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Old 02-26-2008, 12:43 PM
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Is this a Good Idea For a Rebuild on a 305

Ok so I got a 305, for part of a deal that has 100,000 miles on it. And I want to rebuild it stock other than a slightly bigger cam. Im buying a Re-ring Kit out of Summitracing for 190$, which I thought is fairly good. The cylinders have a ridge till the point where u can catch ur finger nail on. So Im going to hone it then put the same pistons with brand new rings back in it. The heads say they are 53cc with 1.72 and 1.55 valves which I figured wasnt that bad. Im sending the heads out to have a valve job done. Ok heres my 2 questions, Can someone direct me to a lowend torquey cam thats isnt to big?. And the real questions is How would you break the rings in ?. Specs on it is it came out of a big van with the 53cc heads and is in the late 80's. Its has some kind of sensor by the pan on the left side of the block. So all together would the parts and a good installation make a good stock 305 ? .

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Old 02-26-2008, 01:20 PM
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If you can feel a ring ridge with your finger nail, there is too much! You can get a ridge reaming tool and cut the ridge before honing, but your rings will probably never seal due to the bores being way out of spec. If you reuse the pistons, they will be very loose in the bores since there is substaintial wear. The block needs to be checked by a good shop and will most likely need bored out. The crank needs to be checked and will also need to be reground.
You need to find a good shop and follow their suggestions for your build.
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Old 02-26-2008, 01:44 PM
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Quote:
Originally Posted by chevy350_Camd
Ok so I got a 305, for part of a deal that has 100,000 miles on it. And I want to rebuild it stock other than a slightly bigger cam. Im buying a Re-ring Kit out of Summitracing for 190$, which I thought is fairly good. The cylinders have a ridge till the point where u can catch ur finger nail on. So Im going to hone it then put the same pistons with brand new rings back in it. The heads say they are 53cc with 1.72 and 1.55 valves which I figured wasnt that bad. Im sending the heads out to have a valve job done. Ok heres my 2 questions, Can someone direct me to a lowend torquey cam thats isnt to big?. And the real questions is How would you break the rings in ?. Specs on it is it came out of a big van with the 53cc heads and is in the late 80's. Its has some kind of sensor by the pan on the left side of the block. So all together would the parts and a good installation make a good stock 305 ? .

Thanks
You've got the cart ahead of the horse. To start with the ridge isn't honed out. In not so good old days a cheap overhaul would cut the ridge with a ridge reamer, hone the cylinder walls to deglaze them, knurl the pistons to restore a tight fit in the weird shaped bore and put in a set of std rings. These overhauls, not to be confused with a rebuild, were good for 10 maybe 20 thousand miles and cost 80-90 percent of a decent rebuild. Hardly cost effective but in the days of driving 5-6000 miles a year the process added 4-5 years of utility to the vehicle. At today's average mileage the expected life of such an overhaul is a year maybe two at best. Adding a bigger cam would assume you intend to get on now and then, that will significantly reduce what little life expectancy this cheapo activity already has.

Bogie
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Old 02-26-2008, 02:12 PM
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Before you go picking a cam, you must know the actual static compression ratio of the motor. I taught you how to do that, so I know you can figure it out.

If, for instance, the motor is 8.00:1, then the stock cam it came with is probably the best choice. If you have a very low stock scr and change to a longer cam with a delayed intake closing point, you may bleed off too much of the already dismal compression in the motor and end up with a pig.

When you go with a longer duration cam, you're simply moving the rpm operating range up from where it was. Any cam you install will have an operating range of about 3,500 rpm's. In other words, it'll make power from idle to 4,200 or 1,500 to 5,000 or 3,000 to 7,500 or whatever.

Again, let's say you have 8.00:1 scr and it runs fine with the stock cam. You decide it needs more cam, but you don't change the scr. Now, the intake closes later due to the increased duration ground into the cam at the time of manufacture and you bleed off some of the cylinder pressure that used to be captured with the shorter stock cam and the motor won't make as much power as it did with the stock cam.

On the other hand, let's say you have a motor that has a scr of 11.00:1 and you decide that you want to install a short cam in it so it is more streetable and you can use a tighter torque converter. So you install a cam that was designed to make power in a motor with a scr of 9.00:1. Now, the cylinder pressure is so high that you can't operate it on pump gas because it detonates (like shaking marbles in a tin can). The intake valve is closing too early and capturing too much mixture for the scr.

So, here's the bottom line: YOU MUST KNOW THE STATIC COMPRESSION RATIO OF THE MOTOR BEFORE YOU CAN CHOOSE A CAM.
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