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High Performance Engine Build Up

8595 Views 36 Replies 10 Participants Last post by  72opelguy
As many of you know, I am in the process of developing a GT-4 race engine to take a run at the SCCA championship. I am trying to make more reliable HP than any one else (including Rally Bob) has ever made in an SCCA legal GT-4 engine... that's a tall order.

Along with this I am writing a series of small articles on a performance engine build using the GT-4 engine as a basis. There is/will be information in the series for everyone building anything from a "grocery getter" to full tilt race engines... ok, maybe not much for the grocery getter.

I have contacted Gary and he has said that it is OK to use this forum for asking questions. You can email me directly, but I would prefer to answer questions here so everyone can benifit from the question. Other inputs are welcome too, but let's not diverge this section too much from the performance engine build up.

The first of the articles... starting with the short block are posted on my web site: www.tgsi.com When you get there, click into "Opel Tech Topics"
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BOB!!!! I'm glad to coax you are back. I'll be looking for your input when I say... or do something... that's going to "hurt" me.
Rally Bob asked about a dry sump. Well, the quick answer is yes... but it's not that simple. I have never had any oil problems with a stock oil pan modified with baffels/"trap doors", a windage tray, and an accusump. However, a good dry sump system will actually pull a vacuume in the crankcase which will lower windage... thus a little more HP. So far, I am using my F-Production car as a test "mule" for the engine. I won't go to a dry sump until (if) I build the tube frame car.

The problem with the dry sump is finding a way to do it. I have not worked on figuring out how to do it. The problem is how to replace/bypass/block off the stock oil pump. So, Rally Bob... any input you can give here will be greatly welcomed.

Paul asked about chamfering the crank. The next segment in the series is crank prep and I'll cover that in there. As far as the front engine (timing) cover goes... There is no real magic here. Just make sure the gasket surfaces are cleaned well. Then the trick that I use is I soak the FelPro timing case cover gaskets in oil for at least 1 hour. The gaskets will soak up some oil and when you torque the cover on, you'll see some oil squish out. Using this method, I have never had any leaks from the front cover. By the way, I never use any "goop" on any gasket and only use FelPro gaskets.
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Rally Bob... Really Good Stuff! The best solutions are usually the simple ones. So I think that the easiest way to do this is to run the "pressure" feed in from the external pump (cooler etc.) into the center of the oil filter boss like you have done. I would also put a block off plate over the oil pick-up holes in the block. (I'm not sure the block off plate is necessary, but it seems like I should)

During the process of "align boreing" the main bearing bosses, the inside diameters are "re-sized" to be exactly original specification. This is done by machining a little bit of material from the bearing cap mating faces... thus making the inside diameter too small. Then when the bosses are bored out, they are restored to their original size. So, that's a long way to say that there are no special bearings needed.


There will be some oil pressure drop with an external cooler. So you need to do a couple of things. First, you need to increase the pressure output of the oil pump. This can be done by increasing the tension on the oil pressure relief valve spring. Second, if you are using an aftermarket external oil filter adapter(to get the oil out and back into the engine) you need to block off the oil filter bypass valve (the little ball in the oil filter housing). (The increased oil pressure will cause the ball to open and bypass the external filter/cooler.) Rally Bob has shown an excellent way to do this by by taping the hole and plugging it. In fact, Rally Bob has shown an excellent way to eliminate the need for a external oil filter adapter. The biggest problem with an aftermarket adapter is that it is difficult to cleanly route the hoses to/from it without chaffing. Rally Bobs solution eliminates that problem.
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I have put the next "installment"... crank prep up on my web site. Go to the site and click on Opel Tech Topics and then click into the section you want. As usual, post any questions here

The web site is
I've been told that someone is having problems with my web site... asking for plug-ins. If any one else is having problems getting to the site, please email me at:
[email protected]
With the renewed interest in ITB raceing, I've gone back into the engine build up segment and made some comments on ITB specifics. I have included the appropriate rules from the SCCA General Competition Rules (GCR) so those thinking about going racing will know what the rules say. I'll continue to do this throughout the rest of the series. Some day I'll probably do something similar for F-Production and GT-4, but for now I don't have enough time to keep the articles comming at a good pace
Where to begin...

SCCA rules do indeed allow anything to be done to the head as long as no material is added to the head.

Yea... Rally Bob has done a ton of work on the heads. But I don't think he had some of the very sophisticated computer programs that have become available (at a mere "oh my god" price) that I am using for some of the work.

It would take many pages... and probably a couple of books to completely talk about modern head, port, combustion chamber theory. When I get to that part in the series of articles I will describe some of the things that make more HP. In the mean time here are some questions to ponder... How does Honda get 240HP from their 2.0L, smog legal engine on "pump gas" and run the compression they do; How does a "box stock", street legal 947cc Motorcycle engine make over 150HP... on pump gas. How does NASCAR make over 750HP from a 50's design pushrod 5.7L engine. These are the places I am drawing from to "think" I can make over 200 HP in a SCCA legal (GT) 1.9L Opel engine.

About doing a CNC port for the head... CNC machines are great for duplication of stuff (port work). But the CNC is only as good as what you tell the machine to do. Tell it to do something bad, and it will do it bad to every head. And there is no substitute for human porting. Even the big buck NASCAR teams who do all their heads on CNC machines finish the porting by hand. Also, the NASCAR engine builders are continually trying out new porting... by hand.

About the carbs being the limiting factor. Well... they are not the limiting factor. The NASCAR engines pull enough through smaller than 4 45mm holes. In fact, the restrictor plates NASCAR mandates for super-speedways have four 7/8" holes for all of the air/fuel to go through into the intake manifold... that's about 23mm each... and the "restrictor plate engines" make about 550 HP... hummmm

About the "choke" size. I believe SCCA is going to restrict FI throttle bodies to the same size the "choke" would have been for 45mm carbs.

About no "chokes" or almost straight through "chokes". I keep putting chokes in quotes because "choke" is a mis-nomer... or at least mis-leading. What they should always be called is a Venturi because what they do is create a Venturi in the carb. A venturi creates a low pressure area. The low pressure area is NECESSARY so that fuel can be properly drawn from the jets and properly atomized into the air stream. So, cutting down or eliminating the venturis is a bad thing... making them too restrictive is also a bad thing. That's why Weber makes a variety of different Venturi sizes for their side draft carbs... so us racers can spend a ton of $$$ to "dial up" our carbs... or so the governing bodies can mandate a venturi that is also a "restrictor plate". (F-Production allows 40mm carbs but mandates 32mm venturis... restrictors. Still 9mm larger than the NASCAR restrictor plate.
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Yes... we should petition the comp board to reduce the weight to 1900 pounds... 50 pounds lighter than the F-Production. I'll get on it.

You are on the right track. Port velocity is indeed critical. More on this when I write the section on heads. And indeed valve train mass... not just the valve, but all moving elements of the valve train are very important. Also more details on this when I write about the head.

About the valve size. The area of one 1.65" valve is about 2.14 square inches". The area of two 1.21" valves is about 2.3 square inches. If you take into account that there are two 7mm valve stems in the way of the two valve ports and only one 9mm valve stem in the way of the Opel port, then the difference is very small. I'm sounding like a broken record, but more on this when I write the article.... sounds like I had better get to it, huh.

Rally Bob... you are absolutely correct about a plenum vs individual runners. So, maybe my example was not a good one. But I was trying to point out that 45mm carbs (with venturis) are not necessarily the limiting factor. Lots of SCCA GT cars make well over 50 HP per cylinder with individual runners and 45mm or smaller carbs. Of course carb size can become a limiting factor, but just not in the case of our Opels with 45mm carbs.
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Peter is right. consistently 1 second a lap faster than the other the other guys always wins. Almost everyone will turn one or two really quick laps during a race. It is the person who is consistently faster that runs up front.

Over a season, consistently winning yields championships. consistent 2nds yield 2nd place for the season.
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