Is bigger better? - How much air is too much?

2 thoughts to ponder?

1) Can you put a "too big" throttle body on your engine? If so, what happens when you do (say you put a 1500 cfm tb on a 355 LT4?) Let's say that fuel tuning is not the issue.

2) Can you put a cylinder head on your car that is too big (Say AFR 227's that flow 320 cfm on the intake). If so, what happens when you do?

Do either of these scenarios cause turbulence in the intake manifold that would hamper performance?

i have heard on a lt1 when you put a 52mm on you gain like 5rwhp and a little throttle response. (but not worth almost $300)when u put the 58mm on it acctually boggs a little.
(on a mostly stock motor) mods are a different story...

On the tb, assuming you can feed it enough fuel for transition, from a power standpoint, no you cant over tb it. You may not be able to drive it anymore due to how touchy it is without using some sort of goofy bell crank or elaborate linkage to modify the input/output behavior of the throttle.

On the cylinder heads, that is too deep a rabbit hole. I am not even going to start talking about that, it would take me 10 hour shifts every day the rest of the year to make a dent in that discussion. I will just dumb it down, not too big, not too small, get the heads just right and your engine will be very happy. Use pipemax to get you close.

Yes you can put too big a head on a motor and you have ported LT4s on a 355 held within the pcm's rpm limitations you are already guilty of it.

1. Theoretically you cannot over throttle body a FI motor. I have had a 48mm, 52mm, 58mm and currently a 1300cfm monoblade. I also have a Yank SS3600 torque converter which may tame things somewhat but drivability is just fine.

2. Yes you can get to big of a head. Air velocity is all important. With to big of a runner the car will be a dog until the rpms really get up there. David Vizard just did a test on heads with different runner sizes. It was an interesting read.

Yes you can put too big a head on a motor and you have ported LT4s on a 355 held within the pcm's rpm limitations you are already guilty of it.

Here's what I am trying to get at. I'm not making the top-end power that I think I should. I am getting 350 at the wheels at 6400 rpm, but it is relatively flat from 5400-5900 (340 hp).


http://i249.photobucket.com/albums/gg231/elisowski/DynoRun.jpg
Sorry for the image, I scanned and rotated it 3 times and can't get it to work right.

I shift at 6500 and it drops to 5500. I cross the line at 5900 rpm. I'm in 3rd gear for 3.2 seconds and only increasing 400 rpm. It just seems like a dog up top.

I'm being told that I need better flowing heads.
I'm also being told that the heads are a restriction and my 58mm tb is taking in too much air.

You mention my heads are too big for the 355 (2.0, 1.6 valves;291 cfm int, 196 cfm ex) and with the PCM rpm limitation. (Is this not 7200+ rpm for PCM?)

Can you expand on why you say the heads are too big? I've been working on this for 2 years and am trying to sort this out. Any more explanation would be appreciated.

Thanks.

"I'm also being told that the heads are a restriction and my 58mm tb is taking in too much air." That is pure nonsense.

Looks like you are running out of air around 6200 rpm and that is the reason for the flat line. You have other issues around say 5300 rpm. Maybe spark retard?

The question is why are you running out of air? Could it be something as simple as to small of an air filter?

What are the lobe specifications on your custom camshaft?

yeah, something else is probably going on...

You probably need a tune and if those heads flow what you say they do then your car should be trapping 117+. FWIW, my 355 with ported LT4's dynoed 383 through a th400 and ran the numbers in the sig. I never shifted over 6400rpms as it did not make the car run any faster.

Looks like you are running out of air around 6200 rpm and that is the reason for the flat line. You have other issues around say 5300 rpm. Maybe spark retard?

The question is why are you running out of air? Could it be something as simple as to small of an air filter?

What are the lobe specifications on your custom camshaft?

Datamaster shows no spark retard during the runs. Sometimes (1 in 6 or 7 runs) it will pull 1-3 degrees of timing at the launch, but never on the big end.

Current Cam Specs: 12.03 @ 110
603, 576 ;240, 250; int CL = 110, ex CL = 114

Old Cam: 12.21 @ 108
562,562; 236,236 107 CL

I've had it tuned, but the best times it has put down are with my tuning.

The best run in the sig was in Speed Density mode with the MAF and Moroso CAI removed (11.87 @ 111) but it still had the same problem with a lack of power on the big end.

I need to figure out why it's a dog from 5400 to 5900 rpm.

What was your A/F ratio on those pulls? You should shoot for 12.5-12.8-1 and lean it out from there. You have a tighter lsa so they tend to like a little more fuel than wider cams. Your combo should be low low 11's @ 120 with heads and cam like that. I looked at your mod page and everything seems to be right. Question though. Was your valve springs matched to your cam? That can cause all sorts of problems if they bind or are not properly matched. It looks like you are down about 60rwhp.

What was your A/F ratio on those pulls? You should shoot for 12.5-12.8-1 and lean it out from there. You have a tighter lsa so they tend to like a little more fuel than wider cams. Your combo should be low low 11's @ 120 with heads and cam like that. I looked at your mod page and everything seems to be right. Question though. Was your valve springs matched to your cam? That can cause all sorts of problems if they bind or are not properly matched. It looks like you are down about 60rwhp.

The AFR during the posted dyno pull was 13.4:1-13.5:1. We started at 12.6:1 and it improved slightly as they moved it up. It was about 335 RWHP at 12.6:1.

The springs were part of the head cam combo for the previous cam. They are comp 918 bee hive springs. When I ordered the second cam from Cam Motion, they said the springs were right for the new cam also. I took the heads to the machine shop between cam swaps and they said I had plenty of room before coil bind (I don't remember the numbers though).

As for the 60 RWHP - that's about what I'm thinking. I was looking for 402-408 RWHP when I was shopping the head/cam combo.

I'm starting to wonder if the heads are holding me back, are they too big or maybe they don't flow the numbers I was given.

Hmmm...was the cam degreed in? Did you do a compression/leakdown test? I would try and talk to LE and see what he has to say about the heads/cam/etc. If you want I can send you an Lt1 edit tuning file from my combo to try out and see if it helps. I was using 30or36 lb injectors so you would have to change the injector constant but everything else should be good. Your parts were pretty much what I had in my combo so your should perform similar.

Hmmm...was the cam degreed in? Did you do a compression/leakdown test? I would try and talk to LE and see what he has to say about the heads/cam/etc. If you want I can send you an Lt1 edit tuning file from my combo to try out and see if it helps. I was using 30or36 lb injectors so you would have to change the injector constant but everything else should be good. Your parts were pretty much what I had in my combo so your should perform similar.

I would love to have you send me a copy of the program. I'll pm you with my e-mail.

I did a leakdown test and compression test this winter before I took it apart and the compression was within 5 lbs and the leakdown was very minimal (5-8% - I can't find my notebook right now).

I did a compression and leakdown test (warm engine) two weeks ago and had very good results as well.

I talked to LE on the phone several times and he hasn't been able to figure it out.

The first cam was degreed in by the machine shop. That's why I took it all apart last winter, to see if the shop did it correctly. It was the last thing I could think of. I wanted to check the heads for coil bind and degree the cam in myself.

So the 1st cam was degreed correctly, and the 2nd one is degreed in as well.
I put the second cam in after I found out it the first one was in correctly.

The rockers are set to 0 lash + 1/8 turn.

When I look at Datamaster, I'm only taking in 358 g/sec of air at 6500 rpm and 280 @5200 and 304@5900.

Thanks for your help.

"603, 576 ;240, 250; int CL = 110, ex CL = 114"

That is a pretty big cam for a 355 unless you are really winding it up. Also the 10 degree split is pretty big unless you told the cam grinder you would be using NOS. A split that big is usually used for a poor flowing exhaust system.

Interesting that your previous cam was a single pattern. That usually is used with a pretty good flowing exhaust system.

Hard to say on the heads with out knowing the final CC's of the intake. With that big cam and posible big heads I can see why the motor does not start to wake up until around 5500rpm. But then something is choking it around 6200rpm.

Could be mismatched ports? Ports are going sonic? Something is causing the ports to backup? Hard to say exactly what. I would also say your combination is probably not friendly to lower rpms.

"603, 576 ;240, 250; int CL = 110, ex CL = 114"

That is a pretty big cam for a 355 unless you are really winding it up. Also the 10 degree split is pretty big unless you told the cam grinder you would be using NOS. A split that big is usually used for a poor flowing exhaust system.

Interesting that your previous cam was a single pattern. That usually is used with a pretty good flowing exhaust system.

Hard to say on the heads with out knowing the final CC's of the intake. With that big cam and posible big heads I can see why the motor does not start to wake up until around 5500rpm. But then something is choking it around 6200rpm.

Could be mismatched ports? Ports are going sonic? Something is causing the ports to backup? Hard to say exactly what. I would also say your combination is probably not friendly to lower rpms.

I questioned the cam grinder on the 10 degree split. He said he felt the exhaust needed some help due to the flow numbers I provided him.
FLOW NUMBERS:
0.200........144/110
0.300........197/142
0.400........243/177
0.500........286/188
0.600........291/196
0.650........293/199

He wanted to get it closer to 70% exhaust to intake, from 0.500 up they are around 67%.

It starts to put you in the seat around 4200. It runs and idles great on the street without any surges (due to drilling the tb).

And yes it plateaus from 5400 to 5800 then wakes up again at 5800 and runs out of steam at 6200, then plateaus again.. The problem is I'm running from 5500 to 5900 in third gear at the track. And that's in the really poor part of the power band. I can't get over that hump.

Can you explain the ports going sonic? I'd like to understand this better.

"sonic" is when the speed of the air in the port starts approaching the sound barrier. Not good for air flow. ;) Not likely that is what is happening in your case.

You have an airflow problem somewhere. It will just be a matter of figuring out where it is at. I would start at the airfilter and work my way back through the motor to the tailpipe. You don't want any steps or ledges in the way of the airflow.

As for the restriction, it's down to the following:

Throttle body
Nitrous plate (bored out for 58mm TB)
intake manifold (ported and port matched to heads)
Heads

a) I've run it in Speed Density with all the intake parts off (elbow, MAF,CAI, filter) for a best of 11.87 @ 111 with no difference in 3rd gear (5500-5900)

b) I have long tube headers that exit straight out through electric cut-outs, so that eliminates the exhaust system.

Have you ever used DataMaster to look at MAP over a full 1/4-mile run?

"I have long tube headers that exit straight out through electric cut-outs"

Actually that could be "a" problem. The cut outs need to be properly located in the exhaust system as part of the "collector length". Typically the best location for the cutout would be 18" beyond where the primary pipes end in the collector of the headers. Other lengths would be 36 and 72". In your case I bet something an inch or two shorter would be best.

Those dimensions may not be optimal for your car but they are in the ball park. If your cutouts are at say 27 inches or 54 inches that would be the worst locations and you could actually lose a few ponies. This is "wave" tuning.

Collector diameter is the next most important thing regarding the exhaust. I would suspect your best collector pipe diameter is somewhere 2 3/4" and 3". What size exhaust collector pipe do you have?

I have enough experience to say, it depends. On an EFI car, the speed the ECU responds to changes in TPS voltage and the vacuum signal from the MAP sensor is the limiting factor. I have put a single plane manifold and a large TB on a '92 350 and there was just no way it could be tuned for throttle response. We must have burned 50 chips proving it and burned through a tank and a half of gas. Slapped the original TB back on and voila - it ran fine. OTOH, I am using a 2,200CFM TB on my race car (with an Electromotive TEC3r) and the throttle response is fine. LT1's seem to do fine with 58mm TB, I have not tried larger.

Rich

Is that cam a solid roller cam? I sure hope so as that is a huge hydraulic cam for a 355 that could be taxing the lifters.

BTW, I will send you a couple lt1 edit files to try tonight. FWIW, my cam was a 235 242 .567 .592 (with 1.6's) 112lsa.

Have you ever used DataMaster to look at MAP over a full 1/4-mile run?

Here is a snapshot of three 1/4 mile runs:

This is in speed density mode with all intake parts removed except TB:
MAP averages 98.5+
11.87 @ 111

laptop lost connection right after launch - you'll notice the missing data from 1st gear

http://i249.photobucket.com/albums/gg231/elisowski/DSC01295.jpg

This is in MAF mode with all intake components attached (elbow, maf, cai, filter):
MAP averages about 97
12.13 @ 110


http://i249.photobucket.com/albums/gg231/elisowski/DSC01294.jpg

This one is in MAF mode witha all intake components and THRU MUFFLERS
MAP averages about 96
12.43 @ 108

It pulls timing thru the mufflers at launch - my guess is some added vibrations due to exhaust going thru entire system.

http://i249.photobucket.com/albums/gg231/elisowski/DSC01293.jpg

"I have long tube headers that exit straight out through electric cut-outs"

Actually that could be "a" problem. The cut outs need to be properly located in the exhaust system as part of the "collector length". Typically the best location for the cutout would be 18" beyond where the primary pipes end in the collector of the headers. Other lengths would be 36 and 72". In your case I bet something an inch or two shorter would be best.

Those dimensions may not be optimal for your car but they are in the ball park. If your cutouts are at say 27 inches or 54 inches that would be the worst locations and you could actually lose a few ponies. This is "wave" tuning.

Collector diameter is the next most important thing regarding the exhaust. I would suspect your best collector pipe diameter is somewhere 2 3/4" and 3". What size exhaust collector pipe do you have?

I have 3" diamater collectors on Hooker Super Comp headers.
I have a set of Flowtech Race Readies (pictured) attached to the collectors and the cut-outs are on the straight end of the race readies.
http://i249.photobucket.com/albums/gg231/elisowski/big-53030flt_w_raceready.jpg

They are 10 inches long - so add 10" to the collector length on the header (I can measure later when I get home) for the entire length of the system.

The "wyes" angle toward the center on both race readies (assume the race ready pictured is on the drivers side collector - looking from behind). Both "wyes" join together into one pipe that rides along the driveshaft and goes into a dual outlet Flowmaster system. I do not have cats.

I will get an exact collector length when I go home for lunch.

Is that cam a solid roller cam? I sure hope so as that is a huge hydraulic cam for a 355 that could be taxing the lifters.

BTW, I will send you a couple lt1 edit files to try tonight. FWIW, my cam was a 235 242 .567 .592 (with 1.6's) 112lsa.

It is a hydraulic roller.

I have the stock lifters. I didn't want to mess with the Comp R's because I drive it to the track and around town on Saturdays.

I intended to buy a set from Cam Motion (I do not remember the name) when I got the cam, but I waited 3 months for them and I was told they were still 3 months out on back order, so I cancelled the order.

That's great for the LT1 edit files. I plan on going to the track tonight and getting the AFR down to 12.5 or so and start working up. I am very interested in the timing tables.

Thanks

"I have long tube headers that exit straight out through electric cut-outs"

Typically the best location for the cutout would be 18" beyond where the primary pipes end in the collector of the headers. Other lengths would be 36 and 72". In your case I bet something an inch or two shorter would be best.

Those dimensions may not be optimal for your car but they are in the ball park. If your cutouts are at say 27 inches or 54 inches that would be the worst locations and you could actually lose a few ponies. This is "wave" tuning.


lightbulb starting to come on:
18, 36, 72 = full waves (waves lengths appear to be doubling -yes?)
27 = half wave (1/2 way between 18 and 36)
54 = half wave (1/2 way between 36 and 72)

Very good information :D

That is correct. :D To get the lengths absolutely correct you would have to test at the track, dyno or buy a program like PipeMax to dial it in further.

What was the barometer for each of those pulls?

What was the barometer for each of those pulls?

#1 = 100.8 kPa
#2 = 99.7 kPa
#3 = 100.8 kPa

I have 3" diamater collectors on Hooker Super Comp headers.
I have a set of Flowtech Race Readies (pictured) attached to the collectors and the cut-outs are on the straight end of the race readies.
http://i249.photobucket.com/albums/gg231/elisowski/big-53030flt_w_raceready.jpg

They are 10 inches long - so add 10" to the collector length on the header (I can measure later when I get home) for the entire length of the system.

The "wyes" angle toward the center on both race readies (assume the race ready pictured is on the drivers side collector - looking from behind). Both "wyes" join together into one pipe that rides along the driveshaft and goes into a dual outlet Flowmaster system. I do not have cats.

I will get an exact collector length when I go home for lunch.

The collector lenght is 22 inches from the beginning of collector (at weld to primaries) to the cut-out. They cannot be cut shorter, as seen in this picture:

http://i249.photobucket.com/albums/gg231/elisowski/DSC_0377.jpg

It seems hard to describe so I added a picture. Here's what it looks like from the front showing how the wyes turn to the inside and enter the single pipe to the muffler.

http://i249.photobucket.com/albums/gg231/elisowski/DSC_0372-1.jpg

There is most likely an inch of primary pipe in the collector. So probably not optimal buy most likely not hurting anything either. :)

Lifters.....

When I purchased my Cam Motion cam, the tech told me that the stock lifters were only good to about 6200-6300 rpm. The ones I had on backorder were supposed to be good to 6700-6800 rpm.

What happens when they are above their intended rpm range?
Do they pump up and hold the valves open, or do they collapse and not give the intended lift? (less airflow).

That could be a problem or the valve springs not being up to the job. I once had a situation with the Comp 918 beehive springs giving out on me. I had a dyno graph that look like yours but at a lower rpm. The motor would not make over 350rwhp and peaked at 5200rpm. Turned out to be the valve springs. Now the motor is peaking at 6400rpm. :D

When the lifters go above their intended rpm range they cannot fill with oil fast enough to pump up so you will effectively lose lift and duration. I had the comp R's in my combo with a stud girdle and AFR rev kit. However, matched valve springs, lifters and a nice stud girdle should be good to 6800.

OK, so here's the plan.

The only two parts that are the same from the previous LT4 hotcam conversion motor were the lifters and the heads (even though the heads were ported to stage II, they are the same heads).

So I am doing the following:

1) I borrowed a set of Comp R's that were in a race only car with about 40 passes on them.

2) I purchased an AFR hydra-rev kit and will install that as soon as I get the installation tool (tomorrow).

Hopefully I will get to the track on Friday.

If this doesn't do the trick, I have been given a set of LT4 heads with bigger valves (2.08, 1.60) that have been ported and gasket matched to the same intake gasket that my current heads are (GM #12367777).

What do you guys think about this?

I would not go as far as changing the heads. However, you will be able to identify if you solved the problem or not. I just have a gut feeling it is the valve springs. While you are doing that you should get a nice stud girdle for the rockers to stabilize the valvetrain a little bit better. I'll try to find a link to the ones I had.

I've always been a little suspect of the springs myself (blue stripe beehives) Comp 918s.

We tested two of them when I had the heads off and they met correct pressure specs. But I've always been suspect.

Any suggestions on springs? I looked at the Thunder racing web site some time ago (6 months or so) and they seem to have a couple of stiffer springs, but they're not bee hives.

psi springs are some of the best. I would give Advanced Inductions a call as they know their stuff about the valve springs. They will need some specifics on your cam so a cam card would be helpful as well as installed height and retainer to seal height, etc. They will get a valve spring that will match your cam perfectly. http://www.advancedinduction.com/

I contacted them a month ago about my new setup and they were very helpful.

Thanks for all the help. I will definitely call them.

I put the car all back together late last night. I woke up to rain. It's supposed to rain all weekend.

I'll have to wait till next week to see if the lifters worked or not.

What was the barometer for each of those pulls?


Any thoughts on barometer readings?

#1 = 100.8 kPa
#2 = 99.7 kPa
#3 = 100.8 kPa

I don't think it's the lifters.

I installed the Comp R's and the AFR hydra-rev kit. Went to the track last night and only got one run. Problem was, I ran it with the stock ignition set-up (MSD coil and MSD Billet opti) instead of the MSD Digital 6 box with a blaster II coil and billet opti. After the first time trial I returned to the all MSD set-up.

Car ran 1.630, 4.808, 7.539 (8th), 89.64 mph, 9.843 (1000), 11.935 @ 110.84 Still about a 1/2 second off.
Had much better air. AFR was 12.7:1. Stock tach showed I shifted at 7000, but my Wideband O2 logger said I shifted at 6200 and Datamaster showed 6300. Stock tach does not do well over 6000 rpm apparently. Can't say for sure that the liters did not work but the car ran and felt the same.

After the first time trial, I kept my computer plugged in and checked my AFR and looked at Datamaster. There were several oildowns and a deer almost got clipped at the top-end. Needless to say I had it plugged in for a long time (1-1/2 hours).

In the lanes waiting for the 1st round of No-box, my car wouldn't start due to a dead battery (computer plugged in). I was pushed out of the lanes and told the starter what happened. He gave me a booster from his car and let me get back in to the lanes. Car started, I went into the lanes, and overheated due to me turning off the water pump when I was trying to start the car. Puked water everywhere and I was done for the night.

I am going back next week with same set-up to say for suew, but I think it's something else.

The AFR rev-kit adds addirional spring pressure to push the lifter down on the cam. This wpould be the same as having stronger springs, no?

So what's left? Heads not flowing what they are supposed to?

Any thoughts welcomed.

Hmmm... This one is tough. The ignition system probably wouldn't give you any ET. What gears are in the car? What size tires are you running? Also, did you try out any of the tunes I sent you to see if they made any difference?

Yes, the Hydra rev kit adds pressure to the lifter body and in effect does the same thing as a stronger spring without stressing the plunger. You should get a shift light to dial in your shift points to eliminate that variable.

There's 4.10 gears in the rearend. Tires are 28 x 11.5 x 15 ET streets (27.9" tall). I cross the line at 5900 rpm (which calculates to 119 mph if it were an M6) So there's roughly 8% slippage in the TH-350 with 8" converter) which I am told is in the ballpark.

I took your matt12.lt1 file and used the 75 MAP and up timing and fuel tables, plus the PE RPM and PE Temp tables. It ran about 11:1 AFR from 4500 rpm up. I made a couple of runs down an old country road and dialed the PE rpm table in to get it to 12.7:1 AFR. from 4500 up.

I have a sport comp tach, but its hooked up to the MSD tach signal, so when I run on the stock ignition, I need to run on the stock tach.

I screwed up by running the stock ignition first. I was trying to see if I could pinpoint something in the MSD system. I thought I could rev to 7000 on the stock ignition since that's what the tach reads, but the stock tach is way off on rpm (600-700 rpm when it blasts over 6000). I really shifted at 6200-6300 based on data loggers.


The MSD system only allows me to rev to 6500 before it breaks down. (And I mean breaks down. It gets to 6500 them breaks down and bounces all over the place - 6500, 5500, 6500,4000,6500,5000,6500,3000 back and forth with a very violent hit, not like a soft-touch rev-limiter). So that's why I screwed up and went with the stock system first.

I will go next week and see if I can do better with the MSD system shifting at 6400, I doubt it.

I need to get this figured out. Why am I only making 355 RWHP?

Who speced your cam? Also, do you have a set of 26" tires you can borrow to see how your car repsonds (even if they are drag radials). My car was a different car NA with a set of 26" tires vs a 28". It allowed me to be deeper in thrid gear and pull much harder in my power band.

I wouldn't worry too much on the dyno numbers as I was able to run 11.45@118mph only dynoing 351rwhp 335rwtq before I tuned in my combo. The dyno tune only netted me peak numbers above 6200 rpms but not too much on the low end.

Cam was spec'd by Cam Motion. Picked up 2/10ths over the prev cam.

My Ford rearend is narrowed 2" per side, so salad shooters do not fit. I would actually have to buy 26" tires and mount them to my 15 x 8 telstars (5" backspace).

I may buy 26 x 11.5 x 15 ET Streets and mount them tomorrow, so I have them before I go to the track on Friday.

I bet the 26" tall tires would net you .2 tenths and 2-3 mph or more. I would get ET drag radials as the ET streets tend to grow a bit on the top end but both will still work either way. If you can get a 11.6@114-115 then you are tecnically only .2-3 tenths and 2-3 mph away of what a combo like yours should run.

FWIW...When I ran with my 4.11's and 26" tall tires I ran consistent 11.4-11.5@117-118mph and when I switched to 3.73's with the same 26" tall tire I could only get 11.7-11.8@115-116mph.