Dyno testing

[Michael Oritt]

A few weeks back I did a couple of pulls with the Courier on a rolling road setup. The fuel-air was was way off and in the limited time we had I succeeded in getting the mixture squared away to the extent that I gained about 25 ft/lbs of torque and 4 or 5 HP.

In any case I have arranged to have a significant amount of time--probably as much as I want--for next Saturday and would appreciate receiving advise on what I should do to "maximize the experience", both prior to and during the pulls.

Obviously I should get my carbs balanced and valves and timing set but what if anything else prior to the pulls? What about tire pressure? And what should I be playing with from pull to pull?

All help appreciated....

 

[Hap Waldrop]

Normally the only two things you can sort on a dyno, chassis or engine, is ignition timing an fuel mixture, so take whatever you need with you to be able to accomplish that. All our cars are SU carbed, so when I head to the dyno, (going tommorow with a race customer), I have my tools needed to make make carb adjsutments and other carb needles if needed, and my timing light and a wrench for tightening/loosening the dizzy clamp.

The biggest gain you can get form a dyno is pefecting the fuel mixture, by taking air/fuel ratio rading, I would suggest on race to shoot for a AFR number of 12.5-13.0 at WOT. You cna lso learn where the cam quit pulling, and that will tell you true redline, no need to ever go further than the engine makes power at.

Hope this helps, have fun at the dyno.

 

[Hap Waldrop]

Michael, here's the chassis dyno run we did the other day. The car was local SCCA racer in his MG Midget limited prep 1275, the LP engine rules are no head porting except 1" gasket porting, stock rocker arms, stock rods and crank, lightening/polishing allowed, stock HS2 carbs .450" total valve fit and 11.0 to 1 compression ratio max. We make a pretty good average of mid 90s with this engine formula at the rear wheels. The secret to these engines is flowing alot of stock cylinder heads and finding the best examples, Mike Miller and myself have wore out my flowbench checking 1275 heads, probably flowed 75 heads at this point. Anyway the guy built his own engine and it not making the number we used to seeing, but it's our first run on this dyno, so it could read low, we'll know more when do another LP 1275 engine next week or so, that I know exactly what is in the engine, and it should make more HP that this engine in the video. However the owner wanted to get the tune right, and know when he got to race track it would run, and not issue. I had him change his carb needles before we went to the dyno and I'm sure that made hugh difference and then tune the engine to AFR numbers I wanted to see, around 12.5-13.0 at WOT. I was able to pick the car up from the time we got there about 5 hp, I also advanced the the igniton timing a couple of degrees as well, in the end the top HO was 81.5 HP. In the end the car ran good, and th AFR numbers were accomplished, we did about 5-6 runs, and was in and out of the dyno with a one hour session, so it was good day at the dyno.

Here's the video of the final run

https://www.youtube.com/watch?v=fvIpLgVNDvo

 

[Michael Oritt]

All--

Attached find a file showing three of four pulls I did this past weekend on the Courier (MGA 1600 engine w/twin 1-3/4" SU's).

The first pull was done with 30 degrees of advance (shown) and when I went to 32 degrees (not shown) both HP and torque numbers dropped off by about five. I then cut advance back to 28 and 26 degrees (both shown) and you can see that the best result was achieved at 28. This surprised me, esp. as I have always run at 32 (gulp)! BTW Fuel/air seems to be nailed pretty well.

I am wondering why I am finding more power at what I would consider a low amount of advance? It has been suggested to me that my cam timing may be off by a couple of degrees and putting in two more degrees of cam timing will allow me to make better numbers with more spark advance.

i know it would be helpful if I included info on cam profile and present tIming but the fellow who worked with me when we assembled the engine has the notes and he is unavailable for a couple of days. In the meantime I would appreciate comments on this data and any suggestions re changes in cam timing or anything else.

BTW what is the rough conversion factor to use to convert numbers achieved on a chassis dyno to those that might be obtained on an engine dyno?

 

[Michael Oritt]

The cam profile is:

Intake opens 63 deg. BTDC
Intake closes 84 deg ABDC
Exhaust closes 53 deg ATDC
Exhaust opens 96 deg BBDC

Overlap at 0: 116 deg.

The assembler said he believes we set the cam timing with "4 degrees from centerline of lobes".

 

[Hap Waldrop]

Yep B series engines more so than the Midget A series engines like alot less advance igntion timing as the compression ratios goes up, when I raced the the Huffaker MGB years ago, Dave Tabor did a race head for me, we ended up at about 15.5 to 1 CR, that engine didn't like anything as for igniton timing over say 25-26 degrees advance, if you tried to run it even at 30 advanced it would blow a head gasket in quick order, B series engines defiantely like much lower andvanced timing than it's A series cousin as the CR rises, so your findings back up everything we've seen over the years as well.