My Road Trip Motor Progress

[rick m]

Hey JHU....nice blog you have running.  The intent of this thread is to get people thinking. There is no "ONE WAY" to do everything.  If that were the case, there would be one car manufacturer, one home builder, one plastics manufacturer, etc., etc., etc. .    Innovation is the result of trying different ideas and still achieving results.  Having driven dual carb motors on the street since 1970, I am always looking for new ways to improve my street motor and street-ability.  There are a lot of different ways to achieve a desired result.

Rick M

[richie]

 Keep in mind you do not want a lot of deck.  I run "0" deck with a copper gasket.  I know Joel is running a tight deck too.  .

Rick M

Rick I am just catching up having been away for 10 days,but something I want to point out that i am sure you know but is a little missleading

you are not running 0 deck,you are running 0.050 deck if your copper gasket is 0.050 and you set the piston at zero with the top of the cylinder,
some may not understand that from what you wrote,and tight deck is a relative term,for me 0.035-0.040 is "tight deck" but everyone has there own ideas on that

You will need 58-63cc in your heads with that 0.050 deck in a 2276 to get 9-9.5/1 compression which is still pretty large,are you thinking of using dished pistons as well in this engine?

I too am interested to see you final chamber shape after you have flycut it down,dont forget the camera before you assemble the engine

cheers richie

[rick m]

Richie,

I have 62cc in the head at this time. Still working on it. Not done with the final shape.  I like those dished Weisco's you show on your website.  :-)

Rick M

[Zach Gomulka]

Rick, how much have you flycut the heads so far? I imagine your heads pre flycut must have been in the 72cc-ish range? What was your deck height and compression previously?

[rick m]

Another shot of the chambers after polishing. Not quite finished yet. One final CC to determine if I at my target figure after I align the barrel seating area with the cylinders.

Rick M

[andy198712]

nice! what tools are you using for this? ie what grits ect?

i'm still pondering my chamber design, i've just unshrouded to the barrel and blended it, removed any sharp edges where the seats were cut and its looking pretty open to me....

[rick m]

I use some carbide cutters for some of the blending, then move to 60 and 80 grit cylindrical sanding cones used on a 13,000 air powered die grinder (with 1/4" arbor for the cones).  Will post some pictures tonight. I then go to a 180 grit cone to get the majority of all sanding marks reduced so my polishing compounds and buffing tools do the rest.  The intent of smoothing the machined and cast portions of the chamber are to create a reflective affect where the head is not a heat sink. It is a less expensive way of doing this than having space age coatings applied.  If you have the money, the thermal barriers are worth it.  I am doing it this way to test it out.  I have done both.

I still have a little more shaping and blending to ensure that the top of the piston as it slams toward the combustion chamber is not pushing against any steps or sharp corners. Will post shots when the final chamber and CC work is done.  I also polish the tops of my pistons.

RM

[Zach Gomulka]

http://en.m.wikipedia.org/wiki/Hemi_engine#section_2

Rick, how much have you flycut the heads so far? I imagine your heads pre flycut must have been in the 72cc-ish range? What was your deck height and compression previously?

[karl h]

limbach aircraft heads have something like a semi-hemi chamber

[andy198712]

I use some carbide cutters for some of the blending, then move to 60 and 80 grit cylindrical sanding cones used on a 13,000 air powered die grinder (with 1/4" arbor for the cones).  Will post some pictures tonight. I then go to a 180 grit cone to get the majority of all sanding marks reduced so my polishing compounds and buffing tools do the rest.  The intent of smoothing the machined and cast portions of the chamber are to create a reflective affect where the head is not a heat sink. It is a less expensive way of doing this than having space age coatings applied.  If you have the money, the thermal barriers are worth it.  I am doing it this way to test it out.  I have done both.

I still have a little more shaping and blending to ensure that the top of the piston as it slams toward the combustion chamber is not pushing against any steps or sharp corners. Will post shots when the final chamber and CC work is done.  I also polish the tops of my pistons.

RM

Thanks for going over that for me bud!

did you notice any benifit with either the coatings or polishing? how did they look when torn down?

Thanks

[rick m]

Andy,

The intent with both is to reflect the heat into the combustion area and out the exhaust rather than have the head absorb it as a heat sink. However, being an aircooled head, obviously the head will dissipate heat through the surface areas of the fins and the fan will (if working correctly) blow it off the head. The open chamber design is not just for lower compression as some seem so stuck on thinking.  Other improvements I know work and I am working to achieve is to reduce heat retention and have it help the combustion and torque produced. 

Will show the results when the motor is back together. Again, I am not trying to be an 11 second street car.  Just a car that can drive anywhere, any distance, in any weather,  any time.  Already did it with one combination during the early days of the BERG CRUISE to Detroit (1997).  Working on a variation of that with this new motor.

RM

[andy198712]

Andy,

The intent with both is to reflect the heat into the combustion area and out the exhaust rather than have the head absorb it as a heat sink. However, being an aircooled head, obviously the head will dissipate heat through the surface areas of the fins and the fan will (if working correctly) blow it off the head. The open chamber design is not just for lower compression as some seem so stuck on thinking.  Other improvements I know work and I am working to achieve is to reduce heat retention and have it help the combustion and torque produced. 

Will show the results when the motor is back together. Again, I am not trying to be an 11 second street car.  Just a car that can drive anywhere, any distance, in any weather,  any time.  Already did it with one combination during the early days of the BERG CRUISE to Detroit (1997).  Working on a variation of that with this new motor.

RM

Cheers bud, i agree on your points, and i guess the coatings help get more heat out to the exhaust instead of soaking into the head, longer life span, happier engine.  i have similar goals to you, reliability close to a stock engine

[rick m]

Spent Saturday finishing up the final polishing on my combustion chambers.  Will be running a .04635 copper gasket between the heads and the barrels (running "0" deck in the barrel).  With my combustion chamber mods and cam grind, will be running a FLAT TOP (not dished piston) on this redo. Ended up with 65cc in the heads.

From here...the assembly begins.  Running a 106 lobe center cam with .473 lift at the valve.  Intake valve will close at 35 ABDC to achieve the dynamic compression we were looking to hit.   Cam grind was ground to help me achieve my driveability goals of coming off idle to 5000-5500.

We are calculating for 7.6 dynamic compression and 8.7 to 8.8 for the static compression and running on 91 octane pump gas. Primary goals are driveability, improved bottom end and better cooling.  Top end after 5500 is not a consideration for this combo as the cam design will simply not achieve any measurable increase in horsepower after 5500 to 6000 rpm.

Rick M

[rick m]

Finished the chambers on my street heads, polished the crowns of the pistons and dialed in the cam this weekend.  Now it goes back together. Will be interesting to see what was accomplished towards gaining more torque down low.

Rick M

[13bussing]

I'm liking this polsing lark allot.

Am I right in thinking it would be so good in turboed engine?? Getting more heat in to the turbo should help with the turbo spool earlier.

[jamiep_jamiep]

How soon would you expect any build up of the waste products of combustion on the finish Rick, and how would that diminish the effect? Do they need to be redone every so often or something?

[rick m]

The heads will carbon up relatively soon.  Polishing helps tighten the material (get rid of porosity). It is not nearly as good as a ceramic coating but a poor mans way to make incremental improvements. My main objective was really the shape of the combustion chamber for quench. I am running a .0465 copper gasket on top my cylinders with "0" deck in the bore.  Just finishing final assembly of the motor this week. Completed cam degree exercise and checked all clearances last week. My cam has 2 degrees advance built into the cam. Running 478 lift and 218 duration at .050 with 106 lobe centers.

Rick M

[Zach Gomulka]

"Top of the page" cam, Rick?

[rick m]

Top of the page...NO.  Had the cam ground for what I am trying to accomplish rather than taking one off of any page or out of any catalog.

Rick M

[Taylor]

218*@.050 is a typing error,  right?   With that little duration,  I don't care how much overlap you machine the cam with,  at 8.8to1 I would think it would detonate.

[Zach Gomulka]

It was a joke, Rick. A joke.

[rick m]

Zach....not my first rodeo. I get it.  :-)

Rick M

[Fasterbrit]

Keep up the good work Rick

[John Maher]

An interesting read.
I first started using the Berg semi-hemi cut in the late '80s. I've never regarded it as a performance enhancing mod, more a quick and easy way to lower compression ratio by increasing combustion chamber volume. Before that, the only way to increase chamber volume was to reshape the chambers by hand - a laborious task, especially if you're looking for an increase of 4cc per chamber or more - involving hours of die grinding cc-ing, more grinding etc etc. In the '80s and'90s I was building street motors with much lower CR than I use nowadays, plus the fact most heads suitable for street use back then had smaller chamber volumes than the heads we have nowadays (eg 044s). Short of running a ton of deck height (strictly verboten) or dishing the piston, finding more volume in the chamber was the way to go to arrive at the target CR.

One of the clues as to why the semi-hemi cut combustion chamber doesn't perform on a par with a well designed wedge type chamber can be found in the instructions Berg provides with the semi-hemi tool: he mentions having to run more ignition advance to achieve best performance. As a general rule you'll find less efficient chamber designs require more advance i.e. it takes longer to burn all the air fuel mixture so you have to start the fire earlier. Looking at a modern engine design, a typical four valve per cylinder layout with centrally located spark plug will run a max advance of around 20° BTDC. If you can achieve best results with less ignition timing, you have less pumping losses and therefore more power delivered to the flywheel.

On most of the street engines I build nowadays there's no need to go in search of extra chamber volume - partly because I run higher CR than I used to but also because the majority of aftermarket heads start out with larger chambers than I had to work with 20+ years ago. A few weeks ago I dug out the semi-hemi cutter for the first time in years. The project was a mild 2110cc bus motor, with stock heads, Engle 110 and a pair of 40IDFs. I start with a fixed deck of .045" and then calculated the required chamber volume. The semi-hemi route was the quickest and easiest way to get where I needed. On the dyno I started with an initial max advance of 32°. Increasing timing by a couple of degrees at a time to find best performance. I finally settled on 38°.  If I left it down around 30-32° I was giving up power and torque, plus the exhaust gas temps were running higher.  I was perfectly happy with the end result and don't see any problem running semi-hemi heads on an engine of this type but for a higher performance orientated motor I'd always recommend a compact wedge chamber with large squish area and run a tight deck.

rick m... you mentioned you were reducing surface area by using the semi-hemi chamber and further reducing it by blending in the sharp edges. If I understand you correctly, in fact you're doing the opposite and actually increasing surface area. By converting all (or most) of the flat squish/quench area into a concave form you have more surface area than you started with. Now more of the heat energy from combustion is absorbed by the head instead of acting on the piston.

On the subject of hemi cutting and then flycutting the head to get rid of some of the extra volume you've created....
A dyno test I carried out many years ago threw up something odd. I'd previously built a normally aspirated 2165cc race engine for a customer. He raced for a season, then brought the engine back for a refresh. He'd also acquired a pair of Super Flow heads from another racer that had been intended for a turbocharged engine. They'd been semi-hemi cut, with all the edges carefully hand-blended in. A really nice pair of heads but the chamber volume was HUGE! I can't recall the exact figures but CR would have been down in the 8s on the 2165cc n/a engine. I flycut them as much as I dare in order to increase CR. On the dyno all was fine until it got up around 6500rpm. At that point the engine started making this horrendous noise. It sounded like a box of firecrackers going off. Pushing it beyond 6500rpm towards 7000rpm and above the noise would go away. At the time I didn't figure out exactly what it was but subsequently came to the conclusion there was something weird going on in the combustion chamber as a result of the reduced height semi-hemi cut i.e. combustion efficiency was going haywire.

I fully accept semi-hemi heads can work just fine on a relatively mild torquey street engine - I've done it several times. But if you're building an engine where optimum performance and efficiency is the goal, I don't believe the semi-hemi approach, at least as I understand it, is the way to go.

Rick and Joel, hope you don't think I'm dissing your findings. If you're achieving good results in the real world with your updated version of the semi-hemi I can't argue against them and appreciate you sharing them on here. Just thought I'd chip in with a little of what I've experienced. Look forward to reading more of your reports.

All the best

JM

[Fasterbrit]

 Just to add to the use of the semi-hemi chamber design in racing, the Salzburg Rally cars (Austrian Privateers) used the semi-hemi chamber with great results. It worked really well on the highly-tuned 1600's with twin Weber 46 IDAs. Reading the info on the cars, the team found it worked for their given application. Unfortunately, they don't go into great detail as to why it worked much better, perhaps it has something to do with the duration of the events and how long the car would be subject to full-throttle and heavy loading. It would be really interesting to find out their specific CR...

[Jon]

http://www.1302super.com/page35.html

[Fasterbrit]

Thanks JHU! 9.1 CR and 120 hp for a 1600 is pretty darn respectable! And all through 39mm intakes and 32mm exhaust valves...
They were very reliable cars, too 

[Jon]

[John Maher]

Thanks JHU! 9.1 CR and 120 hp for a 1600 is pretty darn respectable! And all through 39mm intakes and 32mm exhaust valves...
They were very reliable cars, too 

More than respectable, especially considering it was back in the early '70s!

A quick bit of maths.... assuming a deck height of 1mm, it takes a chamber volume of 43cc to arrive at 9.1 CR (flat top piston).
They'd've had to heavily flycut an 040 hemi chamber to achieve that, which brings us back to Rick and Joel's method and therefore contradicts what I said above!  

There are more than a few engine builders today who could extract superior performance from the same configuration - but that's only to be expected with the benefit of 40+ years progress  

[Jon]

Thanks JHU! 9.1 CR and 120 hp for a 1600 is pretty darn respectable! And all through 39mm intakes and 32mm exhaust valves...
They were very reliable cars, too 

More than respectable, especially considering it was back in the early '70s!

A quick bit of maths.... assuming a deck height of 1mm, it takes a chamber volume of 43cc to arrive at 9.1 CR (flat top piston).
They'd've had to heavily flycut an 040 hemi chamber to achieve that, which brings us back to Rick and Joel's method and therefore contradicts what I said above!  

There are more than a few engine builders today who could extract superior performance from the same configuration - but that's only to be expected with the benefit of 40+ years progress  

Thanks for contributing John! Are you up for a bit of guessing? What would be a possible gain of removing the squish area like the salzburg boys have done. And would the engine run cooler with squish?