This is more or less a duplication of the latest post on my Racing Engines 101 thread with some additional thoughts added . . . .
Here is a bit of free advice as my Holiday gift to everybody who reads the midget's diary.Since I get asked this on a fairly frequent basis, this is how I typically approach an analysis of an unknown engine: (say like maybe a Rover K . . . .
)
1) I run a geometry study for the engine as built, or as you want to build it, to reveal whether there is a "geometry" (typically rod length/stroke ratio) "issue". Poor geometry can affect the "flow demand", by advancing/retarding the point of maximum flow demand a few degrees, say 75/76 degrees ATDC Vs. 80/81 degrees ATDC. Unless your cylinder heads have "exceptional" low lift flow (doubtful on any two valve engine, especially with restricted valve sizes) this will negatively affect cylinder "filling/pumping" with the net result of a low volumetric efficiency and possibly a low bmep. Knowing the "flow demand" for the displacement, rpm range and V/E is critical to "useful" planning
2) I then flow the cylinder head(s) with inlet and exhaust adaptors by themselves. I collect the data with a software program to eliminate "optimistic" eyeball values & hand entry. I then also flow test with the manifold attached, with a radiused adaptor. I then add the carb/whatever to the manifold and flow test the complete inlet tract. I know this is a lot of flow testing, but it also ISOLATES components so that any "issues" can be "identified". Knowing the flow test results for the complete inlet tract allows you to calculate two important pieces of information:
a) Does the inlet system flow enough to fulfill the required flow demand at the V/E and rpm the engine needs, or is being designed for?
b) The total inlet flow allows you to "predict" the peak bhp using SuperFlow's well published formula, INDEPENDENT of any other simulation software.
3) I then run the cam (or cams) profile with cam data logging software, although this can be done by hand, if it is done carefully. You can then "combine" the cam/valve lift profile with the inlet flow data to get "net valve flow data". This can be extremely useful, in my opinion, to evaluate differing cam grinds. It is also useful to know things other than the net valve lift curve, such as:
a) cam/valve velocity
b) cam/valve acceleration (not by hand)
c) cam/valve jerk rate (not by hand)
Most older, "vintage" engines have "packaging" limitations for valve train components, and it is helpful to know this ahead of time. BEFORE selecting some "killer cam" that breaks valve train components on a regular basis . . . . .
4) Once you have collected the basic data/info, THEN, you can formulate a plan to improve output, based on sound engineering Vs. limitations/rules/costs.
Calculate your bmep @ your peak torque rpm. Well developed N/A engines should make 195/205 psi. 185/190 psi is my minimum bmep for respectability as a professional.
Very well developed N/A engines can achieve 225/227 psi!! But this is in professional racing with multi-million dollar budgets for development and research . . . . .
As you have already guessed, I spend a lot of time on analysis, either via spreadsheet or with proprietary commercial software written for the industry. One word of warning though. "Good" software to perform analyses is expensive, $500.00 and upwards . . . . AND, that is just the first issue, if the "analyzer" has little internal combustion experience.
BTW, it may be difficult to accumulate some of this data for your "oddball" little jewel, based on its' "oddity". But you knew that already, didn't you? Just fabricate your own airflow adaptors from mdf sealed with varnish or lacquer. No whining allowed . . . . . . just do it.
It is also important to point out that when increasing an engine's output, costs rise at an exponential rate to returns. Sometimes raising the bhp output significantly REQUIRES commitment to a "system" of componentry that is a "cascading nightmare of costs". As in titanium valve train for example. In a non-professional racing situation, ONLY the end user (the check writer) can determine if the expense is justified. But you knew that already too.
And also, these are some examples of the type of additional analysis I've performed on a couple of threads besides the ones on the Milwaukee Midget's Build Diary:
A) Australian Belly Tank/SOS Build Diary, reply #3648:
http://www.landracing.com/forum/index.php/topic,862.3645.htmlB) XXO/BVGC '38 Chevy Coupe Build Diary, reply # 1497:
http://www.landracing.com/forum/index.php/topic,8271.1485.htmlThese types of spreadsheet analyses can be easily done to provide extra engineering "insight" into your special little jewel . . . . .
OK, this is the point where you now get to gather some data about what
you are doing. Then you get to put on your thinking caps, grab your calculator or sliderule and figure out where you can eke out some advantage or benefit for your particular powerplant, the way you are building it.
Keep in mind that data gathering and analysis can reveal some serious problems with a given build spec. The big issue seems to be that most of the time: "ignorance is bliss". When you don't KNOW the maximum load on a part, or the maximum acceleration forces applied to assemblies, everything is "great", right? Knowing this information ahead of time can prevent poor choices of development path and/or poor part selection choices . . .
Information, in and of itself, is neither "good" or "bad". My experience is: that once you start making information based decisions, you will also want to stop guessing about any engine related decisions . . . . JMHO.
And before I finish, I just want to make a comment about decision making. I have witnessed a few types of decision making in my career, I rate them in the following fashion:
1/ Information based decisions = * * * * *
2/ Science/info based guess = * * *
3/ Experience based guess = * *
4/ Letting your supplier decide what they "think" you need = *
5/ Wild a$$ guess = ?
6/ Hope for the best = ? ?
7/ Dartboard decision = ? ? ?
8/ Checking chicken entrails @ midnight = ? ? ? ?
9/ Other "Voodoo" or "magic" based choices = ? ? ? ? ?
The bottom line ALWAYS ends up being: Your engine, your wallet, you get to decide . . . . . CHOOSE WISELY . . . . .
Just a few additional steps in the preparation process, seems simple enough, don't you think?
Although you are on your own for devices that supply additional "brain cooling". I recommend tasty, fermented and chilled beverages and/or a beanie copter cap.
Best regards of the season to all, and
Fordboy