1988 302 build
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5th Wheeling
Joined: Oct 2025
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yes sir, I’m aware the bore doesn’t dictate the stroke of the engine. Only reason I brought it up is the machinist was telling me if I was spending the money stroking it. He would’ve bored it out
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5th Wheeling
Joined: Oct 2025
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the reason being with the increase in pressure being forced in the cylinder it overloads the rotating assembly? I’ve read on it some but haven’t actually wrapped my mind around it
Fleet Mechanic
Joined: Oct 2025
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detonation and pressure on pistons is the issue caused by the increased pressure, from the research I’ve done. Mine is currently 9.5:1 ish, but when I finally get to force it, I’ll change heads to lower the CR.
Hotshot
Joined: Jun 2015
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You need the CR lower with boost because, if not, you can have too much cylinder pressure unless you want to run 100+ octane race gas.
Cargo Master
Joined: Oct 2020
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He probably recommends boring it when doing the stroker because you have to buy new pistons anyway so you might as well start with a fresh bore. Also many 5.0 blocks do not come with bores that are 4 inch from the factory. I've seen them at 4.005 quite a few times so a standard bore piston would not work correctly stroker or not.
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5th Wheeling
Joined: Oct 2025
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I not a machinist but I don't know why he would have said that. You can only bore an engine so many times. Boring the cylinder more than it needs to clean it up doesn’t make any sense to me.
You need the CR lower with boost because, if not, you can have too much cylinder pressure unless you want to run 100+ octane race gas.
You need the CR lower with boost because, if not, you can have too much cylinder pressure unless you want to run 100+ octane race gas.
also, I’m gonna keep dailying the truck so no race gas. My main reasoning for such high compression was to keep from spending the money stroking it and making a mistake in the assembly process and costing me more money than just new pistons, rings and bearings
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5th Wheeling
Joined: Oct 2025
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He probably recommends boring it when doing the stroker because you have to buy new pistons anyway so you might as well start with a fresh bore. Also many 5.0 blocks do not come with bores that are 4 inch from the factory. I've seen them at 4.005 quite a few times so a standard bore piston would not work correctly stroker or not.
Fleet Mechanic
Joined: Oct 2025
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10:1 compression daily will need premium octane unless you custom tune the timing curve to prevent pinging. Mid grade would be ok probably if you keep it in the lower rpm ranges (defeats the performance build!)
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Hotshot
Joined: Jun 2015
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He probably recommends boring it when doing the stroker because you have to buy new pistons anyway so you might as well start with a fresh bore. Also many 5.0 blocks do not come with bores that are 4 inch from the factory. I've seen them at 4.005 quite a few times so a standard bore piston would not work correctly stroker or not.
Last edited by My4Fordtrucks; Apr 1, 2026 at 09:20 PM.
Cargo Master
Joined: Oct 2020
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No you don’t. So what was the point of the machine shop only honing the bores if they are tapered and needed boring? You’re saying the bores are not the same from the top to the bottom and the shop sent it anyway. The 351 I got from a ‘94 conversion van needed .030 to clean up the cylinders.
Cargo Master
Joined: Mar 2007
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I don't know, but any engine that is 30 years old will need boring. I know that is not true, but that is how I think. I'm not going to spend that much time to 'rebuild' an engine with used pistons and bores.
Hotshot
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If you build a stroker you will have to buy new pistons. The compression height will be different to allow for more stroke to fit within the same deck height. It is quite possible that the bores were not excessively tapered in the original engine and just deglazing and reusing the original pistons was fine. But this is only if he wasn't going to change the assembly. Also piston availability isn't usually very good when it comes to building a stroker or any high performance/non stock engine in std bore sizes.
My 351W supposedly only had 150K miles on it and was in a conversion van so it didn’t have a hard life. It still needed to be bored .030 so I don’t understand how the shop said honing was all that was required.
Logistics Pro
Joined: Aug 2010
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From: Chillicothe
It still had cross hatching in the cylinders. And taper from top to bottom was less than .005" top to bottom both directions on the WORST cylinder. It was pulled in favor of a 351 swap that was the only reason. It got throw back together with a dingle ball hone job ( didn't keep track of what set went to which cylinder), with the original rings ( gap checked out to be .028" so super good in my book) on the factory pistons. Dropped in 79 f150 and driven for another 50k miles before the truck fell apart.
Sometimes there isn't enough wear to worry about boring.... not always, but sometimes.
Cross-Country
Joined: Mar 2025
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Easiest way to think about it is that forcing additional air into the cylinder effectively increases the compression ratio; once the piston reaches full compression, you have crammed more fuel/air mixture into the same amount of space. This is the same as keeping the same amount of mixture and reducing the volume (increasing compression ratio). Therefore, you need to increase the volume (decrease compression ratio) as well if you want to keep the other conditions the same. The other option is increasing octane (and therefore compensating for the increased compression) as others have mentioned. Note that you don't lose power by doing this because you're burning more mixture (and therefore more fuel), which means more power to your crank.
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5th Wheeling
Joined: Oct 2025
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No you don’t. So what was the point of the machine shop only honing the bores if they are tapered and needed boring? You’re saying the bores are not the same from the top to the bottom and the shop sent it anyway. The 351 I got from a ‘94 conversion van needed .030 to clean up the cylinders.