Torque & HP Open Discussion

As we start to see all the discussion of winterizing it must be time to start talking about winter upgrades.

With the help of a few guys on the site(ReidP & TimB)and a program called Desktop Dyno I've made my decision and parts are ordered. Reid and I thought it would be interesting to post results of the sim dyno program for all to digest and maybe we could start a good informative thread regarding the gains/losses of certain known engine component upgrades.

So this is not just about my project I decided to post the dyno results of a stock 351PCM engine first and then a few upgrades and what people could expect to get in return.

We've also simulated a few other engines that guys are running as well as the 60mph Mustang so maybe we'll get into the 302 engine and a stroker or 2 later.



Graph A is a 351 stock 240hp PCM




Graph B is a 351 stock short block with GT40P heads.



Graph C is my 351 is it sits now, 351 .030 over, 9.3:1 CR, Gt40P heads, .466 Lift cam, 1.7:1 roller rockers and a Performer intake.




Graph D are the anticipated results of a top end upgrade. 351 .030 over, 9.8:1CR, RHS180CC heads, .466 Lift cam, 1.7:1 roller rockers and and Edelbrock RPM intake. The heads are being custom ported and intake/exhaust manifolds will be port matched but we don't have the flow data yet so these number are advertised flow rates.


So study the data and ask away, if you have particular performance items that you want to ask about we can set up a dyno for your engine, I'll let you know what specs I need to set it up.

M3Fan wrote: Can you specify MPI or TBI? I'd be curious to see what they show for the "GT40" MPI setup.

Can't get that specific Joel, the induction menu shows 4v carb and Fuel injection as the same. If you could find the CFM value for the fuel injection we could play around with it. I also don't have the specs for a stock 351PCM cam so if anybody has that info or has a few minutes to call PCM and get it that would make these numbers more accurate.

Well this is torque and horsepower but in the vein of torque vs horsepower my guess is you would now need to run a smaller pitch prop to get you up to your max speed potential. Even if not by much pitch. All just conjecture at this point mind you...

Holding the prop the same for the moment I would guess your running in the 5200 to 5300 area (with your hightest speed prop) with your current setup which is about where your horsepower/torque graphs cross and not a bad all around place to be in terms of speed vs fuel economy. Lets say based on the graphs it takes you 325lb-ft of torque to turn your prop at your current high speed of 53 or so...

Well if that remained the same at your new high speed the new setup could get you all the way to 6000 rpm 60 mph with the same prop, but my guess is that the torque required is actually going to go up with the additional speed due to the increased drag (mostly water but air as well) of the boat. My guess is with this theoretical prop it goes up about 12ftlb/mph in this range, why twelve well because it is about twice linear and there is an offset and yadda yadda I think twelve.. this number is extremely important and it would be good to really know it but I havent done the research... Anyway if its 12lb-ft your not going to be able to turn this prop past 55mph or 5500 or so as thats going to cross your new torque curve at that rpm. If the number is 20 or worse yet is not fixed but exponential then your not going to see more than another 1 to 1.5 with the same prop.

Besides changes to the hull the only way to change change this number is with a smaller pitch or diameter prop. In an ideal performance world (gas mileage being the lost cause) you would want to shoot for a prop that got you to the 6000 rpm point (maybe 5900 to be conservative) while your speed should be theoretically the same as a prop that got you to 5600 or so your holeshot and mid range would improve without costing you on the top end.

If you go with too small a pitch you will over shoot on rpm be past your maximum potential on the curve and simply be slow and use too much gas, holeshot wont even be great as you wont get enough bite..

Anyway this is a lot of rambling to suggest that proper propellor sizing is just as key to actually getting a boat to move. Hp vs Torque curves are a great tool to know if your prop is giving you all you can get

Very interesting conversation, especially for a drag racer.

Granted I haven't spent much time tuning I'll have to agree with Joe.

My boat will turn 5,300 RPM max. The cam I have should peak at about 5800 according to Comp.

This cam has a more aggressive lobe (larger duration at .050") and higher lift than my last cam and it still maxs out at 5,300. I intentionally went larger on the cam in an attempt to improve the top end to no avail.

A couple weekends ago I got bored and tried 2 carb spacers and 2 carbs to see if there was anything there. I tried a 750 dp, 650 dp, 4 hole 1" spacer, and open 1" spacer; all on the same day. All were within .5 mph on the gps! All ran, you guessed it, 5300 rpm.

Frustrated, I decided having points triggering my MSD could be a problem. Maybe points "bounce" was causing the limitation. I found a new electronic prestolite on ebay to my door for $55! Installed the distributor and still turns 5300 RPM!

Looking at the stock manifolds, the collector area is really small compared to what I would run on a similar car engine. I have experienced instances where the exhaust was so restrictive that an engine simply wouldn't turn any more RPM. We put on a nice set of headers and made a huge difference. In another case I had a small restriction in an exhaust system and after resolving it picked up .5 sec in the 1/4 mile.

As you can probably tell, I'm beginning to doubt the efficiency of the Osco (PCM replacement) manifolds.

Is anyone with a 351 turning more RPM than about 5,300 with the PCM manifolds?

Any A/B test results with PCM vs Hi-Teks (since they're the only obtainable alternative)?

Great topic for the fall!

Matt

Matt,
   I believe Reid is working on an A/B type comparison for the hi-teks, my swap included a bunch of differences. Last time my engine was on a dyno (different setup than now but same heads and bottom end) my hp peak was at 4900-5000, I currently run 5300 with one prop and 4500 with the other so I hit both sides of the curve but miss the middle. I dont think the hi-teks were a huge improvement over the pcms, but dont doubt that they could be on some setups pushing more rpms.   

Matt, all the aggressive cams and high-CFM carbs in the world wont do a whole lot of good if there are bottlenecks in the rest of the system. My bet is that your limiting factor was most likely the heads- though the exhaust and intake could have been playing a part as well. Remind us- what heads do you have on your boat?

Joe, not all of Reids boats bounce- and I would say that Alan's hull has more in common with the 16'5" Mustang than it does with my 19'6" tugboat. Those boats are still light and run bow high enough to outrun the laws of physics that drag us down so quick. Notice that the new powerband has him making 350lb-ft at 5700 RPM, where his current set up has him at that same level at just under 5k. I still maintain that the extra 50hp or so will get him close to another 400 RPM, and a good 2mph, maybe 3.

Hey Joe, How much do you think those Hi-Teks weigh? (Matt wondering how much shipping would cost ) You're going to laugh but I considered removing the cover and installing a set of car headers upside down for a test run to the end of the cove and back!    

Tim...it has stock heads with full port and polish and 1.94 / 1.60 valves, 9:1 compression, Performer RPM, 1.6 roller rockers, balanced, ARP rod bolts, etc. My first cam is this one but with 111 LSA:
http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=870&sb=1
The current cam is this one except with 112 LSA:
http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=878&sb=1


I wouldn't want to go any bigger on the cam than the second one as idle quality could become a concern. Unless of course it's a bigger engine!

It is quite possible the heads have reached their full potential but I wouldn't think so? My current hypothesis is that the manifolds are limiting the exhaust flow. If I can disprove, it's got to be the heads!


Matt

Matt,

Several of us have had discussions about the PCM manifolds and the concensus is they may not be as constricting as they appear. Based on the results of those that have installed hiteks there seems to be a little disappointment to the performance improvements with that bolt on, not to say they're not worth it but the return may not have been as much as expected.

With that said Reid seems adamant that the PCM risers are more of a problem than the manifolds themselves. I have a few ideas on that but need to do some more homework on alternatives first. Also if anyone replaces a set of PCM manifolds this winter because of rustout I would gladly pay to have them shipped to me so I could cut them open and get a cross section of them, I would expecially like to do that to a riser as well.

Alan,

I'd be interested in borrowing your adapter when you're done. I have an Innovate LM-1 and Innovate LMA-2 for tuning my race car and would love to try it on the boat but never had a way to install it.

I totally agree it would be interesting to cut the PCM manifolds and risers apart to see the inside. I chunked mine years ago when they were replaced. I was just thinking the other day that I'd love to have one back to cut open!

The risers have a very small inlet and outlet. In fact, I'm betting the inlet is only about the same area as a couple exhaust ports. If I recall correctly the outlet is only about 2" diameter (inside). If the riser is the restriction that would be nice as it wouldn't be that difficult to fab a replacement.

Anybody have an old manifold or riser for Alan or me to cut open? Maybe pictures of one cut open?

Matt

I just pulled a spare riser gasket from my tool box and it measures 1 1/4" X 3". That's only 3.75 in^2. Usually on a similar engine in a car we run a 3" collector - 7.065 in^2!    It's fairly common to run a 2 1/2 exhaust system on similar engines which is 4.90 in^2.

The car that had an exhaust restriction I mentioned earlier picked up almost .5 sec in the 1/4 mile due to a 2 1/2" exhaust system with a pipe the installer shrunk to slip fit and weld together. No other changes except removing the restriction picked up almost .5 sec!

Maybe we're on to something!

Unfortunately, I don't have any flow data on the heads.

Shoot me the report when you have a chance. brktracer@hotmail.com

Alan..Do you think you could run that program on my motor with what i have now plus the upgrades I am going to add soon, I think the CR is close to 9.75 now, its has 30 over with flat tops, 1.7 rockers, block is decked with a wiend stelth intake, with stock heads now but i am going to add a set of alum AFR 185s, and a cam with around 470 lift and a holly 715 cfm and a set of edelbrock manifolds and alum under drive pullys with a fluid dampner, my Brother has been telling me the heads and cam could add 75 to 100HP, I would like to see if your program agrees...thank you.

I know this will get a chuckle out out you speed freaks, but I am wondering if an upgrade to GT40P heads would give any fuel
efficiency gain at 2500-3000 RPM range.

It looks like the torque went up a little, as opposed to stock. Is it correct to assume that is with same fuel usage?

We run at this midrange 95% of the time & I have all the power I need.

Joe, A final note before I get to work today. A while back I set up a simple spread sheet to calculate prop, slip% based on known data including RPM, MPH, prop pitch, & trans ratio.

My boat currently runs 52.6 on GPS at 5300 rpm, with my 540 prop with the added cup that calculates out to 16.16% slip.

If the slip percentage holds true and I could possibly turn the motor at 5700 the speed comes out at 56.5 mph.

Several unknowns there such as will ssip stay the same and will the engine actually turn 5700. I think 5700 may be a stretch.

If I change props to the 13x13 the spreadsheet shows it should only need to turn 5500 to get to 56.5 mph. Experience to date still leads me to believe that will be a challenge also. I firmly believe I will need exhaust work to do that and possibly a taller cam.

Sorry I'm late. Couple of things from well up above. In regards to me thinking the risers could be a bottleneck, my thoughts were from this: My aluminum Barr manifolds on my blue '69 302 have 3-1/2" risers, and they perform very well comparitively. Port openings on the manifolds were enlarged by me, but mainly the outlets on the risers are larger, falling in line with what Matt above suggests as critical. On the PCMs, the outlets, just like the manifold-to-riser passage are significantly cut down.

These are some good and thought-provoking points above which will make for some really interesting conversation. Alan, I'd like to feed you some cam/head combo info for a good solid 302 build-up also. I'll try to do a PCM/HM/Hitek comparison some time in the not too distant future.            

Now If someone were to comit to both fancy heads and hi-teks, that begs the question - "why stay with the hindrance of Windsor-style heads"

Quest for speed opens the door to make a clevor.
The sb Hi-teks are the same price no matter the port arrangement, so its a chance to start fresh.
Please use your calculator to see the potential in using CHI 3V heads. They are available in Alloy and Iron, and three different port volumes so the low end won't suffer as much as you think and the canted valves really boost breathing.

Yes, different pistons are in order to optimize the whole package but that could be rationalized.

I think its a worthy exercise. I predict you will be able to exceed the performance above and be able to keep the CR in a more practical range for pump gas.