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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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race crank

wow bob, that race crank is almost a piece of art. I'm truely amazed by the sheer amount of work that went into that..again wow. I'm going to barley be able to affoard the basic 2.4 this summer (just was fired from work), but I'm going to save all winter for the opel, so we will see what happens. Keep up the wonderful articles and amazing work!
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
(TGSI) Bob I've been biting my lip not wanting to say anything ever since I came back on this forum.

First thank you for sharing your thoughts and wisdom on racing and high performance engine building.

my first reaction when i here a money is no object engine build up i think "i can image a hole lot" (herd it in some movie)

so what are your thoughts on the Opel Head i know when i talked to rally Bob he has just about tried every thing there is on the Opel Head

it would be nice to here someone else's view not the mech. buildup of the head but the thinking behind the build up of class leading Opel Head

I asked a shop last week how much to CNC a Head and the said $500 to develop a program that don't sound all that bad

in GT4 cant you do just about anything to the Head

then again lets say you did do every thing that could be done to a Race Head wouldn't the 45 mm Carbs get in the way

you know pushing up against the weakest link in the chain again
(i mean the 45 DCOE Carbs being the weakest link)

David Ligon
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davegt27 said:
then again lets say you did do every thing that could be done to a Race Head wouldn't the 45 mm Carbs get in the way
Dave, the carbs are definitely the weak link. Or should I say the choke diameters. I suspect FI will make a huge difference, since the TB's will have no chokes....45 mm straight through. You can't do that with carbs. With no chokes, there's not enough signal to pull fuel from the mains. 40 mm is the largest available off the shelf from Weber. In dyno testing, machining a set of custom chokes to 41 mm gained 6 hp. That's a TON of power, so I imagine the 45 mm TB's will help a bunch. Just my opinion.

Bob L.
I had some custom 41 mm chokes made for some Mikuni 44's

they are almost straight shots

Talked with a few people that said they ran 40's with no chokes.

the last guy the worked on a cylinder head i took him said these things need a lot of work

he was talking (i think) like moving the ports around

my info says 8 inches from the air horn to the back of the valve

but i am talking to much again

What are Bob and Bobs thoughts

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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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Not to open up a can of worms, but having a set of small venturis on a V8 with a shared plenum is vastly different than the same thing on a 4-cylinder with individual runners. This is the primary reason the SCCA does not allow anything other than individual runner intake manifolds for GT-4.

Even with fuel injected V8 with a common plenum, it needs a far smaller throttle body than a 4-cylinder with a common plenum and single throttle body, even to make the same power.

I guess I should have worded my question what are some of the obstacles you think you will run into on your quest for Max power.

from what i can tell the Honda's make power by using modern 4 valve technology.
for example "it has been found that there is a correlation between the inlet mean gas velocity and engine volumetric efficiency"

"it has been said that. at maximum power, modern multi-valve engines are probably achieving mean port velocities nearer 300ft/sec"

from-- How to build, Modify & power tune Cylinder Heads
by Peter burgess & David Gollan

so if i was to take a look at my Toyota 4ag MR2 and compare it to the Opel

with out getting into valve curtain area but just looking at the size of the valve

the Toyota has 1.21" intake valve the Opel 1.65" (F-Production spec) oh did i mention the Toyota has two 1.21" valves

so the Opel would need one 2.42 valve

and we haven't got into the weight of a 2.4" valve

so i would say a bunch of small valves are a lot better then one big valve

now based on bore size we start to get into trouble after 1.84 size valves

so that means if we want to take full advantage of the rules of GT4 we would need to move the intake valve closer to the center of the bore

Not much but it would still need to be moved so now we have a NASCAR type Canted valve head.

Now we see the money starting to really fly out the pocket.
I think we should write the comp board and ask that the weight of the GT be lowered to 2000lbs.

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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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Hadn't considered valve stem diameter

I here 197hp is the Max GT4 motor

i will be sitting on my hands and biting my lip waiting for your article


davegt27 said:
I here 197hp is the Max GT4 motor
I wouldn't say max, since that engine was far from optimized. The owner prefers durability over max power, hence the 197 hp rating. I know of at least a half dozen areas that could be drastically improved to gain power. But the current engine also is good for 2 full seasons between rebuilds. There is no other competitive GT4 engine that can go half that distance between rebuilds.

Rod ratio can be improved, the crank could be lightened, the rod journals turned down to reduce friction, more windage reduction, smaller stem valves, hotter cam, tricker intakes and a better header could be built. Still room for more, I'd say another 12-15 with dyno work and the same basic head/shortblock combo.

I would suggest that consistency can usually beat outright speed through the course of a season. Although there is a time and place for both.
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.
I would add one other bit of criteria to running during a race or season. Found this to be true during my model boat racing, and motorcycle racing, this old addage still holds true: "In order to win, you have to finish."

The timing cover mod is a beautiful piece of work, Bob. Regarding the Aeroquip steel braided hoses, and probably all manufacturers of steel braided hoses that are the real thing and not the phony braid covering of oem hoses. The internal hose that carries the fluid is a teflon tube, the steel braid allows it to maintain shape under extremely high pressures, but it is susceptible to kinking and subsequent failure. If one is ever kinked, replace it immediatley. Many years of working on aircraft high pressure hydraulics has proven this to be fact.

prices for nitriding

this is part of an email reply to me from jim smith at accurate ion technologies they nitride process HTC's winston cup billet racing cranks

We do process crankshafts for HTC and many others. Our daily average
>over 20 a day.
>We can process the materials previously mentioned.. The costs are
$65.00 +
>14% in
>surcharges. If I can be of any further assistance, please let me know.
[email protected]
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