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Old 09-25-2020, 12:08 AM   #1
TimS
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Default B21ft manifold swap.

I have a stock KJet b21ft, intercooled and was wondering about swapping intake manifolds. I have managed to acquire both a b21 and a later manifold. Which one should I use? is it worth the trouble?
Is it just swap manifold and cables get everything mounted, good to go?
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Old 09-28-2020, 11:59 AM   #2
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Am I the only guy with a stock b21ft left....
Did I kick someone's dog?
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Old 09-28-2020, 01:25 PM   #3
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From https://www.swedespeed.com/news/volv...rbo-rally-car/

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Old 09-28-2020, 04:19 PM   #4
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I'll throw in my $0.02 on the swap.

I did the b230 intake swap a few years ago and I had to replace some piping for Idle control valve as well as all the cold side IC piping, the TPS wiring and throttle cable / body.

I didn't really notice and better performance but IMO there are some other advantages.

Easier to service under the intake manifold.
Readily available throttle cable replacement.
Cheaper Cold Side IC couples and pipes.


Looking back at it there was a reasonable amount of effort and the gains were minimal at best.

If my throttle cable wasn't snapped and I had a NOS one to spare I probably would of left the FT intake in.
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Old 09-28-2020, 05:22 PM   #5
Kjets On a Plane
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Honestly, aside from the B21F plenum intake/wouldn't bother, especially if keeping it stock/K-jet.

The exhaust housing/stock exhaust/intercooler/wastegate housing/pre-90 pancake/log exhaust manifold/cylinder head/k-jet plate restrict things worse and make for worse efficiency/economy/longevity issues.

Won't really help fuel econ or longevity, the pancake manifold does suck for flow, but other things are worse and it makes the car less orginal/more hacking and maiming, would not convert. The accordion hose sucks, but D088 repops it or heavy duty wire-reinforced high temp fuel hose for truck/heavy equip and military applications works, or bubble flex couplings & hard pipe with metal end tank D088 intercooler/similar?

Maybe with an auto trans/3rd engine mount & eliminate the leaky/brittle plastic tank IC that is so woeful/deficient/defective on these cars before hard/super rigid piping it though?
The flex in the system is there for a reason?

That said, if you do manage to solve/upgrade all that, but still keep it SOHC, the B21F plenum intake is worth ~+40ftlbs on the fairly mild SOHC motor of the best of the stock casting intakes if you don't lose your mind drinking the redblock timebomb k@@l-@id (Rodney dangerfield impression genie alladdin eyes?) & go 16V or Nathaninwa intake?
There are less $ per HP more powerful engines that fit in the 240 bay at that point...

Highest stock performing metal corvette intakes for the ellis-juans & the really pretty EFI intake (very similar to the 'vette intake, just V6) for B280 are pretty?
For broad powerband, cast, single throttle body/low dollar high volume warranty/lemon law compliant mass production pieces, anyway.

It's sorta like the E-fan conversion on a 240T;
You can do it/it's easy enough to hack in there for low dollars initially (quintessentially TB)/gives you something do mess with if you're bored or /.17¢/hr / first tweak hit's cheap/free.
Might not hurt per se, but not amazing.
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Last edited by Kjets On a Plane; 09-28-2020 at 06:45 PM..
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Old 09-30-2020, 10:24 PM   #6
TimS
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I was hoping to swap some minor factory stuff, I also have a 90+ exhaust, but it seems like not really worth it.
Right now I'm at the stage 0 with 8lbs of boost on 87 octane and things are all good. Thinking about MBC to 10 lbs maybe with a solenoid to go back forth. Would also considering a mild cam. T and adjustable gear, but I still have to get through a smog test, so whatever I can slip by with no/ least amount of long term hassle.

Basically pull the best combination of factory parts that I can bolt on to the motor I have and and still keep it a KJet.

Baby steps ( and I guess baby gains) are fine for me...
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Old 10-01-2020, 12:00 AM   #7
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^If it's all in there/tubes/hoses aren't leaking/everything works, wouldn't bother/focus on other stuff, especially if keeping the stock FI system?
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