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| porting questions??? https://www.ausmini.com/forums/viewtopic.php?f=5&t=59068 |
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| Author: | jimmy_ams04 [ Wed Nov 25, 2009 8:53 pm ] |
| Post subject: | porting questions??? |
Hey guys, this is a bit of a noob thing but i want to get it right, Im porting my mini head, its off an 1098cc engine, the manifold im putting on has bores of 38mm across...... What are my options or how far can i take the porting before hitting the water chambers?? Scared of mucking it up but its something i have to learn 
Thanks guys 
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| Author: | drmini in aust [ Wed Nov 25, 2009 9:04 pm ] |
| Post subject: | |
Short answer.. Buy either: How to Modify your Mini (David Vizard) Tuning BL's A series engine (David Vizard) read first before attacking head... 
[edit] but that manifold sounds a bit big for a 1098... |
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| Author: | jimmy_ams04 [ Wed Nov 25, 2009 9:17 pm ] |
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oh ok, thats good to know, ile get onto that thanks
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| Author: | jimmy_ams04 [ Wed Nov 25, 2009 9:43 pm ] |
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does anyone have any suggestions on extractor sizes for an 1098? if so should a port match it? |
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| Author: | sgc [ Wed Nov 25, 2009 9:55 pm ] |
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jimmy_ams04 wrote: does anyone have any suggestions on extractor sizes for an 1098?
if so should a port match it? Lots of people throw Perry-style 3-1 extractors on smallbores because they're cheap. I had these on my 1100 until very recently when I decided it was time to throw them out in favour of a set of LCB's. On my engine these made a significant difference not only in power, but also in sound 
Don't be tempted to install the biggest exhaust you can buy, it'll be wasted on your engine. If you've got a few modest mods, a 1-3/4" system into a single box RC40 is perfect. As for porting, with the exhaust it's actually beneficial to have a slightly larger extractor pipe than exhaust port in the head. This helps prevent "reversion" in the exhaust gas -- basically, the small step acts as an aerodynamic "brake" which causes a little turbulence in the exhaust gases as they enter the extractor, which makes it harder for them to go back in than out. The LCBs I bought recently are the Chinese copy of the Maniflow design. I reckon (as do a few others here) that they're actually superior -- they have cast steel flanges which are a less abrupt turn out of the head, and with the way the pipes are welded in, the welds don't distort the flange or get in the way of the big manifold washers. Mine fit absolutely perfectly first time, no tweaking necessary. |
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| Author: | mini7boy [ Wed Nov 25, 2009 10:05 pm ] |
| Post subject: | |
there's also this guide to modifying cylinder heads written by a highly regarded A-series specialist named Adrian "AC" Dodd in England. Even though this guide isn't for the 1098 head, a lot of the information Dodd provides is not specific to one engine size. Lots of good photos also help to convey the instruction. http://specialistminiforums.yuku.com/topic/4576 one problem that makes it more difficult to avoid breaking into the water jacket is a phenomenon called "core shift". This is when some parts of the molds used to cast the head actually come loose during the pour of molten metal, thus causing certain features of the head, such as water jackets, to be slightly relocated from their designed location. Knowledge of core shift and how to deal with it is something that only comes with experience. |
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| Author: | Phat Kat [ Wed Nov 25, 2009 10:25 pm ] |
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mini7boy wrote: one problem that makes it more difficult to avoid breaking into the water jacket is a phenomenon called "core shift". This is when some parts of the molds used to cast the head actually come loose during the pour of molten metal, thus causing certain features of the head, such as water jackets, to be slightly relocated from their designed location. Knowledge of core shift and how to deal with it is something that only comes with experience.
Hi mini7boy, I've heard about this but (knock on wood ) never been victim of it... I've done a few heads but never had this problem.
On heads where this has happened can you tell us just how much it was shifted? Are we talking a 0.040" or 1/4"? Thanks mate. Just curious is all. |
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| Author: | mini7boy [ Wed Nov 25, 2009 10:49 pm ] |
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Hi Phat Kat, curiosity is very good and you have hit the nail on the head. Meaning that core shift varies widely both in location and distance because it is the result of the casting mold coming partially adrift during the molten metal pour process. Each head is different any only the skill and experience of the head porter enables uncovering the extent of the core shift problem. I know of head porters who purchase relatively large quantities of head castings and then inspect them assessing the fitness of each for producing power. Some of the castings are scrapped or used for road heads because the core shift is so bad as to compromise its potential. Perhaps you may be able to have a professional head porter assist you by examining the casting(s) you have available and giving you some pointers on what to look for and how to work around core shift when porting the head. Good luck with your project. |
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| Author: | Phat Kat [ Wed Nov 25, 2009 11:07 pm ] |
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mini7boy wrote: Hi Phat Kat,
curiosity is very good and you have hit the nail on the head. Meaning that core shift varies widely both in location and distance because it is the result of the casting mold coming partially adrift during the molten metal pour process. Each head is different any only the skill and experience of the head porter enables uncovering the extent of the core shift problem. I know of head porters who purchase relatively large quantities of head castings and then inspect them assessing the fitness of each for producing power. Some of the castings are scrapped or used for road heads because the core shift is so bad as to compromise its potential. Perhaps you may be able to have a professional head porter assist you by examining the casting(s) you have available and giving you some pointers on what to look for and how to work around core shift when porting the head. Good luck with your project. Thanks for taking my curiousity in good will. I think I have a chat with a pattern maker about it and see if they can give me any pointers in identifying internal casting defects. I'd rather learn to do it myself, thats all. I might know a few "professional porters", and I'm pretty sure that you're right in that they could teach you how to work around core shift,, but,, I just figure who better to learn about casting defects from than a pattern maker and it just happens that I know one of those too. I'll let you know what they say if you like? After all, it never hurts to be well informed 
Geess,,, you must wonder how some of those heads made it thru quality control hey? Especially if so many of them are just good for scrap?
Cheers |
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| Author: | mini7boy [ Thu Nov 26, 2009 12:37 am ] |
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Phat Kat, I used the word "scrap" somewhat loosely. What I really meant was that they were not candidates for an investment of porting. They could be used on road engines. without porting, and live happy lives. It's just that they could never be made into good racing heads. Kind of like a puppy born with minor defects as to his "confirmation" or show quality. Those with defects can be great family pets, but are not really fit for showing. Not quite sure how this turned into a discussion of show dogs. |
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| Author: | drmini in aust [ Thu Nov 26, 2009 5:58 am ] |
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My 12G1316 head (now on my 1412 stroker) found water in 2 intake ports when I was porting it, a la Vizard. I had about 40 hours work in it... After nobody in Sydney would look at welding it in there, I preheated it on a 2 burner camp stove and gas welded it with manganese bronze filler rod. No it doesn't leak- after I'd decked it, I bolted 2x 1275 heads together and connected the garden hose (about 120psi). All good. It has done about 20,000 miles since then. I'm lucky it was the inlet ports, if it was the exhausts it would probably have gone in the bin. |
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| Author: | TheMiniMan [ Thu Nov 26, 2009 7:36 am ] |
| Post subject: | |
When i was a little fella i wanted to do some head porting & dad told me to go grab some small bore heads & start off by opening up chambers & shaping them how he showed me,,, & i argued that i wanted to work the ports out really big to make them flow heaps , but he got a bit abrupt & said "Do as you`re bloody well told"!!! & so of course when he`s really mad i get scared & just do what he says right (well some of the time) but little did i realise at the time that all this was just a ploy to get me some experience with the die grinder before i totally stuffed up a whole heap of good heads after i wrecked quite a few small bore cyl heads (Un-be-knownst to me they were allready "throw-away" items & that`s why he told me to play with them) i ended up (after a few months) doing some pretty smart chamber jobs & dad (& the other mechanics) were more than impressed he then told me to work the outer 2x exhaust ports on the same heads & "Try" to make them "look" like the center exhaust port,,, well that was a challenge & so i then wrecked quite a few more heads (they were allready stuffed tho so it wasnt an issue) but i slowly worked out how far we could go & also found out the variations in castings. It`s only After i showed him a few fairly decent exhaust port jobs he then said "ok time to play with inlets",,, he showed me a few big port inlet jobs on some small bore race heads & said "now go & try to copy these" off i went & wrecked a few more cyl heads, breaking through in all sorts of places, jamming the tool, breaking the burrs & stones, wrecking valve seats etc etc etc,,, well Lucky my dad knew what he was doing putting me onto a pile of stuffed small bore heads first hey???,,, just imagine if i`d just happilly ripped into a pile of good nick 1275 heads to start with ... Hhhmmmmmm Yes
that wouldn`t have been funny hey? sooo,,, my suggestion here is much the same as dad`s --> to go have a play learning & feeling & experienceing the use of the die grinder on some stuffed cyl heads first,,, then work your way up learn to crawl "well" before you can walk,,,, learnt to walk "well" before you can run,,, learn to run "well' before you can sprint,,, learn to sprint "well" before you try to climb Mt Everest
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| Author: | david rosenthal [ Thu Nov 26, 2009 10:11 pm ] |
| Post subject: | |
I have a 998 and a 1100 head that I have sliced thru in sections so you can see exactly the shape and position of the water jackets. These are used by the blokes who want to do heads so they can measure to get it right. If you have any U/S heads cut them up to see it will save a lot of drama. The problem with rusted sections is that less than 1mm thick you can not see thru but it will leak , and that is not good. Matt is right in saying crawl before you run etc etc. |
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| Author: | gafmo [ Thu Nov 26, 2009 10:24 pm ] |
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david rosenthal wrote: I have a 998 and a 1100 head that I have sliced thru in sections so you can see exactly the shape and position of the water jackets.
Ow David can you or some one you know good with a camera take some good photos for us all as it will be brilliant just to to know what to expect
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| Author: | david rosenthal [ Thu Nov 26, 2009 10:37 pm ] |
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gafmo wrote: david rosenthal wrote: I have a 998 and a 1100 head that I have sliced thru in sections so you can see exactly the shape and position of the water jackets. Ow David can you or some one you know good with a camera take some good photos for us all as it will be brilliant just to to know what to expect the 202 head is being borrowed but the 296 is here ,so I will lay it all out and take some pics tomorrow. there does not seem a big difference in internal water casting between the heads, just port /valve areas. If you work to the 998 head then you would be safe for a 1100 head. One little trap is the area between 2&3 comb chambers. It looks like it would be all solid ,but the water jacket cuts between them a lot. Big trouble if you under cut around around the exhaust v/v's |
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