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Bottom end? Can it hold?

forman621

New member
Joined
Nov 21, 2010
Location
Selah, WA
So I have rebuilt the bottom end on my b21ft with just new bearings and rings and block cleaned and what not. so pretty much a good condition stock bottom end.

My top end is or will be and have parts for.

Volvo 531 penta head
porting
.005 shave on intake
.020 shave on exhaust
Heavy duty valve springs rated to around 7500rpm
New everything else
seal, retainers, guides

I am putting in SS valves
46mm Intake
38mm Exhaust

My question is
Should i have done more to the bottom end to run this head setup?
 
nope!

boost it!!

But really a much lighter rotating assembly from respectable dealers on this board would be a good option, the b21ft rotating assembly is heaaaaaaaaaaaaaaavayyyyy.

they are bullet proof though.
 
I dont think its ideal to have the 531 head on the smaller bore , and esp not the larger valves ?
 
I am thinking about those rsi H beam rods.
But i am not sure what pistons i should use.
And if i get lighter pistons and rods would the crank need balanced?

And i am going to be running an IPD turbo cam
 
I dont think its ideal to have the 531 head on the smaller bore , and esp not the larger valves ?

i've done effectively the same thing with non-volvo engines, the only difference is that you lose a little low RPM potential. maybe. :e-shrug:
 
I have has a 531 on a 21 and the gasket was very close to the chamber.
Have read here that they tend to blow under stress. mine didn't but maybe use a 2.3 gasket..:e-shrug:
I run 25 psi, no problems....
 
B21FT head gasket, and go for 30 psi if the rest of your set up can handle it. B21FT's are friggen stout, but as Brett said, heavy internally. The smaller bore and low compression help immensely if you run high boost.

If Budget allows, try to lighten the internals and longer rods and better pistons, but keep the bore size the same and have fun. RSI would be the likely outlet for those goodies.

PJ
 
So rsi has a set of pistons that use stock length rods at - 145mm
and they also offer piston set that uses - 156mm rods.
Piston spec is 92.5mm
I have C and D cylinders which range from C 92.6992 - 92.08008 and D 92.08008 - 92.09024
so it will have to be bored is what i am thinking.
I am using a cometic head gasket at 0.036" with a bore size of 94 mm. I bought this from Knox

what would be the difference between running stock length rods VS the slightly longer 156mm rods?
 
running the longer rods will lighten the piston end of the rotating assembly (very good thing)
one of the biggest issues when taking a engine to higher RPMs and bringing those RPMs back down in a controlled manner is figuring what,where and how to lighten things up, so they rev faster, and remain intact.
if your going for RSI pistons and rods, go for long rods. though at that point I wouldn't want to run such low compression as factory... I prefer throttle response with my power, unless your takin it to the 1/4 mile.
 
Yeah I probably will tomorrow. Thanks you guys for the advice.
I was hoping to bring the compression up a little. So it doesn't have to rely in boost all the time.
 
ok, i've got a 130k b21ft with a ported 530 head w/upgraded springs. so i am in the same ballpark as you. the bottom end is fine, i just don't feel ok throwing those big heavy pistons around over 7500-8000. i wouldn't be surprised if some sweeds have done it, but really, i don't need to go that high most of the time. i just wanted the spring upgrade for peace of mind.

the head is basically the same as my 530, it works fine, just use a b21ft head gasket.

to upgrade the rods/pistons.......i wouldn't bother, use what you got and see how you like it. if i were gonna buy rods/pistons i'd build a b230 bottom end, much easier to find in good shape, have piston squirters, much more common parts - so easier to find stuff on the shelf/used, and there were people who found really bad casting flaws in the older blocks - so i'd have it sonic tested/etc

good luck, you'll be fine with what you got. and you can reuse the head later if you change to a b230. mine's easily got 300whp, i made 265whp straight off the wastegate at 20psi on a ebay t3/t4, with megasquirt
 
yeah where's my replacement WG actuator? :-P

I don't wanna be a jerk or anything, but I'd rather a JY b230ft freshened up over a stock b21ft bottom end.

And if I were buying rods and pistons, I'd definitely use a b230 bottom end.
 
Ok that makes sence I can see how I like it with stock pistons and rods and maybe find b230 to build under it. So I put the stock pistons in and the ring gap I measured was .014" for both top ring and second ring which is the bottom of the range. Which is .014-.022" I think. Is this not a good idea or should I file the rings to get around .016-.018" just to be safe but I don't wasn't it to loose either. I bought the deves rings fron ipd.
 
yeah where's my replacement WG actuator? :-P

I don't wanna be a jerk or anything, but I'd rather a JY b230ft freshened up over a stock b21ft bottom end.

And if I were buying rods and pistons, I'd definitely use a b230 bottom end.

When you're at it bore up the pistons, thats what I did on my B230f project
 
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