What is the biggest cam I can put in a motor with a speed density TPI. The one I have now is a comp cams .428 lift(I don't have the # in front of me). I purchased this cam because I was told I couldn't go any bigger because of vacuum problems. Is this true? Is there any way around it? Thanks a lot!

 

And you want to run 19# injectors...you should combine your questions in a single thread or you are going to get conflicting answers.

Yes you can go to a larger cam with SD. Lift is not quite as much of an issue as duration, or the ecm gets unhappy. But at some point, you will need to change your eprom, no doubts about it. The GM eprom is actually quite forgiving because it tends to be on the rich side and you can increase the fuel quite abit to handle WOT.

The problem is the idle. A long duration cam severely reduces the vacuum and this causes a problem on SD cars as they are MAP driven. You can compensate quite a bit in the Fuel (VE tables) within the eprom, but at some point, you have to also increase the rpms a little to have sufficient vacuum and adjust the IAC counts, again all done in the eprom.

 

Like Glenn said, lift isnt the problem with speed density TPI, its the duration. And it has to do with the rest of your engine too. I've used the ZZ4 cam (208/221) on the stock chip, and I know you can go more. I'm switching to the LT4 HOT cam (218/228) with my new engine going in next week, so we'll see how well it likes the stock chip.

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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 am putting in a 230 duration cam similar to the CC306. But, I have the ability to burn by own chips.

Tim

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• Program your own PROMs!. Read my article to get started!
• Research and Experiment before asking questions.
• This is not a chip store. Go to the classifieds if you want someone to sell you a chip or give you a BIN.

TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Thanks a lot guys. When I do put a bigger cam in I will buy new injectors. I do plan on learning how to burn my own PROMS, so I have this basically stock setup to work with and practice. This setup may be on my car for a year or two, then I'll pull the motor and swap the cam, heads, and injectors. I guess right now I just want to get it to work with what I have. I have a limited budget and I'm sick of driving around in my crappy little honda.
I just pulled the prom out of my computer and it says DR. K on it. I never heard of it before. Do you think I can use it for now until I learn to burn my own?
I got the TPI from someone who had it on a mild 350 in 35 chevy street rod. Street Rodders generally go for looks rather than performance and I am pretty sure he never had it at WOT to often. That's where my concern is because I do some weekend bracket racing every so often. That's how I killed the TBI 305 that is in it now.
Anyway, you guys are a big help. I'm new to fuel injection, but I have already seen huge advantages over my crappy carbs.

 

BTW, everybody is telling theat the speed density system is crap. They've been telling me I'm better off with a MAF system because of my future cam mods. Is this true? Will I run into a dead end?

 

Glenn, Trax, and I all have speed density systems and we think they're the best. But if you have a MAF system now there is no need to change it.

------------------
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=-

 

Ditto what Kevin said, I DO like my SD system. Not saying its better than MAF (let's avoid that debate), it's different and it has its own advantages. Personally, I say one is best to work with what they have.

From a prom burning perspective, I think SD is easy because the Editor (TunerCat) makes it so easy. The VE Table that ultimately controls the injector flow (inconjuction with a few others under certain conditions) is very easy when you have a scan tool to monitor the engine at certain rpm/map areas.

Also, more people on the PROM board tend to be owners of SD cars and the SD system seems to be better hacked and defined. Thus, if you have an SD car you will get more guys to assist you just because there is more of us there. But we could use more MAF guys for sure, and if there were, they would help round out the PROM board IMO.

Possibly the reason the PROM board may have more SD owners is because we are aware of the importance of the eprom to the proper operation of our engines. So we (SD owners) are more willing to get into PROM burning.

But I believe MAF owners would benefit just as much as we SD owners do if they were to get into PROM burning. While I personally couldn't advise them on specific tables or what they do for a MAF car (since I don't have one or any experience burning eproms for them), I would be more than willing to help them. The basic tuning technique would be the same, it just have to be approached in a different manner. But the key is to know what your engine is asking for, and then giving the engine what it wants.

 

The advantages of the MAF with PROMS is you can be quite a bit off in calibration and it will self-compinsate... Of course a custom PROM helps, but i've heard that modifying anything on the intake side of SD requires a custom PROM. I'm not sure about the truth of this. My car had many mods (cam, headers, themo, 1.6rr) before i ditched the stock PROM, and i really didn't notice a huge increase, but I hear horror stories about SD's not even feeling a perf increase with major mods... sometimes running poorly and wasting MPG's for nothing, until they get PROMed. The whole burning chips thing seems slightly overrated to me since the increase was so small from a stock chip to a TPIS stage 5 burned to specs (Including my burning a**hole from the $500+ I paid for it) and I sure noticed maybe 95% of the cam and mods before the swap. I thought I might get lucky and see maybe 2x the power cause of all the stories the SD guys have been telling me... Need the chip.. need the chip...

 

Hey Joel, just for a point of reference, my 91 Z28 with a 350 engine, ZZ4 cam, ported L98 aluminum heads, and ported stock intake ran the stock 305 5-speed chip with no troubles. Now I'm swapping in an LT4 HOT cam, and TPIS intake/runners, and we'll see how far the stock PROM gets me.

 

Yes, Kevin is living proof that the Speed Density system can support a lot more modifications than originally thought. And after diving into eprom burning, I know why: the stock eproms from GM are actually quite rich.

With my fuel pressure adjusted to a low as it would permit (41-42 psi), I had to adjust the Injector Flow Constant from 22#s to 25#s, or lean it by 15%. And I still had to pull about another 5-10% out of the various VE (fuel) tables. By increasing the fuel pressure up to 48 psi, I had to pull another 5-7% out of the upper part of the fuel tables.

That means I could have developed another 20-25% HP with my stock eprom and possibly another 5% by increasing the fuel pressure. Of course, my custom eprom greatly enhances the smoothness and driveability of my car and makes the engine feel much "crisper". But I had a lot of room for additional mods before an eprom became a necessity instead of a niceity.

As I said before, the mod that seems to give Sd its greatest problem is long duration cams, and a custom prom will over come any "street cam". And for the track...who cares about the idle, you only have 1 light to worry about.