Projects 3 port Olds on a T motor - Poor Mans Rajo

That Looks pretty good! My only suggestion is to make sure there are no sharp edges, as these can incandesce. That's another cause of detonation and precombustion.

As a thought about combustion chamber shape, you have probably seen the chamber shape of the Austin A-series engines. This is actually a very efficient chamber, and if you can imagine that, you'll see that it's very close to the chamber shape you are developing.

I find it interesting that the adapter plate is actually becoming the side walls of more modern engine designs. Your valve angle is the same as the A-series i.e. in line with the axis of the cylinder. And the sparkplug will end up in a similar location. One benefit of the head you are using is the cross flow configuration. The A-series is not, so carburetors end up right above the exhaust, causing some issues.

I'm looking forward to seeing you finish this engine and get us a video of it running. And winning some hillclimbs!

 

I went out and did some playing with some clay.


This is a 261 piston for my Leroi Chevy. Top of piston is .907 down, I added clay to within .0625 of the head. The black outline is where the spark plug is located. Am I heading the right direction?

 

Well it looks like the mixture movement should be towards the sparkplug. Just remember to not shroud either of the valves and in the finished chamber to provide sufficient clearance for flame travel from the sparkplug.

Oh and another issue is scavenging the burnt charge. If there's a way to bias the chamber shape so that when the exhaust valve is open, and blowdown has started, that will help with getting sufficient scavenging. There's always tradeoffs. Some residual exhaust left in the chamber will lessen the overall efficiency of the intake period, lowering the volumetric efficiency of the engine somewhat. However, it can also lower the peak temperature in the chamber, allowing you to run slightly higher compression.

Overall efficiency of the cycle is directly related to the compression ratio, so that can make more power. R R R, MORE POWER!

Enough for now, I nerded out again... sorry guys! Can't help myself sometimes

 

Hey, GG & BB;
You guys are getting there. GG, Squish can be anywhere, usually isn't near the top of the cc, but at the outside edges. Easiest area to work with & control.
I'd bias the charge to the exhaust valve, keep the plug area unshrouded. Since this isn't a hi-rpm mill, I'd look for quench in the ~.045" region. Well, even iffen it was a hi-rpm deal. . Once you get much over .045->(maybe).060, you lose the effectiveness of quench. Notice I didn't say it wouldn't run(it will - it's just a matter of how well, relative to how it could be) - quench has been called Artificial Octane for eons, for good reason. Dave wrote well. As long as clearances aren't sloppy. I'd rather put the pop-up completely under the intake valve side, w/o any notches if possible. Raise or lower the area under the exhaust valve to get whatever comp ratio you want. Note that the offset weight will be over the piston pin, if I'm seeing the pic correctly. just turn your clay model 90*. Pop-up could be wedge-shaped, or what-have-you. Your cam timing may or could, change, depends on how much lift, when in the cycle, & what the L.C. is also, for Intake valve clearances. You don't necessarily have to get the dome a-kissing the cc around the intake valve, just bias the charge as well as you want to, or can. Could maybe widen the cam's L.C. out if needed to change valve opening event timing. Will also change the useable power-curve Spend a bit of time on Larry Widmer, TheOldOne's site, Endyn. He still has a small amount of tech articles up. They explain, & have some diagrams. You should find that less ign lead is needed, + the other benefits mentioned by Dave. You end up w/a odd looking piston, but one that works better.
In the fwiw dept, for proof-of-concept, you probably could make piston-tops that'd bolt on, since you have very thick domes. If the 261 pistons are cheap & there's enough piston-dome thickness, you could mill the pistons flat on top, & bolt the test-domes on from underneath. They should give a decent rpm to test the theory. Wouldn't be the 1st time that was done. A past poster, Dave Doelmetch(sp?), had a couple of threads, one of which he cast-up his own pistons, machined them & ran them in his Chry S/6 dragster, just to do it. Extremely lo-buck, & done knowingly a bit crude, but effective. It worked for him, longer than he needed to test with. I think the thread is still around.

BB, Doing good. Follow up on what I wrote to GG, same applies to the adaptor. I'd still put as much quench in as possible. If the pop-up pistons are the ones you're going to use, is there enough material in the piston head to mill the corresponding bore-offset flat for the quench, & then use the rest of the pop-up along that area to extend the quench in a thin hemi-shaped band that covers the thickness of the piston/vs the adaptor plate? Hard to describe, easier to draw. Iffen for some reason, you need larger quench thickness to the point of ~.100", then I'd look at the Singh-grooves. He found that ~3, which were a given depth n width, pointed at the plug, really helped. & for some reason, didn't work well w/"normal" quench thicknesses, but needed ~.100" at least. More compression helped, too. Again, the high-speed turbulence mixing of the fuel n air is the goal.
Don't know if this is useful, but when I saw the head adaptor plate, & the flat non-combustion-chamber; the 1st thing I thought of, was cool; now put in a super-thin sleeve over both, & you'll be able to run the ring package up high. But that would require a longer rod. Maybe off of some latter 6 or a straight 8? Some of those things had some looong rods. The offset part of the head sitting on the adaptor becomes nothing more than an easy way to lose cc's to gain comp, & it kinda looks like the adaptor plate wouldn't matter iffen it was bore-sized. Piston design becomes whatever you need it to be to get what you want. I'm guessing I'm missing something, since I don't have it here to eyeball up-close.

I like this thread, & these old mills. Thanks for putting pics n thoughts up. Kudos. .

Marcus...

 

Thanks GG, Dave G and Marcus, great input much appreciated. Herb had discussed fitting tops onto '28 Chevy pistons to up the compression in the Chevy four thread to useful effect, I am thinking of going that route with my Chevy motor. I reckon I can get the shape a lot better by mill and die grinder, Im going to get some ply blocks cut over the holiday and see if i can improve the design a bit before carving ally or steel (thinking ally for the finished plate) I'll have to check the T pistons to see how much meat is in the crown, I hadn't considered fitting tops to them.

GG I'm off to the shops for some modelling clay to do a reverse version of the piston that is the adapter bore .. then I can carve away sitting at the stove

 

I am confused. Maybe confused with different site. Are u really building top of piston or building quench in conversion plate? If building plate seems that where put quench. Calc space needed for compression ratio you want, start high grind away to lower ratio. Question, modern gas with no lead hard on value seats, will u do steel inserts or just additives to gas.

 

That is a good idea, Mike, iffen you can keep the plug unshrouded, while retaining comp. Definitely will be a "closed" chamber. Other than 2 head gaskets - like shimstock steel or dead-soft copper, + the need to use a flow bench to get your chamber shape correct to work w/the ports/seats arrangement(s), I can't think of any drawbacks. Well, at least one: a huge amount of head-land space that doesn't help in the power/torque/emissions/fuel-economy arena. Although your top ring probably will never get hurt... . Heart-shaped chamber, here we come. Or maybe a semi-hemi. Or, depending on how you can finagle both the piston ring->crown area & the thickness of the adaptor, esp in the cc area vs total thickness of the plate, you might end up w/something approximating the LS chamber. But I think you'd need similar ports to make it work. Be very careful w/the valveseat + seat-entrance area no matter which way you go. It will make a difference. Time to devour David Vizards' Headwork Book, which has a very cheap - but effective - flowbench setup. You'll like it. He doesn't cover Endyn or Singh chamber work. I truly wish he had explored that. But there is so much good info there, you'll be busy wondering which way to go... . Hope you get on this, finish it, post it, + dyno work, then real-life experience(s). Should take, what... a couple of weeks... ? .
Marcus...

 

Been following along Quietly soaking this all in !! Although likely beyond my skillset and slim chance of ever finding a head .My father left me a 27 T which he had put a model a crankshaft and rods in and T transmission.
Was pretty smooth running motor (balanced )
It picked up a vibration (not major) but definetly noticable ,increased with rpm.
Talked to a few people that suggested I check the centre main . Sure would have liked to try a better head on it .

 

Sorry for the confusion, I am building a conversion plate which I intend to mill the bore area out to leave as much useful quench/squish area as possible and aim for around 7:1 CR, we have also been discussing using the Olds head on Chevy 4 's that don't need a converter plate so would benefit from a modified piston, such as the one that GG has mocked up with clay.. hope that clarifies

 

I Took the tarp off my old 1940's belt drive mill yesterday and started to give it a clean up, i'm off to our local smiddy in the next couple of days to see if i can score a lump of steel to play with (can't see me getting a lump of ally locally, and have a couple of new cutters on order, I think I've got to the stage where I should a Mk1 in ply wood then try it in steel. I'll grap a copy of the David Vizard book, Ive been heavily reliant on Phil Irvins Tuning for Speed up til now! A couple of weeks sitting by the fire with a brew and a book suits me fine

 

hey WR good to hear from you, putting an A crank in mine is an option for later, but I reckon I'll save up for a counterbalanced A spec SCAT crank with pressure fed mains, especially if I can get significant power increase with the OHV set up, i don't think the stock crank will last!

 

Jumping way ahead of myself here .. one of my other T based projects is a twin motor straight eight T, see the link below. Ive been working on (on and off) for a while. Its under a cover just now as I've been concentrating on renovating the cottage at our smallholding so we can get moved there in the spring.
Anyhow.. the thought occurred to me that once Ive got the adapter plate sorted out and proven using it in my Gin Runner T , (see below for it's build thread) I could use the same process on the TwinT with one long adapter plate linking the two engines (to help stiffen the whole lump) and a one piece rocker cover. Its highly unlikely that i will find another 3 port Olds head, but I do have a 2 port '28 Chevy head (same bolt pattern) and I have found another for sale at a fair price .. more food for thought!

 

Now that is an interesting concept. Top and bottom plates to stiffen your 2 blocks, and adapt the overhead heads at the same time. It's mind boggling! Keep posting.