low dyno results are NOT always your parts combo

[grumpyvette]

Grumpy, I was reading a magazine article a while ago and decided to build a duplicate of that engine, the guys had the same cam , heads, intake as I do because I duplicated their engine combo,and the engine they build was making 480 HP from their 383 SBC.
My car dynoed 370 RWHP.
Is this possible? why am I getting so much less hp?



A great many guys are operating under the wildly untrue concept that if they simply buy the parts listed in a magazine article and bolt them together out of the box they can duplicate the results listed in the articles they read.
they fail to understand that theres a big difference between bolting parts together and BUILDING an engine correctly.
and even more guys seem to think that they can simply substitute a few random parts or use parts they already own in place of the listed parts in the magazine build list yet expect to get similar results
remember taking the time to research parts compatibility , BEFORE YOU BUY PARTS, can save you a great deal of time and money
IF you have an engine thats not running as well as you expected, drop back and do a logical step by step verification of each components function,knowing your true compression ratio would help, as would knowing your converter stall speed, exhaust back pressure at peak rpms and plenum vacuum reading at peak rpms and your ignition timing and advance curve.
posting clear pictures of your spark plugs labeled to match the cylinders would also be useful, as would any info on jets and power valves, accelerator pump cams , and fuel pressure etc. If you were local we could work out the testing and details far easier, things like voltage, and exhaust,back pressure, fuel pressure get over looked but they can be great indicators
you might be amazed at what a few tests with a fuel pressure gauge can tell you

THIS THREADS A GREAT INSTRUCTIONAL THREAD
viewtopic.php?f=69&t=3814

OK, first rear wheel hp is generally going to be 15%-20% lower than FLYWHEEL HP, so 480 flywheel hp TIMES .825 or 82.5% will give you a power figure abut 17.5% lower than the flywheel hp, so you have a semi valid power figure to look for as a rear wheel hp number,so you find that 480 fly wheel hp = about 396 hp at the rear wheels ,
(OR about 82.5% of the FLYWHEEL HP)
so your 370 RWHP. is closer than you might think, to that listed 480 fly wheel hp, Id also point out that the engine build articles seldom bother to mention the little tweaks like 5 angle valve jobs and intake porting thats done to make engines produce good hp, remember the articles are mostly done to sell PARTS and they are not about to let a well paying customers parts combo look bad, so they do a good deal more to most of those engines than they list.
obviously you can have the heads and intake ported and a good 5 angle valve job and indexing the cam,is usually good for a few more hp, and/ or adding a plenum spacer could give you some gains, but I will point out that I see simple parts miss matches in most combos, I tune and lack of tuning skill in both owners and dyno operators, frequently holding back the results.
Id also point out theres huge tendency for most guys to get a parts list, that will work great, and then start substituting cheaper components or parts they have or purchased dirt cheap later ,and have that deer in the head light silly stare when it, gets assembled and runs like crap, because the components they substituted, are not well matched, so don,t assume any combo you build with a FEW slightly different components will produce near the same power levels.
a simple change like removing a restrictive exhaust during a dyno test, and adding a tuned header collector could easily give a 20 hp boost in rear wheel hp.
guys rarely bother to learn how to read spark plugs or use a vacuum gauge or verify cam or ignition timing, or bother to get the fuel/air ratio consistent and that can easily be a huge problem.
Id first suggest finding some one with experience and a dyno that KNOWS how to tune and trouble shoot a combo.
and check out the simply things your 100% sure you did correctly, because I can,t begin to tell you how many times I see guys who have the firing order on the ignition wrong, or guys that install a 4/7 swap cam and still use the standard ignition firing order or guys that never verify TDC and ignition advance curves.
get an IR temp gun and check for wild variations in exhaust temps, get a compression test done, do a logical check to verify each cylinder fires etc.
guys put the car on a dyno and get a test run, and think, CRAP! thats a good deal lower power than I expected, without realizing the dyno is a TOOL you use to find out what is restricting the current combos out-put. the reason is that Ive seen a near endless number of guys who were disappointed with the dyno test results who assume that their car is tuned and running correctly who later find that there was something an experienced tuner would notice and start asking questions about.
reading spark plugs can tell you a great deal, as can vacuum readings in the plenum,and air cleaner, fuel pressure, exhaust back pressure and watching the exhaust gas temperatures, ignition timing curve and general power curve.
once you under stand what a dyno sheet says you can use the data to locate potential problem areas.
factors like the plenum vacuum, exhaust back pressure and BSFC all can and frequently do point to or indicate areas that need to be examined.
your exhaust back pressure should not exceed 1 psi at peak power, your fuel air ratio should fall in the 12.5-13:1 range, your ignition advance curve might need work, header configs can frequently be vastly improved, etc..
your engines power level needs to be measured the same way ,as any your comparing it too, and little things like carb jetting engine back pressure plug gaps,cam indexing etc. can all effect your results and what you think is a very similar combo to what your buddy built or some magazine article you tried to copy building your engine, but then having you make a "FEW MINOR CHANGES" like changing the HEADS, or INTAKE, changing the compression ratio, forgetting to index a cam, having a different carb, headers, or rockers, and how the exhaust is configured can easily make that 140hp or greater difference, Ive seen a restrictive exhaust reduce power levels by 60hp-80 hp on several engines, that got a big improvement with a new less restrictive exhaust, system when it was eventually changed.
and a cam designed to run in the 3000rpm-6000rpm range matched to restrictive heads and a restrictive intake can very easily cost your 50hp-70hp,or more, plus theres the factor of REAR WHEEL HP, vs ENGINE DYNO RATED HP,or FLY WHEEL HP, a 450 hp engine measured on a engine dyno would be doing good in most cases to pull 370 rear wheel hp

related threads, YES IT WILL TAKE YOU A WHILE TO READ THEM< BUT YOULL LIKELY LEARN A GOOD DEAL DOING SO!

READ THIS LINK OVER CAREFULLY TWICE
http://garage.grumpysperformance.com/index.php?threads/finding-a-machine-shop.321/#post-55314

http://garage.grumpysperformance.co...ers-and-yeah-thinking-it-through-helps.15137/

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http://robrobinette.com/et.htm

 

[grumpyvette]

Ill add these tips

(1) do EXTENSIVE research FIRST, before....... buying parts.... or starting a modification, that INCLUDES making a detailed parts list and researching , the sources, cost, manuals etc. IE FIND OUT whats necessary to do the job, and what results youll expect before you start

(2) ITS a HUGE advantage to have the correct tools, things like engine cranes, diagnostic test equipment, welders,lifts, etc. may seem like a big expense thats not directly moving your project forward, but there NECESSARY in some cases and ALWAYS make the project go faster and easier than trying to do without them.

(3) work SAFELY, if you could get hurt doing something, chances are very good that you will eventually find out exactly WHY you should have done it the safe rather than the fast/easy way, if you don,t think it thru and use the correct tools and precautions

(4 ) Its almost ALWAYS better to have several friends help, on a project, having two or more guys thinking things thru improves your chances of getting it done correctly and safely,and keep in mind ,its always best to do your projects after helping a more experienced guy do something similar on his car so you have some experience doing it, thus be ready and available to help your buddies within their projects and don,t avoid helping so you won,t get dirty, or have some free time thats used on other guys cars vs yours...in the long run it pays big to help others

(5)ask questions and be sure you understand the answers, KNOWING what your doing before you start is a huge advantage

(6)take pictures, label wiring, put small parts in labeled Ziploc bags and take notes, use the manuals, and internet, and if something won,t fit or looks wrong research rather than forcing it with a bigger hammer

(7) actually reading thru the links and sub links,posted above and below,and other info posted on this site, might take some time, but it will save you a ton of money and time later

RELATED LINKED INFO

http://www.youtube.com/watch?v=aATDsYVVcRM

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[grumpyvette]

Id also point out that theres a strong tendency for guys that read a magazine article or see a list of components for a know successful combo, to look for less expensive, or substitute parts, when they build an engine to try to reduce cost.
I can,t tell you the number of times Im asked for a list of components to build a really sweet combo, and later have the guy come back and tell me that the combo I suggested just is not performing up to his expectations, yet once you start questioning the guy you find out he failed to get 3/4rs of the suggested machine work done and substituted different heads,failed to verify clearances, or do much of the machine work, they select a different carburetor and pistons or used a different intake manifold or cam, an has zero idea about how to tune an engine, index a cam, check for port to port variations, has never CC,ed heads and GUYS have a "deer in the head lights look" when you mention checking quench,distance, having the block liner honed, honing the cylinders with a torque plate or checking his ignition advance curve.
and if you ask about checking ring end gaps, ring back spacing, combustion chamber polish, rocker geometry, rocker to rocker stud clearances, bearing clearance or push rod geometry, valve spring load rates, valve spring installed height, spring bind, or a dozen other factors you find they were not only never checked and hes clueless what your talking about, even simple things like checking rod side clearance, bearing journal finish and fuel pressure , and ignition timing or carburetor jetting seem to be alien concepts



RELATED INFO and yes reading the links, sub links and not skipping thru the explanations DOES REALLY MATTER!
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[grumpyvette]

disappointing dyno results?
I recently suggested a combo of parts to , a guy over a long phone conversation, to be used too build a guys 383 sbc engine for a kit car, and he swore he followed the list I had suggested ,exactly and was rather disappointed in the results and was a bit upset, at the money spent, I asked him a couple dozen questions about the combo and he was rather reluctant to do a few tests but eventually decided to do so.
the net result was that his initial rear wheel dyno testing showed he was making about 338 rear wheel hp, when he expected , closer to about 420hp
(keep in mind 338 rear wheel hp is about 415 flywheel hp)
I listened to him awhile then started asking questions and he admitted, that he had yet to check several factors and he had not bothered to degree in the cam,or check valve train clearances or geometry because the heads stated the valve springs allowed a .580 lift and his cam only listed a .558 lift, and installed the cam (dot-to-dot) and had no idea about his true fuel pressure, intake manifold plenum, vacuum, exhaust back pressure ,valve train clearances, push rod length,carb jetting, power valve,ignition advance curve, and a few other factors I ask about.
a few tests showed several problems.
first he didn,t use the cam I suggested but a similar cam from a different manufacturer, and different roller rockers, both of which he found cheaper.
next, was the intake manifold , which he never port matched and cleaned up, just took out of the box and bolted in place.
(same thing with the cylinder heads, which he never port matched and cleaned up, just took out of the box and bolted in place., and those were also similar but not the heads suggested)
the end result was that a bunch of rather "INSIGNIFICANT THINGS" combined to reduce his power levels and once he tested and corrected those rather "INSIGNIFICANT THINGS" like the cam being degree,d in fully 4 degrees too far advanced,
having the carb float level to high on the primary and way low on the secondary fuel bowls,
he needed to up grade the jetting and power valve,
change the accelerator pump and cam on the accelerator pump,
remove a defective exhaust that was causing 7 psi of back pressure on the exhaust at peak rpms
and replace valve springs that came with the cylinder heads that were totally the wrong type and load rate for his roller cam,
and change an ignition advance curve that was coming in way to aggressively to 40 degrees total by 2900rpm from a 12 degree at idle setting,
he was amazed to find he had gained 50 plus hp, and the engine gained about 750 more rpm in the power curve.
once he purchased decent headers rather than the cheap shorty headers he gained an additional 23 more hp.

honestly , Ive never understood the thinking,
example
think about the guys that build an engine based on the info they see posted in some magazine article, who then find the listed parts and machine work, cost more than they are willing to spend so they start substituting parts and skipping prep steps.
if your asking for a recipe for award winning brownies and the list of ingredients listed 3 eggs and 3 cups brown sugar and a 1/3 cup of chocolate chips and 2/3rds a cup of walnuts , and you substituted , that with 2 eggs and 3 cups of white sugar and no chips, no walnuts ,but you got a deal on sun flower seeds, so you used those, could you really reasonably expect to get the identical results?

BTW, some rather interesting linked info
http://airflowresearch.com/articles/article085/A-P1.htm

http://airflowresearch.com/articles/article031/A-P1.htm

http://www.chevyhiperformance.com/tech/ ... ewall.html

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[grumpyvette]

I pointed out this thread and its sub links to a member when he asked me why his engine that he built failed to reach the intended power levels, after a lot of detailed questions it was very obvious that his "EXACT DUPLICATION" of an engine in a magazine article from several years ago (in fact two decades or more old) had very little in common with the original parts list, nor did it have much of the similar machine work done! what he did build may have started out with the best of intentions but as happens far too frequently, budget concerns, suggestions by the machinists, deals on lower cost components and substituted parts contributed to eventually make the completed project have only a vague resemblance to the original goal, and as might be expected the results differed significantly.
for example the (KILLER heads the original article promoted are no longer available, but that's not a bad thing as by today's standards 22-24 years later they are marginal at best)the company that supplied the pistons is no longer in business,the intake has been out of production for at least 10 years, and its generally considered that the ring gaps quoted would by today's standards be too tight.
now keep in mind technology advances and components become obsolete, or are no longer in production so if your intent on duplicating a decades old engine build you might find it rather difficult to even locate what was once rather common components, but on the up-side, your also generally going to have access to several new and improved options.
the problem, is that they may or may not be compatible with the rest of the original components so careful research may be required.
Id also point out that I think a great many magazine dyno test results in the past were and some still are designed to "SELL the PARTS OF THE WEEK" and may be, let me say, not easily duplicated on an un-biased dyno!
Id also point out that an engine thats set up to make impressive peak power with little re-guard for long term durability holds little of my interest, if you can,t reasonably expect the engine to make it to its 5th oil change , with out a major tear down and rebuild, its certainly not something Id promote, yet time and again I see engines put together with the major goal of impressive peak power numbers at the obvious expense of reasonable durability.
OR and obvious INTENDED,DESIGNED IN MIS MATCH of components , being used, in dyno testing so that when they swap in the part they are promoting, it makes a killer improvement once its installed.
Id also point out that theres commonly a difference of about 18% between the dyno result an engine shows and the reduced rear wheel power levels due to drive train losses.