Do domed KYB 399’s interfere with 302 cast heads?
- Thread starter waldune
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waldune
Active Member
I s
I Searched and I couldn’t find the info I needed from anyone using these heads with the combo. The domed pistons are almost the same shape as the stock 273 high output domed pistons which were used with the same heads im looking at. However they are t stock and non stock pistons tend to come closer to the deck at their lowest point than stock replacements. I really think they’ll work, and worst I’d have to grind down the part of the quench pad between the valves. But yea sadly no undo that helps me :/ I know the lowest point of the heads and highest point of the piston but it’s sorta the area right in the middle. I wish I had a model of each part incCAD I could look at, I tried to find a downloadable small block mopar blueprint for cad but could t find one for the entire engine
waldune
Active Member
But the optional factory domed pistons have nearly the same dimensions and ran with the heads im using, I know the highest point the piston will be above deck and lowest points on the head and how far the valve lift in planning on having is going to go, honestly all signs point to them fitting and giving me a static 10.82 to 1 compression ration with all otherwise stock parts which is what I’m doing, heads will be ported and will have a cam but valve clearance I know isn’t a problem. I’ll grind down a small about of the quench pad if needed but I think they should fit so I figured I’d come here and find out if anyone has, search feature was fruitless on this one but similar comes work in the 273, same head I’m using and everything just a smaller bore; the high point on the piston is the same it’s just is the slope on the new pistons too steep and will that cause contact. I know what measurements I’d like with flat tops, I’ve done dozens of 318s decks with kb67’s at 0 deck with 302 or 920 heads and with the right supporting parts they have no trouble making 450-509 crank, I think with the added compression and the right cam choice I can get maybe 550 crank just with different pistons than usual. The dynamic compression with the cams I’ve been looking at will be about 10.7 to 1 almost exactly which would be perfect for me. Not too wild, can run on premium pump gas no problem but will still get up and go without hesitation. I’ve made 318’s with more compression with aftermarket parts and they were awesome, up to 13 to 1 compression as long as you have a quench pad with a small enough gap running premium doesn’t cause knock at all
It's one of those instances where you want to be 100% SURE. Even if UEM says it will clear, that's not enough for me. I have to measure. It's not worth the consequences if somehow someone is incorrect, OR if your combination is somehow "off the map".
There were no optional factory domed pistons for the 318. Not in this country anyway. The closest comparison would be the 273 Commando and those domes are entirely different.
waldune
Active Member
Tbh I think my only possible point of contact is actually the center of the quench pad on the head; I’d rather grind that down a bit. I’ve said it here a bunch now but the 273, same stroke smaller bore; same rods and crank; and the same heads that I’m using essentially (they had 920 castings which are closed chambered with smaller calves than the 302) had optional dined pistons almost the same in shape and tan fine from factory. So I honestly think they should fit and I’m willing to buy them and try anyway because I have normal 318 heads and I can deck those a bit if need be. Using factory adjustable rockers from a 283 because oh my god rockers are expensive
Let us know how it works out once you get her done.
waldune
Active Member
Im talking about the 273, and they’re a perfect comparison considering I’m using 920 heads from a 273, a cast crank from a 273 and the rods that were with it because they’re interchangeable. And I have commando pistons on the shelf next to me; where the dome is at its highest is the same as the commando pistons, I’m wondering if they are going to hit the quench pad between the valves. I’ve used 399’s no issue on stock 318 heads (I mean the 920’s were stock for 2 years so were cast cranks) thatre open chamber so 68+ and they don’t even make a ton of compression so I think they would fit. I know how far out of the hole the cylinder goes and the lowest area other than the quench pad in the head. Plugs definitely would clear I don’t question that from experience building these in all sorts of other ways and knowing was will fly. But yea might get them anyway because I have plenty of heads I can use I have some X heads that are open chamber but the valves are bigger than I’d like. Even the 302 has bigger valves than I’d like which is why I want the 920s. I know I can get more power even with the slightly smaller valves from experience
Here's the 273 Commando.
Now here's the 318 dome you plan to use. Not even close to the same. All we're doing is trying to be the voice of reason and advise you to be SURE, instead of doing something "just because you read it on the internet".
Now here's the 318 dome you plan to use. Not even close to the same. All we're doing is trying to be the voice of reason and advise you to be SURE, instead of doing something "just because you read it on the internet".
waldune
Active Member
Either way I have heads thatll work if the 302’s end up having more than slight issues that are easy to fix like between the valves where the quench pad drift slightly into the bore it the only spot I think I may possible make contact. If I could find the smaller valve heads I’d use 0 deck flat top 167’s because they flow way better than 302’s in 318s because of the small bore, in a larger bore motor they flow great but the valves get so shrouded in the 318s bore and even for smaller valve heads on 283’s you have to notch the cylinder walls. I’m not on here much and it’s being made for an aspen r/t im building for my mother in law, she had a 4 speed one it was her first brand new car and she wants another; her since passed away husband left his old b200 van and it had no miles, but the body rusted so bad it looked like it was on airbags because the body collapsed around the wheels. Anyway, it was his last vehicle so I’m building that engine to put into a car of hers which is why I’m so set on it being a 318. Also I love the 318 they’re super great motors and can do anything a 340 can; anything a ford 302 can, more than a Chevy 305 ever could haha. And could do Al isn’t anything a 351W and a 350sbc can it’s just tough to get a hold of the parts
They are FAR from the same. If you already have your mind made up, then go for it.
waldune
Active Member
I get what you’re saying, I have other heads I can use that I’ve used 399’s with before I have 302’s and was to see if they’ll fit or what material would have to go to make them fit as the measurement of how far they stick out of the block it fine. It’s the center of the quench pad that I’m worried about. But I’m curious. My main questions was if they interfered, just in case anyone knew from experience. I can make pistons at work we do all the time but asymmetrical domes aren’t easy to make and making all 8 for my own car so not getting paid would be rough. Also I need to go look at part numbers as the 399’s aren’t the only pop ups I saw just the only ones from a brand I’ve used successfully literally hundreds of times now.
waldune
Active Member
Also when I say they’re a perfect comparison it’s because at a side profile you can see that where the slope starts and goes up looks like it should be gradual enough to clear the quench pad. I know they are different designs completely but the profile shape towards the center where the concern is is close between the two and helps me get a bit of a guess. I have my mind made up on the pistons; I already have multiple sets of heads and I wanted to know mainly so I could get started refinishing the heads but I’m just going to wait until I have the pistons then I can just check. I’ve used these with 340 J heads before and they are fine and I have like 4 sets of those so I’ll use em if I have to. Just trying to get 10.5 ish dynamic compression and these plus the 302’s would help me get almost exactly there with the right cam choice. Not deciding on cam until I’ve decided on almost everything else
Once more. They are FAR from the same. The dome is but one part of the picture. The KB pistons have a larger dome and they have a taller compression height. No one is trying to talk you out of using your pistons, chief. Nobody. We're saying you need to measure. Mock up and measure. Good luck.
waldune
Active Member
I am a professional engine builder I port heads for a living and have build literally hundreds of engines for work and dozens of mopar small block and I’m a mopar guy, the 920 heads on the 318 flow more air than 302s into the cylinders, the larger valves are too shrouded, we end up getting more air through our 318’s with 920’s than 302’s that goes for stock and with bolt ons like headers, street cam, intake and carb. If you’re aiming for over 5-600hp then you’ll want larger valves for forced induction but 450 crank is a very easy number to crack out of a 318. We build a ton of them for all the people buying 318 cars because big block cars are so expensive, 340 cars even. The 302’s are superior on the 340 because that shrouding isn’t bad. But for a street engine with a mild cam, 600-750cfm intake with whatever carb combo you’d like and headers when I port 920s and 302s the same just basic porting even not me referencing my cutaway head shelf to see what material I can remove they have a higher port velocity and his high enough that we measure more air coming through them than any other head made by Chrysler that fits a 318. Unless you go notching the cylinder walls for no shrouding. I’m saying this from experience at work and the fact it’s my job. I came here just to see if anyone had tried running that combo before but I guess I’ll be the first to try and I’ll post about it, I’ve got almost every small block head Chrysler has made lying in storage here so if the closed chambers are a no go then I’ll let y’all know what the smallest chamber I was able to use was. Doing a very budget build with a 450 crank hp minimum and a goal of 500 with only pistons, intake, carb, cam and I make headers for the engines I build at work so I’ll probably make those if I have time if not cheapo pair until I can make nice ones. Budget for the engine is $1500 it shouldn’t be hard at all tbh these things are so overlooked. Budget counts for alternator and pulleys/brackets, like it needs to be ready to drop in the car. I’ve actually done it before but I want to make more power, last one I did this way made 418 at the crank with a $1000 budget.
waldune
Active Member
I understand that, I have their models both downloaded in cad to compare and again the only area of concern with how high they’re coming out of the hole is the slope up the dome. Just want to try and run domes, I’ve run these pistons on plenty of small blocks, they always sit at least 10 thou in the hole at their lowest point, like a flattop 167 sits about 10 thou down still if not more, stocks usually like 40 thou or more and the piston will fit the height inside the 302 heads, I have measured that. However I cannot find a downloadable 3D design of the engin and head so that one little spot I just have no way to measure and be sure about without asking someone or trying. From what I can get from the cad scan lined up at the wrist pins with the other the slope on the 399s starts way later than on the commandos. I have a real commando piston next to me but that doesn’t help much besides knowing this clears just fine and trying to get a measurement of how much space between the piston at TDC and center of the quench pad with 399s. I understand what everyone is trying to do, I know they may not fit and have heads picked out of my stash for that case already I just want to try so I figured I’d ask if anyone has done it before. I’m totally aware they may not at all work with the closed chamber heads, if that’s the case I have a plan to deck some open chamber heads a bit at work and go from there. I’d like to see 10.5 to one dynamic compression out of it and with the 302/920 heads, and the 399’s I could be there so I just am curious.
When done give us an update, Like to see the outcome.
woo daddy, that's gonna be one wild cam, massive carb and like, ALL of the rpms
i'd love to see a line item on that 1500.
i'm guessing that doesn't include machine work and i'm also guessing the porting will be "gratis" and you've got a stock pile of hot stuff to snap on it left over from other projects to hit that number.
Like a Pro Shot Fogger?
waldune
Active Member
Yea well if they interfere I’m just doing what I’ve done with these pistons in the past, decking one of the sets of open chamber heads I have. If they work I’ll definitely be posting along the rest of the build, I just need to find out because I’ve built so many 318s with 0 deck flat tops and quench pads and they make great power for 700 dollar fresh builds haha always 400-500 crank depending on the cam profile; head gasket thickness and type because a lot of companies only carry 360 head gaskets.
That’s my other question as I’m not sure where to find 318 head gaskets with a 318 bore size compression ring not the 360 ring because that’ll rob any compression numbers I gain and where I used to buy them stopped stocking them. Idec what type it is but fel pro composite is probably necessary for these to fit
Cometic will make anything you want. Being a professional engine builder, you should know that.
waldune
Active Member
No like I said in other comments I’m an engine builder so yea, I take my parts to work and machine them myself; I fabricate headers as well. Engines are all I do from exotic cars to pre war stuff at the shop and track cars, I have a decade of porting experience; we hold a contest every year to try and get 1hp per cube out of an engine NA with only the parts that came on it and we’ve done it with a 318. You don’t have to go that crazy to make good power with these. I never said that budget was totally possible for everyone but that’s my budget personally. Also I use junkyard heads, junkyard blocks usually, marketplace you can find an edelbrock 4 barrel with an intake for 75 bucks for small block mopars all day long. I make my own headers since I do it for customer cars
waldune
Active Member
I know they’ll make anything but it’s not exactly cheap and I keep my personal stuff on a low budget. I’m looking for a company that just sells them; and also I don’t order the parts that’s not my job lol I write down the parts I need
To my knowledge, there is no one.
waldune
Active Member
You don’t need crazy cams for those numbers, I said at the crank. Anything over 500 lift on intake with that combo has no low end to it so I like to hangout between 474-492 lift on both intake and exhaust, this is probably going to be on the higher end of that number with a longer duration than usual and a bit more overlap than usual to keep dynamic comp. Where I’d like it to be. Always experimenting
muh huh.
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