I just got the latest Car Craft in the mail last night. They did a dyno shootout between the super ram, the multipoint injection with a 1000cfm throttle body and the TBI. I don't have it with me, but I don't remember if it was the 670cfm one or not. Anyway, this engine made ~400hp on the superram and in the article the author said the TBI was down only 10hp at peak. The graph showed it was down all along the curve by a little bit. The other thing they pointed out was that the TBI was much less expensive than the other two.

Dan

 

No ****? This is the new issue of Car Craft? I think I might make a trip to the mall tonight!

 

Interesting, but it doesn't suprise me. Just because you add a larger cfm rated induction system does not mean it's gonna make a lot more power. The engine is only gonna pull in the amount of air that it's capable of.

There's a statement hiden in their findings.... There's something else in the engine that is being restrictive. If going from a TBI (we'll assume it's the 670 cfm) to the 1000 cfm Super ram, then engine is not really receiving more air. A little more, yes, but not a whole lot. This shows since there was only a 10hp increase with the MPFI.

I don't have that mag yet or have read the article, but my guess would be that the Superram probably made more torque on the lower end than the TBI.

Something this test shows, TBI's is just as good as the MPFI!! There's the proof!!!:hail: :rockon:

 

Minor correction, not the super ram but the Stealth Ram was used. As mentioned above it was against the Holley TBI and a MPFI system. The MPFI and Stealth Ram were almost the same power wise.

The TBI was down on power (only a little!) along the whole RPM band. Due to this I feel as though they either backed down the timing or the AFR was off. Otherwise it doesn't make sense.

If anything I could expect the TBI power to be down at the peak RPM. This would be due to an air flow restriction. But down on power the whole RPM band, not likely. Unless something else is incorrect.

Didn't the TBI use the same manifold as the MPFI system? I'll have to double check that fact.

RBob.

 

I wish I had the issue in front of me. I don't remember if they put the TBI on the MPFI manifold. If wasn't a monster motor, but 400hp isn't nothing. Well, you know how half the time the power graphs are small and not very detailed. The TBI was down at several places, but equivalent in several places. What I'm trying to say is that it wasn't as if the TBI was up in the lower RPMs and the SR was up higher up, if I can remember correctly, and it was right before bed last night, TBI was down on the bottom, down on the top and equal in the middle. I don't remember the RPM range of the dyno graphs. The first comparison was SR to MPFI(1000 cfm throttle body) and they were basically the same. The second comparison was SR vs TBI and again the TBI was down a little, but the max was 10hp at peak. Now, I wish I remembered the details about the engine.

Dan

 

What was the peak hp for the tbi system? Im curious as to what they were using for injectors, too. A few myths could be disproven here if they infact were making more than 360 hp.

 

The peak TBI was ~390HP, but they could have been using the 900CFM Holley TBI system - Commander 950 #950-21s which they rate up to 500hp. As an aside, are the 454 TBI injectors available from GM? If so, how much?

Dan

 

Yes, the injectors are still available from GM. They run about $75 each. Just ask for injectors from a 91-93 454 SS pickup.

 

Somebody needs to get the issue and scan it, then post it!!! I want to read the article.

 

PC the scanners hooked to is broken, so howzz about a quick run down:

30 over 350 SBC, Holley 20deg aluminum heads, Lunati cam, 225/235 @ .050, 112 LSA, .477/.507 lift.

They used three different induction systems. All run by the Holley 950 Commander ECU. Both port systems used 30# injectors. First up was the MPFI system. It is a single plane carb style manifold with a 1000 CFM throttle body (system #91004101).

The TBI system is a Holley 4bbl (# 950-22S) that was placed onto the MPFI manifold.

The StealthRam was fitted with a 58mm throttle body. And of course has the short runners and huge plenum.

Results: The MPFI was just below the StealthRam in power from 2,600 through 5,000 RPM. And I mean just. At 5,000 to 5,700 RPM (the highest RPM measured) they were equal.

The TBI: From 2,600 to 4,100 RPM the TBI was equal to the MPFI. This puts it just below the StealthRam in power. From 4,100 RPM through 5,700 the TBI system had less power then the StealthRam. The power curve gradually fell away from the StealthRam curve until it was about 10HP down at the peak.

Looks like StealthRam peaked at 405HP/425FT-LB and the TBI at 395HP/414FT-LB. Not too shabby.

Previously I mentioned that I thought something other then flow was contributing to the TBI making less power. After evaluating the article again I think that the TBI was flow limited (compared to the MPFI & StealthRam).

Look at the sizes of the thottle bodies used on the MPFI & StealthRam. Then look at the four huge injector pods hanging over the TBI bores. Hmm, still, only 10HP down. Not much.

RBob.

 

Of course, it still seems like an unfair test of the TBI. The MPFI used a 1000 cfm throttle body, and the SR used a 58mm throttle body I got the following quote from some site selling TPI throttle bodies
(58mm throttle Body this throttle body will flow 1050 CFM). BUT, the TBI was a 750 cfm. Stick the 900 cfm TBI on there and I'll bet there is no difference in power levels. Of course none of this speaks to making the stock TBI do more than it can already, but it does point to possibilities. This guy http://www.joesperformance.com/mods/throttlebody.html says that the 48mm throttle body which is what we'd bore the stock TBI out to flows 783 cfm w/o an airfoil and 821 cfm with an airfoil. So, figure that's about the max airflow for the stock TBI and figure that even with HYOOGE injectors there's going to be a limit to how much power it can support. Now, I don't know what this says RE: Holley rating their 2 barrel TBI at 670 cfm, hmmm.

Dan

Dan

 

Heh, heh, I should have checked Holleys web site first. Here is the info on the 950-22S TBI:

Commander 950TM 4-bbl, 700 CFM
700 CFM for engines rated 225 - 400 horsepower

Now that explains the drop off past 4,100 RPM. Hmm, couldn't have a lowly TBI make as much power as a port system now, eh?

RBob.

 

To add my $0.02 in favor of TPI I'll say that the port fuel injected systems should perform better on the track because the fuel distribution will always be even even during hard acceleration. That won't be true, initially, for the TBI system because the heavier fuel will tend to enrichen the aftmost cylinders (near the firewall) and lean the forwardmost cylinders (towards the radiator).... so the TBI wouldn't be making optimum power. All other things being equal, the TPI would win because of this advantage.

You could tune all three systems on a dyno (like CC did), but on the track they will behave a little bit differently because of the effects of acceleration, as just mentioned. That said, it would have the most effect in high-G situations, which really means at launch. After that, when the acceleration is reduced, the TBI could perform as well.... but it wouldn't catch up (again -- if all other things were equal.... which is easy to do in benchracing, but harder to do in practice).

In relation to the test that was performed and described in the Car Craft article (which I haven't read yet), it would seem that using the same engine, same cam, and same exhaust, went a long way to make it a fair comparison of intake systems. I also agree with the previous comments made concerning the cfm capability of the TBI used. If the TBI had a smaller cross sectional area (to flow) than the other two throttle bodies, then IF the TBI was a bottleneck, you would see a gradual reduction in output at high rpms, and you should see no difference at low rpms (within the back-to-back noise of repeat testing that is). That sounds a lot like what they got for results btw.

Now if only Car Craft would test a 9C1 LO5 (205 fwhp) TBI engine from a 92-93 police Caprice against a 91-92 Fcar L98 TPI engine. These engines had, IMS, the same block, the same cam, and the same (iron) heads. They could use one engine and just swap intakes & ECM controls, and they could share the same long block and exhaust.

We know the TPI would have better mid range torque; and we know the peak hp on the TPI would be greater because the TPI is using a 48mm bore throttle body and the TBI uses a 42.8mm bore (20% smaller by area). Then they could bore the 42.8 out to 48 and revise the fuel tables. That would level the throttle body playing field. And I think the result would be that the TPI would still have better torque from 2000-4000 (due to the tuned port runners), but above 4500 the TBI would be equal or better because the TBI isn't fighting the small size runners.

The testing could progress beyond that in the usual fashion (cam, heads, and intake manifold/runners). The tests that Car Craft did somewhat represent the last step in the mod progression, with the shortcoming being that the throttle bodies weren't equal in flow.

Did they include the prices for each of these systems? That's the other big point made in the TBI-TPI wars: cost.

 

The 9C1 L05 IIRC uses the horrible flowing swirl port heads.

 

If your in favor of TPI, then what are you doing on the TBI board

Cause you know that theres good stuff in here. Period!

 

uh where did you come up with that crap about the G forces affecting fuel in suspension traveling through the intake manifold at ludricous speeds because its first class horse ****e

i suppose thats why pro stock drag cars are so slow, what with the g forces on those 6 second runs and a wet flow manifold. They must only run on the rear two cylinders.

 

Well, it is not completely ludicrous...

"To avoid gravity influences which could cause uneven distribution of the liquid fuel, the manifold floor and carburetor base are typically parallel to the ground -- instead of parallel to the crankshaft centerline which may be angled for drive-train alignment."*

*Mike Urich & Bill Fisher, _Holley Carburetors & Manifolds_, Tucson, AZ: H.P. Books, 1976, page 102.

If you are accelerating (or decelerating or turning) at over 1G, then that would have a commensurate effect on the fuel distribution on the walls of the manifold, etc. I think that these effects are largely ignored rather than not present, e.g. it would be too difficult (impossible?) to completely optimize a manifold used on a roadracing car.

A similar quandary is likely found in the wet sump. Up to a point, you can use pan-design, doors, and baffles to control the oil but at some stage you need to move to a dry sump.

It may be that the successful drag racers do take this into account but simply don't broadcast that knowledge.

Just because something is traveling at ludicrous speeds does not change vector addition of forces. The net effects may become relatively insignificant --- that's an empirical question/issue.

 

You also have to take into account vacuum forces on the effect of fuel, more than likely a well atomized spray of fuel will be more influenced by manifold vacuum than graviational/acceleration forces which in effect is greater than any g a standard car will experience. In other words, the effect is negliable for standard cars and more than likely will not come into play.

In other words, unless you're racing sonic acceleration 1/4 dragsters, acceleration forces will not come into play on fuel distribution in a TBI vs TPI, sure the flow is uneven, but its more due to throttle body valve plate angles and even then that's at part throttle. At wide open throttle the throttle plates are <15 degrees off being perpendicular to the throttle opening. A TBI spray is conical and at that point air fuel distribution among the cylinders are within a good 5% of each other due to manifold vacuum than any acceleration gravitational forces. Carbs have the same manifold flow characteristics as a TBI setup.

The only system I would imagine suffering from low acceleration forces is the oil distribution system. That's a different matter entirely though.

 

Here we go trying to sound like rocket scientists again.

The subject is irrelevant to what the topic of this thread is. And the angle of throttle blades has very little influence on what cylinder gets what fuel at what time.

It's like everyone thought that the 5-7 cylinders were battling each other for fuel. Well after years of dyno tests, changing the firing order had NO significant gains to speak of and wasn't worth all the trouble of changing it.

It's more myth than fact. If what you're saying is true then they should have made the throttle blades open like this.... *front view at 1/2 throttle*

|/||\| or |\||/|

Develope the linkage, shafts, and plates to do that and make your own.

AJ

 

"Develope the linkage, shafts, and plates to do that and make your own. "


Weber progressive/synchronous downdrafts open that way -- counter rotation (good starting point). You also might be able to vary that parameter by using DCNFs for comparison (parallel rotation). No doubt some engineer at Weber (if not Holley, etc.) has researched this (but maybe 50 years ago).

 

Pablo thoughtfully writes:

uh where did you come up with that crap about the G forces affecting fuel in suspension traveling through the intake manifold at ludricous speeds because its first class horse ****e

I suppose I got that crap indirectly from a first class horse *****e named Newton, and from a few years studying engineering. And speed has nothing to do with this btw. But acceleration does.

i suppose thats why pro stock drag cars are so slow, what with the g forces on those 6 second runs and a wet flow manifold. They must only run on the rear two cylinders.

You'd suppose wrong.

The more successful teams, who (are stuck) using wet-flow systems (by rule), understand exactly what I am talking about and they adjust their fuel systems accordingly. Other than for stationary engine applications, the main weakness of wet-flow is that it leads to uneven fuel distribution (front-to-back) during strong acceleration (and braking, but engine power isn't needed there). They can see the average effects of this by reading the plugs at the end of a run. That's exactly why they remove the plugs and place them in little holders that correspond to where they are positioned on the engine. The effect of this gets more severe the harder/longer a car accelerates, so a really good team will find ways to compensate for it by slightly different carb tuning.

And I think I already said that this effect would NOT show up on any dyno (chassis or engine) because there are no inertial forces at work.
Why do you suppose that the seasoned racers will tell you that you can tune and engine on a dyno but it will behave differently during an (acceleration) race? That's not as true for a loop race event, where the peak acceleration is much less than for drag racing. And I am not talking about chassis design, or hookup or power transfer. I am only talking abut the engine.

For legal street acceleration, the above has a negligible effect. For racing, even with a 15 sec car, it can have some effect and that's one reason why a port fuel injected motor has an advantage over a non-port injected, or carb, motor of otherwise equal design. And the quicker the car, the more significant the port vs non-port injection issue becomes.


RS Camaroguy92 writes:

If your in favor of TPI, then what are you doing on the TBI board... Cause you know that theres good stuff in here. Period!

I didn't say I was in favor of TPI. TPI and TBI both have pros and cons. And sometimes there is good stuff on the TBI board.

Bone stock, TPI wins. TPI cars were always rated at higher outputs than their TBI brethren, BUT but TPI got bigger cams and were also developed for F/Ycars and hence for street performance. TBI (other than the early Crossfire systems) was designed for low-cost use in low-power fuel-efficient non-sporty passenger cars. Different applications and intentions. So it's no surprise that TPI beats TBI, bone stock, in an otherwise identical car. Saying this, or staing the obvious, doesn't mean I'm in favor of TPI.

TBI starts out with more shortcomings. When those shortcomings are corrected, there's a lot less difference between them. That's the very argument that gets posted on this forum repeatedly, and one I agree with.

TPI gets better torque (from acoustic tuning at mid speeds) but wheezes at higher speeds (the acoustic tuning starts to hurt it). TBI is not acoustically tuned so it loses some in the mid-range but it doesn't wheeze where TPI does. Pros/cons.

Oh and Kevin Johnson: nice reply and use of "vector of forces". I haven't read Urich and Fisher's book but I've read other stuff by Fisher, and he's good.

AJ_92RS writes:

Here we go trying to sound like rocket scientists again. The subject is irrelevant to what the topic of this thread is.

I don't work for NASA but I could be a rocket scientist. <g> And you're right, this is getting OT. Finito.

 

Point 1: I don't think the L98 and L05 share heads.

Point 2: Ken is right about the TBI fuel distribution. I checked my plugs and carefully documented what each looked like, and once you saw which plugs came from where, it was EASY to see that the rear-most plugs were subjected to a richer fuel mixture than the front most - period.

 

fuel dist like that would be teamed with any wetflow manifold system would it not?

 

you gonna kick me out of this board cuz i dont have TBI, its not really my fault me and my car like a carb better

 

Hmm...and yet carbs seem to have the same performance at the strip as an equally setup TPI setup, go figure.
What's even funnier is how you guys are trying to bring up these "problems that were never addressed in the TBI setup." Yeah, sure stock they back cylinders get rich but how many can tell me they've used an adaptor plate that moved the TB towards the frong of the manifold (square bore)! I can't tell the difference between my plugs and I usually just check the #1,3, and 7 cylinders. If I go WOT for only a 0-100mph run and turn off the car and coast I STILL can't tell you that my back is running richer than my front. I'm also not running any crazy pumpshot usecs nore am I running the car rich.
Oh, one more thing. Don't forget that the fuel and air isn't sitting in suspension for the WHOLE trip down the quarter. The suspension is setup and sucked into the engine faster than ANY kind of acceleration. BTW, if you've got rich rear cylinders and it's noticable, advance the timing a little and lean it out some. What's probably happening is fuel puddling in the intake manifold and running to the back cylinders. When you slow down you'd think the fuel goes to the front cylinders but hehe, you've got Decel fuel cutoff so no puddles cause no fuel .
Why the **** didn't these guys run the holley 900cfm TB unit?
This crap makes me want to go out and screw with some ricers head again. All these technology's and still people focus so much on how the air and fuel get mixed rather than how it's combusted in the chamber. Power does not care what intake you have so long as it's not a restriction and you can still distrib the fuel and air evenly (carbs have been doing this for a long time now). My final point; TPI sucks and so does EVERY other fixed runner intake manifold be it wet or dry flow. Dual length runners or adjustable length runners (something I'm working on), maybe even a 3d pattern cam instead of this BS about TPI vs TBI. Sometimes I wonder if all these high performance guys got sold by GM to believing that TPI was the future and to ignore TBI. GM obviously has made lots of money from selling TPI, TBI is for the smart guys that know to ignore arguements .

 

I just went out and bought the new car craft and it is not the holly 670 tbi unit it is the holly 4-barrel unit.

 

Yes you are correct. As previously posted it is only the 700 CFM TBI unit. The question is: why not the 950 CFM unit? It would have been much closer to the total airflow available with either the StealthRam or MPFI it was compared against.

RBob.

 

I've got it scanned. If there aren't any legal issues (or if somebody isn't afraid of 'em if there are) e-mail me and let me know and we'll see about getting it hosted or something.

 

and what is your best time with all of your custom tuning and 670 TB?