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Old 10-14-2020, 03:29 AM   #1
Swagen
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Default NA build 230F Compression Ratio

Yep,

Thinking of swapping the A pistons with their .6mm dish in the early F block which has 2.2mm dish.

Factory Spec for the A motor is 10.3:1, F 9.8:1...

Not sure about the numbers though, I thought the B230A has ...the 5 other 3 head 1 ... while the B230F has the 530 head. Is that correct?

Anyone out there build an engine with this configuration?
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Old 10-14-2020, 01:58 PM   #2
klr142
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Hello. What are you wanting to do? What camshaft are you going to use and are you going to get something larger in the future?

There are B230E pistons that have a shallower dish, I am not certain what the dish is on B230A pistons(maybe they're the same pistons?). I do know that the 530 head has a smaller combustion chamber than the 531 head, assuming both are original and have not been shaved, so the 531 would have lower compression on the same block as a 530. The B230A, to my knowledge, is a single carb engine that has no performance aspirations and thus likely was not ever equipped with a 531 head that is designed for performance. The smaller dish with a 530 head could account for the compression difference.
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Old 10-14-2020, 05:24 PM   #3
hessam69
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The actual measured SCR for a B230F is more around 9.3:1

Not so much the advertised 9.8:1
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Old 10-14-2020, 06:40 PM   #4
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Quote:
Originally Posted by hessam69 View Post
The actual measured SCR for a B230F is more around 9.3:1

Not so much the advertised 9.8:1
It depends on what you use for your cylinder head combustion chamber and piston dish volume. What's popular on TB right now are the 54cc head and 8cc piston dish volumes that Shoestring measured, where if you look elsewhere on the internet you'll find people mentioning 48cc, or even 50cc for a stock 530 headm and 6cc for the B230F piston dish volume.

Here's a relevant link: https://ozvolvo.org/discussion/8971/...r-measurements
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Old 10-15-2020, 03:10 AM   #5
Swagen
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Really what I'm trying to narrow down is what the compressions ratio will be. I have a burette in the mail but until it comes I'm trying to guess at it really. Not sure why the B230A comes rated for different octane, and poking around the parts book shows it comes with an A cam. Since two octane ratings are listed I just want sure if the B230A came with the 531 head, maybe some do? If the B230A CR is listed at 10.3:1 with a larger head volume 531 I didn't want to build a grenade out of the B230F... again, I don't know but wanted to ask if anyone had any experience building something similar. My goal is to get the car back on the road and get a little more power out of it since the parts and machine time pretty much all cost the same. I also have a T cam that came out of another car I had and wanted to see how that played with the higher CR.

Looking through the parts book, 240-260 series 1985-1987 (OTP pubs, 212846-eng-02) the:

B230A
Head PN 1277680-3
Cam PN 1335767-7 Marked A
Pistons 91/93 have different PN for size and octane rating, 91/93 and 97/98

B230F
Head PN 1277678-7
Cam PN 1336779-2 Marked M
Pistons have different PN for size, no octane rating included in PN's

B230A and B230F share the same connecting rod PN 3531260 listed with a little star (new part umber, I guess) and in the notes (1378797)
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Old 10-15-2020, 10:21 AM   #6
klr142
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Do you already have parts? Regardless of what head you use, putting pistons in with a smaller dish is a good idea. It means you don’t have to shave the cylinder head as much for higher compression. To make more power, you need a bigger bang with more compression, air and proper fuelingl. A larger camshaft gives you more air, and to make a larger camshaft drive well from low rpm, you need more compression. It’s a balancing act.

I would not use the T cam in a higher compression engine. If you raise the static compression, depending on how much higher you go, you may need to use a larger camshaft with more duration to bring your dynamic compression ratio back down. If your dynamic compression ratio gets too high, you will need to use higher octane fuel and/or reduce your ignition timing. If you build the engine for a lot of power, you will need to do both of those things anyway(which is ok, I’m just letting you know).

You will not grenade anything by using the smaller dished pistons, if that’s what you’re curious about. That isn’t going to be a large enough increase on its own to cause problems if you make sure to shoot for a decent piston to head clearance(.030-.040”/.8-1mm maximum).

If you haven’t read through my sticky’d thread about NA performance, please do so.
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Old 10-16-2020, 01:02 PM   #7
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Just popping back in here to confirm that the B230A pistons(at least for the 97/98 octane engines) are the same as(or supersede to the same as) the B230E shallow dished pistons from what I am gathering from VIDA.
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Old 10-17-2020, 02:22 PM   #8
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Ha! I never checked if VIDA went back to the older 240 models, doh!

Found the F pistons I was looking for after all so I'm goin' with a standard build now.
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