[sbc charlie]

i finnally had hippo help me to respond to your group i am not good at
computers.i have been in the motorcycle industry for 38 years and
have been an instuctor years ago at MMI. i own a sunnen machine shop
this is the same equipment that harley factory uses in there engine
rebuilding department.one of my part-time employees is a retired
genral motors enginneer worked on vortec head project.he also spent
a week at joe mondellos school of cylinder head porting. we spent
over 6 week and are still updating tc88 and evo cylinder heads.
we developed the vortec heads for tc88 and evo engines.a vortec
is designed to increase torque which i feel harley engines need.it
was hard at first to weld up an intake port and increase air flow-
but it happens. besides increasing air flow it really increases air
velocity. i feel that harley is on the right track with there httc heads
but disagree on combustion chamber design,we all have our opions.
there cnc heads are pretty i have seen but have not got to flow test as of yet.they did not cnc the combusttion chambers. i will keep this board posted when we do.i believe in mild cams and10.1/1 compression ratios
my objective is to build torque engines.if there is question feel free to ask
be patient some times to get back to you.
thanks short-block charlie

 

[Kags]

Qusten: are polished chambers only needed for high CR or do lower CR get any bennefit from them as well?

 

[HIPPO]

Like everything else it is debatable. We do not polish the chambers or the exhaust port as we have not been able to see any significant gains from it on street kits and it would just drive the price up.

If you want to get fancy the way to actually go is with thermal barrier coatings.

 

[Kags]

Hippo its been around for years (my background is with cars) that the best thing a polished chamber gives you (for high CR applactions) is less pointed edges for "hot spots" to start up that could lead to preinigiton. Is this not the case with Harleys?

 

[sbc charlie]

i do not polish ports or combustion chamber. i really see no need for it.
there are lot of people that polish ports. i have there heads in shop to rebiuld and the carbon is there. it does come off easier.
short-block charlie

 

[HIPPO]

Hippo its been around for years (my background is with cars) that the best thing a polished chamber gives you (for high CR applactions) is less pointed edges for "hot spots" to start up that could lead to preinigiton. Is this not the case with Harleys?

Yes, that is the case with very high compression ratios. Note I said street engines.
There are also some very knowledgeable people that believe the reason a polished chamber can reduce detonation somewhat is the initially greater heat rejection that increases burn rate to some extent and allows you to run less advance. This theory has been proven over and over with hypereutectic pistons.
Point is the new thermal barrier coatings are much more effective then polishing in this respect.

All these approaches have their limitations when running on the street as you don't tear engines apart every race or couple of races.

The polished chambers and exhaust ports eventually acumulate just as much carbon as natural finish ones, and with the coatings you have the possibility of them breaking up over time.

It makes more sense to build a relatively simple engine dialed in from the get go for adverse conditions, then a high strung one that requires constant readjustment. Unless of course you have factory sponsorship dollars, then you can go for the moonshot and leave nothing on the table.

 

[HIPPO]

There is another consideration, since you mention cars and Harleys.

Other then dimensional differences in cylinders this has nothing to do with it.
What really matters is the shape of the combustion chamber. A shovel chamber has much more in common with a Hemi chamber then with a TC chamber.
The polishing goes back to the days of the Hemi. It was very effective then as they were incredibly detonation prone and had to be run incredibly rich to make any power. Every tiny bit helped then.

With the modern bath tub chambers squish is much more the determining factor. With the proper squish you just don't have the same type of conditions anymore.

 

[Kags]

Thanks for all the input. What you all are saying makes good comon sence to me.

One thing, on my TC heads I notice that the carbin build up on a polished exhaust port was smoother than the frist time I tore it down (factory cast). I guess because Im old fasion and have the time to do some things mayself I will alway go that way.
I take you would agree the polishing exhaust ports dont hurt?

Thanks again...

 

[HIPPO]

No, it doesn't hurt. It quite likely doesn't hurt to polish the chambers either if you keep the shape consistent and don't significantly increase cc's.
They look pretty before use and off the bike.

 

[shag]

If you are not going to rev much past 6000rpm`s and are not going to go with a super size cam is it necessary to go with different valve springs if the stock heads are massaged? Thanks Shag

 

[HIPPO]

No, Harley springs are good for 6200 rpm.

It would be good to know the lift of the cams, but we clearance even the mild heads for .570" lift.

One of the reasons I like Andrews cams is that as long as you don't go overboard their lift is just around .500" and nothing has to work real hard.

 

[shag]

When talking about gasket thickness all things being equal, what would the difference in compression ratios between a stock twin cam headgasket and the thinest practial gasket be?

 

[HIPPO]

You have to define the engine first.

If you assume a 1550 with flat tops and 0 deck height and 82cc chambers, the CR with a stock .052" head gasket would be 9.23 and with a .032" gasket 9.59.

If you were to take the same engine at 1450 with nominal 85cc heads the CR would only change from 8.51 to 8.81 with the same difference in head gasket crushed height thickness.

Keep in mind the exact displacements are 1546 and 1448 cc.

 

[Kags]

What happen to the stock (1450) CR of 8.9:1 ?

 

[sbc charlie]

You do the numbers. Not even HD can argue with math. There are quite a few bikes out there with less CR then that due to chamber volume variations.

Sometimes you see bikes where the deck height is as much as .020" down the hole.

Why do you think some stock bikes are much stronger then others.

BTW, this is the Hippo. The hard drive on the puter at home went south and it will be as long as a week for me to have full access again. Puters are just too expensive in AZ and I'm having a new one shipped in, and it will take some time to recover data. As it is the boards are a relatively low priority. Not much time from work.


Maybe I should sign this one

Hung like Einstein, the brains of a horse

Blahahahahahahahaaaaaaaa!!!!!!!!!

 

[Kags]

What do you do to get a .000 deck from a .020 ? I know how to make the CC's the same so thats one up for myself.

 

[HIPPO]

Cut the cylinders down a little. 99% of the time the piston is down the hole. Just as an example the one I did yesterday was down .006".

These are the little things that someone at home or even a dealer can hardly take the time to measure and correct.

 

[shag]

This is interesting stuff! Never would have known that on my own. So when the piston is at the top of the stroke it should be level with the top of the cylinder if they are flat top pistons?

 

[rat509]

Hippo, think most people might be suprised about their factory tolerences? I bet you seen some pretty interesting stuff! Nice to read your posts, full of good info!

 

[tsuter]

Since this post is about correcting the small tolerance stuff - don't forget to index your plugs into that chamber "squish" Hippo was refering to earlier. Depending on head design, this is "free" power. I like free and it can't hurt. To idex the plugs, mark the gap side of the ceramic with a black marker. When you tighten it down align the black mark (gap side of electrode) so the gap faces into the "squish'. No reason to shroud the spark from the squish. You may need to add indexing washers to get the alignment right or switch plugs front to rear and try again. Dont add indexing washers to bevel seated or "washerless" plugs.