Bimmerheads vs VAC motorsports head rebuild

[ForcedFirebird]

Stock cam seems to do better than 272+ on stock compression, even up to low 9:1 area. Stock engine with a 272 will comp test at ~145psi. That low of cranking compression is an indicator the engine will be lazy in low RPM.

[digger]

I would try for 9.5:1 as minimum not sure if that’s possible on stock bottom end with just the combination of head gasket and skimming head as I’ve never bothered to modify a stock bottom ended engine I’d be surprised if it was an issue to achieve that .

generally people go too big with duration so you end up sacrificing bottom end and mid range for a very small if at all top end increase.

[82eye]

Stock cam seems to do better than 272+ on stock compression, even up to low 9:1 area. Stock engine with a 272 will comp test at ~145psi. That low of cranking compression is an indicator the engine will be lazy in low RPM.

who sits in low rpm lol

[It's Soda Not Pop]

I've been using a BH head for over 5 years now with zero issues. Great guys. They are on this forum as well.

MR 325

[aavani90]

I called bimmerheads and spoke with the engine machinist. Super patient and friendly guy, was willing to answer all my questions and explain everything in detail. From our conversation it sounds like the 274 cam won’t affect low end torque and will add a nicer power band through mid to high RPM. No timing adjustments will be needed. I didn’t ask about the compression rate stuff you guys mentioned on here.

Also said there’s nothing really wrong with a reground cam, since all cams are technically re ground since they all start as blanks to begin with. Even with the brand new ones they’re ground before Install to get the duration and lift dialed in to spec. If you choose the regrind 274 option from them you’re actually getting a used genuine oem cam that’s been reground VS the brand new option which would be a FEBI cam ground to spec, so either way brand new Or used it’s being machined before install.

Also said there’s nothing wrong with using used valve springs, the used ones they use are all pressure tested and are within extremely close spec (I believe he said a pound or two) to the brand new ones.

They only use FEBI rockers, which I’ve read on here have known history of some iffy integrity maybe in their earlier production days, but sounds like they have been fine in recent use. They haven’t had any issues using them, and run them in their own engines.

Overall a really helpful customer service experience, and I can’t help but trust and believe what was said due to the fact that he didn’t try to up sell me on anything and assured me the differences between reground cam VS brand new, used springs VS brand new is quite minuscule. They sound like they do honest work, and I’ll be spending my money with them.

[ForcedFirebird]

who sits in low rpm lol

I invite you to my m20 dyno thread. Results speak for themselves: https://www.r3vlimited.com/board/for...20-dyno-thread

We made more power with a stock cam on a 9.4:1 m20b27 than a 272. I go with results, rather than talk. ;) You put a 272 on a stock engine and your cranking compression will drop from ~180 to ~145psi.

I've been using a BH head for over 5 years now with zero issues. Great guys. They are on this forum as well.

MR 325

Matt and Shant are enthusiasts through and through. They have helped me in a bind, more than once.

I called bimmerheads and spoke with the engine machinist. Super patient and friendly guy, was willing to answer all my questions and explain everything in detail. From our conversation it sounds like the 274 cam won’t affect low end torque and will add a nicer power band through mid to high RPM. No timing adjustments will be needed. I didn’t ask about the compression rate stuff you guys mentioned on here.

Also said there’s nothing really wrong with a reground cam, since all cams are technically re ground since they all start as blanks to begin with. Even with the brand new ones they’re ground before Install to get the duration and lift dialed in to spec. If you choose the regrind 274 option from them you’re actually getting a used genuine oem cam that’s been reground VS the brand new option which would be a FEBI cam ground to spec, so either way brand new Or used it’s being machined before install.

Also said there’s nothing wrong with using the used dual valve springs option, the used are all pressure tested and are within extremely close spec (I believe he said a pound or two) to the brand new ones.

They only use FEBI rockers, which I’ve read on here have known history of some iffy integrity maybe in their earlier production days, but sounds like they have been fine in recent use. They haven’t had any issues using them, and run them in their own engines.

Overall a really helpful customer service experience, and I can’t help but trust and believe what was said due to the fact that he didn’t try to up sell me on anything and assured me the differences between reground cam VS brand new, used springs VS brand new is quite minuscule. They sound like they do honest work, and I’ll be spending my money with them.

Yes, the new Febi rockers are far superior to the ones that have been out for about 20yr. New part number, and they come in a box of 12 now, not in vacuum sealed baggies individually.

Sounds like they have my same view about stock springs. Many times I put them in the ultrasonic cleaner, and the factory paint is still evident. digger is correct, these cars are old and may show signs of oxidation, YMMV.

[digger]

I invite you to my m20 dyno thread. Results speak for themselves: https://www.r3vlimited.com/board/for...20-dyno-thread

We made more power with a stock cam on a 9.4:1 m20b27 than a 272. I go with results, rather than talk. ;) You put a 272 on a stock engine and your cranking compression will drop from ~180 to ~145psi.



Matt and Shant are enthusiasts through and through. They have helped me in a bind, more than once.



Yes, the new Febi rockers are far superior to the ones that have been out for about 20yr. New part number, and they come in a box of 12 now, not in vacuum sealed baggies individually.

Sounds like they have my same view about stock springs. Many times I put them in the ultrasonic cleaner, and the factory paint is still evident. digger is correct, these cars are old and may show signs of oxidation, YMMV.

I'm with you, a 16+ degree bigger duration cam will not make the same bottom end torque as stock cam on a bone stock m20b25 bottom end. Whether the OP cares about this is another matter. A 27x is basically enough cam for 2.9L with ITB making north of 230whp so on a stock b25 you aren't nearly able to utilise the additional duration without bumping the CR to offset reversion. Will it work yes, is it ideal no.

I've reused stock springs on stock cam when doing head refresh job and but i knew the history of the car and springs, they weren't from a "random core".

[82eye]

I invite you to my m20 dyno thread. Results speak for themselves: https://www.r3vlimited.com/board/for...20-dyno-thread

We made more power with a stock cam on a 9.4:1 m20b27 than a 272. I go with results, rather than talk. ;) You put a 272 on a stock engine and your cranking compression will drop from ~180 to ~145psi.

.

my comment wasn't meant to be taken serious


but since we're there, what's the difference ? just the duration ?

i'm curious as camming is often right at the top of fairly standard m20 n/a builds on stock, or refreshed stock bottoms, a recipe i followed myself. my compression was no where near 180 before i began. pretty sure i was in the high 150 / low 160 range, i haven't run the engine yet or checked since. i'd be surprised at the drop, but had figured it would probably be about 150 - 160 on uneducated guess. won't bore with details but i've gone with really dirt simple mods you've all heard thousands of times.


edit : quick glance shows all were in the low to high 150 range. one dipping lower, and one at 160

[82eye]

I called bimmerheads and spoke with the engine machinist. Super patient and friendly guy, was willing to answer all my questions and explain everything in detail. From our conversation it sounds like the 274 cam won’t affect low end torque and will add a nicer power band through mid to high RPM. No timing adjustments will be needed. I didn’t ask about the compression rate stuff you guys mentioned on here.

Also said there’s nothing really wrong with a reground cam, since all cams are technically re ground since they all start as blanks to begin with. Even with the brand new ones they’re ground before Install to get the duration and lift dialed in to spec. If you choose the regrind 274 option from them you’re actually getting a used genuine oem cam that’s been reground VS the brand new option which would be a FEBI cam ground to spec, so either way brand new Or used it’s being machined before install.

Also said there’s nothing wrong with using used valve springs, the used ones they use are all pressure tested and are within extremely close spec (I believe he said a pound or two) to the brand new ones.

They only use FEBI rockers, which I’ve read on here have known history of some iffy integrity maybe in their earlier production days, but sounds like they have been fine in recent use. They haven’t had any issues using them, and run them in their own engines.

Overall a really helpful customer service experience, and I can’t help but trust and believe what was said due to the fact that he didn’t try to up sell me on anything and assured me the differences between reground cam VS brand new, used springs VS brand new is quite minuscule. They sound like they do honest work, and I’ll be spending my money with them.

exact same info i got. also said the regrind would be fine and not affect low end. i went with IE hd rockers which they were selling at the time. my machinist told me to re-use the stock springs as they were fine and no reason not to. i got a regrind 270/272 cam from colt. i have other supporting mods though. i was also impressed with the customer service, especially since i was only sourcing parts and not the work itself from BH.

[ForcedFirebird]

I know it was a jest ;)

My fresh spec e30 engines do ~180-185psi. In that dyno thread, the very first graph was an engine sitting at 145psi cranking.

I rebuilt/cammed a head for a local fellow, way back in 2010? (I'm getting old lol). Did a comp and leak test before pulling the head, they were sitting 175-ish. Rebuilt the head, fresh valve job etc, installed a 272 cam and the cranking compression dropped to 145. Customer got alarmed at the numbers until; I explained it to him.

I would not be surprised if you now see in the 130-140 range with the cam. You have to remember, the more the duration and overlap, the longer both valves hang open simultaneously, which "bleeds" off compression. Much over 230psi cranking and you'll have trouble running on pump gas (think high comp and small cam), a fresh s52 sits right about 210psi.

It's all about trapped mass. More compression can take advantage of the overlap. Lower compression and big cams often tend to put the true cam peak beyond the usable RPM range.

[82eye]

I know it was a jest ;)

My fresh spec e30 engines do ~180-185psi. In that dyno thread, the very first graph was an engine sitting at 145psi cranking.

I rebuilt/cammed a head for a local fellow, way back in 2010? (I'm getting old lol). Did a comp and leak test before pulling the head, they were sitting 175-ish. Rebuilt the head, fresh valve job etc, installed a 272 cam and the cranking compression dropped to 145. Customer got alarmed at the numbers until; I explained it to him.

I would not be surprised if you now see in the 130-140 range with the cam. You have to remember, the more the duration and overlap, the longer both valves hang open simultaneously, which "bleeds" off compression. Much over 230psi cranking and you'll have trouble running on pump gas (think high comp and small cam), a fresh s52 sits right about 210psi.

It's all about trapped mass. More compression can take advantage of the overlap. Lower compression and big cams often tend to put the true cam peak beyond the usable RPM range.

impressive replies and knowledge. the overlap and hang makes perfect sense to me. though i was warned it won't have as much of either on a regrind cam as opposed to a fresh blank, due to a smaller base circle. i'm not so sure i'm thrilled about a 130 - 140 mark though lol.

i did aim for a freer / higher revving build on purpose, taking weight off the rotating mass with a crank scraper and a 4 kilo flywheel. at the time it made sense, though i may have been wrong. i'm also adding an IE long tube header as it was suggested to add some more back in to the bottom end.

build requires 91 octane and matching chip. went with a sssquid 1.5 stage chip.


edit : should add there's absolutely no chance of accessing a dyno here. would have to travel a 1000+ kilometers.

[82eye]

I know it was a jest ;)



I rebuilt/cammed a head for a local fellow, way back in 2010? (I'm getting old lol). .

you have the knowledge but i'm near positive i have a sad edge on the old lol

[aavani90]

I invite you to my m20 dyno thread. Results speak for themselves: https://www.r3vlimited.com/board/for...20-dyno-thread

We made more power with a stock cam on a 9.4:1 m20b27 than a 272. I go with results, rather than talk. ;) You put a 272 on a stock engine and your cranking compression will drop from ~180 to ~145psi.



Matt and Shant are enthusiasts through and through. They have helped me in a bind, more than once.



Yes, the new Febi rockers are far superior to the ones that have been out for about 20yr. New part number, and they come in a box of 12 now, not in vacuum sealed baggies individually.

Sounds like they have my same view about stock springs. Many times I put them in the ultrasonic cleaner, and the factory paint is still evident. digger is correct, these cars are old and may show signs of oxidation, YMMV.

Interesting read on your dyno thread, gotta love evidence to back up a claim. After going back and forth on this and doing some more research, I think for my goals for this particular build I will be more than content with the stock cam on a freshly build head. I thank you all for your input in helping me make a decision. Sounds like I’ll have a couple-few months of waiting for the head to be built, looking to knock out a manual swap during the waiting period. If anyone is selling a g260 or manual swap parts in the SF Bay Area let me know!

[TobyB]

Yes, I prefer used OEM BMW (not Febi) rockers

I have been strongly suspicious that BMW are, in fact, selling SOHC rockers made by Febi.
And have been, for close to 20 years now, unless something's changed relatively recently.
The castings are darned close to identical, right down to the patterns of the voids...
The Febi logo is omitted in the BMW casting, but there is a blank spot where it is on the Febi part.

I too used OEM rockers as long as the supply (for M10s, in my case) held out,
but even the voidy Febis have held up (on M10s) to 7500 with a heavy enough spring...
if you pick the best 2/3 of the Febis you get in any one order. And then smooth them
externally...

t