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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 5:37 pm 
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I did answer your question. the best combusting engines on the planet are made by BMW. Copy what they do. Its not a matter of me listing out a combo thats perfect, I can tell you exactly whats in the best race engine, I have no trouble with that, but its not the right engine for a different use other than what its good at.

What do you mean I never tell how to fix them. I just said what I think is wrong with the engine in this thread. If people read proper scientific research books that were written decades ago they wouldn't build engines with dished pistons, or incorrect ports that create fuel separation for high performance engines. They would have enough compression and wouldn't have too big camshafts.
The engine of this thread has the piston .011 from the deck and a .050 head gasket to hold the CR to 14.5. That makes the quench area static .061" clearance, that immediately breaks the well researched rule of " do not set the quench clearance to between .050" and .150" as it promotes detonation". Read the book, The internal combustion engine by Harry Ricardo, the inventor of the squish.
It has 4.165" bore and a 4" stroke. Heads flow 420 range claimed in the text. It makes 800hp or 850 if you fudge it differently.
Heres an engine I know, Its 3.75' stroke, 6" rod, 4.185 bore, 14.8 compression, .042" quench clearance, flat top pistons, 245 psi cranking pressure, it has 406CFM flow on the heads, a 258/265 on 112LSA cam. 1900cfm carburetion, gasoline, 30 degrees timing, makes 882 hp at 7800rpm superflow dyno. This engine made 780hp with bigger cams, 268/276, 275/?, 289/296, were tried.
Here's another, 3.75" stroke, 6"rod, 4.165 bore, 15.8 compression, .040" quench clearance, custom dome fitted to the chamber exactly, 300psi cranking pressure, 365cfm head flow, 268/268 112LSA cam. 1600cfm carburetion, gasoline, 28 degrees timing, 903hp at 8200rpm. Also made 875hp with 1300CFM carburetion.
Neither of these engines have dished pistons. They are less cubes, more outright power, more power per CFM of head flow.
Ive physically pulled a customers engine that had dished pistons with a long stroke, installed shorter stroke crank, custom domed pistons, same heads and cam etc and made more power and torque.
Necessitating a dished piston because the stroke is too long is a bad move in my opinion.


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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 6:11 pm 
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[quote="shrinker"] " do not set the quench clearance to between .050" and .150" as it promotes detonation".


How do you do that with a big bore engine where there is a short piston skirt ?? The piston will rock
and hit the head...

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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 9:05 pm 
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You just change the skirt, use the appropriate parts. People use big bore pistons with small skirts and tight clearances all the time, the skirt has to be right for the job thats all, not wrong for the job. Why do people use small skirts to try to save weight, thats not where you save weight from, you save weight by machining the piston correctly and not using off the self standard parts that fit in a generic fashion.
Why do people concentrate on things that save weight to enable it to rev etc when they should be concentrating on how to make combustion go fast enough to obtain the RPM in the first place. There is no point spending money on something that enables RPM higher than what your combustion will generate. For titanium conrods I wouldnt care much about shaving weight from the skirt, I'd run a bigger skirt than normal to get less rock and reduce leakage. That's using the conrod's strength to gain an advantage thats better for combustion.
The most important thing in any engine is to control the combustion efficiency because thats where the power comes from, it doesnt come by shaving down the piston skirt so that it rocks too much and you have to increase clearance.

The engine of this thread has an issue with valve clearance to the piston. The cam is one factor of that but if the head was larger CC with the valve seat height higher above the piston then the piston could be fitted with a 3 to 5mm dome so that the ejection could be used to advantage.


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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 10:48 pm 
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When you say
Beretta wrote:
It seem that you always find a issue with our home built bracket motors
I'm not picking on the person who builds their own engine design combo etc. I am upset to see a simple thing obstruct someones project potential. Mankind cannot fully predict a combustion event so a lot of the skill is in measuring how a design is performing. There are people who know far more than we will ever find out (they work at BMW).
What really annoys me is the industry is full of people who shouldn't be giving advise in the areas they dont know enough about. For instance, go find an engine dyno that uses an oscilloscope. its a pretty basic old school tool that it tells you exactly whats happening in the mixture preparation of the engine. There not expensive to buy so why dont dyno shops have them or use them? They connect direct to a laptop now days and data log the run. The humble oscilloscope is able to display the in cylinder AFR differences per event, it displays where in the RPM band the vaporization became insufficient (and that will correspond with the RPM where the HP starts to drop), it tells you about flame kernel growth. All this stuff is so important to the power range of the engine. It shows you every firing event of every cylinder for the entire dyno run.

Find a dyno shop that uses a gas bench, without a gas bench you have no idea of the efficiency of the engine or where to look to improve it. Without a gas bench your not an engine developer, your just a tester. There are even gas benches available for high dollar that can sample an individual cylinder IN THE CYLINDER at high RPM. These gas benches display the HC formation ratio of the mixture prior to and during combustion. How cool is that! Why doesnt a dyno shop have that? Why dont dyno shops have in cylinder combustion pressure data loggers?

You guys spend a lot of money purchasing parts and it only takes the design of one part to limit the performance of the engine. Its not your fault that someone doesnt tell you intricate details. I try to remedy that but there is only so far I can go. Its taken me 7 years to train some people here to the reality of combustion. Thats not going to happen on the internet in posts.


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 Post subject: Re: Engine upgrade
 Post Posted: Wed May 09, 2012 8:41 am 
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I started a new post shrinker for us and others that may want to join in this discussion..

Chuck sorry for all the drama with your thread here...

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 Post subject: Re: Engine upgrade
 Post Posted: Mon Jun 25, 2012 4:27 pm 
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So Chuck, you've had some time to put more runs on this new bullet so have you been able to fine tune it to run any faster? :-k

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 Post subject: Re: Engine upgrade
 Post Posted: Mon Jun 25, 2012 10:57 pm 
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I haven't really been able to test much. I try to make changes during time runs on race day but that's only 2 maybe 3 runs per event. The local track doesn't really prep well on test nights so I don't think I can get much useful data on those nights that and the closest 1/4 mile track is 90 miles from here and I feel I need to test on a 1/4 mile track. I don't change anything after the last time run unless I'm desperate. Such was the case at the last race. At the Clay City race my car kept making a move to the left. It wasn't that bad so I just rode it out and managed to win that race so the time between that race and the last race I got the car on some scales and made some small adjustments. It was a little lighter on the left rear than I usually have it so I neutral'd the anti-roll and set the preload. It only took 2 flats on the top bar to get me there so I figured that should do it. On the 1st 2 time runs at the last race it still made a move to the left so we swapped the slicks around. It was due for that and I figured it couldn't hurt. On the next pass it was worse, in fact so bad it took a little driving to stay out of the wall. Back at the trailer while discussing what could be wrong I had an epiphany. I had seen this problem before and knew exactly what was wrong. A quick check of a couple data logs confirmed it. I told Eddy that the car needed more clutch. It was obvious he doubted that would help and I told him to go ahead and grill the burgers while I made the adjustment. Time runs were over so I had to take it to 1st round to see if I was right. I was, the car was on a string the rest of the night. 1st round the guy I ran had such an awful light I caught him before the 1000' and lifted, dropping 19 MPH from my best time run of the day. Next round I lifted just under 8 seconds into the run and was about 7 MPH below my best speed. I went red in the semi's and ran it out for the best pass of the night 8.25 but the MPH was 4 MPH below the best pass. I think that may have been a problem with the track's timing system because all of my incrementals, including 1/8 MPH than my best earlier pass.

I tested at US60 and had made a jet change then. I was up to 87 and 97. The AFRs were still a little lean at 14.4/14.7 and the rear cylinders were 150+* hotter than the front cyls so I stepped the rears up to 100 before the Clay City race. After the 1st time run there it still looked a little lean at 14.0/14.4 and the rear cyls were still a little hotter than the front. I wanted to step the rear jets up a little more but the only jets I had any bigger than the 100s were some 106s. I figured at least I would know if they would make any difference so I threw them in. The AFRs were better at 13.8 and most of the EGTs were within 50* of each other. I had planned on changing jets at the last race but the struggles with getting the car down the track shot that down. 16 jet sizes seems like a lot of difference for a PV and overall it seems like a lot of jet but it doesn't seem to be slowing it down any. I have bought some more big jets and was thinking of stepping the front up and the rear down some then jet it up until it slows down. I really need to get to the track some weekend and just tune on it. Now that I have it leaving straight again I can concentrate on tuning.

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