hey there.... i finally got the iroc on the road and running good enough to drive it to the dyno and get a base tune down.. here is a list of whats in my engine
fresh rebuilt 355
flat top hyperutectic pistons
I beam rods and balanced crank
268xfi cam
stock 062 vortec heads machined for the lift
1.6 harland sharp rockers
scoggin dickeys base mild polish
completly siamesed slp runners with port matched plenum
24 pound injectors with bbk AFPR
stock throttle body with 3 inch CAI with stock MAF
egr delete
stock ignition with msd wires and coil

transmission wise its a 700r4 freshly rebuilt by a local reputable shop, vette servo, transgo shiftkit and a 2800 vigilante
exhaust is hedman longtubes into a 2.5 inch y pipe and then 3 inch midpipe to a hooker aerochamber and dual 2.5 inch tips
aluminum driveshaft
rear end the stock 9 bolt with 2.77 gears
walbro fuel pump

i originally had 30 pound injectors in the car and it barely ran.... when i got the 24s in it ran good enough to drive and so i went to dasilva racing to do some dyno tuning. first pull got me 254 hp and 241 torque
after some air fuel tuning the best we got was 267 hp and 275 torque.

i feel almost cheated considering the hours i went through porting the runners and plenum. i was really hopeing for at least 300 at the wheels.

The tuners suggestion was to put a bigger cam in and increase my throttle body side and upgrade to a 3.5 or a 4" CAI...... im not sure if its worth it.... on top of that i just found out that there arent any larger Mafs for tpi cars and thats why everyone switches to map.

the car still doesnt run properly either, more driveability tuning is required...
im not sure if its worth pouring more money into a larger throttle body.... i was under the impression that the stock one can support plenty of power..

id really apreciate some suggestions on a direction.... what am i missing in my setup, i see alot of guys with way better power from their tpi's than this.

 

The camshaft is not the problem. I made 350rwhp with that exact cam. Burnout91 made over 320rwhp with a stock short block and that cam. Did you degree the camshaft when it was installed? What is your compression ratio? How well do your plenum, runners and intake manifold line up? There should be no steps in the path of the air flow.

You are missing a lot of horsepower somewhere as you should be over 300rwhp.

 

heres my dyno sheets of the first and last pull

 

i cannot say about the cam, the engine shop ordered and installed it. the porting is very close, the only major step i can think of is where the siamesed runners meet the base becuase the base is not siamesed and there is the space between the two ports. i beleive my compression ratio is around 9.5 to 1. the car blows a bit of smoke.... im going to do a compression test to see how that is.... im worried the 30s washed the rings. ill find that out this week.

ill post those results when i get them.

 

When I had my 350 dynod I had 290 horse and 320 torque at the wheels, on a bone stock internals with bigger heads intake and exhaust. You are definately missing something

 

wow very low numbers. I bet the power is lost in the intake and alittle on the exhaust. Should have a 3.5" single i feel and have that base fully ported. its not flowing enough to support that cam and heads i dont think

 

Compression test and leakdown test FIRST then see whats what. THe exhaust is good guys no worries its a 2.5 mandrel bent y with a 3" mandrel bent cat back. Same set up in my car did 360 plus rwhp on same dyno same day

 

who programmed your chip

http://www.scotthansen.net/index.html

 

here are the results of the compression test...
#8 180 psi #7 185
#6 185 #5 182
#4 190 #3 176
#2 177 #1 176

seems to be okay to me... i need to do a leak down next.. but i dont have a gauge.. i need to pick one up.
The car was tuned by a guy named Peter.. i never did catch his last name but he was recommened to me by Joe Silva {DaSilva Racing} and thats where i dynoed the car.

something i thought of about the tune... becuase even after its tune it still doesnt idle well and surges a little on startup, and when you drive agressively [foot to the floor] the service engine soon light comes on and then the car seems to loose power.. big time.. im guessing it pulls timing or something becuase i had to give it alot more gas than normal to do low speeds. is it possible than it was tuned in closed loop and when the car starts in open loop thats why it runs bad?

ill post up my leakdown rsults after i get the gauge

 

Definitely need to have the tune worked on.

Could also be losing a bit with the heads, with one step larger cam and AFR heads I hit just over 300rwhp. But I'm also running a stock ported base instead of aftermarket.

 

Those dyno sheets are telling me either 1. the cam is severely retarded, or 2. not nearly enough timing advance.
Your compression numbers aren't that bad.
Any idea what your ignition advance curve looks like?

 

unfortunately i do believe your tune is way off and needs work. Find another place to tune it or try working on it yourself

being 89 MAF it shouldnt take much to get it close to running speed My 383 base tune had minor changes done and the car idled ok and drove fine enough for a base mail order tune. i was happy with it. Granted WOT was way off but the car ran.

Get some tuning stuff and go at it

 

i have all of the tuning equipment.. i have the autoprom with tunerpro rt

i dont know what the timing curve looks like.... id have to dig it out of tunerpro if its in there... but the tuner set the timing to 41 degrees..... im starting to wonder about that cam.....might be in wrong like you said.

whats everyones opinion on breathing? could the 48 mm stock throttle body, and 3 inch cai and maf be hurting me that much? is it possible to overport.. i wonder if my siamesed slps are hurting me...
still have to get a leakdown gauge so no progress there

ill keep you guys posted

 

wont be hurting as much as the cam being in wrong or the tune

41 degrees of timing is too much i think. may want to revist your tune and look at the tables as well as fueling

what was air fuel ratio on the dyno? any spark retard or knock counts?

 

I might as well chime in what I recall. The A/F was set perfect at 13-1 no dips the tuner had that nailed from what i could see. I'm starting to doubt certain things though as he ( the tuner ) was really struggling just trying to make sense of the tables. For instance at first he was reading that the timing was set at 80 degrees or some absurd amount. He wrestled with that alone for over an hour and downloaded a few different definition files until he found one that "seemed" to make sense to him. So now I;m wondering if the timing is way off as mentioned above. I'd have to think the cam was installed properly although the shop that did the work isnt my fav they sure have built many a wicked engine and they've been around for years and years. All they build is hi-perf stuff for the record.

So back to my timing theory if the tuners definition files misled him and in fact he thinks he has put 41 degrees in but instead put 20 ( maybe it is halfed?) then that would sure rob power up top. Really though I'm just guessing here and throwing ideas at this thread in hopes that we find the smoking gun.

How much timing does the TPI computer control anyways? I have no clue as to the relationship between the distributer and the computer in that regards.

 

if you have tunerpro RT, connect to the aldl port and do some real time scanning.

check the spark advance timing relative to tdc at idle and driving conditions. see what the values are and go from there. check your base timing on the motor as well to see whats up. verify its set to what the chip states. if not set base timing on engine to 10 degreees or so. program chip to have 10 as base and go from there

its a 89 so its a 6E mask/ xdf file. load that in and look at your tables/values for your chip. do a read on the chip and open that file to see what is in there as far as spark table and such goes

 

alright.. i went for a little drive in it today... the blms were showing anywhere from 108 to 160 but mostly on the near 130s... during this time the o2 sensor was jumping from 100mV to 800mV which seemed very radical... however later on in the drive it seemed to calm down and then changed relative to the blms.... the higher the blms got the higher the mV from the o2 sensor were... we [ me and cam-] decided to see how high they would go from a stand still at WOT the highest we got was 925mV from the o2 sensor... what does this mean... i would extrapolate that this means the car is running very lean and or the o2 sensor is no good... just to be safe.. i bought a new gm replacement today and after installation i will post up what my values to see if they are different. other values in red were the Integrator values which were 108.. not sure at all what that value means.

ill check out the timing next drive.. but the o2 sensor took priortity seeing that it was jumping all over. how are blms determined.. is the blm value dependant on the o2 sensor? when the car was dynoed the air fuel was perfect... certianly thats not what my dataloggin says.. so my first guess is bad o2 sensor... ill keep you guys posted.

 

Change you oil first. Your o2 could have gotten poisoned by the silicon coming out of the gasket sealant in your new motor.

 

Sounds like the O2 is working fine. Its supposed to swing from around 100 mV to 800 mV or so. The O2 rapidly switches about stoich so the ECM knows if its on target or not. From the BLMs, it sounds like the tune is off, or its misfiring at certain RPMs.

With the vortecs, I found that starting out with around 12-14 degrees at 800 RPM and ramping it up to around 30-34 by 3600 RPM seemed to provide the best performance, although it'll vary depending on your intake, engine, cam, etc. Theyre good starting values, though.

 

"Sounds like the O2 is working fine.".......X2.
And 925 mV from the O2 at WOT is a good safe value (on the rich side) to be at. Definitely not your issue.

 

hmm yes.. ive heard the vortecs dont like as much timing as the older style setups.. i have 41 degress now.. probably too much.. that will be next change.

 

I would set the base timing between 6-8 degrees. Set 28-31 degrees of timing in the chip. The air/fuel ratio on the dyno graph should be around 12.8 - 13.0 across the graph.

Your manifold is your BIGGEST RESTRICTION. You need to do some major porting in the pinch area in the manifold. Get the manifold to flow over 300cfms. Right now it flows around 220cfms.

 

alrighty plugged in last night to double check if o2 sensor replacement changed anything.. the answer is no.. you guys were correct... it was fine.. but now i can rule that out completley, i can gaurantee my iac tps and maf work as well.
i wrote down some numbers for you guys..
Iac postion between 66 ans 70 steps
knock count 1
spark adv rel to TDC 27 degrees on average
spark adv rel to ref pulse 24 degrees on average
the INT is 132
the BLM is 135
02 sensor reads 400-825 mV
the ecm also threw a code 51 at me
all of the above values were about 4-5 minutes after a cold start @ 800-900RPM in closed loop

i checked in the chip and it says base timing is 5 degrees and max spark advance is 41 degrees on monday ill check the timing on the car to compare.

i went for a short drive and when i was drving along blms would go to 108 and then at a stoplight i would see values like 147.. this means im lean at idle and rich on the gas right?

 

here are some shots of the car.. what the heck...

VincentZ28... what do you mean pinch area? do you mean where the manifold meets the head?.. also notice in the picture how close the round ports on the manifold are.. i didnt think i should siamese into the base becuase i have heard of horror stories. hmm please elaborate if you can.

on a timing note.. i definetly think the car has a different base timing than the computer thinks it has...

thanks so far guys

 

heres only manifold pic ive got

 

It's about an 1 1/2inches before the manifold meets the head.

 

Just curious if the converter was locked or unlocked? Not that it's going to find all of your missing power, but I've seen a few cars pick up around 15 RW locked vs. unlocked.

 

well then that would probably be my problem for upper end power.. if you look at the dyno graph the power peaks at around 5600 RPM after that the tpi chokes the motor.. the cam would like to breath to 5800 RPM. so my guess is between the timing issue that i definetly have and my bottleneck base thats where my power is. i was thinking maybe a vortec stealth ram would do nicely when it comes to breathing easily up to 6000RPM. i get back to the car tonight so if i have time ill look at the timing and post.

 

interesting question.. i have no clue.. the car was on the dyno in overdrive but i dont know about the converter. hmmmm another one of those unknowns im starting to get a list of those 1. is cam in properly? 2 base timing? 3. torque converter locked up? thank you for that.

 

Rich at cruise.....correct. Lean at idle?.....not necessarily. Your cam has enough overlap to give you significant charge dilution at idle as evidenced by that "cammy" idle. You have unburnt fuel/air going out the exhaust. The O2 sensors only see the unused oxygen; they are clueless about the unused fuel. The PCM thinks it's running lean and responds in closed loop by increasing the BLM's to give it more fuel.
You may be able to increase the idle speed enough to prevent this. Or, if you have the ability with programming to set a minimum rpm for closed loop idle, make it idle in open loop.

 

kk heres the results of the leakdown test.
#1 3%leak
#8 4%leak
#4 7%leak
#3 2%leak
#6 7%leak
#5 4%leak
#7 5%leak
#2 3%leak

i these small percentages ecsaped through the pvc i did not detect any leaking out of the intake or exhaust so valves seem fine and no bubbles in the rad so head gaskets and block seem to be fine. this prooves the bottom end and heads are fine.
on a timing note i checked it.. base timing was 4 degrees on the car.... i changed it to 9 degrees and set base timing in the chip to 9 degrees, then i set maximum spark advance to 31 degrees and left the stock spark advance table alone... the car idled in open loop suprisingly however after a quick boot up the road the car was backfiring with acceleration and very unhappy all i remember from the datalog while doing this was 15 knock counts and 3 codes.. prom error, EST error, ESC failure... next i am going to back off base timing to somewhere arouund 7 degrees and try.

as for my power problem.. now that ive ruled valves and rings... im thinking impropper cam installation and intake does not flow enough.

ive read about phantom lean condition because of lumpy cams.. not that mines very lumpy.. 113degree lobe separation 218 224 duration... i think there might be a way to alter o2 sensor tables to fix that.. but im unsure.

Speed

 

kk.. changed base timing to 6.5 degrees then changed it in chip as well.. car runs ALOT better.

 

i saw a 355 vortec TPI make 355hp 423tq and it woulda made more wit a tune and a good exhaust

355, 9.3:1 comp.
vortec heads, machined for lift
GM hot cam 218/228 .525/.525 lift
1.6 RR
52mm tb
edelbrock runners
stock plenum
scoggin vortec base unported
stock tune, 24lb injectors

first id say that ur intake its all that restrictive... youve upgraded everything but the TB. now idk if i woulda fully siamesed the runners, u would lose a good bit of tq wit that. is the lift on that cam .567/.571? cuz thats the same lift on my XFI280 and thats wayyyyy to much for a vortec head. usually spring upgrades get u too about .55 like the scoggin dickey heads.

the cam is rated from 1800-5800... which is alil high for TPI. yoursetp will max prob in the 5200 range... the cam isnt bad. but your TPI is gona restict ur HP. also your tq converter is alil on the high side as far as stall for a TPI, i would have gotten a 22-2500 which is wat is recomeneded for my 383HSR wit the XFI280.

vortec heads are great heads in the low flow ranges... they kick @ss in the .4-.5 range. once u get to .5 and above the suck. i wouldnt have gotten a cam wit that high of a lift, u just too it outa the heads range.i put u at the 330-340hp range at the crank wit 22% drivetrain loss due to the automatic. so thats not too bad eventho i would prob calculate 24% drivetrain loss. theres sum HP waiting there but i wouldnt count on that much.

 

Just a little suggestion, the vortec's like alot of timming and fuel early on in the curve (below 3K rpms) and they like very little total timming (under 30 degrees) That said, if you have 41 deg total timming you will be losing alot on top. The vortec DO NOT like that much total timming; change that immediately, and probably add fuel all arround (especially alot on the bottom to match the timming advance)and it should come in line in the BLMs and should wake up the motor.

Fast burn heads have very different timming and fueling curves from the old iron head, or aluminum head designs.

Good Luck.

 

http://store.summitracing.com/partde...8&autoview=sku

i talked to the guy at precision industries about a stall and thats what we came up with. however.. precision industries understands that sometimes one you get it in the car you may decide you need more or less.. so they nclude one free change in the price.. so i can get the stall lowered from a 2800 that flashes at 3000 to something lower.. not otally screwed there.. however... she works pretty damn good now hahaha.

as for the lift... you are making sense there.. vortecs are new technology and require different things... currently my cam has 570 int. 565 ex. with 1.6 harland sharps, i could put on 1.5 ratio rockers and that would lower the lift. to 535 and 530 hmmm i know vortec need their own special recipe to work properly this might be another problem.

 

yea i would def the converter done to soemthing int he mid 2500 range. so it flashes to like 2700 or so. ive seen low 12s in the 1/4 wit a vette aluminum head 350 with a TPIS zz9 cam and upgraded TPI (no porting) run low 12s wit a 2200-2400 stall. the tpi's just dont need that much since peak tq is made at like 2800.

i would try wat kennerz said wit the timing. and def go wit lower lift. low 5's will help, ive done my homework on vortec heads since thats what i wanted for the longest time bc there cheap and flow good. i hope u cleaned up casting flash on the heads in the intake/exhaust ports... they have been known to have quite a bit. i have a pair from scoggin dickey wit the spring upgrade and its got casting flash i gotta take care of before it goes on

 

Interesting. Too bad we cant test the 1.5 vs the 1.6 on the dyno to see if there is gain or not.

Also you guys above the HP numbers your throwing out is that rwhp or flywheel?

As far as the stall goes I'd run it and see how she goes. If your 60' compares favorably ( or beats ) other similar set ups then I'd leave it.

 

okay... lets pretend my cam is severly retarded and degreed wrong.. what should it be advanced to?

as for my head ports they are completly virgin

at scoggin dickeys you can get stock vortecs.. 0.45 lift upgraded .525 lift and even more upgraded 0.57 lift.....

http://www.sdparts.com/catalog/engin...rHeadKits.aspx

hmmm.. obviously they have done their homework and that means i am very high when it comes to lift.

car throws esc failure code when im at wot but only when shes really rung out... possible knock sensor problem?... maybe i should upgrade?

 

yea i read that. umm i would say that ur still pushing it wit ur cam. my lift is .571/.576 i believe i put it wrong in my post before last. thats maxing out the valvetrain.

as far as the ports... my dads are straight from scoggin and they need sum port cleaning since theres a good bit of casting flash. i think u would have noticed if there was any.

 

107 degrees ICL. Given the choice of being off a degree one way or another, 106 would be better than 108.

 

What valve springs are you running????? Are you experiencing coil bind????

Don't worry about the cam being degreed. If it's dot to dot it's good enough to NOT be the cause of this LARGE lack of power.

 

here are the springs i have

http://store.summitracing.com/partde...5&autoview=sku

my engine shop said they were good to .600 lift i also have comp cams pushrods and steel retainers

i dont think i have coil bind... my engine shop should have made sure of that.

 

Hmm, are those the springs comp recommends with the 268XFI and 1.6 rockers???????????

If you had a set of 1.5's laying around, I'd say try those and see if it gets any better.

 

Those are decent springs, but I thought the XFI cams were meant to be used with behive springs like the 918's?

 

Call Comp and ask its free! And you know what I say about that shop....

 

http://www.compperformancegroupstore...Category_Code=

these are the recomended valve springs.. they are the beehive 918s....
i dont like beehives and didnt want them.
----------
heres a link comparing them on summit.

http://store.summitracing.com/compar...=KeywordSearch

speed

 

The springs are fine BUT you have to make sure they are rated for your intended usage whether or not you dont like the other springs ( I dont like singles either ) but its possible that the ones you have dont clear properly with your installed height, 1.6 rockers, and cam lift so call COMP and see what they say

 

talked to comp cams... they said the spring and cam combo was fine.. go figure.. im gonna pull a valve cover off and check for coil bind soon, im curious now.

Lee

 

Even if you're not getting coil bind, you could be getting valve float. But I guess if comp says they're okay even with the 1.6's....... I don't know, I still think I'd try and find a set of 1.5's and try them.

 

kk.. did some research and found out something interesting... maybe false but heres what ive got... most stock gm head installed spring height is 1.75 my engine shop probably assumed that that was the installed height.. subtracted the coil bind. 1.15 from it whitch gives you 0.6... in other words good to .600 lift. however vortecs the installed spring height is 1.7 subtract coil bind and the springs ive got are only good to .550 lift..... sounds like my springs are NO good for my cam lift. im not going back to that shop again.