427SO Blue Thunder motor dyno #'s

[dlampe]

Let me share my build first.
.017 over 68 sideoiler
stock crank, H-beam rods, JE dome pistons 9cc shaped to fit combustion chamber, 13 to 1 comp.
Crane cam solid flat f-252/3574 lift at the valve 629,640 adv dur 288, 292. I think 108 center line.
Holley HP from AED supose to flow 910cfm wet, 88primary, 98 secondary, 5.5 PV
Crane roller rockers
Blue thunder dual plane intake matched to blue thunder yates style heads. std FE size manley valves (2.19x1.8 I think) 5 angle valve job match ported and polished by hand by my builder.

All of our pulls are SAE. This is a dynojet chassis dyno. The first pull was 369HP. I let a tear roll down my face. We were running lean at 3500rpm. Switched to a new holley 110gph mechanical pump and opened it up for 1/2 in. lines (From tank to carb). We finally got the A/F ratio acceptable then ran the timing up and down. The second pull was 396HP. We checked the timing and my initial was only 8degs with 21 in the dizzy for 29 total! So I am thinking thats the problem. We set the intial at 14deg, pulled again, same, same. We finally set timing at 34 total for max torque and 3 less HP to land at 407HP and 428TQ. I think that is really low for what I have. Street motors make more than that on pump gas! What could I have missed to find the rest of the horses?

[Anthony]

407 on the chassis dyno I would think would be about 450-475 at the flywheel.


Did you index the cam?

Does the guy who ported your heads have a lot of experience doing this? with Fe's ? Did he flow them ?

Did you index the crank timing mark? At TDC, my indicator reads 1 degree advanced.

How restrictive is your exhaust?


For standard FE heads/chambers, from what I see other people post, I think timing is optimal at about 36-40 degrees. I don;t know if your BT heads require different timing settings, but on the dyno you should be able to figure that out.


Has your engine builder dyno'ed other street FE engines, 428's. 427's? What HP has he got with them?

[Excaliber]

Sounds like rear wheel horse power is around 400? Not bad, but from the cam specs, head\intake combination it does sound a bit on the low side.

I assume 8.8 or 9" rear? Top Loader trans? Some combinations soak up more horse power than others (IRS with Automatic for instance). Removing my sidepipes made a HUGE difference in horse power, by the way.

Quote from Keith Craft regarding Blue Thunder heads:
"Well this depends on wether you try to run them the way they come which does not work very well because it has the valve shrouded. We had to open the chamber up quite a bit around the valve since the design had the valve seat area kind of sunk and did not let the head flow till the valve was opened to about .500 lift. The chamber design we use and CNC into the head comes up to about 88CCs. There is a lot of deck thickness in the head which is good since we needed to get to 68ccs. We had to mill the heads about .100 to get there. This was on the High Riser style head but would be the same on the Medium riser style head as well. Thanks and good luck, Keith Craft"

[dlampe]

I am running an 8.8 IRS with a TKO 600. My sidepipes have a 3in. ID from stainless specialties. I don't know for sure if the cam was indexed. Rick Kirk did the build and he is an FE legend. That doesn't mean he couldn't make a mistake. The timing was ran from 29 to 38 deg. and 34 is the sweet spot. Why didn't I have a big jump in power when we bumped the timing from 29 to 35? The carb is set right. We did about 15 runs to get the jetting right. I would have thought this cam would have been good to 6500? I have read Keith's post on BT heads before but I also think he said they flowed as good as the Edelbrock heads stock. Rick Kirk did the porting and he did it by hand, not CNC'ed. Having said that, he really knows his way around an FE. Does everyone use SAE power numbers? It is just a little frustrating.

[Excaliber]

I think most h.p. numbers you see posted around here are flywheel horse. Thats why I suspect 400 rear wheel horse is reasonable.

[Power Surge]

Your numbers are right on par for what you have. People have a very big misconception of what their car will make on a chassis dyno. The two biggest factors for being dissapointed are:

- Being told the motor makes XXX hp on an engine dyno, and

- Not knowing the reality of drivetrain loss

I have guys coming in all the time with "500hp" motors, and they expect big numbers at the wheels. The fact is, their motors don't really make the power they think they do, and then their engine builder usually has no clue of real drivetrain loss.

Something else to factor in, is even if your motor DID make say, 500 hp on an engine dyno, that's with real long tube headers usually. Cobra sidepipes cost a good amount of power. Case in point... Had a Cobra here yesterday, with a built 428. Customer was told the motor should make about 475hp. First pull, car made 297 at the wheels. Now, his A/F was very rich, and I told him he'd pick up some power if we adjust the jetting. Of course, he wasn't going to get 100hp from jetting, but that's where you start. When I went to put the probe in the tailpipe, I couldn't get it into the muffler part of the pipe, and found that odd. I also noticed that his car was much quieter than any other Cobra I've dynoed. Upon further inspection with a mirror and flashlight, we found that his side pipe design was SUPER restrictive. He had 4 two inch primaries going into a 3.5" muffler, with whatever inside it, and on the exit side, there was a big baffle plate with a small 2" pipe sticking out of it. So basically, 4 x 2" in, single 2" out. Not good for power. So let's factor all this in.... 475 hp - 15% drivetrain loss for his toploader and Jag rear give you 403rwhp. I estimated he was losing about 70hp through his side pipes. That's 330rwhp. I guessed that he may pick up about 30 hp in jetting, from his 297. We changed the jets a few times, and what do you know, 330rwhp .

The funny thing is, I've had a lot of FE powered Cobras on my dyno. Not ONE of them has broken the 400rwhp mark. The ONLY Cobra's I've had break the 400hp mark were two stroked 351 cars (a 392 and a 406).

So given all your info, I would say you are right on the money.

[dlampe]

That does make me feel a little better. I think I mentioned that I was using pretty open pipes, the set up that another forum member was documenting with the stainless specialties mufflers with 3 in. ID. What do you think about the fact that when I bumped the timing, I only got a nominal bump in horse power? I also have a problem under hard braking and keeping the motor running. My floats are great. What else could cause that problem?

[ERA Chas]

I think your cam is too big for your heads and carb. The shrouding issue is very important. If you mean your LSA is 108deg, you're bleeding too much cylinder pressure. 13.5 on race gas allows much more spark lead, sooner.
My 427 made 467WHP on open headers, 462 on your SS sidepipes. It has 1308 cfm induction, Shelby Stage II's with 2.25" intakes and a .613/.633-244/255 with 110 LSA Ultradyne. Spark is 38-40 deg (same power) all in by 2600. Compression is 10.33.
Your stalling problem is improved by installing vent whistles on the metering blocks and cured by sealing an air pan to the hood scoop.
Good luck,

[Excaliber]

The book that came with my motor when I bought the car indicated a 100 horse power loss with the side pipes in place. That was when the motor was pretty radical, BIG roller cam and 12.5 to 1 compression. Unbolting the side pipes at that time was just an amazing difference in the power level you could FEEL.

Since then I've gone with a milder flat tappet cam and 9.8 to 1 compression. Now when I run without side pipes I can't really "feel" the difference. Horse power is all about breathing, where ever the "bottle neck" is where the horse power is lost. Apparently I'm not flowing near the exhaust cfm I used to and the side pipes can handle it easier.

[JustOne]

Are you planning to run a 13:1 motor on the street? Were you running race gas on the Dyno? What RPM was the Peak power and what was the average power from 2500 to peak? You loose about 20% to the wheels, so I think it is safe to say you are making 475-500.

[RICK LAKE]

Dlampe You are not sand bagging for the Run and Gun are you?? I would start with the exhaust like others have said. You can stick your hand in the turn out and feel that 3" opening? 13.3 is high for street D. When the cam was setup, I know that some cams are made with a 4 degree retard in them. What flywheel are you running? Steel or Aluminium? This will make the motor respond quickier. You may want to run with a A/F meter in the car. Summit has them on sale till the end of August for 3 and change. Alot of guys that are running FE motors have the timing in the 35-38 total when running and all timing in buy 2500 rpm. Mine is 36 with the stock motor. I built a tork motor not HP. I will talk to you later. Rick Lake

[dlampe]

Rick, I set the timing on the dyno at 34 deg. That was the sweet spot. We also did alot of work to get the A/F ratio right. I don't know how the cam is setup. Is there a way to check that? I am running an aluminum flywheel as well. I really wish I knew how much compression I was running. The blue Thunder heads are 66-68cc's stock. We had to free up the intakes and shave the dome on the pistons from 9 to 5cc's. I only run race gas, 110 leaded throught the motor now but was thinking about a 50/50 blend. I feel like I have the right peices and it should be doing better.

[dlampe]

Dyno pictures in my gallery!

[Burgs]

off topic a bit,....

Rick Lake, or anyone else for that matter, regarding the wideband A/F meter in the car,..... which side do you monitor, or both with two meters, or is it not that critical?


back on topic,....

Dean, any idea what brand dyno was used? The "Mustang" dyno gives more realistic, (lower as much as 10%) numbers. As others have said, you're around 500 flywheel, give or take. If the goal on the dyno is to maximize the tune of what you have, which I'm sure yours is, the best dyno machine to do that (Mustang) produces lower numbers, but more realistic, road like, conditions, best done without the "tricks", as you will normally run it. If you want the highest dyno numbers, find a DynoJet, run up the tire pressure, loose the air cleaner/pipes, throw a couple of ice bags on the intake manifold,... ect.

I would assume, your builder knew what he was doing with the heads, cam, and compression ratio. What were his goals for HP/TQ?

[Burgs]

oops, well just saw the "DynoJet" numbers,... there goes that theory

[Burgs]

A little fat down low, but that shouldn't change the top end much, if at all. I'm not sure if you can correct that with the carb or not. That torque curve looks great. (Dean, please remember I'm a noob and have zero experience with these set-ups!)

[JustOne]

Looking at your dyno graph I am a little surprised that the motor made peak power at 5600rpm, and was about the same from 5200 to 6000 rpm. These are results I would expect from a smaller cam. What horsepower and operating range did your builder tell you this motor should run in? I know that going from 10:1 to 13:1 on a dyno is usually worth 50-75 hp, and with a 13:1 motor and the BlueThunder set up I would expect you to be in the 600-675 fly wheel HP range. I would check to make sure the cam is degreed in properly, then recheck timing, and maybe have the heads flowed if you haven't already.
On the chassis dyno a power drop of 100 hp seems to be common, with some as low as 75. I think the mufflers you are useing are very good and you shouldn't get more than a 15 hp loss if any running open headers.
For peace of mind either buy or have a forum member run your head data with flow numbers, cam, and induction through desktop dyno and see what you come up with. If you decide to buy the software I think it is only $50.

[Excaliber]

The heads could still be a big variable. The only way to know for sure how they work would be to put them on a flow bench.

Your cam:
Recommended RPM range with matching components
Minimum RPM 3600
Maximum RPM 7200
Valve Float 7800

Sounds like you got a bottle neck in there somewhere. The cam does specify 13 to 1 as recommended. This IS a "radical" cam. With my roller, high rise heads and high compression flywheel horse was well over 600 (open headers). Worked out to a VE of over 100%. My rpm range was 4000 to 7000 with valve float at 7400. Pulled strong up to 7000.

It has been shown that the accelleration ramp of the cam profile is more important than the peak lift numbers. If the Blue Thunder heads are not "quite there" at lower lift they would not start working "good" until peak lift. Perhaps, to little to late?

I don't want to be the bad guy, maybe your motor is doing just fine! Just throwing out some possible "anamolies" for consideration. Hard to "blue print" a motor after assembly!

[RICK LAKE]

Burgs I am going to run the A/f meter off both sides. Right now I go by my O2 sensor for my FI system. The trick is to get the sensor in the main stream of all the cylinders to get a good reading. EGT sensor are good also for they give you the hottest and coldest cylinders when the motor is running. I have a little more fuel going to either 5&7 or 6&7 for they are the leanest cylinder in an FE motor. This is the great thing about FI system that come with the extras for each cylinder. Give me all the numbers you can I will run your motor on both Dyno2000 and Dynosim and see what comes up on this. If you had a print sheet of the cam that would help. Rick Lake

[Burgs]

Rick, I've got the wideband setup I ran on my Acura when I was running the blower. The v-6 headers went into a y-pipe, so a single sensor, and display, was all I needed. If you run seperate sensors on both sides, don't you need a second display, or are you logging the info from both sesors to evaluate later, rather than running a dual, real time display?

(Dean, please excuse the short side trip.)