rockit

iTrader: (3)

i've been gone awhille but i come back and now people LIKE our heads?? last time i was here they wanted to crucify the things but like 3 posts seem to point towards them as actuall street PERFORMANCE heads vs boat anchors. bit of a flop, what changed your minds?

Dewey316

Not all of us are convinced.

ShiftyCapone

iTrader: (7)

They are not a performance head but they recently have been proven hold some merit. There are a few people that have ported versions and are running respectable times given the parameters of their vehicle. There are far better heads out there and if peak performance is your goal than you do not want these heads. In budget situations however, they can get by if you know how to make the most of them. Read up on the discussions of Fast355, Kdrolt, and JPrevost.

BadDog

Doesn't it also depend on what you're doing with them? AFAIK (which is nothing to you guys), they work well for low rpms. I know this is "thirdgen", but it's become the defacto center of TBI tuning/programming, so I hope this is not out of place.

My trucks are rock crawlers, and while we sometimes need some wheel speed, the most important is snappy throttle response and power between 1-3k. I have no desire to change heads on my dedicated buggy, and they are GM issue 89 truck TBI. When your nose up on a 14 foot vertical waterfall and have only about 1 foot till the tires start climbing. And you got to build some inertia and then maintain wheel speed, you don't really care much about what happens on the top end.

Seems like they would also be fine for anything other than ETs and street warriors. Snappy gut wrenching torque down low is over all more fun for the daily driver and should often provide better economy as well.

Just my current thoughts, may not be relevant.

Dewey316

Yes, the swirl ports do produce good low end grunt. My torque curve from my cammed 305 show that.

Great for a truck, the real question is how would it compare to a vortec head on the exact same motor?

kdrolt

Add Dyno Don to that list. He proved this, posted on it, and it was ignored for a long time before anyone else confirmed it.

kdrolt

That's still a common sentiment here.

Remember though that in none of the older posts that equated swirl port (SP) heads as junk, boat anchors, worst heads GM ever produced, was there a shred of data to support the negative claims. Even in the newer posts on the subject, both here and on FSC, there still isn't. I remember one stubborn TGO-er (FWIW not JP) commenting that said "Swirl port heads are junk, everyone knows that." Everyone may have know it, but no one had any data to back up the claims. That's called hearsay.

OTOH Dyno Don & Fast355 ported SP heads and provided the results, including flow data, dyno data and track data.

HRM ported the LB4 v6 heads and got huge improvement (even though they used valves that were, IMO, too large for what they were doing).

You (Dewey316)and Lo-tec also had data on unported SP head engines, 305 and 350 respectively, that ran 14.5 and 13.6 in the quarter with the usual exhaust and cam mods.

That's five separate instances of SP head engines, 3 ported, and 2 unported, with documented results that are a lot better than the junk, boat anchor, and garbage they were previously claimed to be.



The 187 305 SP heads flowed something like 165 cfm intake and 145 cfm exhaust (Fast355 data).

The Vortec 305 head (520 casting suffix) flowed 199 cfm intake and 177 cfm exhaust (data from one of IHI's posts).

In a small (stock) cammed engine there might not be a lot of difference in the power output because the head flow in both cases is enough to keep up with the demand of the cam; with any warmer cam, then the Vortec would win easily.

The question is: will ported SP heads compare well against stock Vortec heads? The evidence so far says yes. If you compare the cost of going either way, the SP heads are less expensive so long as you are doing DIY porting. The Vortecs require the heads plus a compatible intake manifold. New hardware (heads, manifold) will cost $700+.

The break point, IMO, is how much money do you really want to spend and how fast do you really want to go?

For mainly street use and low cost, porting the stock heads is the better choice. If you go to the track a lot AND you are willing to spent $700+ then it makes no sense to do anything to the stock heads (SP or any other production GM iron head from the 1980s to mid 90s.). For that level of performance, you should either go with the $700+ Vortec route, or get aluminum aftermarket heads like AFRs ($1000+).

rockit's original statement at the top of this thread, that

is IMO correct because he emphasized street performance.

Dewey316

kdrolt--

Yes I am proud of the numbers I did, and the dyno results. I think for as little as I have into this motor, it suprises people.

My point has always been, that I have seen stock 305 TPI cars, with darn near the same cam (or even smaller), put now significantly higher numbers than I did, on the exact same dyno. On in particular, had 30rwhp more than I did, with a stock l98 cam, untouched TPI, AND he made his HP peak later than I did, with just as much torque.

That tells me, my combo is falling behind somewhere. 1) I know it is not my intake 2) the numbers (dataloggin) tell me it is not my injectors, or throttle body creating a bottleneck.

This leaves me with basicly 2 choice, my exaust, or my heads. Since my exaust is pretty free flowing, headers, cut-out. That tells me my heads are piece of the puzzle holding me back from doing better. I really think my motor has 300hp potential. BUT, it will not happen until I optomize everything. That quest is going ot start with the heads.

Fast355

iTrader: (2)

I am very suprised that you are not pulling a good vacuum under the stock TBI. I tuned a TBI setup on a stock 1984 Suburban 165 HP LE9 305 that was pulling down to 92-93 KPA at 4,000 RPM. The stock manifold really isn't holding you back.

I am thinking Valve Springs. When you changed the cam did you also change the springs? If you are on your original set that would explain the high-rpm power drop. Your dyno sheets show that your combo drops off VERY FAST after peak. That generally tells me that your springs are too weak.

It would also be interesting to add a bung to your exhaust and get a backpressure reading on your exhaust.

Finally do you have a dyno printout with AFRs on it. You may not be out of injector but could easily have TOO much or TOO little fuel. Another possibility is in the advance. I run 28-30* of timing at 2,800 RPM MAX with swirl ports. It makes the most power there. I stress as I have seen just 2 extra degrees of timing kill nearly 30 RWHP on my 355 when I was tuning with the swirl ports. 28-30 produced practically the same power, 32* made the power fall by nearly 30 HP, and bringing the timing back to 26 brought back 20 HP. Bumping it to 29* gave me the full 30* back. The magic number seemed to be right at 12.8:1 air/fuel mixture on the wideband and 29* timing.

Also don't fall into the trap of different cars on the same dyno. There are a whole bunch of different variables involved. His dyno numbers maybe better, but there is always the chance your car might walk away from his. Have seen it done, many times.

Dewey316

Here is a graph with the AFR



It is actualy a bit better now, as I took that AFR and adjusted my VE accordingly. I also worked on my pump shot, as it was very lacking.

I have a bung in my exaust, that I use for WB readings. If i was supplied with the proper gauge/loggin, i would be glad to check the backpressure, but I don't have to tools to do that.

I was very suprised to see that I didn't have any major vacume at WOT either. Even at 5500rpm, I was reading 99kpa.

I will have numbers in January, with the new heads on, same cam. I will likely put a BB TB unit on, and some bigger injectors, as I really think this cam has a 240rwhp pull in it. I may step to a slightly larger cam, just because this one was almost too easy to tune. In hind sight, I probably should have gone with a bit more cam to start out.

Fast355

iTrader: (2)

That will be interesting to see. I am going to say that if you ported the heads (Carb era 416s, IIRC) you will likely be in the 250 RWHP area with around 300 ft/lbs.

Don't forget what I have been saying this whole time on cam selection. Cam your 305 as you would a 350, the advertised powerband is VERY CLOSE between the two, maybe 100-200 RPM difference. My L82 cam peaks at the same RPM in my 312 as it did in a L82 350. Also take a look at the L98 cammed 305 TPI vs. 350 TPI with oversized runners.

On a final note with your AFRs on the dyno. You got really LEAN after about 4,500 RPM up to about 13.8:1 from what I can tell. You would keep the power up longer by keeping it in the 12.5-13.0:1 range. I also don't care to see the roughness of the power curve around 4,500+ RPM. Finally, I don't know what caused the little spike in power around 4,500 RPM, but take note that there was also a DIP in AFR. Maybe your engine likes 12:1 on the dyno?

Dewey316

The dassed line is 13.0 or 12.8, so i really didn't go about 13:1 until after 5000 rpms.

I would be tickled if I get 250 to the wheels. My car seems to be very efficient at using the power it has. I am really thinkin go of tossing a hot cam in, ( i have a spare. ). Not sure what the 305 will do with a 218/228 cam in it though. Might be fun to find out.

Now if i could find a 2" TBI unit for cheap, I will be set.

Fast355

iTrader: (2)

I do know a 224/224 @ .050 cam on a 115* lobe center running 4* advanced will SCREAM in a 305 with GOOD heads on it.

Dewey316

What was the RPM range on that?

Fast355

iTrader: (2)

With a 2,000 stall and an automatic, I made PEAK Rear Wheel Torque at 3,350 RPM and PEAK HP at 5,500. Torque is strong from off-idle to redline. Torque really comes on around 1,700 RPM.

Dewey316

Damn you, now I have a feeling I'll be doing a cam too.

Guess we won't get a straigh up comparison on untouched SP's vs hogged out 416's.

But with a set of drag radials, I should be working on some pretty good drag strip times.

DM91RS

John is this a GM "hot cam"?

Fast355

iTrader: (2)

If you are going to spin the engine faster I would advise pulling the engine, atleast changing the bearings, boring/honing the cylinders, and putting in new rings, gaskets, seals, etc. Also measure everything and inspect everything. Add some ARP studs (especially Main Caps and Rods) and have the rods resized. Either have the crank turned (they tend to go EGG shaped after alot of abuse) or replace it with a Forged Piece. At the same time step up to some decent flattop pistons. Also have the rotating assembly balanced. No sense in not doing it. You are going to have it torn apart for the most part. You will have a 6,000 RPM ready shortblock after that.

Dewey316

ack, no way, i'm trying to see what I can ring out of this. But if I was going to do that, I have a small journal 327 in the garage. forget spending any real money on the 305.

DM -- Yes it is the GM LT4 hotcam.

Fast355

iTrader: (2)

Sure sounds like it. Will be a SCREAMER if it is.

http://www.sallee-chevrolet.com/fram...hotcamkit.html

I am missing some engine specs but, using the above cam specs, flow numbers from my ported 601s with 1.84" and 1.5" valves, headers, good exhaust, 660 CFM 454 TBI assembly, assuming 9.5:1 compression, single plane intake(IIRC), assuming perfectly tuned.

RPM-------HP------TQ
2000-----106-----278
2500-----140-----293
3000-----178-----311
3500-----222-----333
4000-----267-----351
4500-----308-----359
5000-----341-----358
5500-----356-----340
6000-----357-----312
6500-----347-----280

If you have a Dual Plane Intake (Read Performer RPM)

RPM-------HP------TQ
2000-----115-----301
2500-----149-----313
3000-----184-----322
3500-----225-----337
4000-----264-----347
4500-----299-----348
5000-----325-----341
5500-----334-----319
6000-----331-----290
6500-----315-----254

We are talking heads that only flow 224/160 @ 28 in/h20 pressure drop and 0.500" lift.

Dewey316

well, I have a single plane, My heads should flow that, only plan to run it with 1.5 RR's, so the total lift will only be .492 instead of the .525, but it should still make descent power.

Fast355

iTrader: (2)

Thats good news, because I ran the calculations at .492" of lift, figured you weren't running .525".

The FUN part is going to be getting fuel at the HIGH RPMS and not FLOODING it at idle. I ended up with 32 PSI @ WOT with 68 lb/hr 454 injectors and a VAFPR with 22 PSI at idle.

Sounds like a decent recipe for 300 RWHP to me.

Dewey316

yeah, I have a set of 1.5 RR's in my closted, along with a few other fun stuff, that I need to put on.

And I hope it will idle. I can always try to bump the idle up to like 1k. :: shrugs ::, in hopes of taming it a bit if I need to.

Fast355

iTrader: (2)

From the experience of others the LT4 Hot Cam typically idles at about 700 RPM in a LT1 with about 14-16 in/hg of vacuum unloaded. In a 305, it should do well at about 750 RPM in OPEN loop with about 12-14 in/hg vacuum.

FYI, the LT4 HOT conversion package is good for 425 Crankshaft HP in a 350 LT1. Granted the LT4 heads are better and it has a few more cubes. 350 FWHP out of a 305 is very realistic and obtainable with that cam!

83 Crossfire TA

iTrader: (2)

Dewey, I’m sure that I’m just behind the curve here, but can you post info on your current combination? I’m assuming stock or ported swirl ports, current cam specs? What intake? Headers?...

For at the wheels numbers for a 305 those are some pretty healthy numbers showing good efficiency, it just sounds like the powerband is not where at the rpm that you want it to be at.

What originally used the VAFPR? I’m thinking of digging one up and experimenting with it. How was tuning with it/happy with it otherwise? What ECM are you using?

what are your flow numbers on those heads? Are these the 224/160 heads that you mentioned later on? With 1.84” intakes?

I’m not following, are these actual numbers or numbers generated by some simulation/software?

Fast, when I get the chance I’m going to start a thread based on what we were going back and forth about in the other head thread, because I would like to explore that a bit more without polluting that thread. But for now I’m just looking for details while fixing my messed up LO5 (got the truck back on the road and suddenly I had a solid week of flaky behavior that I can’t really trace down to anything, that just went away as suddenly as it started)

Dewey316

Mark,

Untouched, bone stock swirl-ports. Untouched 305 bottom end.

Cam, UltraDyne 272/282(adv) 206/216 @.050 .447 .447 112 LSA (106 CL), Wieand 7525 Intake, STOCK tbi unit and injects, Hooker 1 5/8" shorty's, 3" Y and a cut-out. Cranked up the fuel pressure, and spent many late nights tuning the thing by running 1/4 mile passes, back to back to back, and comparing trap speeds.

I am pretty proud of what it runs, the amount of power under the torque curve is nothing to be ashamed of, I really did expect to see power higher up (on the dyno), when you are driving it, it feels like you should be shifting later than the dyno indicated.

dimented24x7

iTrader: (2)

Nothing changed my personal opinion of them. Theyre still boat anchors or future soup cans in my book.

Granted, people have achieved flows similar to what the stock TPI heads have with porting. If youre experienced and can port them for nothing theyd be worth hanging on to. Once you have to spend money, then it would be time to look elsewhere.

cali92RS

Its like anything else in hot-rodding or life.
It all depends how much time and money you want to spend. If you have no money and a lot of time, you might as well port them. If you have a lot of money but no time, you of course would get aftermarkets.
The way i feel , if your not willing to spend money, you have the wrong hobby, especially if you want to go fast (I mean real fast, not 14's)....Heads are where your money should go with a real performance build up.

83 Crossfire TA

iTrader: (2)

Dewey... wow, curious… all the parts add up to something that should make max power over 5K rpm, you say that’s what you’re feeling but that’s not what the dyno curve says. From the dyno curve I’m seeing a pull that really started around 3K rpm and I wouldn’t be surprised if your torque peak was really higher at a lower rpm then that.

Does anyone actually have flow numbers for a set of STOCK 305 swirl ports? The only real explanation that I can come up with for what I’m seeing there is if the ports are flowing about 155-160cfm at about .400”…

It would be interesting to leave your setup as it is and just add some heads that flow about >200 cfm below a bit below your max lift. I’d bet that with no other changes you’d gain top end power proportionate to the increase in port flow up to about 325hp (at the wheels) or wherever your fuel delivery tops out.

I think I need to get my hands on a set of 305 swirl ports to experiment with (I have the 350 ones and some 416 305 heads, but these things have me wondering)

83 Crossfire TA

iTrader: (2)

Stock TPI heads have no redeaming qualities, they flow worse then stock early 305 heads do with smaller valves, have crappy chambers and worse swirl characteristics.

I could see these being usefull on a truck engine that you're trying to keep compression up on

Dewey316

Mark, I'll have numbers in Jan. Ported 416's are at the machine shop right now, being cut for studs, guidplates, and being decked for striaghtness. I'm leaving the same cam, intake, exaust on. And also sticking with the stock 1.84/1.5 valves. I will most likely be putting bigger injects, and possibly a 454 TB, but other than that the combo is going to be the same. I was suprised that my torque peak just straight dropped. there like it just kept dropping because it couldn't get more air in there. If the torque curve flattens out, the HP numbers will really climb.

ShiftyCapone

iTrader: (7)

lift_in-----I-------E
.050-----35-----27
.100-----65-----54
.200-----90----113
.300----135----120
.400----158----133
.500----165----140

I believe this was provided by Fast355. I soon will have flow numbers for various 187 head configurations.

MrDude_1

hey, if it helps, ive given up on ANY head that still has a 23* valve angle...

GOY

Is there an 18 degree intake that supports EGR?? That would be a whole new option if so...

Fast355

iTrader: (2)

I still say you are out of cam! Up the cam and you will be suprised. A cam of about 210* duration @ .050 WILL make peak torque around 2,500-3,000 RPM on a 305. A 224* cam will make it at around 3,500 RPM (3,350 @ the Wheels)

Dewey316

No offense Fast.

But I will take the cam designers word on the powerband. I spoke with Harold for hours when we picked the cam, about the powerpand, the motor ect. When I picked the cam, it was with the 416's in mind. That is why I was suprised to see the powerband much lower than he said it would be. I am going to blame that on the heads.

You may like the swirl ports, great for you, more power to you if you make them perform. I am not going to waste any of my time with them. I've seen what the torque curve is doing, and I **think** that I will be better suited with something else. We will all see what happens when I re-dyno this combo.

MrDude_1

none that i know of.
and even if there were, i dont think anyone makes a 18* manifold with EGR.


im just sick of the limitations of the SBC... sure theres unlimited parts, but they have to fit the generic SBC design to be affordable.
throw one change, like the valve angle, and everything goes up in price so much that it could be any engine, not the cheap SBC....

IMO, if you're building a engine to use 18* heads, you'll find a way around the emissions issue... one way or the other.

if you really want the performance and to stay legal, then just jump to a different engine architecture..

Lo-tec

Just looked at your cam specs, and saw it's in there 6 degrees advanced. I wonder if that might be the cause of the lower powerband. For a reference, I ran a crane TPI compu-cam 214/220 duration .452/.465 lift on a 112 in my 350 with swirl ports. It came ground with a 107CL (5 degrees advanced). When I degreed it, it was 6 degrees advanced. It had killer midrange torque, but was done around 5K rpms. I retarded the cam 3 degrees (109CL), lost some of the midrange, but picked up power up top. It ran faster in the quarter also.

Fast355

iTrader: (2)

I am not trying to offend you but, I think even with the swirl ports out of the picture, you will still be dissapointed, especially if your cam is 6* advanced. Here is what I get with the old numbers from my 601s, 454 TBI, single plane, your current exhaust, and your current cam at 6* advance.

RPM--------HP-------TQ
2,000------131------345
2,500------165------346
3,000------203------356
3,500------237------355
4,000------260------341
4,500------269------314
5,000------261------274
5,500------235------225

That is roughly 228 RWHP @ 4,500 RPM and 313 ft/lbs @ 3,000. That is rougly 20 RWHP. I am assuming a 15% loss at peak horsepower and 12% @ peak torque.

No offense but IMO your cam and intake do not match!!! That results in lower power throughout the RPM band.

Dewey316

What about my intake doesn't match. Runner lenght? Go measure the stock runners, then compare them to my single plane.

Notice the torque peak on your (as always) desktop dyno print-outs. The torque peak is 3500 RPM. My torque peak was WAY lower. If I had peak torque at 3500 RPM, I would have been happy with it, my torque had a downhill trend no matter what RPM i started the pull out, I made peak torque at 2000rpm. That peice alone is telling me that something isn't right there.

Fast355

iTrader: (2)

Runner length is about the same, but the resonance is not there like it is in a dual plane. The plenum volume is alot more in the 7525. IME, a Dual Plane would have been better until about 3,500 RPM. WEIAND rates that manifold at like 2,500-6,500 RPM while an intake such as the RPM is 1,500-6,500.

Your swirl port heads made peak torque at 2,400 on a stock engine with a smaller cam. Don't forget that your dyno numbers are not at the flywheel rather the wheels. That alone drops the peak RPM. You are probably actually making peak torque around 2,500 RPM. Just as my 3,350 is more like 3,700 at the engine.

dimented24x7

iTrader: (2)

I think that pretty much describes most early stock SBC heads. Large chamber, spark plug way off to the side. The TPI heads also had smaller runners to help enhance the tuned part if memory serves me correct. I think they would do ok with porting. I wouldnt go and spend sums of money on them but if I had them laying around and I didnt mind doing some grinding Id be open to using them.

Dewey316

And they still do with a bigger cam, and intake. hmmm.

That is the point that I am getting at. The lack of head flow is keeping this combo from making torque where it should.

How much of that rating is because of the carbs inability to properly meter fuel at low RPMs do the loss of vacume signal. Remeber this intake was not meant to be used with TBI, all the ratings for the RPM range are for carbed applications. We know this manifold will have metering issues at low RPM's with a carb. It obviously made power just fine below 2500 on my car.

Fast355

iTrader: (2)

I have seen the exact same dyno on a 454. Single Plane vs. Dual plane with a TBI 454 SS. The single plane lost about 40 ft/lbs @ lower engine speeds and boosted HP by about 15 RWHP but used an extra 1,000 rpm to make it. It lost power at all engine speeds under 5,000 rpm. I will call my friend and ask specifics later, but that is the reason I am still running a dual plane.

TBI is prone to the same reversion issue as a carb. It can be seen as a fuel mist cloud coming back out of the TBI at low-engine speeds with a small cam. TBI still use vacuum to meter fuel, it just controls it via the MAP sensor and electronics. Intake velocity can still suffer as can resonance with a large plenum volume. Not saying a single plane can't run hard, but it needs more cam to be of a great benefit.

Back to my originol point LB4 heads flow 138 CFM on the intake. The L03 heads that I measured were roughly 158 CFM at about .050" under your cam's max lift. By the typical rule of head flow vs HP you could in theory make about 315 FWHP. I don't think your engine is generating 315 FWHP @ 3,500. Just the same as it won't make 276 FWHP @ 3,500 per the LB4 heads. Just some food for thought, I don't think its your heads. But I guess we will find out soon enough.

GOY

Hell got mighty cold....

.... I agree with Fast355. A single plane will hurt a TBI application in a similar fashion to a carbed application - in some aspects. There is more than runner length to bare in mind. Runner taper, shape, diameter, etc. Dual plane's typical have a few more bends in the intake track, and that does several things. One thing it does VERY well is increase the air speed of the intake charge at lower rpms. That's just simple intake design 101. Then there is runner diameter, taper, etc all affecting air speed as well.

When you have a single large plenum, with fairly straight - large diameter runners, you will create a large amount of "intake stall" when a valve closes at low engine speeds. The air stalls, and just at about a dead stop, the valve opens again - it takes a momment to get static air moving, but once it gets moving, the valve is closing again, causing further stall. Then since it's a fairly direct path to the plenum, you get a wave of that mixture moving back towards the plenum, stalling that air, or even worse - causing the mist of fuel/air to come out of the TB like Fast was talking about.

It's not about runner length - it's about the speed of the charge moving into the chamber. I personally think your combination would make more power with a Edelbrock Performer RPM and adapter plate.

Fast355

iTrader: (2)

I ran that combination, on a 355 with a MTC1 cam and ported 601 305 heads, I pulled 255 RWHP @ 3,800 and 360 ft/lbs @ 2,400. I learned that 10.4:1 compression, short valve timing, OD, Tall Gears, High ambient temperatures, 93 octane, 32* timing, a good grade, and a heavy Van, pulling a trailer don't mix. Can we say a hole in 2 pistons!!!

GOY

Well... at least you were making good torque. That compression ratio was "A little" on the tall side though for my taste. 10:1 is about as high as I would go w/ factory castings, and I would be VERY conservative with timing at that.

83 Crossfire TA

iTrader: (2)

Wow…

Hey Tim… which car did you run swirl ports on? Were they 305 or 350 swirl ports? I thought that all of your stuff went from the stocker parts (L69 in the camaro…) to your odd, early/mid 90’s caddy sourced 350 rebuilds. Did those things have swirl ports?

Dewey, stick to what you’re looking to do, you’re going in the right direction. I find it really cool how looking at your parts, playing with some numbers and I came up with “I bet that your heads flow 155-160 at…” and the flow numbers shifty posted put them at 158. Obviously, something is adding up, huh?

Intake design… runner diameter/taper/length being the same, the straighter runners will be more efficient. You make a turn and all the air sticks to the outside of the turn, the inside volume is worthless, you have to make the non-turn axis wider to make up for it. In wet flow that same turn tends to create a spot for atomized fuel to slam into the wall and puddle out or at the least prevents a homogenized mixture by the time it gets to the chamber.

The small weiand is pretty similar in all those categories and is a very good choice here. The bigger, open plenum will actually allow for a better mixture and slightly more RPM up top then something like a performer/rpm will. What you guys are saying about it vs the performer stuff is true _if he was running a carb_. A carb relies on the vacuum in the plenum below it’s bores to meter fuel. Splitting the plenum results in a cleaner signal to the boosters, making the carb easier to tune for midrange (and if carbs were more tunable for load this really wouldn’t be an issue here either). With the TBI setup it doesn’t matter. There is no booster to react to the vacuum below the bore. Yes, it does use a MAP to determine fueling, but also TPS, temp… and you can adjust for just about any conditions in the plenum, making the whole divided plenum vs one big one a moot argument, except for the fact that the single large plenum will help a little up top flow wise and give the fuel a longer distance to drop and atomize in before it hits a solid surface...

And of course, the whole upper rpm deal of the larger plenum does nothing if the heads don’t flow enough to take advantage of it.

Retarding the cam… well it will move the power band up, but I doubt that it will significantly change the area under the curve since the heads just won’t flow much more. I’d bet that no matter where you timed the cam at you’d see less then .1 difference in the quarter on that combination.

18* + egr… run it like you do on a vette. Tube going from an exhaust primary to the valve to a port plumbed into the plenum and you’re done. Most 18* heads have small chambers that will work for emissions, but most also have very large ports that will not work well. If you wanted to fill those ports some or use the heads on a VERY large engine then you should be able to make it work, but it still won’t technically be legal anywhere (at least anywhere where someone looking at what you did recognizes what you did), so I don’t really see the point.

If you want to play that game, drop a small block mopar in there. The basic layout is close enough to an SBC that it will confuse most people, has lower valve angles and other small tweaks that are a lot like race head features on street heads… I’ve joked about putting a 318 in an f-body (probably the only less loved small block then the 305), which could be loads of fun with the right production heads and some boost…

Lo-tec

Engine was a takeout from a 90-92 cadillac fruitwood brougham(came stock w/a 350 TBI).

Fast355

iTrader: (2)

I know what I have witnessed. Same everything except the intake on a 454 (tuned for each).

Unless it is a single plane converted to port injection (YOU WILL LOSE bottem end torque, FACT). It has to do with reversion, period. Single planes will have more reversion than a dual plane. How would you explain the fuel mist coming out of the TBI during WOT low-speed operation.