zz's z28

SO i have an 87 iroc z, with the 5.7 tpi.

My valve stem seals are shot, so shes smokey upon startup. Its pretty bad at times.

Anyway, im either gonna rebuild the stock heads, or buy some aftermarket heads.

My question is, What would be the best cylinder head manufacturer/specs to run with a pretty much stock setup. For a decent price, im on an 18 year olds budget.

I plan on running the stock tpi intake, and aftermarket headers.

Do i need and updated PROM?

thanks!!

sofakingdom

iTrader: (1)

If you're not going to do anything else to the motor, ESPECIALLY if you're going to leave TPI on top of it, there's no sense in spending money on aftermarket heads. That's A BUNCH of money and trouble to fix a little smoke but derive no other benefit.

Just replace the valve seals in what you've got. Cost about 5% as much as a set of heads, get the same result (no smoke).

zz's z28

I guess youre right. But at the same time, id like to get a little more performance out of it. Would buying heads and not modifying/swapping the intake be useless?

Twin_Turbo

iTrader: (25)

some nice 180 heads would make an impact, even with the stock TPI, especially if you throw in a cam like lt4 hotcam

zz's z28

Hmmm, that sounds good to me. Would something like that require a custom prom?

sofakingdom

iTrader: (1)

Pretty much, yes.

Change the exhaust and the cam, and maybe some other heads will start to have a somewhat nearly noticeable effect; but those long runners will effectively protect most anything you can do from making much difference, as long as they're there, except for exhaust. Headers are always a good idea.

You make a car go faster by finding the most restrictive thing, and uncorking it. Anything you uncork besides the most restrictive, doesn't do anything. In the case of TPI, the heads aren't the restriction, so it doesn't matter how much you open em up, it doesn't do much.

Twin_Turbo

iTrader: (25)

actually it may not have to be needed, I had a 355 w/ zz409 cam, TFS TW heads and 32lbs injctors, mc farland short ram, hedman shortyies into a 3"to 2.75 true duels (basically my engine w/ the supercharger not hooked up and no 60lbs injctors) and it actually ran pretty good with the stock tune, not rich, evn idles lean @ 16:1 or thereabouts, no lugging or hesitation issues. These map systems apparently are pretty lenient when adapting, as long as you don't exceed the max. measured airflow. I do have to say that the zz409 has less overlap than the lt4 hotcam w/ 1.6R so it's a little cleaner for when using SD but his 87 5.7 is exactly the same as mine

zz's z28

I mean, i know these l98s arent good for much modification. But i plan on holding onto the car and doing an ls swap or 383 build later in life.

But for now, im hoping to get some more out of it. Maybe getting the stock tb, plenum, and runners ported in addition would help?

Twin_Turbo

iTrader: (25)

What 5.7 not good for mods??? wow, that's new LOL

zz's z28

hmmm. good to know that your motor is running so well without altering the tune.

zz's z28

well, based on what ive heard, people end up just yanking these tpi 350s because they money to power ratio is bad. That ratio doesnt exist, but it makes sense to me. haha

zz's z28

sofakingdom, That makes alot of sense. So basically, my tuned port setup is a straw compared to say a stealthram?

sofakingdom

iTrader: (1)

Right; but worse than just being "a straw", think of a musical instrument. A wind one, such as a trumpet or a flute.

If you play one, you probably know, you control the pitch, aka frequency, by changing the length; and given the length, there's only one pitch it will play. The only other pitches it will play are harmonics of that one; which is, integer multiples (2x, 3x, 4x, etc.) of the fundamental frequency.

The pitch that the tube plays is determined by the speed of sound. The speed of sound is about 1100 feet per second. Let's round that off, just to keep the numbers easy; let's call it, 1000 feet per second. That means that sound (a compression wave in air) travels about one foot in one millisecond. Keep that number right there firmly in your mind.

TPI works, and works quite well I might add, by using the effect of the air rushing down the runner during a cyl's intake event, and slamming into the back of the intake valve as it closes, to generate a pulse of compression in the runner. This compression wave, aka sound, travels backwards up the runner, reaches the plenum, maybe echoes around in there a bit, and travels down the other runners. Since it's a pulse of positive pressure, it packs a bit more air into the other runners. None of them really matter, except for the next one to fire... in that one, if everything aligns just right, that peak of positive pressure travels down that runner, and reinforces the cylinder fill event that's in progress, packing a bit of extra air in there. Voilà, higher torque.

So.... over what range of RPMs do you suppose this effect exists? Pretty easy to calculate: all you need to know, is the distance from one intake valve to the next by way of the runners, and the speed of sound. It just so happens that TPIs runners are about 22" long; just under 1 foot. Remember 1 foot per msec: that means, that pulse of "sound" leaves the one intake valve, makes it to the plenum about 2 millisec later, rattles around a bit, and goes back down the other runner to an open intake valve; a total trip of about 4'. Question then is, at what RPM is the time between adjacent cyl events, 4 msec? Turns out, it's 3600 RPM (1 ÷ 3600 RPM ÷ 60 sec/min ÷ 4 cyls firing per rev = 4 msec). Ever wonder why TPI has this MASSIVE torque peak at 3600 RPM? Well now you know.

In point of fact, because of the 1100 to 1000 round-off error, the REAL RPM of TPI's torque peak is slightly lower than 3600 RPM, but not enough to matter materially.

Problem is, what happens as RPM continues to increase? Well at that point you have reflections from all over inside there; and reflections can be either in-phase (i.e. the same either positive-going or negative-going as the original), and might involve harmonics (multiples) of the original frequency. Plus, there's still a bunch of that all running around in there from the same event 2 cyls earlier, and 3 cyls earlier, and so in. Well, turns out all that stuff produces, instead of CONstructive reinforcement like it does at 3600 RPM, DEstructive reinforcement at 5400 RPM (3/2, or 1.5, times the original frequency); and then CONstructive again at 7200 RPM, and so on.

The only one of those higher-RPM effects that's ever reached, in practice, is the one at 5400 RPM. Essentially, at that RPM, the payment comes due for all that CONstructive reinforcement you got at 3600 RPM. Cyl fill decreases steadily from 3600 to 5400 RPM, at a MUCH faster rate than can be accounted for even by the poor-flowing runners alone. Which is why if you ever see a dyno run on a LB9 or L98, it will show this "Mount Everest" feature at 3600 RPM, and then instead of holding somewhat flat for a few hundred RPM and then gently decreasing at an increasing rate like a carbed motor for example will show, instead it will just CRATER. I'm sure you've noticed, if you just hold it in say 3rd gear and floor it, it pushes you back in your seat more and more as you approach 3600 RPM, and then as you pass 3600, the pressure into the seat falls off QUICK. That's torque.

Nothing else you can do to that system will change this "tuned" effect, except for de-tuning it. WHich is what siamesing the runners, aftermarket runners, etc. etc. etc. all do to it.

Bottom line, the L98 itself is a good motor, one of the better 350s that had existed up to that time; but is crippled by having those long runners on it. Until those are gone, its potential cannot be realized. I guess GM did what they thought they had to do at the time; but I can tell you, since I had 2 good friends who went out and bought 85 Vettes in 85 IMMEDIATELY after riding in my 83 L69 car and were BOTH underwhelmed, that big rush of torque at 3600 RPM just doesn't satisfy for very long when it's followed by a giant flat spot if you don't shift RIGHT THEN.

The Stealth Ram and MiniRam for example both work without any of that "tuning", and help unloick the true capability of that motor; and will reward you for putting aftermarket heads under them. Carbs too, since most of those don't significantly use any "tuned" effect of that kind, but I personally don't advocate that swap, IMO it's easier and more effective to swap EFI to EFI or carb to carb but not one to th eother. TPI, not so much.

zz's z28

Mind blower, but quite an insight. Thank you!

I didnt think it was the length of the runner that mattered, only the size, and volume of air carried.

So the shorter/wider the runner is, the better?

Thats great insight.

sofakingdom

iTrader: (1)

Depends on what you're looking for; but certainly, for higher RPMs, the shorter the better.

Look at the LT1 intake or the MiniRam which came out a few years BEFORE the LT1, for a picture of the difference.





Here's a MiniRam.

Not hard to see how this is going to behave, compared to TPI.

GOTCHEVY

iTrader: (1)

Dude Procomp makes good heads for a awesome price...
Check this out
http://cgi.ebay.com/ebaymotors/SBC-C...Q5fAccessories

A hot cam is an ok cam but if your going to chip it you could go bigger maybe a cc503...
You have to get headers...Hedman or Hookers dont get no flowtech or f*ckin pacesetter they're crap
You running auto or stick?

GOTCHEVY

iTrader: (1)

Oh your runnin auto....
Save some cash and swap to 5 speed or even a 6 speed it'll be the best upgrade you could ever do

zz's z28

Thanks for the pics! Im thinking about porting out the intake base, and plenum. Then maybe siamesing the runners. Because i have a spare intake setup. Thats until my broke self can afford an aftermarket intake.

Im also thinking about some afr 195's.

cams, cams. So many options. To be honest, im not looking for something TOO lopey. This car is driven to work every other day. (my wrangler was my daily until i bought this iroc)

As far as the manual swap. Id love nothing more. However, ive heard that unless done perfectly. They always seem way more "rickety" than a car manufactured to be manual.

LS1/t56 is my dream. Ahaha.

GOTCHEVY

iTrader: (1)

if money is tight the best thing to do for now...
take the heads to a good machine shop have them do a good multi angle valve job, new guides, seals and resurface...if you can squeeze a little extra for new springs that'll really help
And buy some thinner head gaskets that will help you boost compression a little

InfernalVortex

iTrader: (4)

Just wanted to concur with the good advice here that any major investments you make in power are going to be ruined by the TPI you have.

The cost of swapping EFI systems can be ridiculous, on top of buying the other parts to take advantage of it. Seriously consider going to an LSwhatever engine.

I built a nice 355 and swapped from tbi to carb, and I love the car, but it's just not quite as practical as it was before, and I wish all the time that I had spend that money on doing an LS swap these days. The same money would have probably netted me 100+ more horsepower with an LS engine.

zz's z28

Thanks for the advice everyone!

Im still thinking of cam/heads/intake upgrade combos.

Although in the end, itd be cost effective to do an LS swap if im going for power, i just dont have the facility to do all the work. especially if id want to take my time, and do it right.

So for now, im looking for weekend jobs i can do to boost power at my buddy travis's home garage.

He has a car lift, engine stand, trans jack, tools, welder, and parts out the ***. He's actually holding a couple TPI parts over my head.

No wonder he can make so many cool toys.

Im no mopar guy, but he has a 69 satellite/roadrunner that he's continuously swapping things in and out of.

Oh, also.

Anyone know why the hell my voltmeter keeps fluctuating, as well as my headlight brightness. My alternator is hooked up, although the wiring could be gone through.

But im no electrician, so i was wondering is this happens often?

Thanks!

Curious_George

I think the proper term here would be "re-tuning", not necessarily "de-tuning" the TPI system. GM learned a lot from TPI and the LT-1 / 4 motors. The LS1 is basically what TPI should have been had they had the knowledge at the time. Almost every (if not every one) fuel injected car has a tuned intake runner nowadays.

Here is what I just rebuilt (https://www.thirdgen.org/forums/tpi/...355-build.html and it is more fun to drive than my LT1 '92 Corvette.

It pulls hard to 5500 RPM, no flat spots.

CG

Street1989

Did u do all that with your stock pistons,rods, and crank? How much power did you make with that combo?

cuisinartvette

x2 LSx style intake has the runner length, plenum volume does it all

Look closely at say a FAST runner, how its shaped, tapered and you figure how they did it. Same wiht the heads, big volume good airspeed

You can make improvements to the TPI just dont expect the world.

tom3

Those old heads aren't terrible. Vortecs would be nice but I'd go with a new set of seals, a good performance valve regrind. Then I'd look at the rear axle ratio on your IROC. Not unusual to see a 2:77 gear back there, that is sure not ideal for performance. On your limited budget getting that regeared to, maybe, a 3:23 would make a real difference and not hurt highway driving.