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Squish vs. Swirl

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adrianpike

adrianpike

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Joined
Apr 4, 2005
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53
Location
Belllingham, WA, USA
Let's discuss squish vs. swirl in a high-compression (>9:1, <10:1), moderatly boosted (between 1 and 2 bar) engine. (Specifically a Volvo B21, hogged out to accomodate B23 forged internals)
Currently, I'm planning on building up a tight squish (< .040") clearance motor, and mostly ignoring swirl, as most of the car's time will be spent heavily in boost, and I'm more worried about getting the flame front to propagate as quickly as possible to prevent detonation time.
I'm keeping an 8v head for now, as the 16vs seem to have a problem with detonation, and require pretty good tuning, whereas the 8vs are practically bombproof. Flow would of course be improved with the 16v, but not enough that I can't compensate with more boost.
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Discuss?
 
Ok so I am guessing its a four banger?

I don't understand what the number of valves have to do with detonation, (if someone could explain that to me that would be tops) but I think to get the most out of your engine I'd go with the 16 valves. It will breathe better if tuned properly.
 
Leppy said:
Ok so I am guessing its a four banger?
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Correct, sorry I didn't specify that earlier.
Leppy said:
I don't understand what the number of valves have to do with detonation, (if someone could explain that to me that would be tops) but I think to get the most out of your engine I'd go with the 16 valves. It will breathe better if tuned properly.
Click to expand...
It's not actually the number of valves, it's the combustion chamber design. The Volvo 16v head seems to be especially prone to it, I don't have photos at the moment, but it appears as if it doesn't have as much of a quench area as on the 8v's.
Getting the most out of the engine N/A, I would use the 16v head without hesitation. I'm going for a heavily boosted approach, and with the watered-down cat pee we Americans call gasoline, detonation is a signifigant worry. As much as I'd love to be able to afford race gas, I'm still paying tuition for a few more years, and it's the pump stuff for me.
 
You're in the states??? Gees even if you paying 3 bucks a gallon for 98 RON fuel its cheap.

When I was there in 2001 for a year, I always made anyone in the car fill up with 98 RON (then it was only 1.70/gal)

back on topic... Are the heads hemispherical or are they more squareish?
 
Leppy said:
You're in the states??? Gees even if you paying 3 bucks a gallon for 98 RON fuel its cheap.

When I was there in 2001 for a year, I always made anyone in the car fill up with 98 RON (then it was only 1.70/gal)
Click to expand...
Short of travelling 50-60 miles for every fillup, the most I can get is 92 octane, at about $2.50 a pop. Not many know how to start my car, let alone fill it at the pump. Highest octane one can find is what goes in, I haven't set up knock sensing yet, and there has to be knock present for a knock sensor to detect it... :thumbsdown:
The current block's just a learning tool, but I'd still like to keep all the important bits within the block for now.
Leppy said:
back on topic... Are the heads hemispherical or are they more squareish?
Click to expand...
Here's a (bad) photo of the CC of a 531-casting head, most likely the head that I'll be using:
DSCF0088.jpg

Note the deep combustion chamber, angled spark plug, and large quench pad.
A 16-valve would make plenty more power guaranteed, but it's a signifigantly more complicated endeavour, and it would be somewhat sketchy regarding classification for race events. It is quite enticing, though. The Swedish boys have achieved plenty of power out of the 8v heads though, if detonation is kept to a minimum.
 
i have no experience with 4-stroke engines, only from what i read on internet.

but from what i know about 2-stroke, you're doing the right thing, swirl is very important for good breathing and power through revs. when boost is involved squish is the way to go.

you have to be careful though, when the squish is increased, combustion temp rises, and i think when a turbo is involved it might rise significantly. while you're piston will get less hot, caus the squish chamber will drect the combustion down, to the middle of the piston. so you do have to be carefull for burn-through

with increased squish, you're combustion will be faster, so you'll have to advance you're timing a bit. again, on a 2-stroke you have to
 
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