Inliners International Forums General Discussion Engines Shaping head bolt boss- 292.

I'm going to use a 73cc head off a 230 on my street 292, with some mild porting. I've decided not to run port lumps (sorry Larry), but thought I would have the shop modify the head bolt boss into an airfoil shape. does anyone have pictures or more info on doing this?. I assume you shape it kinda like a cam lobe...rounded leading edge on the intake side, and taper to a sharper trailing edge on the valve side, right?

you do have the correct idea about the air foil shape. sorry i have no pics.
to install lumps is really not that bad. they will add flow and not rob power. i have a install video on youtube. check in my sig below. tom

Great video! Thanks. Do you have pictures of port work? Tom

The bolt boss is such an intrusive obstruction in the intake port, that anything you do to it, besides remove it completely, wont really yield any additional benefits. Like tlowe said, installing "lumps" isn't that difficult or expensive, and since the head will be removed anyway, your almost half way there....

beater, i do have some pics of before and after porting. no vids yet.

cncdude, whats that funny # after your name? a new addition to the fold? what good news it is. i am sure you will contribute many good things to the club. tom

Heater,after years of "shaping" the bolt boss (including machining for a thin wall Satinless insert)I recently followed the advice of many here and removed the boss in preparation for lumps....I spent a third of the time in removing as I normally do in shaping....in terms of time and effort the lump process wins hands down ...from all reports the gains in flow will too.....it really opens up access to the bowl area of the port allowing further refinement ; the back wall of the common area between seats always gave me fits before.....fats

Yep, I guess im street legal now(LOL). Jean called me back this past Saturday, and it came in the mail on Thursday. So im ready to go now....

Actually, if the bosses are left in. They should be sharp on the leading edge and rounded on the back. Why? Because the air coming in is straight and can be divided by a sharp edge but on the back, it has to turn and go either left or right and needs a rounded corner to do that easily. Just my opinion.

Heater63
if your going to spend the money to have the machine shop reshape the boss. You would be more money wise to have them machine out the bosses the right way, and install the lumps. Not sawzalled OUT. I guess thats ok for the back yard butcher who REALLY needs to save a buck,But it is also a good way to mess up a Head. Just my 2cents.But if your really dead set on keeping the boss in then follow what Armond has said.

the sawzalling in the vid is a option for removing most of the material that would need machined out of the way. i have yet to damage a single port doing this. either i am getting lucky or it really is that easy. tom

IMO, the only way to install lumps the correct way is to have them milled out so the new hardware will sit perfectly flush.

No high & low spots.

The cylinder head needs to be just bolted straight down to a milling table,in parrallel w/the head surface.

There are machined pads on the side where the spark plugs go, so it will sit on these machined pads as it needs to (flat on the mill table) be to facilitate machining the bosses out.



MBHD

totally agree with you hank. the new hardware has to meet the head squarely when torqued down. the cutting out of the boss with a sawzall simply allows the installer to only machine down 1 time for the plug hole and the seat for head bolt in 1 operation.
the bolt boss if left in would then still need to be removed in another machining operation from the port side. tom

Tom, I know you have a Bridgeport mill in your shop, and are capable of using that method as well to remove the bolt bosses. I saw your videos, and as we have discussed in several conversations recently, you are giving the do-it-yourselfer a step by step, on how they might be able to do it with common tools they might have access to at home, since that seems to be the biggest percentage of people buying the "lumps" these days, and not everyone has there own mill at home. Good videos, and very informative for the novices out there wanting to do it their self....

Thanks to all of you! The reversed airfoil shape make sense Armond....I can also see that it still sucks to have any boss there.
I am rethinking the lump port now. Actually, I have a head I picked up in a "lot" of used parts that has the ports milled out, at least the initial cut...not all the way to the floor.
If it is a good head, I may go ahead. I will be doing some more lump research...Have Leo S.'s book, and often at Twisted6's website.
You guys are most helpful!

it is best to lump a head that has not had the intake port "ported". the lumps fit the stock floor best. most porting should then be done to the top and sides of port. tom

OK...so I'll be the village idiot and ask the dumb question.

Are lumps only for use in high flowing, high RPM applications? Do they have any value on a street engine or just screw up low end torque?

the lumps will aid the performance of both stock and performance engines. they increase the velocity of the intake charge and also improve airflow thru the head.

engines put simply are air pumps. the more air you can flow through it increases the efficiency. the lump improves the efficiency. tom

Lets see some low lift flow numbers, with and with out lumps.

How many times does this have to be Repeated???????
First off it has been posted here more then once and IT's also
In the BOOK. A stock head & stock valve only flows about 170 at best. Same head all stock Meaning Only change is installing the lump can now flow just over 200 with the stock valve.

joeh,
that is a good request to help make a decision with. i can readily provide low lift flow #'s for the heads with lump or open port. But would need to flow a stock head to get low lift flow #'s. From my testing the lumps really take over @ any lift over .300. so the average flow on even a stock head with lumps and a stock cam with around .400 lift would still give a higher average flow.

somebody can surely post flow #'s at all lifts for a stock head. tom

Total stock intake, good valve seat and guide, ZERO modifications

.050" lift 27.3 cfm
.100" lift 52 cfm
.200" lift 103 cfm
.300" lift 149.5 cfm
.400" lift 164.6 cfm
.500" lift 168.5 cfm

same port with epoxy molded in and around head bolt boss

.050" lift 24.5 cfm
.100" lift 47.8 cfm
.200" lift 102 cfm
.300" lift 151 cfm
.400" lift 177 cfm
.500" lift 190.2 cfm


Just like you said Tom, it takes over .300" lift before you see any gains from the modifications. With a stock cam or even a slightly bigger one, the gains are minimal. These test were done with a stock diameter valve. I couldn't find the paper we were writing on for the exact number, but during the test we pulled the valve clear out of the hole to test just the port. It wasn't much more the 190 cfm we got at .500" lift. The seat area was the restriction on this head. Even with a stock 1 barrle intake bolted to the head, the flow numbers didn't change.

Remember,,just because it does not flow that good @ low lift,,does not mean it will not make your engine have more torque/power.

I other words,,,it's not always just about flow.Two cents thrown


MBHD

Very true, but if you move the torque and horsepower out of your normal driving range, then it will feel and drive worse.

By installing the lumps you will make more torque in the lower RPM range.

I installed upper lumps w/no devider & it improved my lower RPM torque.

Installing the lower lumps will help it more than upper lumps that I made.
Most times you can make the ports smaller & increase velosity,you are going to have more low end torque.

It is a win win install. No drawbacks. Twisted6???


MBHD

Boy!, look what I started.

Ya'll can quible over flow bench numbers, but I think the proof has been out there for a very long time (Kirby,Sissell,et al)that removing the boss and adding at least the lower floor lumps makes a big difference.

Anyway, my original question about boss shaping has been answered as a waste of time/effort...its either lump it or leave it stock IMHO.

Tom, it appears in your video (great by the way) that the head of the bolt sticks up past the surface of the lump! Also why can't the new bolt go into the block as deep as the original? thank you Herb

[quote=Joe H]Total stock intake, good valve seat and guide, ZERO modifications

.050" lift 27.3 cfm
.100" lift 52 cfm
.200" lift 103 cfm
.300" lift 149.5 cfm
.400" lift 164.6 cfm
.500" lift 168.5 cfm

same port with epoxy molded in and around head bolt boss

.050" lift 24.5 cfm
.100" lift 47.8 cfm
.200" lift 102 cfm
.300" lift 151 cfm
.400" lift 177 cfm
.500" lift 190.2 cfm

This is a head with 1.84 intake valves and 1.60 exhaust valves. It has had valve unshrouding done to it and the guides have been coned shaped.

First port is a intake that has had the bolt boss removed and has a cap screw sitting in the bottom, like it would be in use.
1.84 intake @28" on a superflow
lift flow
open port no lump same port w/lump
.100 62.1cfm .100 61.7cfm
.200 115.3cfm .200 115.6 cfm
.300 168.7cfm .300 171.5 cfm
.400 184.3cfm .400 207.9 cfm
.500 195.6cfm .500 229.1 cfm
.600 202.0 cfm .600 242.7 cfm

1.84 intake with a HI-FLOW bolt in intake lump
lift flow
.100 57.8cfm
.200 112.9cfm
.300 166.9cfm
.400 202.0cfm
.500 215.6cfm
.600 226cfm


JoeH,
In comparing your findings again. it is is easy for me to see the gain in flow even at the .3 and .4 lift values. granted i have not tested a 1.72 valve head with lumps for flow , yet. but with my others tests have certainly proven a 10% increase @ .400 lift. Hopefully that would follow with the 1.72 valve. tom

Its nice to see numbers to back up the statements. When I get time, I will see about testing just the valve size difference.

Joe