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Total Eclipse Smokefiend
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174 Posts
Discussion Starter #1
Hey guys

Still playing with lots of ideas in my head about what to do engine wise down the road. I'v pretty much narrowed it down to either going for a performance build on my current L31, or go with the Lq4. I know I can build either motor well over what I am looking for (which is in the 425 range crankwise and similar torque numbers), but I have lots of respect for the new lq4. I really dig the block and it's construction, which is part of the reason I am thinking of doing the swap in the future. Not to say the L31 isn't a good motor, just an old dog with new tricks.

My question today is about head flow. If I keep the L31, I will go with the Fastburn 385 Gm heads (Unless I find better flowing units for around the same money), and possibly a stroker crank to get some extra torque.

Since one of the biggest issues with making power and making it efficiently is headflow, I need to know here is what the Fastburns flow CFM wise. I know the lq4 uses, in essence, z06 heads. I'm pretty sure the regular Ls1 heads flow in the 280 range. I know with extrude honing, this number can greatly increase. Ls1 heads are amongst the best flowing stock heads in the business. The new hemi is flowing around 330 cfm I believe, and nothing else is close. I really have no idea on how the Fastburn heads flow. I would imagine they are in the 350cfm range, but really I have no clue here. Need the info.

Also, the Fastburn heads are more oriented for top-end, correct? I know they can make tons of power, but I really haven't heard anything about them other then "wow, lots of power!". Opinions needed here. Would I be better off modifying the stock vortec iron jobbers?

Edit: One other thing I thought of just now....The fastburn heads should be compatible with l31 injection, correct? As far as I know, they are centerbolt valvecovers and require a vortec style intake, If I'm wrong please correct me.
 

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Built Not Bought
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23 Posts
The fastburns dont even come close to touching 300. I found some flow numbers and they only flow [email protected]" lift. Stock vortecs (062 casting) flow [email protected]". But flow is not all there is to performance. In test after test when comparing an old closed chamber head to an open chamber head even though the open chambered heads may flow up to 15 to 20 cfm more the closed chamber heads will make more power because of a much more efficient burn. The name says it all. Fast burn. The heart shaped chambers lend themselves well to an efficient burn. Another thing to look at especially in a truck is port velocity. Do a set of AFR 220's flow a ton of air? Yes. But whats the port velocity like? Alot slower then say a well designed set of 170cc heads. Now dont get me wrong Im not saying buy the Fastburns. As far as Im concerned Id buy another set of aftermarket heads first or mod what you got. And in your case as you have the vortec heads Id mod them. With some good porting the vortec heads (062 casting) will flow [email protected]" and [email protected]" lift. But another thing to keep in mind is the fact that these heads have good low lift flow figures. High low lift figures are important to low speed and mid range torque development. The exhaust can also be made to flow 220 cfm @.600" which is huge. Flows [email protected] and it can have some huge flow numbers on the exhaust seat. Though flow numbers these high on the exhaust create I/E ratios (about .9-.95+ in this case) only needed for forced induction or when heavy amounts of N2O are used. For a normal street motor you want around .8 I/E flow ratio. Plus the smaller 170cc ports help to keep port velocity alot higher making for a very strong low and mid-range.
As for the lq4 heads I want to say they have 210cc ports and their design helps to flow a TON of air but I have a 99 3/4 with this engine and it just has no umph below 3k rpm. The ports help mid-range and top end but hurt low end. Frankly Id rather have a STRONG low and mid range tq monster (especially in a heavy truck. where it in a car id sacrifice some low end) as this makes driving extremely fun.

In the vortec engines head flow is not the biggest concern. Its feeding the engine. The fuel injectors cant be replaced by anything bigger though GM does now have a more standard injector to replace the problematic pintle design but they still dont allow replacement by any aftermarket injector unless you want to make you own intake and then make a wiring harness adapter to allow the stock "plug" (big plug which connects to the spider on the top of the intake towards the back) to work with all your new stuff. Ive been planning for a long time how to do this and I think I have it figured out (its good having a machine shop at your disposal). I just need to find a victim whose willing to let me work on their truck with it. Ok now that we've addressed the intake problem now you'll have to have tuning done. You'll have to send it out to one of a handful of shops that do it. You can overcome fueling problems by running auxiliary injectors controlled by another ecm (be it a megasquirt or some other factory ecm). I have a friend who is doing this on his whipple blown vortec truck. Hes controlling it with a chrysler 4cyl ecm. Id personally go with the megasquirt but thats just me. THe megasquirt is a homebuilt ecm and for <$250 is really quite a deal especially considering it is decently powerful. I suppose being as you have an NV4500 you could just toss the entire factory set up and use some other injection system assuming there are no emissions laws in your area.

I hope I didnt scare you. Problems can be overcome with time and patience you can have one fast and fun to drive truck. I cant tell you how many people told me there was no way I could make my TBI 383 run let alone run well and make decent power. Well I did it. Anything can be done. I just dont want you to jump in to deep.

Josh
 

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Total Eclipse Smokefiend
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174 Posts
Discussion Starter #4
Scared? Not at all ;) This is exactly the kind of technical discussion I was looking for...I was almost starting to think there were no real true motorhead tech nerds here, but thankfully I was wrong.

So basically what I am looking at here for a bottleneck is the intake flow. I think I heard CFM-Tech is making a new intake, but not aware of what kind of injectors it will be running.

I'm looking for the majority of the punch in the lowend and midrange. After finding some specs in the past few days, I think I'll just go with another set of the good old iron heads. I would end up spending less money building a set of vortecs then buying the fastburns outright, with a superior powerband for my vehicle.

As for the intake bottleneck, a carb could be a viable solution. The easy way out, yes (though tons of easy horsepower could be had, carbs are fairly tit), but I'm 18 and make squat...and I dont have the priviledge to work in a machine shop anymore (had lots of fun doing that). However, It looks like you can get to around the 425/425 mark crankside even with the stock injector bottleneck and tuning...which is about my goal anyway.

Basically what I'v decided on in the future is this...
383 stroker
Modified vortec heads
Reinforced lower end (mains/caps/rods/etc)
Slightly higher compression pistons (maybe 9.8:1)
Cam, beefy valvetrain
Headers
Homegrown Cai/polished throttlebody/removal of restrictor/180 tstat

I'm pretty sure this would make me pretty satisfied in the power department...a motor making more then any stock smallblock out currently and probably more reliable if done right..
 

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Built Not Bought
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Kilborg said:
real true motorhead tech nerds
:LOL: Ill take that as a compliment. Dont worry notice this was my first post since joining in january as I never really see any topics I want to reply to. But I saw the title of this and thought ohh Ill have to check it out.

You say your going to go with another set of iron heads. If you want a set of aftermarket Iron Vortec heads Id go with a set of Pro Toplines heads. They are a steal and are a very nice casting. They have thick decks and already have improved airflow over the stock vortecs, screw-in rocker studs. But dont get me wrong your stock heads when modified are also more then up to the task. As for CR you could easily run 10:1 or slightly higher no problem. The nice thing is you truck already has a roller cam so Id recommend sticking with the roller cam. You can re-use your original roller lifters so long as the rollers still spin free and you might want to tear down and clean up (really easy to do). Then when your putting it together you're going to want to get a pushrod length check to measure for pushrod length before you order some pushrods.

As for the carb vs. efi debate Im a huge fan of EFI myself. There is no way a carb can ever touch efi for performance. Now many people will read that and say "What are you talking about. A carb can make just as much hp." While this is true I measure performance in more aspects then just Horsepower. To me Performance includes hp (obviously), reliabilty, driveabilty and fuel efficiency. Notice the word efficiency. I dont expect a truck to pull 20+ mpg (Though I can kiss that on the highway) but I do expect it to be efficient and not just a hog. My 383 beats out my stocker by about 2-3 mpg all the time and if I can keep my foot out of the throttle I can better that yet. Besides the fact the 90% of people cant tune a carb worth squat. Dont get me wrong Im no carb tuning guru but with some time I can do alot better then most. I think alot of people forget that the main jets on the holley should be used for tunign for driveability and not for WOT. The power valve is for that. Most people wont touch high speed air bleeds etc. either. But for tuning this stuff you need a dyno and or O2 sensors.

As for power numbers about the highest Ive seen from a 383 NA vortec is about 340 hp and 390 tq at the wheels. You're going to want an AFPR so you can get your injectors to flow enough without going static. Unfortunately you cant tune your own engine with the vortec trucks. I tune mine and as far as Im concerned the only two ways to tune is tuning yourself or having a shop dyno tune it and make sure the shop also gets some seat time tuning it on street driving so as to make sure that the vehicle operates flawlessly on the street and doesnt just produce good WOT numbers. By tuning yourself you can do this. But as mentioned previously unfortunately this option doesnt exist for the 96-98 vortec trucks. Though running aux injectors and ecm does give some tuneability.

I just need to get off my butt and buy a cheap reg cab sb 2 wd vortec truck and then make my own intake. Im starting my own business (dealing with GM EFI and GM diesel performance) anyways so I can right it off as a business expense :head: Ill definitley have to look into this when I get it started. There is a whole market of guys who need a real efi manifold for the vortec trucks which would allow these guys to make some real power. One bummer is the lack of an injector constant in the pcm. Though there is some talk about possibly using a pcm from a 01+ l31 engine which is Ls1edit compatible. Now I dont know much about programming in hex format and modifying the stock code but I know a guy who wrote his own code for his 7747 so Im wondering if you could change the formula for PW calculation to include a injector constant. Because tuning with a hot engine with big injectors can be royal pain without an injector constant. Im getting ahead of myself.

Josh
 

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Total Eclipse Smokefiend
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174 Posts
Discussion Starter #6
340 horse and 390 ft lbs at the torque is about what I'm looking for tireside (And I don't plan on using cheater boost or giggle gas). The l31 injection looks like it's going to stay on there until a comprable upgrade can be had. I myself am a fan of Efi ever since I took auto shop in school. I was really into computers then, and my teacher basically showed me how to integrate what I know about 'puters into what I know about tuning older carb equipped stuff I learned about in my backyard and it really took off in my head. I got about a 15 horse gain on a 3.8 reatta fooling with what I could, not even turning a wrench...Big difference from that caveman mechanical fuel metering shit.

Today I did some work on it, just cleaning it up and put the 2 skidplates I could (tcase and replaced the plastic front with the alum off my halfton). Next step (when $$ comes hehe) is to order up some headers, make an air intake, and polish the TB/remove restrictor. Might throw a TB spacer on it as well, It works in theory and people say there is a slight gain usually. Also throwing a centerforce dual friction on. I figure the 25 horse or so I gain from this will keep me going until I get the parts rounded up for the internal mods.

So, some of the l31 guys are running a "cheater injector"? From what I know about the l31 (shop teacher had a tahoe I did some stuff to, been in love with the motor since), no other injector looked like it would be comptible. Nobody makes any sort of aftermarket unit I take it? The stockers were certainley different then any others I have seen. What about the 454 vortecs? Do they use a similar design?

Anyway, its nice out, so I'm gonna go do some more tinkering and such.
 

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OG
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181 Posts
sorry if i repeat anything, i don't have time to read everything at them moment... but --

i flowed my 6.0 LQ4 heads about a week ago and they flowed [email protected]" intake and [email protected]" exhaust, Stock, i am in the process of porting and polishing right now. These heads are designed very well. They have a stock 3 angle on the intake and a 30º back cut on the valve itself as well - the intake ports are 'cathedrel' shaped.. tall and skinny... so they have the same volume as the round ports... yet much more velocity cause of the slenderness of them. The exhaust ports are D shaped which aid in exhaust flow and scavenging as well. I'm Very impressed with these heads in the stock form. I can't wait to see the gains the port and polish, and the three angle corrections turn out!!
 

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OG
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181 Posts
Hey guys, i flowed my heads last week and they turned out pretty well. at .500" lift intake i was pulling 249cfm and at .500" lift exhaust was pushing 220cfm. I'm very impressed witht these heads!!!
 

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Kilborg said:
...What about the 454 vortecs? Do they use a similar design?
I can answer that for you. The Vortec 454s use a standard good ol Bosch style injector (I can't remember if they are pencil style or old style) removing them from this stupid injector problem.
 

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badburban said:
...One bummer is the lack of an injector constant in the pcm.
Josh
So there is no injector constant in these ECMS? Wow, that does really limit a person.

badburban said:
...Though there is some talk about possibly using a pcm from a 01+ l31 engine which is Ls1edit compatible. ...
Yow, now there would be some work. Maybe.... Help me out here, I may be misunderstanding you on this one. Are you referring to the 5.7 Vortec engines (with distributor) or the LS1 5.7?
 
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