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'78 W72 400 Dyno Results
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We thought we'd share this in the Street Forums. Dan had a good dyno session last week with the W72 400. He rebuilt the original numbers matching engine with .040" over Icon forged pistons w/4.5 cc valve reliefs that are .005" out of the hole and with .045" x 4.328" Felpro head gaskets to provide .040" quench depth. The 6X-4 heads were minimally cut for trueness and measured 92.45 cc's average for an final static compression ration of 8.75 to 1. Dan replaced the cast rods with forged Eagle H-beam rods. New 1-pc valves (2.11/1.66) with CC dual springs were installed. He had a Summit 2800 cam (204/214/112 @ .422"/.444" is pretty close to the original W72 cam specs) on hand, so was utilized, along with new 'old' Crane hydraulic lifters along with a new Melling 60 psi oil pump. The one modification/upgrade was the use of factory D-port ram air exhaust manifolds with the 2.1" outlets with Pypes 2.5" mandrel headpipes. The original 17058263 Q-jet on the factory cast iron intake with the EGR system and plumbing were reinstalled.
The base (and all) pulls were made with 42 degrees total timing in by 3000 rpm, 45 primary rods/74 jets/CH secondary rods on an I hanger. The 3rd (and best) base pull made a corrected 360.3 hp @ 5000 rpm/456.1 lbft torque @ 3600 rpm (351.2 hp/444.5 lbft uncorrected). The correction factor was a low 1.026 as the weather conditions were very good...low humidity, high barometer, and cool temperatures (65 in dyno cell). After rejetting the carb to 40 primary metering rods/72 jets/DA secondary rods on an 'I' hanger (same total timing at 42 degrees), employing the 'big' dyno room dumps for the headpipes, and installing the air cleaner base, the max hp jumped to 371.4 hp @ 5000 rpm/459.2 lbft @ 3600 rpm (362.0 hp/447.6 lbft uncorrected) on the final pull (#14). The highest torque reading was on pull #13 at 460.3 lbft. This engine surprised us by exceeding our first 350 hp/450 lbft prediction. Pretty good for a smog motor! Dennis |
That’s very nice!
Surprising numbers seeing as it was not even 9 to 1 compression and it was driving its own water pump in the test! To make that level of power it would seem that intake flow wise the motor was using 180 cfm out of the about 208 average cfm that those heads flow. I would be interested in what muffler might have done to those numbers in regards to that 8.75 comp! Congrats and thanks for posting it! |
Nice build, thanks for sharing
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Nice build! About what I have in the 81 except a Peformer intake and a 73 Qjet.
Big WP pulley! |
Very nice!
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Nice numbers! Just goes to show how well a basically stock engine with the right combo of parts can run.
I'm curious why you used 42 degrees timing and didn't change or experiment with it? That seems high...? |
..good results but seems for me a but high for such a tame cam ....
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Dennis,
Thanks for sharing some more information. Dennis posted this in the race section. Quote:
Stan |
Interesting..I've always thought those engines were underated..many enthusiasts get hung up on the low net hp ratings. Also combined with the lazy gearing most came with from the factory. I've always found on those low compression engines cranking the timing up in that 40 degree total or higher range works well.
My son's car with a worn out stock 400 with 342 gears mild convertor full weight ac car dips into the 13's easily. |
Really impressive numbers for that small cam and low compression
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Dennis |
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Dennis |
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Dennis |
Thanks Steve25, PAUL K, Skip Fix, and dragracerx2813 for the compliments!
Dennis |
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Dennis |
That would make a great daily driver,thanks for sharing
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Hmmm. And 400`s don`t make torque.:rolleyes::)
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Figure the NHRA stockers with a 78 motor are running mid 11s!.
The Summit cam in the 400 in the 81 degreed right on "dot to dot". I built the 81 car out of someone else's stalled 301T to 455 SE TA and extra parts I had collected from the 78 (HO oil pan) for the kids to drive to high school. So I did not want it to have too much HP! Son never got used to a car with a carb and a choke in the cold! Put a Shaker hood and extra Shaker scoop on it this summer. |
Wo….pretty darn good!
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I know you have the dyno sheets prove it but I'll never understand how a low compression motor with low performance Dport heads and a smaller than stock camshaft can make the same horsepower that was claimed on a factory assembled '60s high compression motor with Ram Air heads and manifolds.
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The way we measure horsepower has changed ?
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I was fortunate to have access to a Clayton Rear Wheel Dynometer at the college down the road from where I lived. They had a Automotive program there. A/C work, Engine work, Chassis work, some welding classes, etc. On the Calibrated Clayton Dynometer several vehicles that the Hot Rod Boys owned were tested. 1) A 375 hp advertised 396 1966 Chevelle made 285 rear wheel hp. 285 hp times 1.15 = 327 engine horsepower. the 15% adder is the typical drop from engine to tire hp loss. The 375 HP rating was probably correct if you tested the engine without the water pump/fan drag and the accessory drag. (Power steering). Looks Dead Nuts on the money to me. Tom V. |
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Tom V. |
In a few cases I think they were under rated because of insurance. In most case I think the engine tested by Pontiac was select fitted parts and not a mass produced engines. Don't Royal Oak sell thinner head gaskets to get the CR up? How much farther down the bore are the pistons on a production engine from the blueprint spec?
Stan |
Probably the only engines that could be called under rated would be the 73-74 455SD engines.
Tom V. |
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Yes, most engine dynos still use the SAE J607. The car manufacture in the early '70s changed SAE J1349. I believe some chassis dynos also use SAE J1349. Stan |
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I dont claim to be an expert and have no problem with your disagreement... as state, I was under the understanding that was the case.... I've read ( interweb facts of course) that was the case... I drove a bonestock 68 bird with a 400 and It sure felt like more than 330ish... seat of the pants kind of thing.. |
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Looks to me like Steve Linden matches everything I posted except for 1m FACT.
The rear wheel HP is not measured at the Axles/"Brakes" unless you take the tires and wheels off the vehicle. Tires do consume horsepower. A thing called rolling friction. So the driveline has to include the tire contribution. Emissions people (EPA and CARB) require on the track confirmation testing to assure the Coastdown) numbers used to dial in the dyno rolls matches the actual road measurements. I did Coastdown work for Ford and supplied the data under my name to the EPA as the "Coastdown Test Engineer". I did the larger Trucks, F-150 thru F-350 vehicles and the Econoline vans. Other Engineers did the Car platforms and the Small Truck and SUV type vehicles. If the EPA/CARB was not happy with our numbers, they witnessed a reconfirmation of the track numbers. Most times it was vehicle to vehicle variability and the track numbers were the final numbers used. So back on the HP numbers, Steve Linden is correct on 98% of his post. Thanks Steve C for the link. Tom V. The AERO Contribution was confirmed at the Lockheed Wind Tunnel at Atlanta Georgia. |
25 seconds with a needle nose plier on those early FB 330 hp motors and you did then have more than that amount of HP!
Removing the limiter they had got you the 350 hp motor. |
Either the RAIV was under rated or the RAIII was overrated sine there is no way only 4 HP separated the two.
I remember an old Roger Huntington article where he had the factory dyno curves for some 60's hipo engines. If they wanted to rate conservatively they pull the HP from below peak. For instance the 426 HEMI was rated at 425Hp @ 5000 rpm when it actually peaked closer to 6000 and 470HP. Factory advertised ratings were just that, advertised. |
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I digress, I wanted to comment about something else entirely; I noticed this: Quote:
Because unless there has been another rule change, the rods alone should disqualify this motor... Also iirc this engine should have had an advertised compression of 7.6:1, and if I am correct this would be a bump of more than a full point - which should again make it disqualify. I have not read of any builds here that have the piston out of the hole, most are (if my memory serves me) about 0.020" down so that was interesting for me to read. I normally read that with the piston down and the thicker fel-pro gasket, that engines like this often yield a marginal drop in compression; granted the overbore helps kick it back up; And in this example the reduced cc valve reliefs would help too - I cannot off hand recall the size of the cc valve reliefs in pistons from this period - can someone post this to help me out? This is pretty cool to see the honest to goodness power that can be made from a very stock appearing motor. You guys sure do some interesting engine builds! |
This is pretty cool to see the honest to goodness power that can be made from a very stock appearing motor.
[/QUOTE] There is a lot more power to be had in the F.A.S.T class.. stock appearing engines that make big power... |
Folks consider this tid bit.
A 426 Hemi tipped the scales at 843 pounds!! It needed every spec and more of that 425 hp rating to really beat up on a well tuned RA4 engine! |
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This is exactly what they been doing for sometime on high HP cars. They use a hub dyno. It eliminates the tire slippage and give much better results Stan |
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I don't know how long people have been using them. I first heard about them 4 or 5 years ago. A few years ago there was a nice video on Tommy Youmans' car when it had the Warp 6 Pontiac engine on a Hub Dyno. Stan |
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Seems the hub dynos are the new thing... I had mine dyno'd on an old school chassies type.. pretty much destroyed a set of slicks... when I'm done with my new build, it will be on a hub dyno.. I can't afford to ruin another set of slicks... |
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Before I figured out my plan for my car, I was always faced with the "well I could do this" scenario, which kept the scope of my plans somewhat muddied... I decided to stick with the PSMCD because this limits the scope of what I'm going to, or willing to do to my car - and in doing so, it also theoretically keeps my expenses within reason. This was a key factor why I sold my 455 last year. |
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Axle-hub type dynamometers have been in operation for 45 years.
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I've only seen them in the last 5 years or so like Stan said... Only dyno I'll use after my last experience.. |
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