Quote: Originally Posted by mcbchild Ok, I just gotta ask what specs are on your motor and what is your race weight? motor 1994 LT1 stock crank stock rods stock pistons stock heads (have been ported) comp nitrous cam 23x/24x hydro roller comp 977 double springs comp 1.6 rockers victor jr. intake converted to efi, 1200 cfm throttlebody 42# injectors, powered by megasquirt raceweight is 3050. pulls 12-13" of vacuum at idle.

Ok, went to the track again yesterday and this time with full 3" dual exhaust, tried locking my timing out by drilling a hole by the counter weights and placing a pin thru the hole with the mechanical advance all the way opened and I go to look at the timing and it still advances like 4 to 6 degrees at 3000 rpm. Not sure what is going on there, but total timing was at 36 degrees at 3000 rpms. Only ran a 12.8x. So it seems I lost over a half a second thru full exhaust compared to open headers. This is really getting to be a pain on what is going on. Here is my time slip. Shifting at 6800 rpms.

RT: .230 (don't know where my attention was on this one)
60': 1.890
330: 5.361
1/8: 8.237
MPH: 85.62
1000: 10.725
1/4: 12.822
MPH: 109.44

So now I am nearly a full second off of what this car should be doing with full exhaust.

did you put the motor together? are you SURE the cam is installed straight up? it seems to not be making any power at all for the combination....
i know a local shop puts huge cams in his customers street cars but installs them advanced to bring the rpm range down. why he does this i have no idea. i know of one car in particular with a solid roller 24x/25x duration 388 with dart heads and vic. jr....... it peaks around 5900-6000 and makes 50 rwhp less than my car does with much smaller stuff.

No, I had the cam custom made at isky and they told me to install it with 6 degrees advance.

if it was custom, why do they want you to install it 6 degrees advanced?

So the exhaust is dual 3 inch? Thats wierd. I run mine with cutouts after the headers and it runs close to the same with the full 2.5 inch exhaust and old flowmasters. What mufflers did you put on?

How many runs did you make? were they all high 12's?

Make that 2 full seconds!


I think you need to figure out why the car is down on so much power before you pull the converter out. If you put in a higher stall thats meant to go with a long duration cam and good power, it's not going to work well with a car thats down on 150 HP. Your better off at the moment with what you have.

Just curious, does the car feel normal going down the track? Does it feel like a fast car? Like it pulls hard?

i'd be wondering the same thing honestly.

First, I did make 3 or 4 passes and they were all in the high 12s, The cam manufacturer told me to install the cam 6 degrees advanced and not sure why maybe vp clearance. The car launches alot better now that I locked out my dizzy although it still advances about 4-6 degrees after 3000 rpms and not sure why when I locked out the mechanical advance weights. Should I have removed the weights? I do not have exhaust cutouts installed yet, so the runs were thru full exhaust. The only thing I can think of that is slowing me down would be the dizzy, I was told that the pertonix race dizzy was a good unit to use. Fuel pressure is good, maybe I need to do another compression test. I did have the heads mill down to 63cc from the stock 65 or 67 cc brodix heads came with and my intake was not milled down. The front and rear intake seals will not work so I used rtv sealer. Could it be that the intake ports are not lined up correctly to the ports on the heads and that could give me these issues? The car does pull hard even from launch. Can my carb be off that badly?

Before you do or buy anything else for the car, I would go get it dynoed. I don't know the prices where you are but around here 3 pulls are only $75 and a hour is $125. If your power is down do to something not being right in your motor you may be doing it harm by beating it up at the track. You are missing a crap load of power for your combo and 3 to 4 degrees of timing isn't it. Find out what kind of power, afr and your hp/trq curve you have first, the fix maybe something simple. IMO

I think you need to figure out why the car is down on so much power before you pull the converter out. If you put in a higher stall thats meant to go with a long duration cam and good power, it's not going to work well with a car thats down on 150 HP. Your better off at the moment with what you have.

Dont spend anymore on parts until you find your power cause it's not there!
Had a 92 RS do 109mph on a 12.68et with a 2500 stall b&m and a 255/50-16 bfg dr with a bad trans. It dynoed 351 rwhp.

I just did a compression test and they are around 190 psi except number 6 cylinder which is at 180 psi. Could this be the issue? either valve or rings?

my bet is the cam. its probably making peak power more like 5,800 instead of 6,800, and its not making what it should be since its advanced so much. i would get it on the dyno as well. my guess is the hp curve will climb to 5800 and do a nose dive.
some people on here may tell you to keep track tuning it, though.

That could be one of many little things that is causing such a hp loss. But I don't think that is it by it's self unless you have a bent valve. Do leak down test on all of the cylinders to see what's up.

How do I do a leak down test?

Might be but with a solid cam and that much duration I don't think it's going to nose dive IF everything is ok. If he peaks at 6300 rpm then he can shift at 6800 for best acc. If you had any valve float at that high of an rpm then that might have caused the piston to hit a valve. IMO

Like Big Dog said, Do a leak down test on all the cylinders. You also need to visit a Dyno. You need to see a graph of your power and you need to know your air/fuel ratio at certain RPMs. Also what is valve spring pressure? (installed and open) If it's not enough, you'll have crazy valve float and all hell can break loose.

The heads cam with springs for a roller solid cam and the race car shop I took them to for the correct valve spring pressure for my solid flat tappet and he said all he had to do was remove the inner spring which should be around 150 closed and around 475 opened pressure.

Well IF the springs are ok then I'd have to have more info (dyno graph, numbers and afr) to find out what's going on with your motor. You have to find out what you are working with now. From your race weight and mph you are putting down about 340-350hp to the rear. To do a leakdown test you need a dual leakdown gauge. Do a search for the step by step procedures for the test. That will give you some more info on the condition of your motor without beating it up at the track.

this situation sounds identical to the guy i know with the 388 that cant get out of its own way. his cam was installed advanced because its a huge solid roller and he wanted to have driveability on the street.
his dyno graph falls off at 5900/6000. made somewhere around 385rwhp i think.
this is a 388 all forged motor, dart 210cc? heads that were ported, 25x duration solid roller, vic. jr intake w/750 demon carb. th350 trans. missing a good 100rwhp.

Just curious...Have you considered going to a dyno? Lots of people here have recomended it including myself but you hav'nt made a single comment on it. You have been chasing these problems for a bit now and seem to be going backwards.

Your car should go at LEAST 10.80-10.90's at 123. At LEAST!

388 sbc,400 cast-steel crank, forged pistons 0.060 over, 11 to 1 forged flat top pistons, Isky custom 252@.50 260@50 108 LSA mechanical flat tappet. .580 int - .583 exh lift, 1.6 Aluminum rr, Brodix track 1 heads, Victor Super intake with Holley Race 830 cfm carb, NOS, Pertonix HEI Race Dizzy, Weiand Aluminum water pump, Holley black electric fuel pump w/regulator, Turbo 350 trans w/3500 stall, 9 Bolt 4.10 rear disc, Comp Cams SFC, Eibach Drag Launch rear coil springs w/passengers side airbag, 90/10 struts, Weight 3400lbs. with me and half tank of gas, 1 3/4" Doug's LT headers, 3" complete dual exhaust, Stock Torque Arm w/ poly mounts to the trans, Lakewood LCAs, 27x10.5x16 M/T ET

I've been following your thread for a while and I see that you haven't resoved the problem (at least at this point).
May I ask for a few engine specs that aren't in your sig?
Piston dish/dome volume or part number.
Camshaft advertised duration.
Installed cam angle ( I think I saw 6 degrees advanced)
Combustion chamber volume.
Head gasket specs or part number.
Connecting rod length.
Perhaps there is a fundamental issue that's being overlooked ( although you seem pretty thorough in your approach).

I did think about going to the dyno, but I wanted to look for what is holding me back that far. I can see if I was searching for that extra 20-50 hp before I go to the dyno. I have to admit that I am getting closer and closer to taking it to the dyno and spend the extra to see where my 100-150 hp is missing. This car was not meant to have that much street ability. If I could drive it 10 miles round trip to a car show 1 maybe but rarely 2 times a year. The rest of the time the car is in the garage or at the track. I mostly put a dual 3" exhaust on it to be able to drive those 10 miles. I will be taking the exhaust back off for the track.

.

Piston dish/dome volume or part number. flat tops 5cc
Camshaft advertised duration. 286-294
Installed cam angle ( I think I saw 6 degrees advanced) Yes
Combustion chamber volume. 63cc
Head gasket specs or part number. felpro 1010
Connecting rod length. 6"

Using those specs your engine shows good numbers for static and dynamic compression ratio. Although I neglected to ask what the piston deck height is, using a range of .025" below deck to 0.0" you get a SCR of 10.7 - 11.37:1 and a DCR of 8.5 - 9.0:1.
The 9:1 DCR is starting to get into race engine territory (the books say a healthy street engine should operate in the 7.5 - 8.5:1 range). The 6 degrees of cam advance is bringing the DCR up. This will build low RPM torque at the expense of top end breathing capability.
What I couldn't find at the Isky web site was your cam specs. Most modern cams are ground with 4 degress built into them. A 108 LCA will have an intake center line of 104. Do you know what the actual installed ICL is? If by chance the cam was installed with 6 degrees advance in addition to a ground in advance, then you will have some significant problems getting the engine to work at the top end of the rpm range.
Just a thought.

The cam was custom made on a small base circle for rod clearance by isky and is not an off the shelf cam. I have the card that came with the came and just shows the LCA is 108. As I stated before, Isky told me that I needed to install the cam 6 degrees advanced and am not sure if the installed any advance into the cam as they made it. I will talk again with them tomorrow and ask and ask what the ICL is also. I was thinking that if it was made with a build in 4 degrees advance and I set the cam in the engine with no advance, just straight up and down, wouldn't that hurt my DCR?

absolutely. and if that is a problem, you dont have the right cam to begin with. a smaller cam installed straight up would work better for you in that case. advancing/retarding a cam is intended to tweak the performance of the car/application once you have the correct cam in there. its not meant to make a huge cam more driveable on the street.
imo, you could put an off the shelf 230-240ish cam in that motor and pick up 10mph in the 1/8 from where you are right now.... (if there was no clearance issue with the rods/crank)

10 mph increase??kind of wishful thinking. looking at mcbchilds engine spec that engine should be making about 450 ish fwhp. Imo the times that mcbchild run is about what i would expect for a engine making around 450 hp.

blah blah blah, my 305 made 243rwhp and went 12.3x's...450hp should be way faster than that.

Once again, with this guy.


My combination is way less and makes about 500HP at the flexplate.
DaveRR your in left field.

Sounds like you guys may be on to something with this cam issue. I would research it. It could be the weak link!

lmao!! you gotta be kidding me. 450fwhp?
my 350 with 23x/24x cam and ported stock heads runs 95+mph in the 1/8. i cant see any reason why a 388 with aftermarket heads and bigger cam shouldnt be running at least somewhere around that.
mine makes ~425 AT THE WHEELS.

Mcbchild, even with that cam advanced 6 degrees you still should be making 490- 510 hp at the flywheel and your not. I've built a lot of sbc, LS1s and olds motors and your parts list says to me 490-510hp. Yes I agree with Diggler you could have went with a much better cam that would have gave you the best of both worlds. I've built a 350 with a roller comp cam that had 212-218 @.050 and put it in 6deg retard, car pulled 6400 rpm on dyno with some ported sportsman IIs and 1 5/8 inch SHORTY headers with one of my custom dual terminator box exhaust systems so with your combo rpm should not be a problem somthing else is wrong. FIND OUT WHAT YOU HAVE.

Tryin to tell em. For all of those good parts he has that car SHOULD BE flyin. I meen 388, track 1s, 3000+ stall 3400 race weight, 4.10s come on high 12s maybe with 5 1/2 cylinders and 2 flat tires.

lol.... my stock LS1 camaro trapped 85mph on 17" street tires. i dont see how someone could think a built 388 with good stuff should run 85mph also?

The ICL is something that you'll have to measure. Then take into consideration the ground in advance (if any) and whatever you add yourself by way of offset bushings etc.
The thoughts from the other posters regarding your potential are probably not far off considering the size of the cam you're running. It may be that you'll find that you have to take some advance out of it. If that's the case, yes, your DCR will decrease. It seems to me that a cam with that duration may require something along the lines of 12:1 SCR to get the most performance out of it.
By the way, did you find out what the piston deck height value is?

Come on man, that 350 with the small cam I built went 86.8 mph in the eight and that was on 17" nitto dr. He should be ALOT faster than that.

The shop that built my motor told me that he did not deck the block, so far as I am informed it is the standard deck height .025.

The shop that built my motor told me that he did not deck the block, so far as I am informed it is the standard deck height .025.

SCR 10.7
DCR 8.5

Maybe the cam is too much duration with the 6" rods, but I would've thought for sure that would work with my heads and exhaust system for great breathing.

By all accounts, you can't put too long a rod in a small block chevy (theoretically). I don't think the 6" rods are the problem.
At this point it seems you have a few choices.
Keep working your jetting and timing as you have been doing.
Book some dyno time.
Personally, I would investigate the cam installation and redegree it verify the specs. If you find that the cam is too far advanced (which would explain the lack of high rpm performance) you can fix that. Then it wouldn't hurt to bump up the SCR a little by way of a thinner head gasket (that would also improve the quench value). That in turn brings your DCR up a little too.
I would also do a compression test.
Everyone that's posted here agrees that you have a potent combination with 500hp potential.

I did do a compression test and here are the results so far:

Cylinders:
1=190
2=195
3=198
4=190
5= (Can't get to that cylinder yet with the headers)
6=175
7=200
8=185

And I just talked with isky tech dept in drag racing and he stated that I should install the cam straight up and down since it already has a built in 3 degrees advance and he is not sure why the tech I talked to early when I purchased the cam told me to install it with 6 degrees advance, but then again he could not find any info on my cam since he couldn't locate the invoice number I gave him off of my invoice. So maybe I will just go ahead and install it straight up and down.

ah HA! hopefully this will fix the issues...so if it's got a "+3*" already in the cam, you've essentially have it installed at 9*advanced...wow...

There you go. I guess all that book learnin' might pay off after all!
Installed straight up would be the way to go ( I think anyway). Remember, by doing that you will be lowering your DCR somewhat. It might be a good time to use a thinner head gasket (should you want to tear the engine down). Victor Reinz makes an aluminum head compatible gasket that's .025" compressed. That would help to restore some low end torque and give you a better quench.
Compression test values will drop with the cam less advanced (what's up with #6?). The thinner head gasket will help restore those values as well. 200 psi is what you should expect from a strong running engine (unless you live a mile high in Denver).

I Don't think with that cam 9* advance is going to to take away 100 plus horses and knock off over a second and a half. Food for thought, on my sim I ran the info on his motor and car that is posted with 9* advance and then strght up, the diff was only 25 hp but it lost 20lbs of torque and the hp peak was about 400 rpm diff. The car ran the same down the track but with a 1.5 mph diff. Both were over 122mph. Something else is going on too with that motor. IMO

With the following specs.
Bore 4.060"
Stroke 3.75"
Chamber volume 63cc
Head gasket .039" x 4.160"
Rods 6"
Cam 286/294 LSA 108 ICL 105 (built in 3 degrees advance)
Piston deck .025"
Piston dish 5cc
SCR 10.7:1
DCR 8.33:1
With a .025" gasket
SCR 11.09:1
DCR 8.62:1

I would agree. Still lots of tuning to do after the cam gets sorted out. ( Provided of course we're on the right track ).

Hey Big Dog!
Where abouts in the Chicago burbs? I'm in Tinley Park every couple or three months visiting a bud who works there. If you see a very cool looking 67 Chevelle with Ontario plates...(not mine that's his. I drive the ratty black 86 IROC !)
(Sorry to steal the thread McB)