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What did I do wrong assembling the big bore b20?

mikep said:
Is this the cam?

http://www.iskycams.com/shop/index.php?main_page=product_info&products_id=936

If so, you need a lot more cam to make torque past 4000.
That duration number is "gross" duration. We need the numbers at .020 or .050" to really know the deal when you do find a gross 280-300 degree cam, hopefully in the .450-.490" lift range. (I don't know how much lift your springs and piston/head combo can stand)
Also agree on a possible restriction, but that is a very mild cam.
Click to expand...

Here's IPD marketing pitch on it: https://www.ipdusa.com/products/7389/100823-volvo-street-performance-camshaft-b18-b20-ipd-100823

this model has a broad power band starting at 2500 rpm up to 6000
Click to expand...

I may have used on waaay back in the day, can't really recall. I have used a couple of VV81 cams: http://iskycams.com/shop/index.php?main_page=product_info&cPath=127&products_id=937

And they're pretty sporty feeling. They're a little listless under 3000 rpm, they really kick in at around 3200, and on my engine, pull hard up past 7000 rpm. It's so productive to keep it in the lower gear that I often run it up to 7500-ish, it's still pulling harder than it would in the next gear. (Ahem, probably why I'm taking the PV's motor out again - apparently not a great idea to spin stock parts that fast - but at least the failure mode hasn't been catastrophic so far)

And in practice, that 3000 rpm thing isn't much of an issue - just rev it high enough in each gear to be over 3000 in the next gear. And it's really not feeling all that flat under 3000, probably more power and tq than the stock motor had at that rpm.
 
mikep said:
It's also lean from 3600 or so up.
Click to expand...

mikep said:
Is this the cam?

http://www.iskycams.com/shop/index.php?main_page=product_info&products_id=936

If so, you need a lot more cam to make torque past 4000.
That duration number is "gross" duration. We need the numbers at .020 or .050" to really know the deal when you do find a gross 280-300 degree cam, hopefully in the .450-.490" lift range. (I don't know how much lift your springs and piston/head combo can stand)
Also agree on a possible restriction, but that is a very mild cam.
Click to expand...

As for the lean issue we were getting good AFR (around 12.5) through the entire range on the lambda reading.

As per the cam, I took the cam to ISKY to confirm it is a VV-71 profile, but they told me it wasn't actually one of their cams. This was a NOS IPD big bore kit from the 90s back when they still made it for the 6-bolt crank. So I know for a fact it's the vv-71 profile but can't confirm the quality of the cam since the manufacturer is unknown. Oh, and I forgot to mention in the build notes (updated) that there are dual valve springs.

Additionally, I have gone back to the old Bosch D distributor I was running before and I'm not sure if it made a difference honestly. Seems to pull a little harder, not hard enough to make me go "WOW there's that missing hp!" and it is still a dog down low.
 
JohnMc said:
I wasn't quite sure what the values were on the O2 line.

If you have the carbs bolted solidly to a buzzy 4 cylinder, and the Volvo engine certainly is a bit buzzy - then I think the fuel bowls can get a bit frothy and the jets start pulling in air along with the gas. I've heard you can get issues with that by overzealously tightening down the soft mounts. Or by just bolting the carbs up directly to the manifold.
Click to expand...

I should probably loosen the soft mount bolts.
 
JohnMc said:
Well, there goes the theory that it was really an 'A' grind tractor cam.
Click to expand...

Myth BUSTED! I still need to degree the cam tho, just to be 100% sure of what's going on when.

Also, looking at the valve lash setting, I may have set the valve lash at the wrong time and at the wrong spec. I will mess with that next chance I get.
 
I don't think that incorrect lash settings, as long as they're in a vaguely reasonable range (i.e. not holding the valves open, not so loose the pushrods are ready to fall out) could eat half the HP. But I suppose it could be part of the overall issue.

The timing gears are somewhat hard to mess up - just align the dots. Did you do that work? Do you remember aligning them? It would be a little harder (I think) to get that wrong vs. the way you have to wrestle with a timing belt, aligning it while loose, then tensioning it, then rechecking, etc..

How hard would it be to take the exhaust off, even just unbolt it and tie it up to the side, and drive it around the block? Just to rule out the blocked exhaust thing.

And silly thing, but make sure the DCOE's are fully open when the pedal is all the way down.
 
JohnMc said:
I don't think that incorrect lash settings, as long as they're in a vaguely reasonable range (i.e. not holding the valves open, not so loose the pushrods are ready to fall out) could eat half the HP. But I suppose it could be part of the overall issue.

The timing gears are somewhat hard to mess up - just align the dots. Did you do that work? Do you remember aligning them? It would be a little harder (I think) to get that wrong vs. the way you have to wrestle with a timing belt, aligning it while loose, then tensioning it, then rechecking, etc..

How hard would it be to take the exhaust off, even just unbolt it and tie it up to the side, and drive it around the block? Just to rule out the blocked exhaust thing.

And silly thing, but make sure the DCOE's are fully open when the pedal is all the way down.
Click to expand...

We confirmed we are getting fully open on the DCOE's on the dyno, unbolting the exhaust wont be that hard I just need to find the time to do this all.

As per the dots being aligned, I made sure I aligned them, and took a photo of them aligned to confirm. My thought is that, since the cam is a period knock-off the ISKY cam, that maybe it was keyed wrong, or just wasn't degree'd right.
 
Hey There,

I haven't been on TB for a while so just seeing this but here is my two cents as I have a similar setup:

Right off the bat your timing curve looks like it needs help as you should only use 3 or 4 points and below is my 123ignition timing curve for a B20 with dual Weber45DCOE, 2.1 liter engine and an isky cam that I believe is the same VV71.

TOTAL MAX ADVANCE 34, Static Timing 10 BTDC

Static timing set 10 BTDC w/o Vacuum

Curve - 500 - 0 BTDC (10 BTDC includes static timing)
1000 - 5 BTDC (15)
1700 - 10 BTDC (20)
2900 - 24 BTDC (34)
NO MAP - 0,0,0 (No Vacuum Adv)

I have the timing set static at the crank to 10 BTDC and added advance up to 3000 rpm where you should be at max advance up to whatever rpm your engine can handle, I play it safe at 7000rpm as my rev limiter.
 
1971Gold142 said:
Hey There,

I haven't been on TB for a while so just seeing this but here is my two cents as I have a similar setup:

Right off the bat your timing curve looks like it needs help as you should only use 3 or 4 points and below is my 123ignition timing curve for a B20 with dual Weber45DCOE, 2.1 liter engine and an isky cam that I believe is the same VV71.

TOTAL MAX ADVANCE 34, Static Timing 10 BTDC

Static timing set 10 BTDC w/o Vacuum

Curve - 500 - 0 BTDC (10 BTDC includes static timing)
1000 - 5 BTDC (15)
1700 - 10 BTDC (20)
2900 - 24 BTDC (34)
NO MAP - 0,0,0 (No Vacuum Adv)

I have the timing set static at the crank to 10 BTDC and added advance up to 3000 rpm where you should be at max advance up to whatever rpm your engine can handle, I play it safe at 7000rpm as my rev limiter.
Click to expand...

This is good information! I was having problems using the 123+ because I couldn't get it to run by just setting the engine at 0? and using the 123 for the entire curve map. I'll try this when I decide to put the 123 back in.
 
UPDATE:

I had an hour and was able to do a cold compression test. Results were not good, and I checked on two different gauges.

CYL 1 - 150psi
CYL 2 - 130psi
CYL 3 - 125psi
CYL 4 - 120psi

I also noticed that the VV-71 cam calls for a valve lash of 0.020, set while hot. I don't think I accounted for that lash, so when I get a minute I will warm up the engine, reset the lash, and re-test compression.
 
Three reasons for low compression:
Leak, valves or piston rings.
Too big combustion chamber. (Static compression ratio too low)
Cam timing off. Too late intake valve closing. (Dynamic compression ratio too low)

Dynamic cr is always lower than static cr.

Pressure should be 140-150 psi. Blow-by has bigger effect on max torque than maximum power.
 
It's the unevenness more than the numbers. Unless your gauge is calibrated, it may or may not be all that accurate. But the difference between #1 and the others is concerning regardless of the numbers. Wait - I just noticed you said you used two different gauges - that would tend to make me believe the numbers - and those are some low numbers.

See what the numbers do after running it a little bit - getting some oil up into the rings. Are you cranking for the compression test with the throttle open? Maybe pour a small amount of oil into one or more of the low reading cylinders and see if that improves it. Do you have an air compressor and a way to blow air into the cylinder? You don't have to have a real leakdown tester to blow air in and listen to where it comes out.
 
I would like to see them up around 170, but as John mentioned as well, the bigger concern is the spread between them. Cam timing won't cause that kind of spread between cylinders usually.

If the motor is fresh, there's a chance things are fully seated yet. The oil test John mentioned will help you ID if the rings haven't seated yet.
 
Unless the cam has some lobes ground in the wrong spot, but not all of them.

I guess once you're setup to degree the cam, it would be easy to check #1 valve timing vs. #4 valve timing. Just move your dial indicator back to those valves, readings should be the same.

An oddball issue I came across with my Crane ignition was that I had proper ignition timing (or whatever passes as proper on a modified B20) - but I hadn't paid proper attention fo where the rotor was pointing when the sparks occurred. So it ran poorly at high RPM's - the spark would advance, and the rotor would pull farther away from the distributor cap contact, until it would start to miss a little bit, occasionally misfire (spark jumped forward to *that* contact?). But a timing light showed everything being spot on. Took me a while to figure that out - I needed to reposition the optical sensor to better position the rotor.
 
JohnMc said:
Unless the cam has some lobes ground in the wrong spot, but not all of them.

I guess once you're setup to degree the cam, it would be easy to check #1 valve timing vs. #4 valve timing. Just move your dial indicator back to those valves, readings should be the same.

An oddball issue I came across with my Crane ignition was that I had proper ignition timing (or whatever passes as proper on a modified B20) - but I hadn't paid proper attention fo where the rotor was pointing when the sparks occurred. So it ran poorly at high RPM's - the spark would advance, and the rotor would pull farther away from the distributor cap contact, until it would start to miss a little bit, occasionally misfire (spark jumped forward to *that* contact?). But a timing light showed everything being spot on. Took me a while to figure that out - I needed to reposition the optical sensor to better position the rotor.
Click to expand...

You're the second person to suggest the spark jumping. How did you go about repositioning the optical sensor?
 
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