2012sergen11

iTrader: (1)

Trying to determine some options on a 350 build.

89 350 L98 Roller block, stock internals currently, dished pistons I believe.

Going to add Trickflow 195's 62cc chambers 2.02/1.60 valves.

Planning to top with an Edelbrock Airgap Performer RPM (if I can find an air cleaner to fit)

So with the above I have 2 questions:

1. I would like to know what type of roller cam or flat tappet would work well with my heads and compression.

2. Is it worth the time and money to tear into the shortblock to put in flat top pistons to gain some compression?

Car is going to be 90% spirited street driven with some WOT pulls and track run once in a while. Going with carburetor on the l98 since it is going into an 85 LG4 car.

GeneralDisorder

iTrader: (1)

If you have the TPI setup - keep it. It's not that hard to wire it up. The system is pretty self contained. That's why people put them on trucks and jeeps quite often.

Get a Comp XFI268 cam. Even with a carb this cam is still a good choice. The XFI cams are Comp's most advanced profiles. Look up some YouTube videos on how it sounds, etc.

GD

Biledriver

Dished pistons will probably hurt your performance. If you have the means you should hone the block and swap them for something that will get you closer to a zero deck height for a good quench area. A bigger cam loves higher compression for power down low where our heavy cars need it. I've read dished pistons encourage preignition but I can't really back that up.

2012sergen11

iTrader: (1)

I do not have the whole you setup to use in this car that's why I was sticking with the carb on it.

are there any cams similar that would be better for the carb that aren't necessarily efi friendly like the xfi? Or is it the best over all choice

GeneralDisorder

iTrader: (1)

You can download Comp's Camquest software and plug in all the variables to see what it will do. Here's a post on a vette forum asking about the xfi cams on a carb:

https://www.corvetteforum.com/forums...ed-engine.html

I know comp does recommend them for carb applications too. They are their most advanced cam profiles.

GD

2012sergen11

iTrader: (1)

I downloaded the software and pluged in as much info as i could do reasonably. In the great fit section one of the recommended cams was a 283THR7 grind. Has anyone used this cam?

Specs.

Duration @ 0.050
int. - 227 ; exh - 241

Valve lift std rockers
int. - 0.513 ; exh - 0.498

Main reason I am interested in this cam is because it says it can be used with a stock torque converter and since i do not have a higher stall converter I could upgrade later to get better results from the cam but not be too bad with what I have now. Not sure if the lift of this cam is enough or what side effects there may be from the xfi268 vs. this one.

Thanks again

GeneralDisorder

iTrader: (1)

You don't need a high stall converter right away but besides engine upgrades the BIGGEST performance gains for the fewest dollars are easily 3000 stall converter, axle gearing, and exhaust. Just that changes these cars so dramatically that people will think you put twice as much engine in it.

The XFI cams have some of the broadest power bands of any profile. They make an XFI 280 and an XFI 292. I'll be running the 292 on my 383 build for future addition of a Procharger.

GD

NoEmissions84TA

iTrader: (1)

I believe that is one of Comp"s THUMPR cams. They are marketed towards those who want the race car sound at the cruise-in. But they are not the best choice for performance.

NoEmissions84TA

iTrader: (1)

YES to the above. And get that stock "T" pipe out of there if you are still using it. That is the other "biggest bang for the buck" change.

2012sergen11

iTrader: (1)

For an exhaust I am planning on the headman shorties with y pipe and then possibly a larger custom 3" y pipe later.

I was under the impression the xfi 268 required a 2000 stall converter but perhaps I misread that earlier.

2012sergen11

iTrader: (1)

I do like the sound but not if it would make the car a dog on the street

Orr89RocZ

iTrader: (20)

I like a tighter lsa with a carb deal. Low comp likes it better to, will bring in the low end better

I like the lunati voodoo grinds if you have good hyd roller valvesprings. Comp has good stuff too. Xe 276hr is nice. 224/230 deg, pull to 6000 or so strong. Springs should be 135-150 seat / 350-400 open depending on lobe. Xfi stuff def needs 150/400 lbs pressures imo. Comp xe grinds are nice too, alittle softer. 135-140/350-375 lbs would work well

2012sergen11

iTrader: (1)

Any Flat-tappet cams you guys have had good luck with that are similar to the xe276 or xfi 268 in performance?

I'd like to go roller but the cost of the build is already getting high and flat-tappets are half the price of the roller cams.

NoEmissions84TA

iTrader: (1)

You already have a roller cam block and you can reuse your lifters if they are in good shape. So you are only looking at about $200 extra. I could understand if you had a flat tappet block and had to do the retrofit.

Oh yeah, ISKY 264 Mega HFT.

2012sergen11

iTrader: (1)

After doing more reading and talking to Summit tech I think I am going to go with the xe276hr grind cam.

I am trying to determine my CR for the build with the following specs:

stock l98 dish pistons +12 cc

stock deck clearance .025

compressed gasket height .041

bore 4.0

stroke 3.48

cylinder head chamber size 62 cc


I am getting 9.2 CR is this correct or am I doing something wrong? I do not believe the block has been decked and the 12 cc is what I found here for the factory pistons.

86LG4Bird

iTrader: (1)

Yes, your calc is about right.
I'd run .015" shim gaskets and get the compression up to about 9.7 and the quench clearance down to where it should be. And only then run the XR276 cam.
Down at 9.2:1 CR, I'd rather have the XR270
.

2012sergen11

iTrader: (1)

Would I be better off with flat top pistons to bump compression up or the shim gasket?

I've never used a steel shim gasket before so I'm not sure on the pros/cons

Orr89RocZ

iTrader: (20)

I've used the .028 gm gaskets with lt4 hotcam equivalent on stock L98 bottom, ran fine. Compression helps but not super necessary if you cant get it where you want

86LG4Bird

iTrader: (1)

You lose much of the benefit of flattops when the quench clearance is wide open.
Even your dished pistons have a quench land around the perimeter, so IMO you'll get more benefit, and DEFINTELY more bang for the buck, with the thin gasket. With good head and deck surfaces, never a problem running the .015" gaskets.

2012sergen11

iTrader: (1)

I see what you guys are saying, I basically need to optimize the quench and compression together as opposed to one or the other.

I will look into the gaskets, from what I calculated I'd have 9.45 CR with the .028 gaskets. If budget allowed and I could add flat tops that would bump me to 9.9x with the .028 gaskets. What is the typical limit for aluminum heads on premium (93) pump gas?

Orr89RocZ

iTrader: (20)

If you get pistons, might as well deck block in order to get more conventional gasket sizes .035-.041"

But it doesnt really matter as long as you get what you are after and have good sealing. 0.015 seems thin to me but guys use them fine. Good surface is key. If block aint good then it might not work for you.

Comp limit depends on many things. Very hard to say but big cam usually can do 11:1 static

Tibo

iTrader: (15)

Same here. I did a rebuild with 4 valve relief pistons and the 0.028 GM gaskets with the LT4 hotcam. Never had problems with detonation on cheap gas with aluminum heads (trick flows) with 32 or 34* peak spark advance.

Jorlain

iTrader: (4)

If you do replace the pistons, you could opt for a piston that's a little taller than normal, and go with the .028 or .026 gaskets available to tighten the quench a little.

Such as: https://www.summitracing.com/search?...keyword=9901HC

The compression height on these are 1.565 inches rather than the 1.56 that is stock. This will reduce your piston depth to about .020 under the deck. With a .026 Victor Reinz gasket, that puts you at a .046 quench, give or take. With a 64cc chamber head, this will put you right around 10:1CR. With the 62cc heads you mentioned, it'll be a touch more. A good match IMO for that XR276HR-10 (Make sure you get the 110 LSA, not the 114).

2012sergen11

iTrader: (1)

So far I am looking at going with these pistons:

https://www.summitracing.com/parts/s...make/chevrolet

Has anyone used these Summit replacement pistons? are they as advertised with the 1.56 compression height?

With these pistons of 6cc flat-tops, stock deck height leaving the piston 0.025 in the hole, 0.028 GM gaskets, and the 62cc heads I get 10.08:1 so realistically 10:1

I think the gaskets may be better than shaving the block to help save on the budget and help use the extra money for the cam, pistons, etc

GeneralDisorder

iTrader: (1)

One thing to remember here - going with the highest possible compression will not yield the increases in power that is often believed. Going from 9.5 to 10.5 is only good for 3-5% power. Is it worth it to you to have to run higher octane to have that extra 5%? You can easily make it 9.5 and be in a much safer zone. 10:1 should be fine with aluminium heads but you will have to run 92 at least.

GD

Jorlain

iTrader: (4)

In my research, pretty much all pistons in that $100 range are mislabeled rebuilder type pistons and have a 1.54 compression height. I spent days researching part numbers and my results were muddied. Some people claimed they were fine, others provided evidence otherwise. I concluded that since I saw evidence of the otherwise advertised 1.56 compression height, that I would suck it up and pay a little extra to be sure.

GeneralDisorder

iTrader: (1)

I wouldn't run anything Summit can sell at a profit for $10 per piston.

That, in my opinion, is a terrible idea.

Wiseco, JE, Arias. These are good name's in pistons.

Personally I would reuse some old GM pistons and knurl the skirts before I bought that junk fest.

GD

Tibo

iTrader: (15)

What octane you have to run depends more on the dynamic compression ratio which will be set mostly by the camshaft. My current engine is 10.5 or 11:1 and with it's cam and aluminum heads and my ignition settings I run fine on 90. When I had the 355 with the LT4 hot cam I ran 87 octane all day with no problems with a 9.5:1 CR

2012sergen11

iTrader: (1)

Does anyone have experience with the 9901HC pistons by Keith black linked above? They state 1.565 comp height. Would these be better than the summit replacements?

Orr89RocZ

iTrader: (20)

Imo if you are gonna swap pistons, bore it over and get block decked. Then it dont really matter. The 1.54's would then be fine. They'd be .020 in hole and you can run the .015-.028 gasket with good fresh sealing surface and have the benefit of flat top comp, although the benefit of 9 to 10:1 comp wouldnt be huge. 2-3% imo. Not a lot at 350-400 hp range for the cost of the swap and machine work.

cuisinartvette

x2 on the 264, the 270 Isky mega cam is a real good choice for a strong driver 350, dont overlook them. Some will say "they are older" yeah they are but flat out work and dont hammer themselves to death



That will work with a stock converter but youll love it a LOT more with a 2500ish piece they arent usually real expensive and totally worth it.
if youre short on dough a good trans shop can do one up for you.

JA411

DO A LEAK DOWN TEST, IF GOOD PUT THE .015" SHIMS ON WITH PROPER PREP AND TORQUE THEY WORK FINE. CHEVY USED SHIMS FOR ALONG TIME. JUST KEEP GOOD AND CLEAN COOLANT IN IT. THINK ABOUT BEARINGS AND RESEALING BOTTOM END.
JOE

2012sergen11

iTrader: (1)

Well now that I have gotten farther and farther into this rebuild I'm really debating the idea of just going to a 383 with a new rotating assembly for a little extra cost. I am already planning on new pistons and need a new crankshaft.

2012sergen11

iTrader: (1)

If I go the route of a 383 would the xe276 cam be too small for the engine?

Also would the headman shorty headers and ypipe be too restrictive?

Engine will be in the 450 hp range (flywheel)

Orr89RocZ

iTrader: (20)

I tend to cam 5-6 deg more in a 383 for similar powerband and drivability. That means xe276 would be great in a 350, and step up to xe282hr for 383

2012sergen11

iTrader: (1)

Oh okay.

I've read that the y pipe I can purchase for the headers I have is only 2.5" but is that really a concern for this power level >500 hp? I have a 3" catback for the car

Orr89RocZ

iTrader: (20)

There is some hp in a 3.5" catback vs a 3" at thr 500 hp level imo. All the latemodel cars i see in the 400-550 range def seem to show better results

A good flowing muffler in a single 3" can be used for what you are doing but consider a bigger system down the road or a cutout at the y.

2.5" y pipes should be ok for you

2012sergen11

iTrader: (1)

I think the collector on the y pipe is 2.5. Since I have the headers and catback already I was thinking of using those as long as they won't be too restrictive for the 383 for now until I can do a full dual down the road

Orr89RocZ

iTrader: (20)

Oh i would want a 2.5" into single 3" outlet y pipe

NoEmissions84TA

iTrader: (1)

Here is a chart I had.

2012sergen11

iTrader: (1)

Ive read thru the cheap longtubes and ebay headers threads on here, most of the links lead to out of stock items are these similar below?

http://www.ebay.com/itm/332237660452...%3AMEBIDX%3AIT

Has anyone used or seen these on one of our cars? This would be an affordable upgrade for the exhaust if I go 383 compared to most others Ive come across

cuisinartvette

[QUOTEjust going to a 383 with a new rotating assembly for a little extra cost][/QUOTE]
Do it!! dont need a pricy crank kit unless youre twisting it up a lot
Never once rebuilt a 350 and said "wow i can feel a difference that was worth it"

NoEmissions84TA

iTrader: (1)

You do realize that the pipes are routed differently with this eBay system?
It's similar to this one: http://www.ebay.com/itm/OBX-Exhaust-...3D332237660452
Maybe these would work better: http://www.ebay.com/itm/STAINLESS-HE...3D111470663982

2012sergen11

iTrader: (1)

If you mean differently as in the longtube vs shorty I was looking at the longtubes instead of using the short headers I have now. If they are routed where they dont fit our cars no I did not realize that.

The short headers you linked would require a custom ypipe I think

NoEmissions84TA

iTrader: (1)

I meant that the routing of the pipes would be different than factory.

2012sergen11

iTrader: (1)

I see, I would need a modified cross member.

2012sergen11

iTrader: (1)

Is there any harm to the engine in running the smaller hedman system for awhile until I can modify a cross member and purchase longtubes? I know power will be reduced until then but I would like to be able to buy the headers and run dual pipes from where the y merge connects by the transmission tailshaft

Jorlain

iTrader: (4)

Nope, no harm in running shorty style headers. In fact, some people run them very successfully. 1 5/8 headers shouldn't be too much of a restriction providing the collectors are at least 2.5" and the Y-Pipe doesn't neck down to less than 3" at the merge.

2012sergen11

iTrader: (1)

Ok I will have to look at the specs on the headman y pipe. I think the collectors are 2 1/4 on them.

NoEmissions84TA

iTrader: (1)

Look at this post:

https://www.thirdgen.org/forums/exha...ml#post6122937