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janus 04-18-2011 02:55 AM

some questions about future 350 build
hi guys,

yesterday i purchased a 350 L98 out of a 87 GTA. The owner could never get that thing run properly, he thought it has some mechanical issue, but then again he's a moron.. removed the motor to put it into his garage and never looked at it again, thereby killing an otherwise fine 350 GTA..

At any rate, i told him i want that block since it looked to be a 1pc rms roller block from the numbers (638), which is exactly what i was looking for (hard to find over here as you can imagine). So went there to rip it apart to the shortblock for my future 350 build yesterday. It has about 100k miles on it, looks pretty nice from the top so you can still see the crosshatch etc, but haven't pulled the oil pan to look at the bottom end. So i'm pretty sure it was a fueling/spark issue bugging that car which is exactly what i told him before he started to kill the GTA ;)

Anyways, here is what start out with:
  • The car is a '89 Firebird Formula, stock 305 TBI, with 2055 shorties and 3" from collector back with a highflow Catco in between.
  • Has a 3.27 9bolt right now and 700R4, but looking to put the 350 in with my T56 and some shorter gears possibly since the lower T56 gears are a bit long imho, and still have the 0.5 OD for superoverdrive ;)
  • DynamicEFI EBL Flash ECU, gonna add PFI mod to this.
Parts kicking around:
  • AFR 195cc #1040 castings seem a bit older, but were sent to AFR a while back for CNC porting, bigger valves, etc for something similar as the super competition jobs they have now. bought them used so don't know the whole story and need to inspect them as well
  • TPIS MiniRam (1205 ports iirc)
  • LT1 T56 rebuilt and beefed up, and a DXD stage something clutch kit

Looking for something like 350hp for now and redline at 6k, but dunno what the stock L98 bottom end is capable of, so thought i'd ask the experts ;)

-? I'm going to inspect and refresh the motor some. i was thinking all bearings and piston rings, maybe some ARP bolts (main, rods) if need be to reach my goals.
-? I think the 195 are a tad on the big side
-? Dunno what cam would be a good choice, maybe something like the LT4 hot cam.. also i was wondering what CR i could run

Thanks in advance for any and all advice!

C.A.R.S.005 04-18-2011 08:03 AM

hi andi i would suggest using the L98 heads with a little porting they can put out 400hp they flow at 195 cfm stock. or find at set of 5.7 vortec heads 227 cfm stock they can do it with no porting but you'll need a aftermarket intake only about $150 . both sets of heads can 350hp with no sweat just get the springs for that lt4 hot cam and you should be good to go . :cool:

C.A.R.S.005 04-18-2011 08:10 AM

and with the heads in my previous reply your compression ratio would be about 10:0:1 pump gas safe . :welcome:

janus 04-18-2011 11:42 AM

CARS, thanks for your reply. From what i recall the F-body 350 heads aren't that good of a head, maybe you were referring to the L98 Vette head, or maybe i'm just wrong =)
At any rate, as stated in first post i do have AFR 195 heads and a MiniRam intake kicking around, so i'd rather use these, than get the heads (i just got the shortblock, remember?) and spend time on them with porting.
What do you think?

C.A.R.S.005 04-18-2011 05:20 PM

i was referring to corvette . what is the cfm flow rating on your heads ? and i'm not 100 % positive that the lt4 cam will fit any roller motor i think in only fits lt1/lt4 and the zz4 .

C.A.R.S.005 04-18-2011 05:39 PM

i looked up the specs and the heads you will work fine for 350hp and a lot more . i was not familiar with afr heads before. and like i said not sure on cam fit you could go with a compcams roller cam instead .

janus 04-19-2011 01:56 AM

thanks all the same, but i'd rather have some input from people who have experience with at least one specific of my combo.
at any rate, i know for sure that the Gen I (SBC) & II (LTx) cams are the same, at least for the rollers and not considering the dowel pin. also, yes - i would venture to state the range for AFR 195 heads just starts at about 300-350hp ;)

C.A.R.S.005 04-19-2011 08:03 AM

my brother has a 350 with 380hp with vortecs and they flow at less cfm but maybe the way they flow is different ? you my try contacting F-BIRD'88 he seems to know a'lot about sbc and how to get the hp out of them .

janus 04-20-2011 07:51 AM

anyone else wants to chime in here please? :)

janus 04-23-2011 02:31 AM

ok some more specific question here:

i heard some of the early 1pc blocks are prone to cracking, anyone on this?

how is the L98 bottom end gonna hold up to 6krpm without balancing?

and do you think the AFR 195 are on the big side for this build?


Bowtie man 04-23-2011 05:10 AM

We will start with the 195's. you do not need a lot of head to do what you want to do. I am sure the 195's have at least 2.02's. You could gasket match your heads an intake an that should be enough. Yes, they are on the big side. But porting them out will just make it worse. All you will be doing is handing them money.

The lower end is going to do ok with around 6000 rpm's. But, you need ARP bolts in the connecting rods. The lower end needs to be gone through an done right. Would be nice to balance the lower end.

All your parts need to work together or they will not compliment each other an will work against each other. That is why you need the right combination. I can not comment on anything else. Because you have not told us anything else about your engine.

janus 04-25-2011 12:20 PM

Bowtie man, thanks for the input. Actually i will accept any good power below 6krpm i can get of course, the 350hp was just a minimum, anything higher that can be done on a rebuilt short block is fine with me i guess ;)

I was assuming the same concerning the heads, thanks for clarification there. I'll go and measure the valve sizes next time i get to the garage. I did already CC one port / chamber and i got 67cc for the chamber, 197 for the intake and 66 for the exhaust runner, to make sure what i got.

From what i gathered, the stock L98 dish pistons are 12cc, so if piston to valve / head clearance is fine, the felpro 1094 should make a good squish clearance. I might have the block resurfaced slightly, but min. squish i'll get is somewhere between 0.35 and 0.40.

The arp rod bolts would be a nice insurance i guess. I would have that done by a machinist. What do you think about the mains? Do i need an align hone when getting better studs/bolts? Just trying to get a cheap bottom end build for now that will hold up for a few seasons (maybe 10-20kmls).

Any other input? Go ahead, i welcome it :)
Thanks again

Bowtie man 04-26-2011 04:42 AM

Yes if you are putting in ARP main studs. Be sure an at least line hone it to make sure it runs true. Good luck with your build an keep us posted.

janus 02-11-2013 06:25 AM

well well... like so many times before ... life got in between ^^

so i'm still working out details for this build and i have hopes of completing it before summer starts :welcome:

i recently came to the conclusion that by retaining the 12cc dished pistons (pre-90 L98 had these for the lower CR) I'd have a hard time setting up a decent CR and squish. so.. i got the idea of putting in a 94/95-up LT1 bottom end, since it's got flat top pistons and in general is lighter, stronger and said to be balanced a lot better than the L98/GenI bottom end i have.

any input on this is welcome :)

another question i have is concerning milling the AFR heads i have.. the 67cc chambers are too big.
i'm considering getting the L98's block deck checked and straightened if needed, so whatever deck clearance i will end up with will dictate my need for HG and chamber size to reach the desired CR.

janus 02-12-2013 04:52 AM


Originally Posted by F-BIRD'88 (Post 1645127)
Just rebuild it 30 over with -5cc flat tops. get the block decked so you end up with a net
.040" quench clearance. EG: .028" gasket .012" deck. The heads are fine as is.
The cr will be 10:1 The GM LT4 Hot cam will work well.
There are many ways to juggle that and many gaskets to choose.

First about the background of my idea.. Concerning this engine's bottom end I'm kinda on a budget because I'm back in college now and I'd really like to finish this before summer. Doing machine work for a SBC here (in Europe) can be kinda troublesome. For balancing, I'd have to send the whole cranktrain out to UK, for instance. So that's how I got the idea to use a good used stock LT1 rotating assy. The -5cc flat tops you mentioned would prolly be in the same range as the LT1 (imho they are 6 or 7 cc). Do you have a pointer as to why I should make overboring an item on my To-Do list?

As for the deck, I'd likely have the machine shop work on it since it can be done local, I'm probably gonna have it decked a little to make it sharp straight or IOW a 'true plane'. So I'm not sure how much deck I will end up with. I was gonna make a heads milling/HG decision after putting the bottom end together.

Imho it all adds up.. New pistons and while I'm at it I could also get some other rods or otherwise I'd prolly need some ARP rod bolts. Add in the machine work and shipping.. An LT1 rotating assembly would be almost in the same range for strength and weight but is cheaper, and if I can find one local I could also save some on shipping, plus it doesn't need balancing. Good idea!?


Originally Posted by F-BIRD'88 (Post 1645127)
Do not under gear it. slowing down a cammed motor does not work well.
Cammed motors need rpm.
the Mini Ram is not a low rpm induction system. It wants rpm.
The exhaust system will make or break it.

I'm gonna start with the 9bolt 3.27 I have in there now, but already have parts and plans for a 4.10 rear. Together with the later-LT1 T56 I have, that should give a decent but not too low geared drivetrain, the T56 being rather long in all gears. I was thinking that should be fine for something in the 3400 lbs range like a 3rdgen F-body?

I am aware that the MiniRam is, depending on displacement, more a mid- to high-rpm intake, but thanks all the same for reminding me ;)

Exhaust system for now is a single 3" highflow Catco and mandrel-bent Hooker Aerochamber catback. Up front is a 'ported' 1 5/8" Hooker shorties system with a 3" Y-pipe.
Thanks a lot for your time and advice :)

P.S. I forgot to mention the cam I plan on using.. I already have a XR276HR, it's 276/281 (224/230 @.050") and .536/.544 w/ 1.6 RR, LSA 112 and IVC is 66. So a tad more than the LT4 HOT (218/228, .525/.525 @1.6RR).

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