B34 vs B35 Under Pressure....

alpinewhite · Post by **alpinewhite** » Apr 28, 2011 7:14 PM

Just of curiosity, which motor makes for a better daily driver/commuter under forced induction.(TCD stage 2) Lets cap the boost @12/14psi for arguments sake.

My common sense says the B35 with the higher compression and more advanced Motronics will lend itself to a more tractable, livable motor on and off boost...

And i'll dare to venture the B34 will be less tractable in commuter duty due to its lower compression and transition itself towards higher boost because of its lower compression and stronger bottom end(rumored)?

But I would love to hear what you guys think?

Cheers,

George · Post by **George** » Apr 28, 2011 7:39 PM

With modern standalone, the b35 is far and wide a more superior choice.

Scottinva · Post by **Scottinva** » Apr 28, 2011 8:40 PM

I agree with George b35 is hands down better. It's not like the b35 has too high of compression for a turbo, it's still low compression i'd say to todays standard.

T_C_D · Post by **T_C_D** » Apr 28, 2011 9:54 PM

I prefer the b34. There is ZERO perceptible difference in drivability due to the CR. The b35 block will crack.

George · Post by **George** » Apr 28, 2011 9:56 PM

T_C_D wrote:I prefer the b34. There is ZERO perceptible difference in drivability due to the CR. The b35 block will crack.

CFM yo!

T_C_D · Post by **T_C_D** » Apr 28, 2011 10:15 PM

George wrote:
T_C_D wrote:I prefer the b34. There is ZERO perceptible difference in drivability due to the CR. The b35 block will crack.
CFM yo!

b34 and b35 head flow abt the same.

George · Post by **George** » Apr 28, 2011 10:17 PM

T_C_D wrote:
George wrote:
T_C_D wrote:I prefer the b34. There is ZERO perceptible difference in drivability due to the CR. The b35 block will crack.
CFM yo!
b34 and b35 head flow abt the same.

Prove it.

T_C_D · Post by **T_C_D** » Apr 28, 2011 10:20 PM

George wrote:
T_C_D wrote:
George wrote:
T_C_D wrote:I prefer the b34. There is ZERO perceptible difference in drivability due to the CR. The b35 block will crack.
CFM yo!
b34 and b35 head flow abt the same.
Prove it.

I have no interest in proving it. Paul B. told me they flow about the same.

Shadow · Post by **Shadow** » Apr 28, 2011 10:41 PM

Is this tested with cam and valves or just the casting?
where does the b35 block crack at?

ealinn · Post by **ealinn** » Apr 28, 2011 10:43 PM

Please tell more...

Cactus · Post by **Cactus** » Apr 28, 2011 10:58 PM

T_C_D wrote:
George wrote:
T_C_D wrote:
George wrote:
T_C_D wrote:I prefer the b34. There is ZERO perceptible difference in drivability due to the CR. The b35 block will crack.
CFM yo!
b34 and b35 head flow abt the same.
Prove it.
I have no interest in proving it. Paul B. told me they flow about the same.

B34 cam has no overlap, B35 does. That's worth at least something in a turbo application.

Scottinva · Post by **Scottinva** » Apr 29, 2011 12:34 AM

T_C_D wrote:
George wrote:
T_C_D wrote:
George wrote:
T_C_D wrote:I prefer the b34. There is ZERO perceptible difference in drivability due to the CR. The b35 block will crack.
CFM yo!
b34 and b35 head flow abt the same.
Prove it.
I have no interest in proving it. Paul B. told me they flow about the same.

I think thats hard to believe. Larger intake port, I believe the port angle is different in the head, and apparently has a hotter cam. It's hard to believe this would have no affect on CFM.

George · Post by **George** » Apr 29, 2011 12:38 AM

Cam has no effect on a standardized CFM measurement. The only way to compare apples to apples is to compare the air flow at the same valve lift.

T_C_D · Post by **T_C_D** » Apr 29, 2011 11:31 AM

Shadow wrote:Is this tested with cam and valves or just the casting?
where does the b35 block crack at?

Tested at same lift. Block cracks at the cyl head bolt bores.

Brad D. · Post by **Brad D.** » Apr 29, 2011 12:00 PM

I am completely happy with my b35 turbo, however, in retrospect, I wouldn't hesitate to turbo a b34 if that was what was already in the car. I think both would be very close in power output given a similar setup and engine management.

paul burke · Post by **paul burke** » Apr 29, 2011 1:39 PM

Todd is running an UNPORTED B34 head on his E28.

More port area doesn't always produce a better flowing head.

B34/35 intake ports have the same entry angle and both heads share the exact same exhaust port.

Early M30 cams are on a tighter lobe separation angle. B35 cams are on a wider center split. Because the B35 cam has a larger profile than the B34 the overlap is about the same.

B35 blocks are cast using less deck, cylinder wall and case material than the earlier blocks.

Paul

George · Post by **George** » Apr 29, 2011 1:41 PM

Paul, so you're saying the larger intake valve has no effect on CFM?

alpinewhite · Post by **alpinewhite** » Apr 29, 2011 1:43 PM

Okay.... so it is it safe to say without getting too technical; the B35(boosted) makes a better(more tractable) motor to live with on a commuter basis?

paul burke · Post by **paul burke** » Apr 29, 2011 1:51 PM

George wrote:Paul, so you're saying the larger intake valve has no effect on CFM?

Max lift port flow is dictated by the choke area in the port.

Low lift port flow is restricted by area at valve seat.

A larger valve (within reason) will increase low lift port flow until the valve/seat flow capability reaches the flow rate of the choke in the port.

Paul

paul burke · Post by **paul burke** » Apr 29, 2011 1:59 PM

alpinewhite wrote:Okay.... so it is it safe to say without getting too technical; the B35(boosted) makes a better(more tractable) motor to live with on a commuter basis?

Can't answer that without getting too technical.

Air exchanges only when a negative is produced.

The higher the signal strength (negative) the more velocity you will create. It comes back to piston speed (signal) at a given rpm verses volume/area in the intake tract.

Like putting small verses large dia. hoses on your shop vac.

Paul

T_C_D · Post by **T_C_D** » Apr 29, 2011 3:10 PM

alpinewhite wrote:Okay.... so it is it safe to say without getting too technical; the B35(boosted) makes a better(more tractable) motor to live with on a commuter basis?

No. Having had both I can say that I prefer the b34.

bm0p700f · Post by **bm0p700f** » Apr 29, 2011 5:39 PM

Paul you need to write a book on tuning BMW engines or engines in general.

Good & Tight · Post by **Good & Tight** » Apr 29, 2011 9:24 PM

T_C_D wrote:
alpinewhite wrote:Okay.... so it is it safe to say without getting too technical; the B35(boosted) makes a better(more tractable) motor to live with on a commuter basis?
No. Having had both I can say that I prefer the b34.

I've never run a B35 but I agree with Todd. My reasoning is that the older block is a stronger casting IMO.
Like the old Chevy blocks with higher nickel percentage.

alpinewhite · Post by **alpinewhite** » Apr 30, 2011 2:01 AM

T_C_D wrote:
alpinewhite wrote:Okay.... so it is it safe to say without getting too technical; the B35(boosted) makes a better(more tractable) motor to live with on a commuter basis?
No. Having had both I can say that I prefer the b34.

I can see why the B34 would be more desirable for making big power especially in the quarter mile - lower compression = higher boost = more horse power etc. Stronger block = more boost = etc.

What is it from your previous experiences with the two that makes you feel the B34 makes a more tractable boosted(commuter) motor?

From my experience of the two(un-boosted) the B35 was/is the superior motor to live with and in my opinion more tractable than the B34 in terms of torque, hp, idle, power band and mpg's.

Cheers,

alpinewhite · Post by **alpinewhite** » Apr 30, 2011 2:07 AM

Good & Tight wrote:
T_C_D wrote:
alpinewhite wrote:Okay.... so it is it safe to say without getting too technical; the B35(boosted) makes a better(more tractable) motor to live with on a commuter basis?
No. Having had both I can say that I prefer the b34.
I've never run a B35 but I agree with Todd. My reasoning is that the older block is a stronger casting IMO.
Like the old Chevy blocks with higher nickel percentage.

How or why is it you feel that a stronger casting(thicker block?) makes for a more tractable commuter? I can see it beneficial in terms of high boost high horse power applications... but I fail to see the correlation.

Shadow · Post by **Shadow** » Apr 30, 2011 2:42 AM

bigred has had good luck with his 600hp b35 I think.
Hope it's not a common problem cracking b35 blocks.

Good & Tight · Post by **Good & Tight** » Apr 30, 2011 7:36 AM

Shadow wrote:bigred has had good luck with his 600hp b35 I think.
Hope it's not a common problem cracking b35 blocks.

Nope, that block cracked also on a few the cylinder bolt holes.
Saw it with my own eyes.

alpinewhite wrote:
How or why is it you feel that a stronger casting(thicker block?) makes for a more tractable commuter? I can see it beneficial in terms of high boost high horse power applications... but I fail to see the correlation.

Go with the B35 for your daily driver. My comment on block strength had nothing to do with your original question.

Scottinva · Post by **Scottinva** » Apr 30, 2011 10:35 AM

It seems a bit odd to me that they would design the head from what now seems such a small if any performance advantage. I understand the block, i'm assuming for cost and possibly weight of the engine. Why go to all the trouble to redesign only two things, maybe they had something other than performance on their minds with the valve, maybe something as goofy as pollution possibly? Had to be some reason, manufactures don't like to just wasted money. I have not messed with flow rates on heads, or have much experience with how things affect it. It just seemed bigger valve would help get that much more air in, N/A I dont think this would make but a tiny difference. However, when going to forced induction I thought the gains would be more noticeable. Seems hardly worth the trouble of waiting for a b35 to show up in the junkyard if this is the case.

tacomagabe · Post by **tacomagabe** » Jun 20, 2011 4:09 AM

Yeah this is news to me! Making me reconsider my upcoming engine choice for my e12. I'm surprised this b34 vs b35 discussion hasn't raged on. I looked through the FI archives and the idea of the b34 head being just as good wasn't even discussed as far as I can see.
So assuming I go with a b34 block to avoid cracking issues, and you aren't going to ever run more then, say, 15psi of boost... Is there any reason to source a b35 head and have to mess with different pistons to get the CR you want? I don't know much about flow testing, would the b35 head start to flow more then the b34 at a higher rate of FI? Maybe way higher then I'm ever going to need? I'm about ready to go with simplicity and b34 all the way.

M. Holtmeier · Post by **M. Holtmeier** » Jun 20, 2011 12:49 PM

It's my understanding that b35 intake valves and camshaft installed in a b34 head will flow about the same as a b35 head without lowering the compression when using a stock b34 bottom end.

MyE28.com

MyE28.com

B34 vs B35 Under Pressure....

B34 vs B35 Under Pressure....