flame travel ,vrs angle milling

[bunner engines]

hello don ! bunner engines here . i purchased your secrets to winston cup engines , art of cheating , acid porting , and the pro spark plug kit . love the stuff !!! i am a curious person by nature , thats why i like your products and my why i like my job . but i would really like to email you some pics of a late model dirt engine i built for a customer . some really interesting things are going on with the flame travel of this engine ! its a two barrell carb , with the slider plate . if your inerested , please reply to this post . this is the first time i have ever signed up for any kind of forum ,so please have mercy on my typeing...

[speedtalk]

I'll send you an email.

[bunner]

hello don ,happy thanksgiving to you and your family ...i dont mind at all if
you choose to post these pics on the forum .in fact it might bring up some
good conversation .okay here we go ,i had only three weeks to build this
engine ,the driver was a firstyear rookie ,and the car was an out of date
leftover so he could just learn some seat time .suprisingly he was passing
the top guys on the outside ? and he was rookie of the year . they were all
patting me on the back for the great engine .well its at my shop now for a
check up but when i pulled the heads i was SHOCKED , the worst looking flame
travel ive ever seen !4.030 bore but the whole outside of the piston is
clean ,and there is a distinct shark fin clean spot at the intake valve
area .i have never liked the low plug location in the chevy head , and i
sevearly angle milled these heads from 64.cc to 47.5.cc !wich i know just
makes it worse . granted part of this fuel wash is the engine was rich so
that will be adressed , but i doubt thats going to get the complete flame
travel im looking for .what do you think ? ill give you the specs on the
engine in a moment ,but here is the other part of the equation ,the intake
ports at the valve show alot of burnt exh in the bowl area , (could this be a
good thing an a two barrel restricted engine ???? the carb we are useing is
an c&s aerosol billet , hav'nt tested anything else yet thats just what they
had and everyone else is using that style too ,but then again you know how
that goes , a guy will cut his header collecters off and win that night and
the next week everyone has them cut off !..lol the front four cyl's are worse
on the flame travel than the back ,the carb is slid all the way back on the
slider plate ,i know on my flow bench if the carbs back the front runners get
better air flow , if you slide the carb forward the opposite occurs .but i
dont think the dry flow on my bench is a whole lot of help here .we are aloud
to fully port the cast iorn heads (wich i hav'nt done yet ) im using the pro
action 220cc with 2.02x1.6 .but we are not allowed to touch the intake
manifold , we are useing the edelbrock bowtie vic jr #2996 .the cam is a reed
solid roller .625 in x.625 ex duration at fifty is 255 x255 on 106 i picked a
straight up camshaft in fear of over scaveging the exh . in conclusion i just
want to keep the heads for compression ,it dos'nt seem to be to much torque
for this car and the new four link car is coming for next year .but if i
could also get complete burn on the pistons at the same time this thing could
be an ANIMAL !!! thanks for listening to me yak ,but your thaughts would be
greatly appreciated don ....p.s.(man does this guy ever shut up ?)lol...i
forgot to mention we are useing autolite ar AR13 plugs maybe if i can find
somthing with a more progected tip might help ? at least ill get to use my
new spark plug reading kit when i need it the most eh ?...thanks for your
time don ........respectfully.. greg bunner

[speedtalk]

Hey Greg, You've got one of the toughest combinations (restricted 2bbl) on the planet to make "complete" combustion. First off, I don't think the problem has anything to do with the spark plug location - the problem is upstream of the combustion chamber. The first thing I'd try is the Edelbrock 2901 intake - is it legal?
http://edelbrock.com/automotive/man_sbchev_victor.html

As you already figured out, being rich didn't help. Since it's legal, you should port the heads. Last and probably the most important, the carburetor. I'm not convinced that the c&s aerosol billet does a better job of atomization than a dog-leg style carb.
http://www.candsspecialties.com/abcmods.html

I'm sure it's better for airflow, which is most likely more important for your application. You may just have to put up with the [non] flame travel problem to make the most power. Let us know what you find in the future. Thanks for writing, Don

[Lasher]

I hope it's ok to comment on older posts....I'm new here....

Am curious about something here........ I have heard ( dated info ) that many restricted engines have difficulty in getting thier manifold vacuum low during WOT under racing conditions...... I read somewhere that some 311 in engines were pulling 7 inch of mercury @ WOT.....

If this is an oval track engine and if by chance in the turns if one must get out of the throttle and intake vacuum raises further ...... then could this vacuum be pulling any combustion chamber or ex port air right back into the intake runner during valve overlap ?? Since this is a single pattern cam it would seem that would be better than a dual pattern cam that has a later EX closeing....... If this is the case would a wider 108 or 109 LSA help ??

My appologies if I'm all wet here......just trying to learn something and tossing out any ideas....

[SW]

I have seen something that looked like that before. What we discovered (afraid to admidt it), was that the head gaskets were leaking and that the clean spots on the piston was from water and/or steam blasting them clean.We had also angle milled the heads a bunch. I'm not sure if you have checked this or not but it is somthing to look into.
Shawn

[speedtalk]

a single pattern cam would seem to be better than a dual pattern cam that has a later EX closeing....... If this is the case would a wider 108 or 109 LSA help ??

My experience is the exhaust lobe is more important than the intake lobe when it comes to restricted engines. The next time you have one on the dyno, do some lash testing - I think you'll find the intake lash won't make much difference, but exhaust lash will make power changes. I think you're right on the LSA, but these engines still seem to like more duration on the exhaust.

[speedtalk]

I have seen something that looked like that before. What we discovered (afraid to admidt it), was that the head gaskets were leaking and that the clean spots on the piston was from water and/or steam blasting them clean.We had also angle milled the heads a bunch. I'm not sure if you have checked this or not but it is somthing to look into.
Shawn

Good point Shawn. Did the engine show the same pattern on the piston?