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Turbocharge or stroker: which to build


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35 minutes ago, AydinZ71 said:

@madkaw tell me more about running 11:1 on pump gas? Il fascinated. I have not had such luck. Open to it! 

It all about the squish as they say . Ideal chamber design with the ideal Piston to head clearance . Lots of fun reading on this site about this . It is hard to find the ideal number because certain builders didn’t want to say . Unfortunately most of those guys aren’t in this site much anymore . 

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5 hours ago, madkaw said:

It all about the squish as they say . Ideal chamber design with the ideal Piston to head clearance . Lots of fun reading on this site about this . It is hard to find the ideal number because certain builders didn’t want to say . Unfortunately most of those guys aren’t in this site much anymore . 


hmmm… yeah il probably stick to 10:1 until I can replicate someone else’s success. Yep the EP head has polished chambers and deshrouded seats, but I’m not sure what more I can do. I do still need to cut back the excess sparkplug threads. I know those are a definite hot spot. The block has flat-top OEM pistons, with a -0.35mm deck clearance. 

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Bryan Blake was a big proponent of the squish . If you dig deep enough he eeks some info about squish distance . It’s closer than most would be comfortable with . Ive seen pics of pistons he ran and the combustion area is a very defined . He claims that is why he can run 11:1 on pump gas . What was crazier was at the time he was only running EFI fuel - and running a distributor . 

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@jonbill
 

Looks gorgeous. Good old peanut head.


looks like your octane rating in the UK is a combo of higher labeling and truly higher octane.
 

https://aircooledbug.co.uk/usa-versus-uk-fuel-octane/

 

Most we have here at the pump is 91. Everything over that is non-standard at the pump, is harder to find, and significantly more expensive (mostly due to the low volume of sales). In Southern California, a gal of 91 is close to $5 a gallon (~4L), while 100 octane race fuel is $10 a gallon. 


So you still have the weather and Brexit to contend with, but you do enjoy the superior fuel! 

 

Edited by AydinZ71
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3 hours ago, AydinZ71 said:

@jonbill
 

Looks gorgeous. Good old peanut head.


looks like your octane rating in the UK is a combo of higher labeling and truly higher octane.
 

https://aircooledbug.co.uk/usa-versus-uk-fuel-octane/

 

Most we have here at the pump is 91. Everything over that is non-standard at the pump, is harder to find, and significantly more expensive (mostly due to the low volume of sales). In Southern California, a gal of 91 is close to $5 a gallon (~4L), while 100 octane race fuel is $10 a gallon. 


So you still have the weather and Brexit to contend with, but you do enjoy the superior fuel! 

 

Thanks.  I like the weather TBH. Brexit is... hard to explain :eek2:

This pic is of the piston in situ - you can see where the proximity of the head squish area has kept the piston clean. This is my previous engine with 0.6mm head to piston clearance. 

331642503_BK560009(2).JPG.6dace6892aadfedf3ff6346a168b9d4b.JPG

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I never bought the MN hype. Yeah, it has a small peanut chamber, but the ports and valves are smaller too and it has exhaust liners. If you really want that chamber, shaving a P90 seems to be in every way a better answer.

I built an admittedly worse E31 that has less quench with about 11:1 and a bigger cam than most people run at .490/280, polished all the sharp edges in the chambers, etc. and needed 95 or 96 octane to prevent pinging. A bigger cam would have helped and I always tell people to go bigger when they start talking cams (stage 3 Schneider is not a good choice). Having been there and done that I wouldn't build an 11:1 engine again with the idea of running pump gas. Also, there isn't that much power in the last point of compression to justify the hassle that goes with it. You would do A LOT better having a 9.5 or 10:1 engine that can run 91 or whatever you have in your state and have the timing optimized than you will running the extra point of compression and having to back the timing off to prevent pinging.

This is a V8 video but the point carries over. Timing has a HUGE influence on power. To relate back to L series, I think I was able to run 91 and have the timing at 0 or slightly retarded at idle, which would have been somewhere in the 15-20 degree range all in. Did that for a couple days before I started buying race gas and mixing octane booster and stuff like that. Just KILLED power. You can see the same here:
https://youtu.be/HXX4zcPr9IE?t=590

 

Edited by JMortensen
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Long live the MN! I don't know, I think its the best bang for buck performance street head out there . Shaving the P90 just makes a harder turn from port to cylinder. I ran both the P90 shaved and my MN on my stroker. Didn't tell much of a difference . The MN has a slighter higher CR. I didn't dyno the motor with the P90 , but I bet they would have been close . More most builds either would be good with a 3-5CC difference in chamber volume . The ports are not that much bigger on the p90. The liners would only be an issue for the race engines . The liners in early heads(n47) aren't supported as well by the castings as well as the later versions. The MN is a really nice casting with few corrosion issues  . I'm no longer running a stock bottom end so my comparisons are not lemons to lemons. Currently at 226 rwhp with a MN and a stock N42 intake. The intake at this point is the limiting factor. I am running 10.75:1 . 

I think EFI is about an necessity for running on the ragged edge. Blake ran the fuel fat in ping prone areas . Having timing control with knock control helps too.

It is good to have some banter over cylinder heads .        

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46 minutes ago, madkaw said:

Long live the MN! I don't know, I think its the best bang for buck performance street head out there . Shaving the P90 just makes a harder turn from port to cylinder. I ran both the P90 shaved and my MN on my stroker. Didn't tell much of a difference . The MN has a slighter higher CR. I didn't dyno the motor with the P90 , but I bet they would have been close . More most builds either would be good with a 3-5CC difference in chamber volume . The ports are not that much bigger on the p90. The liners would only be an issue for the race engines . The liners in early heads(n47) aren't supported as well by the castings as well as the later versions. The MN is a really nice casting with few corrosion issues  . I'm no longer running a stock bottom end so my comparisons are not lemons to lemons. Currently at 226 rwhp with a MN and a stock N42 intake. The intake at this point is the limiting factor. I am running 10.75:1 . 

I think EFI is about an necessity for running on the ragged edge. Blake ran the fuel fat in ping prone areas . Having timing control with knock control helps too.

It is good to have some banter over cylinder heads .        

I agree, it's good to keep hashing it out, although since switching to LS I don't care as much as I used to. It got pretty heated in those threads 20 years ago. I remember being particularly pissed off when Mack said something to the effect of "I can go half throttle and not have any pinging." LOL

Here's a different angle: if it's not a race engine (at least a weekend warrior), then why bother bumping the compression up to the bleeding edge? If it is a race head, then why start with a head that has smaller valves and ports and liners when you could shave/shim and end up with something very similar and then have a better starting point to go crazy from?

Re the turn from the port to the cylinder, it's not affected at all by shaving the P90, because you're shaving the bottom of the head, and the turn takes place in the port. Might change the distance from the valve seat to the piston, but IIRC the P90 has a deeper chamber and shorter valves, so you'd probably be returning that to a place where they would be more comparable. I think the MN valves would still be closer to the piston. I suppose that's going to matter most when the cam is big enough to put the valves into the pistons, at which point need some flycutting.

If someone were building a race head though, ideally they'd raise the port roof and work on the short side radius, and you would do that on either head. Not sure if one has more meat there and can handle more porting, but you'd start out with more to do on the MN, plus installing bigger seats and valves, blending the bowls would require more work, etc.

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I think I figured out the turn part. You're just saying the MN is superior because it has the port at the same level and the valves lower. OK. Point taken, but again, you're starting with a head with smaller valves, so one might have a better port shape, the other has bigger ports and valves... ???

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3 hours ago, JMortensen said:

I think I figured out the turn part. You're just saying the MN is superior because it has the port at the same level and the valves lower. OK. Point taken, but again, you're starting with a head with smaller valves, so one might have a better port shape, the other has bigger ports and valves... ???

Remember -there is no best on Hybridz-lol.    I think the P90 is better for exhaust port do allow more flow for a bigger engine build. You would have to cut the P90 100 thou or more to get to the CR of the MN . Valve sizes can be matched up. The MN already has the bigger exhaust valve . My engine runs 44/35. 

Your right that trying to manage 11:1 might not be worth it. I've been trying to replicate the squish and CR that Brian Blake said he ran -without issues. I wouldn't try unless I was running efi . But with an aluminum head and a modern combustion chamber shape it should do 11:1 without a problem. 

LS1 is the easy answer for sure .      

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8 hours ago, jonbill said:

Thanks.  I like the weather TBH. Brexit is... hard to explain :eek2:

This pic is of the piston in situ - you can see where the proximity of the head squish area has kept the piston clean. This is my previous engine with 0.6mm head to piston clearance. 

331642503_BK560009(2).JPG.6dace6892aadfedf3ff6346a168b9d4b.JPG

I believe thats the magic number 

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