[RallyBob]

My friend Gregg recently bid on, and won, an Opel Manta GT-4 road racing car. It is in need of a new engine, but in general the car is complete and of very high build quality. It has no rust either, having originally come from New Mexico. So, once a fresh engine is put into the car, it will be run in New England in various speed events such as divisional road racing and hillclimbs by Gregg and myself (since I'm donating the engine). I'll delve deeper into the specs and get some closeup photos of the car at a later date.

 

[RallyBob]

And another photo of the car at speed with the previous owner driving.

 

[okieopel]

Wow! Glad to see someone who will race it won the car. It would of been sad to see it sit in a drive way for years.

 

[RallyBob]

I plead guilty to nudging my friend into buying it. I knew the previous owner, in fact he was my very last customer at C & R before closing up shop. I pretty much knew what was invested into the car, so I knew it was a good deal. The rollcage cost $3500 alone! The P.O. says he had about 15K into the car, so at $1500, it was a pretty good buy!

 

[N61WP]

I saw the car on E-bay and thought it had to be too good of a deal to pass up. I have my engine I just pulled out and lots of extra HP parts to build another one, so I developed a plan.......I'm currently looking for a small truck for my daughter anyway, and need a car trailer. So I told the wife I'd fly up,(Boston area), buy a truck and trailer, pick up the Manta, and pull it home.

So much for good ideas...........

James

living in the automotive wasteland of New Orleans!

 

[RallyBob]

A few updates on the GT-4 Manta. Engine is being assembled as time and money allow. Here are some of the pieces. The shortblock was assembled 6 years ago and bagged, then forgotten. Nothing special, really, just forged flat-tops, Total Seal rings, stock forged Opel rods, Kamax rod bolts, and a lightened crank. But at least it's paid for...

 

[RallyBob]

A view of the lightened crank, about 6.5 lbs trimmed off.

 

[RallyBob]

Modified timing cover with direct-plumbed oil lines.

 

[RallyBob]

Block oil passages and timing cover oil passages have been matched both to themselves and to the gasket.

 

[RallyBob]

Block coolant drain added, and adapter for mechanical oil pressure gauge.

 

[RallyBob]

Completed cylinder head with custom tall valve cover for stud-girdle clearance. Internal specs include 1.85"/1.50" Chevy valves, 1.25" double valves springs, titanium retainers, roller rocker arms, stud girdle, and a solid lifter cam with .504" intake/.487" exhaust lift, 257 intake/248 exhaust duration @ .050", and 108 degree lobe separation. Pretty small cam as far as GT-4 engines go (in fact it's a street cam). But I wanted to retain good torque characteristics for other uses...namely hillclimbs and other Solo 1 events. Normally, I'd use/recommend a cam with about 18-20 degrees more duration and .060" more valve lift for GT-4.....

 

[Paul]

Piston Tops

RallyBob,

What are the dimples on the piston top for? Great Looking Engine, BTW.

Paul

 

[RallyBob]

Re: Piston Tops

What are the dimples on the piston top for? Great Looking Engine, BTW.

Ancient Chinese secret.....

They're to keep the air/fuel better atomized in the combustion chamber. Years ago I found that by strategically adding dimples on the short side radius of the intake port, and on the combustion chamber of the head, plus the top of the piston, I could improve the homogenization (sp?) of the air/fuel mix. The fuel tends to settle out when it hits the combustion chamber walls, and this shows up as heavily carboned areas on the piston top. So I experimented first on my flowbench with aerosol dye to see the patterns it left on the CC walls. I then took it a step further and experimented on the piston tops of racing engines based on the carbon buildup. I didn't gain any power, but gained mpg and was able to lean the engine out a tad, and do it safely. On one racing engine I went from 4 mpg to 6mpg....50% better economy at full throttle. With racing gas costing us $4.75 a gallon, that's worth it in my book.

And thanks, I always try to make my engines look good. Not much for chrome myself, but I like trying different 'schemes'. Lately, it's been hammer-tone paints.

Bob

 

[baz]

$4.75/gallon

oh my that takes me back i've been paying that for pump petrol (thats normal pump gas for tthe colonials) for 4 years race gas of 105 octain is £17.48 (thats $28.50 yes $28.50 )a gallon

i wonder if you can get the us postal service to carry it

naaaah

 

[rallye73]

The finish on the engine is gorgeous! What brand of paint did you use and how well does it hold up under the hood against the heat and oil?

Darrin

 

[RallyBob]

It's Krylon Hammertone paint. I have no idea if it will withstand the test of time, this is my first experiment with it. However, if it's any bit like the hammertone paints used on machinery and tools years ago, it should be fairly tough. Not sure about the temps resistance though. I used silver on the block and head, and black on the rocker cover and various other pieces. They also have it in blue, green, gold, and a few other colors I can't recall.

I just wanted something different. Not black, not orange, not red, and certainly not 'Unlimited Blue'!

Bob

 

[calvin]

With that engine if you were putting DCOE's 40ies on it what baseline jetting would you use? I understand it will have different size carbs and maybe not even webers but if it did have dual 40ies what main jet and idle jet size do you think would be best....at least to start?


And since it is around 60 bucks to change sizes I was hoping you might have some guidance in where a comparable engine, (now correctly timed no less) and of course not quite as nice and without the specialties items but almost the same cam, same valves 1.9 to 2.4 block 30 over flattop 305 pistons, mildly ported 1.9 head should start with the jetting. (street and some small club autocross useage)

The 55 idle and 110 main that are now there seem way way to lean and pop even in midrange and the plugs look like they haven’t even ever been used.

That engine is a work of art by the way.

Thank you,
calvin

 

[RallyBob]

Well, I know you're asking a hypothetical question, but even hypothetically, I would never put 40 DCOE's on such an engine! And certainly, any 2.4 litre engine needs a lot more.
So, I can't make an educated guess at it because it's nothing I've ever done. The engine I'm putting together will use 44 mm Mikunis with TWM intake manifolds. I don't even know the choke size, they are the carbs that came with the car, and I don't have the car here with me yet.

My uneducated guess would be something around 135-140 main jets for a starting point. But it also depends on the size of the venturis you have in your carbs. 28's? 32's?

A larger engine like the 2.4 you have draws tends to have a stronger 'signal' due to the longer stroke and greater cylinder volume. You can get away with larger carbs and/or venturis.
Example: A 22R (2.4 litre) Toyota I built for my cousin had 45 DCOE's with 36 chokes, serious head work, a hot cam, and 11.5:1 compression. Idled well at 900 rpms and pulled hard from 1500- 6500 rpms. But try throwing those carbs on a 1.9 and it'll struggle below 4000 rpms.....it's basically a racing setup.

Sorry if I'm speaking in circles, but I just have no experience with 40's on that size engine.

Bob

 

[RallyBob]

Here are some of the valvetrain parts. The cam is the one previously specced out from Cam Techniques, the stud gridle is from Cam Effects, the adjustable cam gear is a Kent Cams item, and the rocker arms were from my first batch of Opel roller rockers from back in '94.

 

[jstock]

Bob
Those parts look too pretty to put in the motor.
Anyone-
I apologize for this SAQ - but - What is an adjustable cam gear, or how does it work , what is adjusted and how ?
Does anyone have a source for these novice questions so I don't have to post these on the list ? Is there an idiot's manual for SAQ's with regard to engine parts, components and operation ?
I will not find this stuff in a dictionary. Still trying to learn stuff.