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Adding stock turbo to B23F from '84 245

S

SoloWookiee

New member
Joined
Oct 16, 2025
Hello Hive Mind,

So I bought my first Volvo, an '84 245 (LOVE it btw), and the previous owner installed a stock turbo and downpipe into the car. It seems like they knew what they were doing to some extent, but that there were a number of things that indicated maybe not so much. I'm pretty concerned with 10.3:1 compression ratio, and after doing a good bit of work to revitalize the engine (classic stage 0 stuff including the flame trap). Updated a couple other things and got it on the road, just to have the head gasket blow after about 15-20 minutes of driving.

My brother and I are pretty sure we're looking at stock internals, so we're of the opinion it's still at the 10.3:1 cr. I've tried to look up things here and elsewhere, and I'm feeling lost. I saw something about possibly being able to swap the head to decrease the far too high for normal boosted air scenarios, but I'm wondering if there is an easy(-ish) way forward where I can trust my gaskets just a little more.

Help me Obi-wan Kenobi's, y'all are my only hope!!
 
Automatic '84s should be around 10.3:1, manual ones are around 9:1 generally. The way to tell is the stamping on the block just below the thermostat housing. Hopefully they ditched the Chrysler ignition when adding the turbo but that can also be a way to tell which compression ratio you have.

People have done 10:1 and turbo, going to a big cam will help lower the dynamic compression, and deshrouding the chamber is a must on a performance build imo, that can drop the compression by half a point and increase flow. Reducing the piston to head clearance with a thin MLS gasket to something in the .032"-.038" range also helps with detonation resistance.
 
OVERDRIVE said:
Automatic '84s should be around 10.3:1, manual ones are around 9:1 generally. The way to tell is the stamping on the block just below the thermostat housing. Hopefully they ditched the Chrysler ignition when adding the turbo but that can also be a way to tell which compression ratio you have.

People have done 10:1 and turbo, going to a big cam will help lower the dynamic compression, and deshrouding the chamber is a must on a performance build imo, that can drop the compression by half a point and increase flow. Reducing the piston to head clearance with a thin MLS gasket to something in the .032"-.038" range also helps with detonation resistance.
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I'm confident it's the B23F, so the 10.3:1 makes sense. I'm really just exploring options that don't include short block removal. Since I have to get my head machined, I figured I'd explore any possibilities of frankensteining the short block with a different head, or some other process that might help reduce the compression. I do have the B21 head gasket coming, but it's going to be quite a bit thicker at .058. I also have the B23F head gasket coming and it’s indicating it’s got a thickness of 1.2.
 
SoloWookiee said:
I'm confident it's the B23F, so the 10.3:1 makes sense. I'm really just exploring options that don't include short block removal. Since I have to get my head machined, I figured I'd explore any possibilities of frankensteining the short block with a different head, or some other process that might help reduce the compression. I do have the B21 head gasket coming, but it's going to be quite a bit thicker at .058. I also have the B23F head gasket coming and it’s indicating it’s got a thickness of 1.2.
Click to expand...
B23F is available in both high and low compression versions in 1984, hence you should check which one you have.

B21 head gasket won't fit, the bore is smaller. You need a B23/B230 gasket

Thinner head gasket will increase detonation resistance, don't drop compression with gasket thickness it will only work against you. Aim for .032"-.038" piston to head clearance.

Deshrouding the valves in the chamber drops compression while increasing flow.
 
It is an automatic, and I’ve failed to mention that I know that at least the short block is the B23F because I already knew to get that from the code below the thermostat housing. That’s why I was confident that it was the 10.3:1. There are other numbers stamped after the B23F code, but I’ve never seen anything about those numbers, and I’m not sure how decode it them if necessary. If it’s a B23F and has the AW70, is that all I need to know to determine if it has the higher compression ratio between the two.
 
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SoloWookiee said:
It is an automatic, and I’ve failed to mention that I know that at least the short block is the B23F because I already knew to get that from the code below the thermostat housing. That’s why I was confident that it was the 10.3:1. There are other numbers stamped after the B23F code, but I’ve never seen anything about those numbers, and I’m not sure how decode it them if necessary. If it’s a B23F and has the AW70, is that all I need to know to determine if it has the higher compression ratio between the two.
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Assuming the motor hasn't been swapped, yes. The other way to be sure is to check the original ECU or ignition computer (if you have them, the part numbers differ between the 10.3:1 and 9.5:1 B23Fs) or put a bore scope down a spark plug hole and look for a dish in the piston.
 
I also just determined that I have the 398 head and there was a code of 94/3 on one of the pistons, I believe it was on cylinder 4.
 
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