chucksrt

I am building a 383 for my 96 Chevy express van. I have read that factory manifolds and shorty headers are not recommended for this engine. I have only come across one pair of long tube headers for this application but they are a tri Y configuration. Doug Thorley says they are more suited for idle to 4500rpm. I do not have the engine together to know where the power band will be. This is going into a large conversion van and will not be a racer however I do like to clean it out from time to time! What do you think about Tri Y headers? the engine info is
summit 4 bolt main block prep'd for stroker and .030 over
Scat rotating assy w/ forged pistons
Patriot Performance 2151 vortec cyl. heads 2.02 in./1.60 in. Valve Job; 185cc Runner; 64cc
comp cams extreme cam CCA-08-502-8

Cam Style Hydraulic roller tappet
Basic Operating RPM Range 1,500-5,500
Intake Duration at 050 inch Lift 218
Exhaust Duration at 050 inch Lift 224
Duration at 050 inch Lift 218 int./224 exh.
Advertised Intake Duration 269
Advertised Exhaust Duration 276
Advertised Duration 269 int./276 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.495 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.503 in.
Valve Lift with Factory Rocker Arm Ratio 0.495 int./0.503 exh.
Lobe Separation (degrees) 112
Computer-Controlled Compatible No
Grind Number CS XR269HR-12

1.5 roller tip rockers the computer is stock but will be reprogrammed once i get some reading from the dyno.
trans and rear are stock for now.
any input is greatly appreciated
thanks,
chuck

SkIdude

Good luck I'm in the middle of assembling Stroker motor now for rafting truck.

SkIdude

Have younresearched Jegs

chucksrt

I checked all of the usual places. I did find that Doug Thorley makes a long tube header for a bus but it is based off of the express chassis and should fit.

T.Neff

The reason why they are trying to talk you into longer header is because the 383's do favor or like the exhaust side of the formula.Much of that is depending on the big picture combo.C/R counts,camming depending on the c/r(details that involve duration,lope centers etc all play a role),what you are running for tranny,rear end gear ratios,rear tire sizes,in fact if it is a roller hydro lifter or not,(I highly suggest the roller hydro cam)the type of induction is also a player in this build.When it come to c/r's with today's gas you do not want to run too high of a c/r even with aluminum heads that ballpark drop that c/r about 1 point.Because if your running any kind of computer controlled engine,the computer will pull back the timing at anything near 9.5 c/r and it will run like a dog.Not a big fan of that brand imported head which has had a history of issues from the field.

So I suggest you start you build plan around the wheel speed calculator which takes into account the rear end ratio,tranny final drive,tire size.Pick a speed like 65 mph and see where the engine is running rpm wise.Torque is king on street vehicles.What sense does it make if you find a peak hp rating where a basic huge box like your van reaches peak hp given the wheel calculator at 140 mph??.It doesn't does it??.I suggest you are mindful of those torque ratings and rpm ranges to build a engine that for the money gives you the biggest bang for the money your spending in normally used driving rpm ranges.Did you know you can in real street every day driving build a 383 that can give you 480bls of torque every day for yrs to come??.Might want to consider that while your building this van...............

T.Neff

To start with for you to know the static compression ratio,you need to know if or how much the block deck was cut.The pistons used(dished,flat top,)what the cc of those pistons is,the thickness of the compressed head gasket.You do know the cc's of the heads.Are 5.7 rods used or 6.0??.Aside from what I posted about speed calculators,the compression ratio is a big factor in determining the rest of the parts.And a long tube header might be the wrong decision given everything else I posted.

chucksrt

This engine from the factory came with 9.4:1 compression so the stock computer should be just fine. I believe my compression is 9.6:1. I have not yet checked to see how far the pistons come up in the bore. I do know they are not quite flush with the deck. They are a dished forged piston with a stock thickness headgasket ( .041 iirc). 64cc heads. I don't know which rods a typical 383 stroker kit uses? It is a Scat 9000 rotating assy. Trans and rear are stock for now but I will not be leaving them alone for long. I want to plan for the van to drive best at around 75mph.

T.Neff

Hey Chuck-I'm trying to help.If as you say the stock c/r was 9.4 and that had timing being pulled out of it to prevent it from knocking,than you can only imagine what is going to happen with 38 more cubic inches.Knowing the static compression ratio is the cornerstone.

You said it is you think 9.6 c/r and my question is that because of the heads lowering it 1 point or before the aluminum head has lower it 1 point.Because I don't have any of the part numbers of the rotating assembly I can only venture a guess that it is .010 down on the deck with 18cc dished pistons on 5.7 rods and a 64 cc head.So one of the uses of aluminum heads is when say you have a 10.0 c/r to lower it down 1 point.It is the nature of aluminum to dissipate heat so it does change the compression ratio.Then the dynamic compression ratio is used in cam profile to drain off some of the cylinder pressure in the duration of the exhaust lobe.So if your at 9.6 without the heads,then with them your at 8.6. Static compression ratios dictate what cam to use.Over camming a lower c/r actually hurts more than it helps and that is especially true when the cam choice duration is bleeding off cylinder pressure making that 8.6 even lower.It is very important to match a cam to the static c/r.Actually critical.

If you like,I'm not around this site that often,but if you can get the info,I'll help with the static c/r's.Or you can use this formula link I will leave for you to use.For you to plug in to a computer dyno program,you'll need that info.
Click on each topic to get to the link to use:

Automotive Converters and Calculators

Engine Compression Ratio (CR) Calculator

Plug in the true values to get the static c/r.The compressed head gasket is usually .040.

This one is for the wheel speed rpm:

Engine RPM Calculator

The wheel speed rpm formula won't be useful until you have run the engine on the computer dyno.I am a real matter of fact kind of guy and I admit the computer dyno's are just estimates.But it does give you somewhat something to gauge the combo your building.

Hope this helps Bud.

T.Neff

One more thought Chuck.I don't know the wt of your van,but I would think it is in the middle 4,000's.It does take torque as early as possible to move that kind of wt.That is something for you to consider while you tailor build a engine for your van.

T.Neff

Hey Chuck.Where ya go??.