CHEVY_EATER

My friend cannot figure out why his 90 IROC has no power. He had the motor rebuilt and installed a SLP cam, the larger of cams I think, ported & polished stock heads, and a dynomax catback. The car had good power before but seems to be pretty dead now. He still has his Hypertech chip in which I think he should toss aside. The intake is all stock and so are the exhaust manifolds and y-pipe. Should he just get a custom chip done? If yes, tell me who can do it the cheapest since his on a tight budget with the car. He ran a 14.6@97 I think before spinning bad and it is not even close now. Thanks!!

NufNuffZ28

iTrader: (10)

What happened is a mismatch of parts. The cam and ported heads moved up your rpm range that the car will make good power with. With the stock untouched TPI and manifolds it is not letting it make the power up top that the cam and heads want to, and the cam and heads are not making the torque down low like the stock stuff did, so overall you car has no specific RPM range. Port the intake, put on some headers and a nice y-pipe and bump the timing to 10. And yes, the hypertech is not helping either.



Chris

KYL98

Well I dont think all the work to the heads will work right if the stock exhaust is still on it.......What good will better flowing heads be if the exhaust cant get rid of the spent gases....He should definitely get rid of the Hypertech chip.....But, first things first...is his timing set correctly???? My exp with a TPI(even stock) is the motor likes about 30*adv @3000rpm.... Im not really sure about the specs for the SLP cam, but have heard it is made to work with the stock TPI intake. Im assuming he already checked the obvious like ignition(plugs, wires, coil) so I would put the stock chip back in, check the timing, and get some better flowing exhaust.....just my .02. Good luck

CHEVY_EATER

I too think the stock manifolds are a major cork. I know that is the case with all the F-body's from 82 on up if I'm correct. He replaced the distributor, cap & rotor, wires, plugs, you name it. I'll see what the timing is set at also.

camarojoe

The guys who mentioned the restrictive exhaust and intake are dead on. Plus on top of that the SD systems don't take lightly to mods like cams and stuff the way MAF cars do. Definitely tell him to put the stock chip back in, save some money, and tell him to get pretty familiar with DIY prom board.

305sbc

iTrader: (3)

Their larger cam is probably recommended to use with headers, very low gearing and a pretty healthy stall converter. You basically have to change everything else to make power in the higher RPM's to match the cam,
OR
you could just put in the right cam.

chevy91z

What typically happens with A cam such as the slp it has longer duration than the stock compression is ment for. Tell your buddy to do a compression test and see if the compression is high enough. if it is below the 170psi mark and below he is loseing his power there. If so put a thinner head gasket in. going from a .040 to a .015 will bring him up a half a point and he'll wake that motor up.

MinionII

Any cam with longer duration is going to lower the static compression, unless its intake centerline is advanced half of the number of degrees bigger it is than stock. If it is 4 degrees bigger, advance 2 degrees from stock IC.
The reason for the lower compression is because the intake valve closes later, bleeding off compression at lower rpm's. If you get 160psi cranking compression with the stock cam, you are going to get less with a bigger aftermarket cam.
All I'm tying to say is I don't think cranking compression numbers is a good thing to match a cam too...

chevy91z

Yes what you are saying is true but it has been proven, If you match the static compression you will notice the proper gains of a cam. If you need proof check the new either Chevy HI PO or Super Chevy. A 400 I was building for a 2nd gen I had wasnt proforming like I had hope and an old timer I always talked to asked me to check and he was right. I got a noticable gain, thinking It was a fluke but two years later I read a whole article on it.

ctandc

Well this is one point for the earlier MAF systems

They tend to take to major mods better than SD systems. Not that EITHER can't be tuned to peak performance just as easily, and SD probably wins on that account, IF you're burning you're own chips, but just bolting it together and running it, MAF tends to COMPROMISE a bit better with major mods.


I'm not getting into a MAF / SD debate.


Just my 2 cents.


HTH

CHEVY_EATER

I wasn't sure if ti was the same as with Mustangs. MAF is far better on Mustangs for doing serious modifications. But with typical small bolt ons the SD makes more power. Weird that Ford went to MAF in 89 and GM went back to SD??

MinionII

As soon as you put a cam in the Ford SD, everything goes to shyt.
There was hardly any difference in WOT power with the change to MAF, and much better response and power at part throttle.

Do the LS1 cars use MAF or SD?

jmd

iTrader: (4)

LS1s have a MAF, and probably have a MAP used basically as a backup, which is what 94-97 LT1s had.

I can tell you from experience that adding a cam to a TPI engine isn't going to be as fruitful as adding one to an engine with a higher flowing intake, not to mention the exhaust being opened up will add power and drivability to the fray.

And yeah, DIY-PROM all the way. :nono: to Hypertech off-the-shelf PROM.

bigals87z28

LS1's use a MAF system. WAYYYYYYY different then what we have on our cars. not to get on the MAF thing, about cams
What needs to be done in order to install the cam right. not parts, about setting up the cam. I deff. need to know more about this before i venture off to do mine. I actualy have the new CHP in the library (aka the bathroom). ill have to take a gander at it for some tips. thanks guys

90Formula-X-F

Is this car an automatic trans car ? So many people think if you put a big cam in your car that it will be faster. Matching other parts will it if you do it right. Match porting, the right exhaust, gear ratio changes and converter stall speeds all come into play. It's the balance of air/fuel and exhaust flow at the right RPM. Do it wrong and it's a dog, it destroys the volumetric efficiency. Do it right and it is a rocket ship...

1990 speed density has a decient fuel curve however it is designed to build it's best horsepower between 1500 and 5000 rpm's. Actually porting the big valve heads with a matched port intake, a smaller cam and better exhaust will increase efficiency and keep the torque levels high and where the TPI can use it.. Torque is what builds street power. Pushing the torque level up higher into the RPM range, closer to the horsepower peak is what fuel injection does in most cases. Building power under 5000 is a good thing for a TPI street car. A cam shaft that runs it's peak figures out of the 1500 to 5000 RPM ranges in a 1990 TPI car require extensive prom work, gear changes and testing. It is a hard road to go when a smaller cam shaft and lots of air movement makes the car a rocket with out much more than just a slight fuel pressure increase.



- 355ci, WS6, 5speed -
* Ported & Polished Big Valve Cylinder Heads (Cast # 993)
* 2.02 & 1.6 Manley Pro-Flo Valves
* Harland Sharp 1.6 Ratio Roller Rockers
* Crane Valve Springs and Retainers
* G.M.P.P. Ram Jet Roller Cam
* Crane Roller Lifters
* Speed Pro/TRW 1.25 Dome Forged Pistons
* Windage Tray
* Lightweight Nodular 16lb Flywheel

* Induction - Ported and Gasket Matched
Plentum
Manifold
Runners
52mm Holley Throttle Body
Custom Built Adjustable Fuel Pressure Regulator
#19 GPH Injectors running at 50lbs

* Exhaust All New
Edlebrock Chrome T.E.S. Headers
High-Flow 3" Carsound Cat
Dynamax 3" Exhaust Tubing and Tail Pipes
Flowmaster American Thunder Muffler



Stealth Ram and Prom Burning Equipment about ready to go.

REDZ28

My 1991 Z28 350 tpi motor with the stock SD chip responded great to my mods! I put in a ZZ4 camshaft and springs and retainers on my Stock Heads! 50 psi fuel pressure, 12 degrees timing BTDC, 160 stat, coolant bypass at throttle body, 1 5/8 headman headers, no cats, dynomax super turbo muffler, marsh underdrive pulleys, 3.42 gears, air foil, trans pac shift improver kit, Ram air in my fog lamp openings. My car ran a best of 13.11 at 101.6 mph. So I think My speed density worked good for what ive done to my car. Remember its still the stock chip. I think you guys exaggerate SD shortcomings. IMHO!

jmd

iTrader: (4)

I think with a 50psi FPR, 12 deg., and stock PROM your car is maybe running well, but at the cost of efficiency. No flame, just a thought.

REDZ28

Maybe it is running very efficient since it runs so well for the mods. Just a thought!

GNR4EVR

Take that Hypertech chip out, the Hypertech chips are designed for stock or near-stock applications.

70formula

IMHO - the engine is definitely being choked out.

These are things that should be improved.

Intake - manifold, plenum, runners, TB, and some fresh air.

Exhaust - headers

An appropriate stall converter to match that cam.

...and rearend gears.

90Formula-X-F

REDZ28 is a good example of what I am refering to. The factory set up for the computer timing and fuel curve isn't bad when building power in the rpm range. Holding that torque level up there closer to the highest RPM range with TPI with out throwing a cam in that performs in the wrong area's is a big plus....

Speed density or mass air, you make do with which ever you have and make it work. I am a G.M. drivability tech and a fan of speed density myself. The 90 to 92 F engine's ( 5.0 liters ) used the same fuel curves and camshafts as the did the L98's and probley other things too. The conversion and a little extra fuel pressure makes them Ideal for a 5.7 to replace a 5.0 with a little extra fuel pressure and some head work. match port and some good exhaust and you have a runner. No other tuning really necc... If you have never been down this road then you really don't realize what I am refering to. that's why the Name

90Formula-X-F .... or .... X-F = no more f engine yet I have everything else right now under the hood less the motor and exhaust that was o.e. and it still will pass California smog and it is way fast. and I've had it since it was new. Stock 13.90's new.

formul8!!

I will say about 95% of the problem is the cam was not degreed correctly. The SLP cam's are designed to work ok with the stock intake stuff. Get the SLP stage II chip if you do not want to burn one yourself.

IMHO, all the intake and exhaust should be done FIRST before even thinking about porting heads or changing cams. The stock intake is severely flow limited to a 350 already and the exhaust stuff just sucks. Once you can get air into and out of the engine better, then you go into the motor.

Hope this helps.

wyclefsirocz

the cam is ok, you just gonna need a set of headers w/ y pipe and some more porting to the intake- would help. (or a HSR would do wonders)- the problem isn't in the heads- its all in the computer. stock computer is the problem- replace that with slp stage @ prom(metioned above) and you will be ok. i mean your friend. oimho. he started in all the wrong places to make power. but had the right idea just needs some guidence.

CHEVY_EATER

Ok, so how is this list:

• Hooker SC headers
• Ported runners or aftermarket runners
• SLP Stage II chip

Is the stock TB ok? Any other suggestions are appreciated! Tanks for all the repsonses already too!!

wyclefsirocz

yeah thats a good start, the stock tb is also fine. once that is all done and the car is running proply i would get a new afpr,some #24 injectors and a new trottle body. but thestock one is fine for now.

CHEVY_EATER

He said he checked the FP and that it is at just over 40psi, not sure if that is with or without vaccum too it. I'm used to Mustang's...so this is all new to me! But I guess same things apply....basics at least.

SinthetikIroc

iTrader: (1)

dont forgot to port the plenum.
get us the specs on that cam plz

so everyone can have a much better idea of whats going on. but if you open up the exhaust and intake. you'll get a whoppin difference. after that its jus all fine tuning in the prom.

90Formula-X-F

Try putting the stock prom back in ...
Most street cars never produce 350 cubic inches of volumetric efficiency. More like a 350 becomes a 270 cubic inch engine. mess with the figues and it could get worse. Get it right and it gets quicker in a L98 TPI application..

The cam in a carb'd car, coming in at 3000 RPM will start to build it's greatest torque at the peak pull point of the camshaft... aprox 3800
It's at this time that the engine builds its best volumetric efficiency even though it's not at the peak horsepower it doesn't run out of air it can pull a higher RPM and the TPI isn't about any of that.
Air restrictive induction becomes a misconception when the car winds up to 5500 and never peaks torque correctly. The results are poor volumetric efficiency. The car max's out at 255 grams per second but is that flow limited ? To be flow limited your gonna need to punch that number up quick in a TPI L98 application. If it drags it's butt up to 255 gps it's now flow limited by the builder not the induction. The engine should max out MAF extremely quick with buckets of torque from off idle to 5-5500 rpm. Push the max torque closer to the RPM range that is the horsepower with a TPI system and you achieve the best efficiency. That means that done correctly Max MAF could be better even at 4500 rpm if the efficiency of the engine is peaking there at a close to cubic inch figure.
The loss of instant throttle responce after a larger cam is installed is normal and makes for most disapointments. .. G.M. used the efficiency of the engine through torque, increasing it and pushing it farther into the power band closer to peak horsepower made the stock engine outstanding.
Chances are greater than not that after the large amount of cash spent on performance it will be a disapointment.

Unless your a prom guru or have help from one you should stay with the stock prom. Stock #19 injectors if in good shape can keep up with 355 hp no problem. The high speed pulse of a 50 lb fuel pop on a #19 injector in my opinion is more effective with a stock prom than a aftermarket prom and larger injectors unless you are or are close to a prom programmer. #22's can keep up with 380 hp and after that you need a programer anyway.

A person with a stock built lower end. Some induction and head porting, larger throttle body, 50 lbs of fuel pressure, a good exhaust and a stock prom will be quicker than most people who push the efficiency out of calibration and spent 10 times the dough doing it.

Make those heads big valve heads and you get more yet.