To add to what Paul and others here have said (which is by the way excellent information/advice), calculate the dynamic compression goal for 7.75 on premium pump gas at the intake valve closing point for the camshaft because of timing chain 'stretch'. This can mean that your actual dynamic compression will result in .2-.3 points lower due to the ~2*-3* or so retard your valve timing will end up being after the engine has been properly run in. Remember also that as the miles accumulate, additional retarding will occur, up to as much as 4*-5* isn't uncommon with lots of miles on it. Depending on the life expectancy of the engine, of course, you may not have to worry about this if the cam wears out before 24,000 miles... Also worth noting is that the timing chain flexes at higher RPMs, effectively retarding your timing there as well. Shoot for around 7.75 and you'll end up with about 7.5 for the 'main sequence' lifespan of your engine. :TU: Gary
Ok guys another question. Can I measure the piston to deck height with the stock pistons in place or do I need to measure it after I get the shortblock together?
You can measure the stock piston to deck just for a reference but it won't necessarily help you figure the end result because of the machining that needs to be done. First the block main line gets bored or honed. Then the block deck should be machined enough to ensure it is parallel to the main line and both banks are the same height. When the rods are resized with new rod bolts they should also be cut so they are all the same center to center length. You cut them to the length of the shortest rod. After the crank has been turned and the block has been bored for the new pistons, you install the crank rods and pistons without piston rings and measure the piston to deck. Then if the piston to deck is more than you want to get a specific compression ratio, you pull the crank rods and pistons out and do the final cut on the block deck. Some builders just install the 4 corner pistons for measurement. Of course this means you need to know the combustion chamber size after the head is done along with the compressed thickness of the head gasket a head of time. Do the heads first.
Ok, yeah I'm doing the heads first and then adjusting the piston to deck clearance accordingly. I'm shooting for 9.5:1 cr like recommend.
I'll have the machine shop go over the heads and anything that needs replaced or fixed have them do, guides, seals, ect. As far as port work I have read some articles about doing it at home. But it makes me a little nervous.
If you are going to do some head work, it needs to be done before you send the heads to the shop. You don't have to go all out. A lot of the gains is found by working around the valve guides in the bowl area. Here is a good article that shows the tools and the how to. http://billiehall.com/jefferson/articals/musclecaren/march06/musclecarenmarch06.pdf When you get the intake manifold you will need to bring out the intake port walls to match the opening at the intake manifold runners (port matching). I also recommend grinding off the locating boss in the combustion chamber that was used during production. It shrouds the spark plug tip and it will be hotter than the rest of the chamber surface. Then polish the rest of the chamber. https://dl.dropboxusercontent.com/u/39382077/Stock 350 head.JPG https://dl.dropboxusercontent.com/u/39382077/350 head.gif
Thanks for all of the help paul. I read through that article man all that makes me nervous haha. I guess once the head is off the motor and sitting in front of me it may be better. Im pulling the motor this saturday.
There is NO WAY I would recommend those porting techniques to a novice...that port work is great and all for professional head porters who have experience unless you have a few sets lying around to practice on. For stock-moderate cams, simply cleaning up the heads provides best benefit, and anyone can do it as long as they DO NOT take out much material, which is easy to accomplish with a simple die grinder and break-away sanding wheel. Have a couple grits available, and plenty of them. Clean up casting imperfections all throughout the head, and polish the exhaust sides only, not the intake. Same can be done with the intake manifold runners. No polishing, and do not widen anything up. Contouring around the guides, smoothing the sharp edges isn't too difficult and is highly recommended. **Also worth noting is if you plan on using exhaust manifolds, polish the runners as far in as you can go, and polish the exit port, taking out as little material as possible to achieve a nice smooth finish** Take out too much material and you kill your low-mid RPM velocity. Even worse, take out too much in the wrong areas and you will kill the heads, period. You will actually LOSE power over untouched heads, and after all that work invested. How much of a bummer would that be hmm? The goal is to improve the existing flow quality, eliminating/reducing turbulence and improving velocity. This will help the flow numbers some, but don't be seduced by larger numbers. There is a LOT more to it than simply opening it up and seeing larger flow numbers. Gary
Yeah that's what I was thinking is just cleaning up the casting imperfections not taking much material at all.
there is nothing wrong with measuring your piston depth before taking old pistons out. gives some reference. head porting is time consuming. cleanup is easiest . keep in bowl/valve area. runner isn't that important at this level. I don't see much point on polishing/grinding in chamber . keep it simple for your first build.
Have the machine shop measure each aspect of your engine including the crankshaft BEFORE you order any parts. I have had good luck with the Northern Auto Parts rebuild kits but I ask them to delete the camshaft and cam bearings then I use a TA 212 cam and TA grooved cam bearings, and an adjustable oil pressure regulator. If you go this route then you do not have to worry about the compression ratio too much as it will be fine to match with the cam even if it is only 8:1.
Port matching has been proven to be a waste of time and can actually hurt flow so don't do that. Try not to remove material off of the "floor" or bottom of the port, just take off the imperfections left from the casting process and make it uniform to the bowl area. The port will only flow as much as the smallest pinch point in the port, this brings us back to port matching which will make a large area of flow that will neck down to the pinch point further in the port which makes the air flow at slower RPM lazy which will hurt low end power. A small investment in a set of inside dividers; http://www.globalindustrial.com/p/t...l/spring-inside-caliper-150mm-6-inch-7249-150 Will allow you to set the inside dividers to the smallest point of the port to see where the grinding needs to be to blend to the larger points of the port and compare the size differences in multiple spots in the port. When you're blending the smaller areas of the port to the larger areas make sure that no more than 1/16" of material is taken out per surface. To determine how much needs to be removed per side, measure the smallest point with a 6" scale(a machinist's ruler) or a tape measure if that's all you have or want to get transferred from the inside dividers. Then measure with the inside dividers the largest point of the port to see what the difference is. If its more than 1/8"(1/16" per side) then the larger areas needs to be avoided to not make larger. The roof of the port can be raised to the top of where the gasket ends, then taper that down slowly to the bowl area making it uniform pointing the air to where it enters the chamber. The bowl ledge to keep the spring from sucking the valve in the bowl should be kept at least 70% smaller than the valve when cleaning that area up. The short turn radius is the most advanced area to grind so keep that in mind when grinding that area. I would say to make the short turn(is the transition from the bowl to the port on the floor side of the port) looking down the port with the head mimicked on a 45* angle like its bolted to the block and that radius can be ground so that it looks like a straightest line of sight to the valve. Don't get carried away in this area, less is more when changing the short turn. This is a basic port job that will be helpful to getting more air in without scrapping your heads. Using the dividers you can replicate your efforts more accurately to every port to try and make them as close to the same as you can so one port doesn't flow to much less or more than any other. GL Derek
Oh yeah I'm having them check and measure everything before parts are ordered. Thanks for the advice!
Yes I agree with simple! Like I said I'm not looking to break any HP records or speed records, just want a nice reliable engine with a little more get up and go than before.
Derek I agree if the intake runner is smaller than the head port opening as it can be beneficial in blocking reversion into the manifold runner If the intake manifold opening is larger than the head port then the airflow is looking at a wall with a sharp edge causing reversion and it actually decrease the cross sectional area of the port entry. Please explain if there is something I'm overlooking. Thanks Paul
Hey Paul, The reversion is not a concern as explained in this article; http://www.onallcylinders.com/2014/...-rectangular-port-intake-big-oval-port-heads/ It says in the article that; "A wider mismatch where the ledge protrudes in 1/4-inch or more, this might be significant. But if so, this may also have more to do with the mismatch of parts for the engine rather than the ledge itself. A very large intake port feeding a smaller cylinder head likely will suffer from low inlet velocity and that could be the real reason the power would be reduced. But often, these questions come up because of intake manifold choices that are based on other concerns besides torque and horsepower." Very good article, I highly recommend reading it. Derek
Thanks Derek, Good article Having OCD I would at least put a small radius if there was a leading edge in the port. It would make me feel much better. LOL I'm used to working with intake manifolds that have a funnel for runners where the velocity is constantly increasing and the pressure is higher than normal against the walls. No leading edges allowed Paul
