Dyno'd the 71 yesterday...

[lowriden58]

well i finally broke down and trailered the beast to SGS in dillsburg PA.

before i show the results let me fill you guys in on the specs

350 bored .030 (10.5:1 comp)
AFR 195 heads 64cc
1.5 rollers
284/296 comp cam 507/510 lift
edlebrock airgap
holley 750 dp
Msd HEI
hooker comp l/ts
electric fan as well...

trans is a TCI streetfighter 350
3k B&M vert

rear is 410 posi

timing was set at 38* with vac plugged and currently still plugged


i really think my numbers are seriously low...

300 RWHP
293 RWTQ
Air/Fuel was 13.1 across the board and right on the money.

am i missing something or is this right on?

[71Dragtruck]

Don't forget your going to loose over 100hp through your drivetrain, likely closer to 150hp with an automatic tranny. Add that back on and it's looking good for the parts you used.

[lowriden58]

well ive always known that a auto loses alot more power but man that just seems really low to me

i am planning on a 200hp NX kit in the very near future

[jkaylor68gmc]

I guess you lose 20-percent in the driveline so not bad.

BUilding rwhp is hard, you would be surprised at what it takes to make the power. SPinning tires only seems fast.

[swb85]

Don't read too much into chassis dyno numbers, especially with an auto trans & loose converter. Take it to the track and get some time slips....that'll be a far better indicator of how much power you're making.

[Billla]

I generally consider about 18% drivetrain losses for an automatic, but completely agree that dyno numbers can be misleading based on a number of factors.

Still - yes, that seems low to me. You didn't note if the AFRs were Streets or Comps, but I assumed streets. I assume the cam is the XE284H? And finally - what RPM were the numbers achived at?

My interest centers on the cam - it's defnitely a high HP cam; I did a quick DD Advanced of your combo and reached 450 FWHP @ 6500 RPM. I haven't done the quarter mile math but based on your gearing it would seem that's in the ballpark. Those heads kind of demand a roller hydraulic, or roller solid IMHO.

I can throw some more research into the pot, but my quick take is a) I agree - take it to the strip and b) not 100% confident that cam choice is a good match for the heads.

[lowriden58]

heads are street #1040. ive been thinkin the cam isnt a good choice as well but right now ill just play with it to see what 1/4 times i get. i dont have the dyno sheet with me at work to see where the HP peaks but they did pull to 6500 per my request

[larry may]

Originally Posted by lowriden58

well i finally broke down and trailered the beast to SGS in dillsburg PA.

before i show the results let me fill you guys in on the specs

350 bored .030 (10.5:1 comp)
AFR 195 heads 64cc
1.5 rollers
284/296 comp cam 507/510 lift
edlebrock airgap
holley 750 dp
Msd HEI
hooker comp l/ts
electric fan as well...

trans is a TCI streetfighter 350
3k B&M vert

rear is 410 posi

timing was set at 38* with vac plugged and currently still plugged


i really think my numbers are seriously low...

300 RWHP
293 RWTQ
Air/Fuel was 13.1 across the board and right on the money.

am i missing something or is this right on?

Looks really low to me too. I agree with U.

btwLoosing 150 HP because of an automatic transmission...I do doubt that unless that number is a typo.Otherwise I smell a little bit of B/S on that comment!

[71Dragtruck]

Well call it what you want, take a motor and crank dyno it, then place it in a vehicle and add a water pump, power steering pump, and a alt. Then on top of that add a auto tranny with a loose non-lockup converter, spin a rear end assembly, brakes and a set of tires, then suck some nice warm underhood air into the motor ( even with hood open the vehicle is sitting still ) and see how much power is lost on a wheel dyno.

If anyone on here has crank dynoed thier motor and then placed it in thier truck and wheel dynoed it post up your numbers.

How much power do you think a drivetrain and accesories eats up? Also how much power do you think his combo should make at the crank?

My ballpark guess would be (with what he's using right now) is 425hp at the crank, that about a 125hp loss with his drivetrain and accesories. I wouldn't bet any body parts on it but I would bet $20 I'm close.

[djracer]

Originally Posted by 71Dragtruck

Well call it what you want, take a motor and crank dyno it, then place it in a vehicle and add a water pump, power steering pump, and a alt. Then on top of that add a auto tranny with a loose non-lockup converter, spin a rear end assembly, brakes and a set of tires, then suck some nice warm underhood air into the motor ( even with hood open the vehicle is sitting still ) and see how much power is lost on a wheel dyno.

If anyone on here has crank dynoed thier motor and then placed it in thier truck and wheel dynoed it post up your numbers.

How much power do you think a drivetrain and accesories eats up? Also how much power do you think his combo should make at the crank?

My ballpark guess would be (with what he's using right now) is 425hp at the crank, that about a 125hp loss with his drivetrain and accesories. I wouldn't bet any body parts on it but I would bet $20 I'm close.

I'm on your side of that BET! I chassis dynoed my old 71 truck that ran 13.5o's and it showed less than 300

[RatPwrd72]

When I get outran by a Dyno, I'll get concerned about HP #'s at the wheel. For me, the drag strip is a much better tuning tool especially in a heavy ass truck where torque is more important that peak HP......

[71Dragtruck]

And I guess while I'm BSing I might as well go the full mile ruffle the hairs of a few more people and ask how a percentage of loss through a drivetrain works as a calculation.

By using a % of horsepower lost through the tranny at say a 20% loss, a 300hp at the crank motor would loose 60hp, and a 900hp at the crank motor would loose 180hp?? Why would the higher horse power motor take more power to spin the drivetrain then a lower horsepower motor?? Would someone please explain?

I know I should just let it be but well as usual I can't.

[Billla]

You're not going to ruffle my hair

Let's start by getting apples-to-apples. Completely agree that engine dyno numbers are useless in terms of looking at the power that will be between the framerails. Dyno headers, open exhaust, accessories (as noted)...an engine dyno is an initial tuning tool - not a power measurement. A chassis dyno is also a tuning tool, but one with all of the accessories in place - and so gives a better indication. So, yeah - the gap between RWHP #'s on a chassis dyno and stripped down engine dyno numbers are way different, but not so different when we consider the power the engine is making as installed at the flywheel.

For chassis dynos, I use that number as a rule of thumb, and as with any generalization it's suspect. It applies to street cars making < 1.2 HP/CID and IMHO it's a decent guideline. It doesn't apply to street/strip machine, nor a dedicated racing machine.

It's fair to call BS on this - but sometimes general guidelines are all we have and can help us focus the research/troubleshooting.

[bigjimzlll]

Chassis dynos and converters just don't play nice together.
They can be useful as a tuning aid but are no substitute for the drag strip or engine dyno.

I'd say our combo should be in the 400-425Hp range. Should run mid 12's all day long

[jeffspower]

I don't know diddly about chassis dynos- so here's a dumb question. How does a chassis dyno factor gearing & tire diameter? I'm assuming it does somehow, or 2.29's & 44" meats wouldn't fare well vs. 6.50's and donut spares with the same engine

Wouldn't you pick up power by going to a smaller carb? Seems too big for a 6500 RPM 350.

[hotrod 80]

480 engine dyno
364 chassis

just use the chassis dyno as a tuning tool , get a base line and inprove on it . Drag strip will give you real world #'s

I started @298 hp on the first pull (vey humbling). Timing first , then carb . This was a new combo and alot of untested parts . 11 pulls later power dropped off . Went back to last pull and duplicated it . Truck went from 12.28 to 11.75 in 1 week . The guy running the dyno was learning how to change jets from me . He had never seen it done , he works on all fuel injection cars . This also was a mustang/lightining shop . i meet the owner in the staging lanes @the track . I set the a/f ratio @12.8 and he said the curve looked better than most of his fuel injected curves . Nice and flat .

[Baresteel10]

I have always used these equations to convert crank horsepower to Rear wheel horse power

For an automatic their is a loss of 30% and for a manual its only a 16% loss through the drive train.

Stock I think the 1970 402 found in these trucks had 330 so by multipling that by the loss of 30% from the automatic I was getting 231 RWHP

Crank HP X .70 for the automatic and .84 for the manual = RWHP

The automatic uses up more horsepower because of all the clutches and also the torque converter.

The manual just gets the power straight from the crank granted is still has to pass the flywheel and one clutch it just has less parts to move and less of a reciprocating mass.

I agree with billa on that they use no accessories when they dyno the motors. They use an electric water pump at the most I think and headers. Thats just my .02 cents

PS: The only numbers I am going to care about now are from the timeslips