Took my 71 to my buddy's shop to try to troubleshoot a slight miss I am getting in the upper rpms. I also wanted to check out the AFR and make sure the secondaries were working on the q-jet. Suprisingly, the secondaries worked flawlessly and the factory jetting in the q-jet was dead nuts on as the AFR was right where it should be. We tested it with the air cleaner on and off and there was a solid 6rwhp gain all the way through the powerband with the air cleaner lid off. Anyway, here is the charts, the dyno is a brand new Super Flow but it also corrects to Dynojet numbers so I circled those for comparison sake.


This chart is with the run with the air cleaner on and one run with the air cleaner lid off.
Notice the drops in the pull, that is the miss I am searching for. Also notice how with the air cleaner lid off it doesn't nose over at 4800. Pretty interesting stuff.

 

BTW eventhough these numbers are quite pitiful, I was suprised they were this good. The engine has 142k miles on it and is a base 270hp L48 with a crane blueprint L79 cam, Performer intake, 1 5/8" headers and 2.5" exhaust going through a TH400 and 3.08 gears. I mainly wanted to test it to diagnose the missing issue and get a baseline for it before I swap motors and trannies..

 

Interesting info. If I remember correctly, you've put a few 1/4 mile passes on that engine where I think you were high 14's, right? That gives you a lot of data to compare with the new pieces.

 

Yeah some good baselines for sure. I went a 15.02@91 but it was nosing over at the top of 2nd gear and I would have to let out, then get back in it. Since then I changed to a 80gph fuel pump and it will pull solidly through the gears aside from the slight high rpm miss it has. I think its either the points or something else in the ignition. Plugs are fresh as is the wires, cap,rotor and the timing is locked at 36* total by about 3500rpms. Could also be valve springs as they have 142k miles on them and I BELIEVE they are the original springs. I am trying to decide on a crate motor, I was really thinking about the Year One 350, its the best bang for the buck but in reality, it will likely only give me about 100hp more then I have now and thats hardly worth spending $3k for.... I am thinking about buying an assembled 383 shortblock from someone, then slapping on some AFR heads and a Lunati Hyd flat tappet voodoo cam, I think I could make 450-475hp pretty easy and not be TOO expensive. Still researching engine builders. I don't want to spend more then $4k for 450hp......That is the limit as I have to buy a new BTO 200R4 tranny and converter also.....

I would like at least 350rwhp with a 2800 stall and eventually 3.55s...That should be enough for low 12s pretty easy in a 3500 lb car and still be daily driveable.

 

Sounds like a realistic plan. Don't forget to budget for a set of drag radials too.

 

cool post/ thanks. You made 200hp at the wheels so say with 20% loss by drive train that motor is making 160hp roughly.

The YearOne crate mnotr makes 400hp for 3000.oo If it has same 20% drivetrain loss its still 320hp...double what you have now.

and the new tranny may have less loss.... maybe?

rich

 

Curious as to where the max HP and TQ numbers are coming from. The graphs and charts don't show anything near the max numbers.



Rick B.

 

the chart does.

 

UH....you got your math backwards bro.. lol..... 200rwhp HP + 20% loss = 240 crank hp. My numbers are at the wheels.You habe to remember though, this is a TH400 with full accessories and stock fan. Parasitic loss would be more like 30-35%, that would put me around 260-270 crank HP and thats what it was rated from the factory at.....ofcourse mine has a little cam, intake etc but....its old and wore out so I was pretty impressed with it for what it is.

Oh and on the chart, the graph above was in Superflow numbers which is around 10% less then Dyno-jet numbers. On the full number charts I posted, it shows the DJ numbers(circled). It also shows STPPW numbers and those are reflected in the graph. Air cleaner on was 183hp STP(Super Flow) and 189 without the lid.

 

lol you are correct i went the wrong way with trhe math dude...lol

still 130 more hp for 3k on new motor is good deal...

 

ajrothm and all,

Very interesting stuff. Next week I have booked a racing shop to dyno my 71, 350/270 AT. - Just to check if it performs well. I have had my car for one year and don't have much tech experience.
Any good advice? Also, do you think I should change the spark plugs and wires in advance?

Thanks.