My Road Trip Motor Progress

[Joel Mohr]

I looked at the dyno sheet Bill, and the timing is at 30*...With Dougs new muffler, I would bet that motor made close to 200...yet drives like a stocker...and the 48 idf carbs are off the shelf... with some carb work, i would estimate 210...through the muffler, belt on.

[rick m]

Johl,

I heard Gene mention when he was still with us that he would put a lot more lead in the timing that 30 degrees. Of course, cam combination/overlap and everything else come into play.

Rick M

[Joel Mohr]

When I worked for Gene, he said max compression WITH a hemi cut was 7.8 to 1...He recommended 7.5 as a max for stock chambers. With the extra static compression, timing will be moved to accommodate the flame travel of a tighter squeeze.

[OC1967vw]

Beautiful! Those look exactly like my street car heads,(but I've got 46x36 valves) I'm running 11.2 to 1 without any problems at all...2442, cam is a special grind, .650 x 310*... makes 215 with the belt on through the muffler...

what type of heads-vw or aftermarket? can that valve combo be used in a modified vw head?

[Joel Mohr]

My heads started life as 041s...

[bugnut68]

I had no problems with my semi hemi heads on my last 1776... I bought them from Rick around 2003 or 2004, actually.    Anyway, I ran 7.8:1 compression, dual Kads, Engle 100 cam with 1.25 rockers, 1-3/8" header with single quiet pack and 009 with Pertronix, loved that motor.  Ran awesome, despite claims from a number of guys that said the semi hemi chambers would lead to raw gasoline coming right out the tail pipe. lol.  

Only issue I never resolved was a slight flat spot off idle... not sure if it was the 009 or the Kads, but I never took the time to fully tune it out.  Great motor though, and it would go anywhere as well as be fun to drive.

I'm at the point of frustration with my 2017 build that I slightly regret ever having sold that engine to fund this bigger one.  It's been nothing but one headache after another and I'm thinking I should have left well enough alone.

[rick m]

Hey Ryan....were those the ported heads I sold you?  That same configuration works on big motors too.  Doing the same exact thing right now to my 2275.  Glad to hear they worked so well for you.

Rick M

[Joel Mohr]

 On the 1776...If you had bumped the compression to 8.5 or 9 to 1, it would have made an easy 10 more horses, with the same temps and no flat spot....

[bugnut68]

Hey Ryan....were those the ported heads I sold you?  That same configuration works on big motors too.  Doing the same exact thing right now to my 2275.  Glad to hear they worked so well for you.

Rick M

Yeah, Rick, those were the ones!  I have no idea where the engine is now, as my buddy who moved to Portland that bought the engine has since sold the Baja that it went in.  Great comb, all around!  Really miss it.

[rick m]

Very cool. Glad they worked well for you. Doing a set for my Wife's buggy right now. Will be very similar so we have a very dependable but affordable performance combo for her.

Rick M

[Joel Mohr]

We should try and keep this thread alive. There is so much new technology that can be applied to a VW, and most people seem to be stuck in the same 40 year old line of thinking. With small stems, and beehive valve springs, you can easily add 1,000 rpm to the same old combo. And with the motor not working as hard to sustain RPM, it just "Unleashes" more power....

[Taylor]

Maybe I am confused as to the point of opening up a chamber and then fly cutting it down to get compression back?? Did I miss something or isn't that what you claimed you did?  11to1 with a hemi chamber confuses me.

[Zach Gomulka]

I'll give my two cents...

If hemi style chambers are so good, why do you need so much more ignition lead with them?

If hemi style chambers are so good, why is the new Chrysler hemi not a true hemi?

If hemi style chambers are so good, why does the new Chrysler hemi use twin plugs?

Hemi style chambers greatly increase the surface area of the chamber, allowing more heat to soak into the head rather than out the exhaust.

[bedjo78]

I have reshape chamber like that. and I installed on 2276 bay windoy. daily driver. with compression 7.1 ; 1  camshaft engle 110. engine didn't like.  pinging a lot and i have to retard igniton quate a lot. it is on tropical country. pump gas is 86-88. removed it and install normal chamber heads

[rick m]

The HEMI chamber works well with more compression. If they did not work why did the porsche engineers prefer them when building the 356, 912 and 911 motors??? It was not just about putting the larger valves in either. With more compression, you do not need as much timing.

For all of you who continue to think they don't work...don't run them. However, they do work better than the traditional chamber for street driving. You also cannot just flycut the HEMI shape.  You have to go in and radius all the machined surfaces and do a little more work on them. 

This is such an mis-understood subject...It requires more than just the hemi chamber to make it all work. If it did not work, I would not have torn my motor down and gone back to it after trying the traditional chambers again....even when I knew what the outcome would probably be.

ZACH...Twin plugs have been done on VWs going back over 30 years.  It was probably initially done by REVMASTER for the VW airplane engines.  I have a few other friends who did it on VW performance motors too.  It is not necessary with the right combustion chamber and ignition.

I like trying different combos...but personally, the hemi chamber has worked well for me for years and is the reason I am returning to it.

RM

[Joel Mohr]

Well Zach....What's wrong with more timing? What's wrong with twin plugs? My head temps are not any higher than normal. I drive my bug to the races,(usually 60 to 80 miles each way) race it and drive it home. Twice I have won my bracket running low 12's on street tires and through the muffler. I can cruise it anywhere I want to go, and I live in the Desert! Temps are not a problem...Most modern motors use a bowl shape of some kind. Some do have a small "squish" areas BEHIND the plug.  Rememeber the Pent-Roof that Honda used? I have a freind that owns a high performance machine shop, and he lets me look at heads that he gets in. ANY BRAND. I invite you to do the same...and Rick, I have gone as high as 10 to 1 on just the Hemi cut...no ping, no deisel, and no extra heat on California 91 octane...

[volkskris]

more timing indicates that the mixture is burning slower.

[Joel Mohr]

Correct! and....

[rick m]

If you think about what goes on in a combustion chamber, the blended hemi has fewer places to have detonation created. I am with you on the hemi head thing. Been messing with it a long time. Just lost my way briefly due to someone talking me in to something that I had a gut feel I would not like after doing it.

RM

[andy198712]

We should try and keep this thread alive. There is so much new technology that can be applied to a VW, and most people seem to be stuck in the same 40 year old line of thinking. With small stems, and beehive valve springs, you can easily add 1,000 rpm to the same old combo. And with the motor not working as hard to sustain RPM, it just "Unleashes" more power....

Where are people finding the correct beehive springs?

[volkskris]

Correct! and....

I was hoping someone else would say the rest I had to learn that this year, but can't seem to find it. having 2 2 inch thick books about combustion engines doesn't help either
it was something about a slower burning mixture releasing less energy or less force

[fish]

I am interested to see a video of this built which proves the Hemi haters wrong 

[Joel Mohr]

Donn at R/D spring does all of my valve train work. He is a spring engineer. Works on Ferrari, Ford, Chevy, Masseratti, you name it, he's made it run better. He's been in the valve spring business for 30 years. He either makes, or has access to any number of combinations based on true lift and duration numbers. Yes, they have a website...

[rick m]

Fish,

When I get my 2275 back in the car, I will take video of it during cam break in and later while in the car driving it. Will be a while but will post here.

Rick M

[Joel Mohr]

There is a video on my website of my street car running a low 12 on street tires through the muffler...Mohrprf.com

[rick m]

Johl,

Does your spring buddy Don at R/D make the behive springs and retainers for the single groove valves like CB puts in their heads for a stock VW spring height?

Rick M

[Zach Gomulka]

The HEMI chamber works well with more compression. If they did not work why did the porsche engineers prefer them when building the 356, 912 and 911 motors??? It was not just about putting the larger valves in either. With more compression, you do not need as much timing.

The Porsche (and Chrysler) engineers preferred to have a greater valve angle (for more airflow) than VW. A hemi chamber was a necessity, not a choice.

[rick m]

My reasoning for the chamber has nothing to do withe the PORSCHE engineers wanting more room for the more efficient cross-flow design. The more surface area...the more heat.  The more heat...what happens? Also, what does the heat in the chamber produce? :-)

RM

[rick m]

One of the key advantages of a hemispherical combustion chamber is that its surface area to volume ratio is the least in the category a compared to other designs like flat head, wedge heads, etc. and therefore they have a superior thermal efficiency than other engines. Its advantages are that it has a relatively low surface area for heat absorbtion and it has little in the way of areas where unburnt mixture can lurk, as all the corners of a wedge design are eliminated and the raised roof of the hemi combustion chamber are well clear of the piston. The low surface area means that there is less area to absorb heat from combustion and this helps to keep the head temperature down. This in turn helps to control detonation. Accordingly, a reasonably higher compression ratio can be run to the benefit of performance. (But not the kind of compression ratio that most people associate with a racing motor, because this design has definite limitations at higher compression ratios.)

The elimination of dead spots of unburnt fuel mixture means that fuel economy is better because more of the charge is doing work.

Another benefit of a well done hemi design (not just a cut one-which means proper blending of all surfaces) is the effect of "squishing" the mixture so that it shoots out of the "squish area" and the resultant turbulence mixes the mixture up bettr. This helps to give even and controllable combustion.  Two stroke designers adapted these findings and put a concentric squish band around a ( usually) hemispherical combustion chamber with the spark plug in the middle.  Remember the SQUISHY discussions that have taken place on these forums.  Guess what....SQUISH with hemi heads is part of the secret. The rest of the functionality is found in the compression ratio, timing, jetting and how well the chambers are finished with the hemi design.  Look at the head on a 2 cycle motor cycle engine.  The 2 cycle engineers have fully understood for years the benefits of a hemi for the squish necessary to get the best burn on a 2 cycle motor. BURN is BURN...and cylinder head design has a great deal to do with it.  The HEMI also helps to optimize what you can get out of lower octane fuels. I had a 1914 in my chop top before the 2275 with heads similar to the ones I posted here that I was getting 33mpg with (that had the HEMI design) I was running 89 octane fuel.

Johl Mohr has mentioned a key ingredient in this whole discussion and that is that you can run more compression with the HEMI design as detonation is reduced with the combustion chamber design, as all the sharp corners are eliminated when after the machine cut the critical finish of the chamber of all the blending work contributes to removing detonation issues normally associated with all the corners and edges found with a wedge design. All machined edges must be blended and no sharp cuts or edges left.

Everyone can keep kicking this to death but if done properly, the HEMI design does work. You can't just hemi cut your heads and throw them back on and expect an improvement. It is not just about cutting a hemi chamber and lower compression. It has to do with a lot more things related to better atomization of the fuel, burn, eliminating detonation and being able to run lower octane fuels.  

Each person is entitled to do what they want. However, for those of us that have already worked with and run the hemi design with all the corresponding work that goes with them...they do work.  However,  you don't have to run them.  Everyone is free to do what they want but don't bad mouth something you do not understand or simply jump on someone else's bandwagon and try to out theorize people on the forum. Some people talk while others DO.  For those who have done this...we an continue to enjoy the benefits associated with them.

Rick Mortensen

[rick m]

Consider what you are viewing carefully.  We are not talking about combustion chamber volume at this point. We are talking about the design. Look at the diagram I sketched this morning and think carefully about the questions posed.  Take your thoughts away from the compression discussion long enough to think about the design only in terms of chamber surface area and the most prone to detonation. We can still get compression with a HEMI design.  Just focus on other things happening in a chamber to get the benefit of the principles associated with the HEMI.

Rick M