs. Your cam has higher lift than mine, and if you go with 1.7 ratio rockers rather than stock 1.6, don't forget to calculate the coil bind.
It ended up being pricier than I would have liked, and I ended up having to find non-stock valve guide seals, but I would have happily paid the price up front if I had known how big of a pain I would be saving myself in the end after fiddling with the studs, pushrods, returns, and delivery wait times in between each new discovery...
As far as stock heads handling the cam, you'll need someone more knowledgeable than me to chime in. But the A heads are the best flowing Olds heads in stock trim, according to some source I can't remember. C heads are much more common and nearly the same in terms of flow, but if you don't want to go with aluminum heads, the ones you've got are about the best you'll get. Make sure you've got a good three-angle valve job, don't bother with porting unless you know someone who really, really knows what they are doing with Olds heads.
Save yourself some headaches; get Harland Sharps, replace the studs, and use a pushrod length tester like this one.
What I finally ended up with was Harland Sharp S5107 rockers, Comp Cams guide plates, Crower short rocker nuts to fit under stock height valve covers, and Crower studs.
The springs I used were Comp Cams 995-16, but you'll need to make sure the springs you use are correct for your cam specs. Your cam has higher lift than mine, and if you go with 1.7 ratio rockers rather than stock 1.6, don't forget to calculate the coil bind.
It ended up being pricier than I would have liked, and I ended up having to find non-stock valve guide seals, but I would have happily paid the price up front if I had known how big of a pain I would be saving myself in the end after fiddling with the studs, pushrods, returns, and delivery wait times in between each new discovery...
As far as stock heads handling the cam, you'll need someone more knowledgeable than me to chime in. But the A heads are the best flowing Olds heads in stock trim, according to some source I can't remember. C heads are much more common and nearly the same in terms of flow, but if you don't want to go with aluminum heads, the ones you've got are about the best you'll get. Make sure you've got a good three-angle valve job, don't bother with porting unless you know someone who really, really knows what they are doing with Olds heads.
Last edited by Erinyes; November 15th, 2014 at 02:01 PM.
November 16th, 2014, 04:00 PM
#21
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Thank you for the information! This build is getting more complicated and Expensive the more I research. I'm thinking of just getting a camshaft with less than .500 lift and use stock push rods, valve springs, and rocker arms. Would it be worth it spending all that money on roller rockers and .40 lift?
November 16th, 2014, 05:33 PM
#22
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Well, that totally depends on what you want out of it, what it's going into, and what your budget is. My setup is just a fun hobby car that I can sink dollars into, and since it was my wife's idea to get a hobby in the first place, as long as I space out my spending she can't complain too much. The only reason I started going down the total engine work-up route is because it needed a valve job, and the might-as-wells sucker punched me.
If you just want to get it running with decent performance, then the 425 is a good performing engine in stock trim. The real question is how long are you going to keep it, and will you regret not going the extra mile while you had it apart?
If you just want to get it running with decent performance, then the 425 is a good performing engine in stock trim. The real question is how long are you going to keep it, and will you regret not going the extra mile while you had it apart?
November 16th, 2014, 07:19 PM
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Well, it's going into a 68 cutlass. My budget is whatever extra money I get is going into this. I'm positive this engine won't be done till summer. At least. I plan on keeping this car for ALONG time. I just turned 20 and can see myself having this engine apart multiple times by the time I'm tired of this car. I just started a fence business this year so if business goes good in the next few years I'm sure I'll be putting forged pistons and rods and aftermarket heads and all that into this car. But until then my goal is about 500 horsepower. Shouldn't be to hard with a stock 370hp engine. It already has headers, intake, and 750 Cfm carb. I just want to replace the broken pistons and put a big cam in it for as cheap as possible, until I can afford to go all out. I found http://www.summitracing.com/parts/cc...ake/oldsmobile
But it doesn't tell me how much lift it can handle. Also this is really cheap so I'm thinking it probly wouldn't be much better than stock. I really would like a kit like this so I don't have to hunt down rocker arm studs and push rods and everything to match together.
But it doesn't tell me how much lift it can handle. Also this is really cheap so I'm thinking it probly wouldn't be much better than stock. I really would like a kit like this so I don't have to hunt down rocker arm studs and push rods and everything to match together.
November 16th, 2014, 09:01 PM
#24
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I don't believe that kit would work, for a couple reasons, and it's all due to having a 1965 A block and heads. Which brings up the cam -- if you are replacing the camshaft, you must get a cam for the 45 degree block.
It is a 45 degree cam angle block, which was made for only limited years. As a result, among other things the pushrods are a different length than the common 39 degree block. The heads have studs in them, but they are 7/16 studs, and if they are original they probably won't work with many new-style rockers. The guide plates raise the studs slightly, causing interference with the rocker, and add to the needed pushrod length - which is already near maximum for off-the-shelf pushrods. If the engine had the original steel head gaskets, the common replacements will raise the heads even more. Chances are pretty fair you are headed straight into the scenario I just went through.
Your best bet is to get components now that you will be able to reuse if/when you go through the engine again. Seriously. Buy the right valve train components now, and you will be able to reuse them later - except maybe the pushrods, which you would want to measure any time you go through the engine.
If you don't want to go to the expense right now, I'd say your best bet is to simply keep the existing cam for the time being, or if you have to replace the cam now, go with something that the stock rockers can accommodate. Even then, you'd be buying a cam, lifters, and timing chain, and only the timing chain would be reusable later when you go for the whole nine yards.
If you decide to go for it now, the links I gave you will work for all the tricky stuff. You'd have to find a cam, with springs to match, but there are people here that can recommend and supply a good cam. The pushrods you'd have to measure for after getting the rest of the engine back together, no matter what route you take. Even if you go stock, you would want to verify pushrod length - but you might be able to bring them into spec with shims.
Finally, as long as you have the heads off, you really should have a machinist check them over.
It is a 45 degree cam angle block, which was made for only limited years. As a result, among other things the pushrods are a different length than the common 39 degree block. The heads have studs in them, but they are 7/16 studs, and if they are original they probably won't work with many new-style rockers. The guide plates raise the studs slightly, causing interference with the rocker, and add to the needed pushrod length - which is already near maximum for off-the-shelf pushrods. If the engine had the original steel head gaskets, the common replacements will raise the heads even more. Chances are pretty fair you are headed straight into the scenario I just went through.
Your best bet is to get components now that you will be able to reuse if/when you go through the engine again. Seriously. Buy the right valve train components now, and you will be able to reuse them later - except maybe the pushrods, which you would want to measure any time you go through the engine.
If you don't want to go to the expense right now, I'd say your best bet is to simply keep the existing cam for the time being, or if you have to replace the cam now, go with something that the stock rockers can accommodate. Even then, you'd be buying a cam, lifters, and timing chain, and only the timing chain would be reusable later when you go for the whole nine yards.
If you decide to go for it now, the links I gave you will work for all the tricky stuff. You'd have to find a cam, with springs to match, but there are people here that can recommend and supply a good cam. The pushrods you'd have to measure for after getting the rest of the engine back together, no matter what route you take. Even if you go stock, you would want to verify pushrod length - but you might be able to bring them into spec with shims.
Finally, as long as you have the heads off, you really should have a machinist check them over.
November 16th, 2014, 10:24 PM
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Ahh I haven't thought about the cam angle making it difficult for parts. That complicates everything. Thank you for letting me know, before I went out and spend $1000 on parts I can't use! I think It may be best to just replace the pistons and put everything else back stock for now then... I may go with a 455 later on when i have the money. I assume it's easier to get aftermarket parts for a 455? I would expect the 425 to be difficult because it was only made for 3 years and has 2 Different cam angles.
Last edited by classicninja; November 16th, 2014 at 10:26 PM.
November 17th, 2014, 06:07 AM
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The 425 is a good engine. In general, it will rev higher than a 455, but the 455 has a bit more torque. Your choice.
Your 425 has factory forged crank and rods (although pay close attention to the rods if you reuse them; apparently they like to stretch), most 455s have cast.
If you really want to get spendy, keep the 425, go with a full roller cam. The taller lifters will help out with the pushrod issues, it's easier to set up, lasts longer, and you can get much more aggressive with the profile. Do your research on parts, get the money in advance, and spend it on the right pieces for what you want out of it.
November 17th, 2014, 04:17 PM
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Best thing would probably be to take them to the machine shop along with the heads and have them check for tolerances and cracks. I'm guessing you probably don't have the micrometers and so on that you would need. For that matter, I'm guessing you'll have someone put the pistons on the rods? If a shop is doing that, they should be able to check the rods at the same time.
November 19th, 2014, 01:57 PM
#30
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i am there right now
some genius thought it would be a good ideal to install a 65 engine in a 66 olds 98
had to get a custom grind cam, could not find rockers so i bought new ones and just reused the inserts
custom pistons 30 over
waiting on the heads to get finished
if i would have known i would have looked for a 66 up engine
some genius thought it would be a good ideal to install a 65 engine in a 66 olds 98
had to get a custom grind cam, could not find rockers so i bought new ones and just reused the inserts
custom pistons 30 over
waiting on the heads to get finished
if i would have known i would have looked for a 66 up engine
November 20th, 2014, 03:12 AM
#32
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Installing isn't the problem, really. Making sure that what you have is still within spec, without the proper measuring equipment, is the problem. Have the old rods stretched a few thousandths of an inch? Are the ends still round? It's best to be sure.
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