more stuff to mull over and, perhaps, figure out. I started this off my post on another topic that was getting off topic due to me .

So I was asking about how the awesome pistons and such from TMI would work with smaller cams- I've attempted to get that ball rolling before. The possible concern i have is folks like me who know some but not enough start piling parts for a low end motor...gets advise towards, lets say, a comp xe262 cam which is more agressive than the 255deh but still mainly low end grunt. He also decides to use the tmi pistons for 9.5:1 CR with stock heads. (or could be the other 9.5:1 pistons for the aussie 2v heads-either way same possible dilemma)

So junior get the parts and puts them together and ends up with a motor with a whopping 8.6:1 DYNAMIC or operating compression. The problem is that the guide and common knowledge will put you to burning 97+ octane. and not many people are wanting a low end torque monster that needs race fuel to run. Quench will help with some of that and i guess i'm wondering how much help.

More specifically i'm wondering if this is, in fact a worthy topic... I know Tim at TMI helps folks put the build together and those arn't the ones i'd be worried about. It those, like me, that red and ask and grab parts and read and 'get er done'....someday...maybe.

I've read a lot of posts where folks are recommending the 255deh type cams for the awesome low end and, in some cases it includes possible use of high compression pistons- beyond the badger's 9:1.

Thats what i ended up with (needing 97 octane) only i was expecting it...not quite that high but it's cool, even better as I'm going with propane.
So where am i wrong yada yada yada.

 

Nothing wrong, it is just that pesky dynamic compression and todays crap we have for gas. If I remember right regular back in the 70's was 91 octane, premium was ~100 octane and the Phillips flight fuel super premium gas I used with a 12.5:1 FE engine was 115 octane. It also had lead in it. I don't know if the gas will get any better or worse as far as octane over the next ten years.

I don't know if there are any fudge factors to use if an engine has squish in figuring dynamic compression. Danlee may be able to come up with some insight on that subject.

Polishing the combustion chamber is supposed to help with detonation but how long will that last before combustion deposits build up? Piston coatings and head material also enter into the picture. An aluminum chamber allows some of that compression heat to escape so higher compression would be allowed. So how does that figure into the dynamic compression??? Lots of questions...

With open chamber heads there is no chance for squish so with my present head and Ertel flat top pistons I have not factored that in.

 

I'm thinking water injection, just in case.

 

and then how does squish equate to propane. flame propigation due to design etc- basically we need builds with these components to see what the limits are.

Is it safe to say that in many ways were at the point of just beginning to figure out the quirks of the 400? There should be some squish info on the cleveland performance heads but even then numbers change due to stroke etc.

We eventually should have a database on what pressures and parts work best at different octane levels. I don't think I'll have a very good chance of burning 92 with this build and i switched thinking i would.

 

Longer rod lengths slow the piston down at TDC, and speed it up at 90 degrees. The slow piston travel will increase the chance of detonation.

The guidelines I have are from David Vizard, and were probably developed from a SBC. I assume that his motors had quench, but shorter rods. I assume 8.5:1 dynamic to be absolute max with iron heads, but a safer DCR is around 8.2:1 for 93 Octane. However, I believe that alloy heads add at least 1/2 point to the safe DCR. CHI and other heads with fast burn chambers will be even better, but I have no hard data to back that up. I am building my 434 with 8.5:1 DCR, but I am not entering it in the Engine Master's competition.

I believe that propane acts just like 105 Octane gasoline, but has less energy.

Dual fuel motors are not very efficient on one fuel or the other or both depending on the trade-offs.

 

right...but from what i can gather a motor that would need to burn 93 would be a solid propane motor and I'd set up single fuel either way....but 8.7 dcr should be a great propane build - still enough room to pull loads etc and not run too hot...still wondering where the calculations differ and why (silvolite and your site).

Why not the challenge? time , $$, both?

 

I am only interested in having a great street motor for my '53. I would have to build another for the challenge, and spend a lot more money.

What is the difference between my site and Silvolite?

 

about .3-.5 dcr depending on calculation.

 

Who is highest?

 

I checked out the KB-Silvolite site. They ask for the IVC @ 0.050" and then add 15 degrees, my site wants the IVC at 0.006" or seat. It makes quite a difference with some cams, but less with others. It depends on how close to 15 degrees it takes for the Intake valve to close from 0.050" to the seat.

If you just plug the seat IVC into the Silvolite site, it will agree with my site. My site calculates the IVC @ seat directly from the seat to seat duration.

 

Those differences are probably why the Desktop Dyno wants seat-seat figures and approximates the ramp rate (and therefore the .050 figures) from the "lifter type" information which most people get wrong. They would probably do better asking for both sets of figures since most cam manufacturers specify both. Some do spec S-S @ 0.006 and others use 0.004 tho, but they could even have a selection for that if it made a big enuf difference.

It would be interesting to have selections for quench and head material with some data to back up the equation differences.

 

your site was higher. I was between 8.2-8.4 on the silvolite site and got 8.68 (or 8.7) on yours.

The difference is notable and i have a feeling yours is closer.

 

I have a program called Dyno Sim, which will let you use either seat-to-seat or 0.050" or both. The most accurate results come when you use both numbers.

I doubt that there is much difference between 0.006" and 0.004".

I would put in selections for quench and alloy heads If I had some data to back up those selections.

As far as selections for 0.050" goes, I don't think that it is accurate enough, and the seat-to-seat results are accurate enough for a free site. I calculate the seat-to-seat timing, so the user doesn't need to know what it is.

 

Desktop dyno allows either figure but not both and they prefer S-S.

I doubt there is either.

All I have seen is theoretical musings also, no hard data.

D-dyno likes the S-S figures also for the same reason.