I am building a 350 for my 89 iroc to replace my 305 the new 350 has bigger cam, heads, headers Hooker, and so on, Im running out of funds and might have to look at running the stock TPI setup except injectors Im switching to 24#. The question is what can I expect out of stock TPI before I switch to Mini Ram further down the road?

 

I think about 300 rwhp is about the limit for a maxed out stock TPI. This is good enough for low 13's or even high 12's. Camshaft/head selection is critical to a good running TPI, don't go too big.

------------------
87 Formula 350 13.94@96.67
98 Z28 1LE 13.15@107.59
1LE Owners Association

 

There is no limit on power from the stock TPI, that is a bunch of garbage. It all depends on the engine you have under it.

ODB

 

Actually it can be calculated. The total airflow an induction system can flow, as measured from air cleaner to intake valve, can easily be mathematically converted to torque potential, which is mathematically tied to hp.

------------------
87 Formula 350 13.94@96.67
98 Z28 1LE 13.15@107.59
1LE Owners Association

 

I hope you're not serious


CFM does not directly relate to torque, so your calculation is worthless.

you actually think a calculation will set a limit on power?

I hope everyone here doesn't think like this, or why even bother trying to go fast.

ODB

 

any other internet-racers care to argue this point with facts & logic?

I will check back tomorrow, I have to go to bed.

but just to let you know, I'm really starting to worry about you guys now.

ODB

 

Power production is not black magic! I know about Internet racers, I want to talk about facts? I am a real racer that has made hundreds of passes at your local track (Gateway, where Stages used to be , Is Wally Kornegay still track manager), not to mention other tracks. I have been racing 3 times in the past 2 weeks. Anyway, I don't want to make college theses out of this, so here is the condensed version of what I believe to be true. Please counter with facts. Hopefully I (we) can learn something today.

The ideal air fuel ratio is between 12.5/14.7:1. Lets assume this to be a fixed constant as it is typically a smaller range than that. This being said, the maximum amount of fuel an engine can ingest under atmospheric pressure (no blower) is limited by total CFM, more specifically the smallest bottleneck in the entire intake path. Roughly one pound of fuel for 14 pounds of air. Since fuel has a specific amount of energy per gram of fuel (or whatever unit you wish to measure it in) and an engines efficiency is also fixed (once assembled), we can easily deduce that maximum power at a specific rpm can be tied to airflow (and the mathematically tied fuel flow). Basically, it takes an exact amount of air/fuel (in the right proportions) multiplied times efficiency to determine torque output. The energy stored in gasoline is directly related to torque produced! The rpm range of a stock TPI is well known, even this isn't a variable. It can also be calculated based on CFM/engine displacement. The cylinder sucks in so much air based on its volume and volumetric efficiency. All of the induction and exhaust mods do is tweak the volumetric efficiency. Once the valves are closed on the combustion stroke, the only thing that varies the amount of "push" or energy exerted on that piston is the shape of the combustion chamber and it's ability to maintain an even mixture and thus an even burn.

I look forward to reading your reply.

------------------
87 Formula 350 13.94@96.67
98 Z28 1LE 13.15@107.59
1LE Owners Association

[This message has been edited by 98_1LE (edited February 20, 2001).]

 

Aaron,, my dog ain't in the hunt for the theories and practices this thread has turned into. Although I think the potential for getting some good info from it will be there. You asked about HP and sure the bigger and badder the engine you put a stock TPI the more HP it's going to produce,,, until you reach it’s maximum flow potential, but you get into diminishing returns pretty quick with a stock TPI set up . The stock TPI intake is a restriction and like most intakes it pulls a percentage of the POTENTIAL power the engine / combination could make with an optimal intake. On a stock or lightly modified L98 the stock TPI more than makes up for any HP loss in torque production based on the runner length. My personal opinion based on old dyno pulls the stock TPI’s reaches diminishing returns on engines with the potential of 330 horses. If you think the engine you’re building could (or should) make more than 330 horses, I’d be looking into enhancing the TPI’s flow characteristics. Once you get into modified TPIs with hi flow LTRunners, Siamese runners, ported bases, ported after-market bases, Super-rams, Mini-rams,,,, all these things increase the efficiency of the intake system and extend and / or eliminates the HP diminishing returns,, but does start getting you into the diminishing returns for the dollar!!

 

Hot Rod Mag-12/'98

On factory fuel injection intake manifolds:

"All of the design work that was executed to develop the Gm TPI system was based upon the flow characteristics of teh lowly 305ci engine. These systems were flow-limited on a stock 350, let alone a modified one. MATHEMATICALLY (airflow at 28 inches of H20*0.257=HP potential), the airflow potential of a stock Gm TPI can support 350 horsepower on an optimized engine."

Here is a calculation that seems to be setting a limit on power, ODB In my past experince Hot Rod Mag is a creditable source of info. Although I doubt any body can get their engine completly 'optimized', but this at least sets an upper limit for stock TPI hp figures. FYI: this hot rod issue has tons of other good tid-bits on FI, including Gm TPI, in their "Fuel Injection For Everybody" section, this is a good, cheap, library accesable, source of info for us TPI'rs.

 

With my ported stock TPI intake, ZZ4 cam, ported L98 aluminum heads, and SLP 1 5/8" headers, my car made 285 HP and 380 TQ at the rear wheels. Thats pretty close to the 300 RWHP number suggested by 98_1LE. I think it could have been a few HP more, as I was getting some ignition miss, and the car was running lean at higher RPMs.

Now I've got an LT4 HOT cam, TPIS base/runners, and SLP 1 3/4" headers. I should be over 300 RWHP and maybe 400 RWTQ.

------------------
West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

I did not forget this at all. It will be a long post and as soon as I get time to sit and finish it (hopefully tonight) I will.

a quick word about the Hot Rod staff. They are writers and work for cheap. There's not a real engineer in the whole bunch, so the math involved did not come from them.
When they act as simply reporters of what they witness and are told then that's fine, but when they pretend to be engineers and engine building wizards ... yet cannot build a fast car to save their lives (even with their resources), then they become a joke. I do not consider Hot Rod magazine as a reliable source for tech info, nor do any real racers. Hot Rod is simply for the backyard gearhead to read while on the john.



here if you can't see picture

http://www.geocities.com/bs_police2000/potty.jpg



for the very short answer on orafice-size putting limits on power, and calculations that limit your power, I have two words for you.
Winston Cup

more detailed post to come.
(happy Hot-Rodding)
ODB




[This message has been edited by The ODB (edited February 21, 2001).]

 

Ok,, I said my dog wasn’t in the hunt,,, but I’ll play.

No question Winston Cup boys make huge power on restricted flow engines They have to spend huge amounts of money in head and engine design to pull that kind of power. Key word being HAVE TO. Pull that restriction off,, sling on 1000 cfm worth of carb and DAMN,, there's what??? A HUGE amount of horsepower is developed with the added flow when the restriction removed,, with the same basic engine package. What did those extra horses cost? Basically nothing (research dollars aside),, it was already there,, just “restricted”. ODB is using a good example to prove a point but no one HAS to run a stock TPI,, there's other and better HP to dollar alternatives,, than building an engine with a restriction. The original post started by asking how much power could you get from a STOCK,, stock TPI. All I'm saying is the stock TPI becomes a major hindrance to HP at or around the 330-horse mark. Not saying that’s all it can produce,, just you’ll lose more “available” HP than you gain in torque,,,, with the stock TPI system.

I totally agree with ODB’s HOT ROD / magazine statement. If it’s written by a Vizard, McFarland, or other reputable researcher,,, then sure,,, it’s worth reading. However, like ODB said when these guys are reporting technical data from reputable source,,, you’re never really sure if they’re relaying the information in the context it was meant. Kinda like that .257 number. These types of numbers are not constants. They’re ESTIMATES based on specific examples derived from dyno research. Increase the cubes, compression, cam profile, volumetric efficiency,,,, whole new number exists.

Tag.

 

very well said BadSS.
I'm still going to throw in some brain teasers for the sake of all the Hot Rod readers out there.
What you said is mostly correct but there is more to the story.

ODB

 

got some $$? the more $$ you have the faster you get. get alot of $$$$ and put it in any car, you'll go fast. If I have 3000$ more to spend than you, I'll be faster, same thing for the next guy...

 

I've always said,, you don't have to spend a lot of money to go fast, but the more money you spend,, the faster you will go. However, you need to know where best to spend the money. I'm not saying you mirage,,, just I know a lot of folks that have a lot of bucks in the car and engine and are not near as fast as they should be.

 

back to top,

see separate post on subject.

ODB

 

98ILE Why do you still have the Formula if you have an LS1 that's faster, and gets better MPG? Curious

 

I believe 981LE has a point... his calculation probably is good to figure out the MAXIMUM power to be produced by an engine.

------------------
1988 Pontiac Trans Am GTA L98 5.7L, Black on Black with 114,000kms.

Best ET 14.559 @ 95.25MPH
Custom 3" Stainless Exhaust Y-Pipe back (High flow Cat and Flowmaster Mufler)