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Discussion Starter · #1 ·
the car is getting closer!!!

Flow bench numbers done today, blow blending and mild porting


Done on a superflow SF 600
Opel 1.9 head
With intake valves of 1.84” with 30 degree backcut for street use (opposed to 45 degree for the track)
And exhaust valves of 1.50

these numbers with 28 test inches of water

INTAKE setting 3
lift scale.200 .300 .400 .450
148.7 148.7 293.7 293.7
% of air flow
66 99.6 62.6 65
ACFM 98.1 148.1 183.9 190.9


Exhaust setting3
158.7 158.7 158.7 158.7
% of airflow
56.8 77 92.4 97.6
ACFM 90.1 122.2 146.6 154.9

Exhaust with pipe setting 4
316.4
% of airflow 53.4
ACFM 169


..257xcfm x4 cylinders =hp .257x`183.9x4= 189.0492hp.

Do I believe that car will have 189 HP? No. Max lift on my cam is .386 not .400 so you lose some there and reality if far different than a flowbench but I am hopeing with dual webers 40ies to have a 150-60hp if I am lucky.

Do these numbers sound in in line?

thanks calvin

Bob if you read this thank you so much for the dual cannon intake tip they are welding away!
 

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Pretty typical numbers, though I expected a little more from the intake ports. Probably due to the 30 degree seat angle, as that number can be achieved with a smaller (and lighter) 1.72" intake valve easily. This equates to about 113 cfm intake @ 10" and 92 cfm exhaust @ 10" (if you'd like to compare to some other published numbers here)

Now, assuming the entire induction system allows 113 cfm
(it won't, simply because of the 40 mm Webers and even smaller chokes), you could potentially have 194 hp. BUT, a rule of thumb (no formula really, just based on my experience), is that you'll be VERY lucky to get 85% of the airflow's hp potential through the entire system for a street engine, assuming EVERYTHING in the engine is optimized. Perfect cam choice, perfect compression, perfect rod ratio, perfect ignition, fueling, etc.

So with a restriction of approximately 12 cfm per inlet runner with the Webers, their chokes, intakes, and air filters in place (this is not uncommon), your inlet airflow would be now 101 cfm. Multiply times .43 to get the potential hp per cylinder....43 hp x 4 = 172 hp. Multiply times the 'Bob factor' and it's now 147 hp. This is a realistic and obtainable number for a street engine that is well-tuned. I'd love to see a dyno sheet to check my math!

Anyhow, your intake/exhaust balance is approx. 81%, a touch on the high side but not bad for an Opel. BUT, throw in the intake restriction, and the improvement the exhaust port sees with a header tube in place, and the proportion changes quickly! The intake port will flow 101 cfm, and the exhaust port will flow 101 cfm! I prefer to see around 90% intake/exhaust proportion with the entire induction/exhaust system installed. My recommendation is to have a cam specially ground with at least 10 degrees more intake duration than exhaust duration, and about .025-.050" more valve lift. This will improve the balance, reducing exhaust temps, improve the fuel economy, and make more power.
 

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I think you could have run a bit more duration than you have, and maybe a little less lift. It depends on the rocker arms you have, stock rockers don't like to deal with higher lift cams with 'peaky' lobes. I tend to stay with more 'rounded' lobes, i.e., lower lift and longer duration. This is for stock rockers only......with a full-tilt racing head and roller rockers and a stud girdle I've run up to .576" lift with no problems.

Out of curiosity, did the head get flowed at higher lift numbers? Such as .475" and .500" and .525"? I ask because Opel 1.9 heads tend to go 'downhill' after .450" lift, and a lot of times (most of the time really) the airflow and power drop with higher lift cams. Let me know.

Bob
 

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Discussion Starter · #6 ·
It seems that when we were flowing the head I, negligibly, thought my came had 386 lift and not 486 so I did not listen or write down the numbers above 450. It did fall off a little after 450 I remember that not as much as it did at five hundred twenty five and above that we did go. I wasn’t concerned as I was thinking I would never be above 400. We were all just relieved there wasn’t to much evidence of turbulence (well below 450 anyway)

Gil (at gtsource) finally is getting some solid lifters, which I re-ordered today that should be in next week and on to me the week after. The crank is packed off to Michigan and the said cam sits at the machine shop where we had planned to use stock rockers.

The roller rockers set up is out of my league but I really don’t want to have glaring holes in the engine. Even though I was not planning on taking it to the track and possible inspections with the obvious welded up cannon intakes, (still a great idea that) I still wanted it to be able to run without problems.

Would more slotting on the fulcrum work? and maybe a rev limiter to avoid binding or do you think I have to have to get a different cam?


Please advise,

Thanks,
Calvin


And I was so happy this morning when I discovered that the 4 spoke revolution wheels that I have were not 13x7 as I thought but rather 14x8…. Allowing me to use the rear disks brakes on the Isuzu rear end that I got to get the .389 gear out of



Like a MSDA
From summit Msd6al a soft touch rev control
 

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The problems with the rocker arms is not the binding at the slot (that occurs as you approach .520" lift), but instead the acceleration of the opening and closing ramps of the cam lobe. This is my reasoning for using lower lift/longer duration cams.

The other issue is valve spring tension. This is very critical with Opels and stock rockers. You have to balance a fine line between enough tension to avoid valve float and bounce, and too much pressure which will break rockers left and right. Opels are especially sensitive to too much spring seat pressure. Try to keep this below 115 pounds with stock rockers, but over 105 pounds. You shouldn't need more than 240-250 pounds with a reasonable rpm limit (8000-8500).


Travis, I haven't flowed a complete 1975 system, only an intake manifold. But it's not really relevant since it was flowed on one particular head. Let's just say it performed better than a stock carbureted intake as measured on that particular head.

Bob
 

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75 FI Intake

Bob,

Maybe you can help us understand where, in relative terms, the 75 FI Intake's flow numbers might fit between a stock manifold and one of your ported manifolds. In one of your other posts you have stated that a stock manifold would restrict the flow to 88-89 CFM from 112 CFM (of a particular big valve head). In the example of this thread you stated that the side drafts (carb, filter, etc) would reduce flow to 101 CFM (I know, different head in this example). It might satisify those of us with FI to hear you "Guess" at where we might expect the 75 FI intake to flow, 90-91??? 94-95??? Or maybe.. its flow would be similar to one of the ported stock manifolds, street, torque-er, etc.

Sorry to be a pest.
Paul
 

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Re: 75 FI Intake

Paul said:
Sorry to be a pest.
Yea, sure!

The FI intake flows better than a ported carbureted intake, that I know. But the air flow meter chokes it down significantly more. I'd have to dig out the flow bench and start over from scratch here, you can't compare two different heads, ported vs. unported sidedraft intakes, carbs vs. no carbs, different choke sizes, with or without filters, bare FI intake vs. full operating system (air flow meter, fluted hose, air box, etc.). There's no correlation between these parts. You'd have to compare all the different induction systems in their entirety, on the SAME head to get repeatable, accurate results. Anything else is an assumption. You're looking at probably 15-20 hours worth of flowbench setup, testing, and teardown time.

I can't *guess* the FI intake flow because it's not a fair test. Sure it *might* flow 100 cfm on a 112 cfm head. But add the throttle body and what is it now? Add the fluted rubber connector hose and how much does it drop? I suspect a lot, I know a smooth metal pipe adds a ton more torque, as I've done that before. Add the air flow meter next...then the air box. What brand air filter? It all makes a difference. Comparing a bare FI intake to a ported carbureted intake is an unfair test, they have different restriction prior to the intakes that have not been tested.

Sorry if I came across as negative, but I take this sort of question in the same light as 'riceboy math'. You know, this header is supposed to make 12 hp on my Honda, and this intake makes 8 hp, these plug wires make 6 hp, that exhaust makes 14 hp, etc. If that were the case every kid with a Honda out there has 250 hp with a stock engine!
 
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Paul said:
The question sure didn't deserve the response.

Paul
Paul, I was NOT trying to be offensive, in fact I was trying to interject a little bit of humor into my reply. But I was simply making the point that I had not performed an apples-to-apples comparison of the entire induction systems (FI vs. carbureted) in all it's possible variations. So I can't make a fair assessment.

In general, the FI flows better than the stock intake with Solex, yes. As the level of modifications increase (i.e., ported intake, 38 DGAS), the carb'd setup closes the performance gap. And looking at the hp figures, a 1975 engine only puts out 5 more hp (80 vs. 75) than a 1974 engine. The only difference is the FI and the Sprint exhaust manifold. How much is the exhaust worth and how much is the intake worth? I honestly don't know if it's an even split of 2.5 hp each or is it's all the intake or all the exhaust. I'm leaning towards the intake manifold being superior in this case.

Irmscher used to built off-the-shelf 2.0 litre rally engines, one version using the stock 2.0 FI system with a modified computer, the other system using twin 45 DCOE Webers. The Webers had 5 more hp (177 compared to 172). This is more than a single Weber can provide, so in this case both the twin Webers and the 2.0 injection flow substantially more air than a single downdraft. A 2.0 air flow meter is nearly twice the size of a 1.9 air flow meter however. Hopefully this will give you more insight into the FI/vs carburetor flow capacities.

Again, I was not trying to be offensive Paul, I apologize if I came across that way.

Bob
 

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That's great info on the Irmsher motor. I could easily see the flap style AF meter causing most if not all the 5 hp drop. We must also not forget that a FI system theoretically should be better than the carb as you don't get the drop across the venturis. Analysis at this level(5 hp) is all moot anyway if the runners are different lengths:(

BTW, it's the runners that I am most interested in. As you know the throttle body is easily upgraded and I don't need an AF meter.

How different are the 1.9 and 2.0 FI intake manifolds?

-Travis
 

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Travis said:
How different are the 1.9 and 2.0 FI intake manifolds?

-Travis
They're the same (the manifolds), other than some different fitting locations. The primary differences with the 2.0 system are the lack of pre-resistors for the injectors, the larger air flap, and the more modern ECU. European hp figures show 110 ps for the 2.0 litre FI engine, and 105 ps for the 1.9 FI engine. In this case, what is the cause for the 5 hp, the larger air flap or the extra 100 cc's of displacement? Probably the 100 cc's.....even a stock 2.0 litre can't take advantage of the larger air flap. But it helps on larger or modified engines.

Bob
 

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Paul most of the combos you Bob and Travis are talking about i tried on My GT (back in the day)

i went trough all most all of the combos except dual side drafts

the drag strip was my dyno

started out with a low comp 1.9 running a 19.2 in the 1/4 mile.
ended with a 17.3 with a ported manifold Bob sent me

the best setup i tried but i did not get to go to the drag strip with was the single side draft Webber setup, and that baby flew with that thing on there :)


list of stuff i tried the order is getting a little fuzzy (getting old)

1) stock motor with new Webber
2) stock with 75 sprint header
3) 1.5 head Webber 1.5 valves (did not go to the drag strip it had an oil leak)
4) 1.5 redid with 1.9 valves performance head job ($90 ha ha )
stock 32/36

5) 75 FI with sprint header stock lower end 1.5 head (ran this setup for a long time 18.5 in the 1/4
the Hal meter said it was rich

6) went to pacesetter header lost a little low in TQ but also added a 3.67 rear some where in the #5 or #6 time frame

7) tried 260z AFM and other FI experiments

8) 2.0 FI from GIL same as 75 with some more loss of low end TQ

9) got a ported Manifold from Bob

10) ported head with 2.0 valves and a special cam for FI (forgot about this one)

i remember i wanted to try it with carb before i stuck the FI back on and that's when i ran the 17.3 (tire spinning 17.3 buy the way)

i was going to try the 2.0 FI but decided to try this single sidedraft i had picked up

this was a strange carb had 36 chokes (i think) 200 main 170 air
it would pull hard to about 5100 or 5200RPM and then hit a wall

at the time i did not know what the problem was but boy was that thing quick. faster then Marty's 2.0 with 38Dgas and i swear it was faster then this 2050lbs race car i have

talk about a guy driving around with a big old grin on his face

:D

anyway three was a write up in the Blitz where they said the FI manifold flowed better then the Carb. once i herd that i was off and running looking to try FI

Bobs ported manifold might have been even better if I had worked on the jetting more (only tried two jet changes) I remember I pulled the carb off in the pits and I had fuel in the bottom of the manifold.

The FI both 1.9 and 2.0 was a very good setup good daily driver setup

I was on my way to trying all the combos over again with the new Head when some bitch hit my GT. a week later the head dropped a valve and destroyed the motor

flow numbers on Bobs Head
1.65 intake 1.45 exhaust valves

intake @28
100= 51.8 200=107.2 300= 151 400=168.7 500=168.7

exhaust 100=42.5 200=95.2 300=127.0 400=146.2 500=155.2

later
Davegt74
 
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