troutster71

Hi guys.
I'm a near fatal victim of project creep. And its not even close to being over!
Engine is '90 L-98, low mileage, less than 16,000 mi. In my '67 roadster since '91. Accel/DFI Gen 6 ECM. Tired of TPI lacking top end.
Simple intake change has morphed into changing the cam and valve train and getting the block decked!

Orig head gasket is .050". Flat top pistons avg .035" down in bore.
Quench = .085" right? Dont want to take too much off block, and I believe I can get .028" composit HG from GM.
So if I take .020" off the block, leaves .015" deck ht , plus
.028" HG = .043 quench. That calculates to 11.02 or so comp. ratio
with the 58 cc 113 casting heads. Perhaps a bit too high.
I have yet to actually CC the heads, or figure Dynamic CR with the new cam.
So I guess I have some questions.

> Is the std .035" deck typical of this era of L-98?

> Anyone reading this actually CC a 113 casting chamber?

> I've read that with good quench, you can get away with a little more CR, because it's basically more efficient. Granted, there are many other factors involved, concerning the dreaded detonation, but all things the same, good quench vs bad?

> In my current career, I am a CNC machinest, and in my devious way, I've been thinking there may be a way to accurately decrease CR
by machining either the combustion chambers or the valve reliefs in the pistons. A large amt of work, but hey, some of us are modern day hotrodders, right? I REALLY dont want to buy a new set of heads.
Thoughts?

Thanks, GA

Churchkey

Stock deck on my block was .032 & .033.

'89 113 heads after a .010 clean up mill & with Manley street flow valves = 55cc. Have a burette, checked them myself. Just a guess, the nub in the cumbustion chamber could be reduced in size to increase cc volume. Did not try it, I can live with 11 to 1 cr.

Many here like .040 quench. I'm at .035 quench with Felpro gaskets (compressed). Close enough for rock & roll on a low HP engine. Don't have the gasket # handy.

GREGGPENN

Typical quench on L98's is stupid bad. .078 or something like that. Getting better quench is a great goal and will serve you well.

Assuming your flat-tops have 4cc reliefs, I think you're pretty close in estimating a 11:1 static compression ratio. The good news is dynamic compression will be about right -- assuming you're picking something at least as big as a hotcam. Using it's config, I got 8.25 -- which is really ideal.

I assumed you'd use 5.7" rods and the stock stroke. 4.1" head-gasket (with your .028 thickness). Victor makes a good nitro-seal in that size IIRC.

Yeah, good porters can remove some material from chambers to get less compression. But, I'm not sure you'll need it.

Cam selection is really what it's going to come down to. And, I doubt you're going to pick anything too small -- now that you're losing the TPI for some higher rpms.

Sounds like you're making some great choices!

rklessdriver

The factory flat top 4 eyebrow pistons are about 6cc.

Victor Reinz makes a .026 head gasket with a 4.100 bore PN-5746.

The factory heads will measure right around 58cc but once you clean them up they'll be down to 56 or so as stock removal is .007 per cc.... As said you can work on the spark plug boss a bit and ge that back.... You can also mark the fire ring off and un-shroud the combustion chamber around the intake valve to get it back to 58cc.

My calculations putting the piston .015 in the hole with 58cc head gives you 10.85SCR - with the above head gasket and .041 quench.

A 56cc chamber is 11.13SCR.

Depending on what cam your changing to either would probably be fine.
Will

troutster71

Thanks, gentlemen, for your informative replies.
Yesterday I downloaded the PK DCR calc and crunched some numbers. If I install the cam 'straight up', (2 deg adv ground in), I come up with 8.88 DCR.
Too much, retard the cam 4 deg = 8.56, (-2 deg). Still too much,
retard 4 more deg = 8.30, (-6 deg). I would go with 8.30 DCR, but
is there a limit to how much you can retard the cam?

Cam is a Schneider custom
Specs 268/274 Adv 211/220 @ .050
.488/.492 w/1.5 RR 112 LSA 110 ICL

The above is with .015 deck, .028 HG w 4.1 bore, 4cc dish,
58cc chamber, 4.0 bore, 3.48 stroke.

On the other hand, If I stayed with plan B, change intake and cam,
leave the heads on, DCR is 8.06, but quench was .083........

Many combos with ICL, HG thickness, deck ht. Waiting on
a burette. Not sure I want to start grinding on the chambers...

And how much is too much is too much to retard a cam?
I need to speak to my cam guy. Cam was selected prior to
eng disassembly. Not good but oh well.

Thanks all, for tuning in, more later, Gary

Churchkey

Just my opinion.

The limiting factor here is the 113 heads. Beside the small combustion chambers the ports & valves are small. If you want to shift @ 6K & have the engine pull hard to 6K you need good heads. The 113's die after 5K. TPI's are great motors for auto trans cars, good torque but are lacking higher rpm power (HP) for use in standard shift cars.

Retarding the cam moves the power band up the rpm scale. If this Vette is a streeter you will be happier if the cam is installed as designed rather than adjusting DCR with it.

troutster71

And I agree with your opinion 100%. I was too focused on
DCR to remember what that much retard would do. I knew there
was a downside, didn't see what was right in front of my face.

Thanks Churchkey, more later, Gary

bjankuski

Use the Felpro 1094 head gasket which is a steel coated shim with .015 compressed thickness and skip decking the block, that will save a bunch of work. This gasket works well and works with alum heads. The cam seems a little small if you pick a cam with a little more intake duration it would help you out.

Churchkey

Head flow data here:


http://users.erols.com/srweiss/tablehdc.htm#Chevy

cv67

Id take a little less off the deck and use a slightly thicker head gasket just to keep options open later. Not saying its the best way but if quench is "off" a tad I wouldnt lose sleep over it.

CC on produciton heads can vary by 1-3cc avg. Valve job, how far the valve is sunk in the seat, aftermarket valves etc all can make a difference.

Kubs

I just went through this with my engine. My flat tops have 4 eyebrows (about 6.4cc according to mnfr), and my 113 heads were just under 58cc stock. I did some de shrouding like Will mentioned, removed the boss by the spark plug and had them cleaned up by taking 0.008" off and ended up around 57cc. These heads, pistons sitting 0.010" in the hole, and the Victor Reinz 0.026" gasket mentioned got me 11.1:1 static compression with an 0.036 quench. Dynamic compression is higher than I would have liked with my cam (about 8.6:1) but still reasonable and OK since its a race only engine. My block is also 0.030" over making it a 355ci.

GREGGPENN

For some reason, I originally read your OP as also wanting another intake. I guess it was the "tired of TPI lacking top end" comment.

I think you really need to consider another intake and bigger cam OR buying those heads you didn't want to get. But, you'd still be restricted by the stock TPI!!!

Since the stock TPI is stupid bad for making power, that's how I figured you were heading down the intake-swap with new cam route. I don't see you getting ANYWHERE constructive with the stock intake -- so that's gotta go. Unless you're changing the heads, the cam's gotta go too.

If you really want more top-end, you haven't started talking the talk yet.

Crepitus

Exellant thread and advice. my 2 cents; If you want to shift at 6000 the cam and 113s are too small. Deshrouding, radius on the edge of the quench and removing the lump will help the chamber cc but the port is just too small. There is a set of LPE ported 113s on the C4 parts board but a set of fast burns or an aftermarket head will be much more robust. I have looked really hard at the 113s because I have 4 of them sitting here but with out porting they just dont flow.

89L98TPI

Where are these LPE 113? I don't see them in the for sale section.

GREGGPENN

Everyone's probably seen it....but here's a good roll-model and example of 113's potential:
http://forums.corvetteforum.com/c4-t...o-results.html

Better yet:
http://www.superchevy.com/technical/...n/viewall.html

Neither used the stock intake trouster71.

troutster71

Thank you all for your valuable input. I am changing the intake, and the cam, and slightly thinner HG. Or at least that's the plan at the moment.
Greggpenn, I had to go back and read my original post to see what I said. A bit vague.... So I think it appropriate now, for 'full disclosure' for you gentlemen that have so kindly offered your expertise.

In cronological order, please bear with me
> Car is 1967 roadster purchased Dec 1990 with nom 150/350
(that's a worn out low hp 350)
> Early 1991 purch 12,000 mi 1990 vette L-98 eng and Gen 6 Accel/DFI system, installed and operational ever since.
(I love this motor. Gobs of torque, runs like a train. 3.36 gears and
I need to be on top of it to not break the rear end loose. Could be
old tires though....)
>Only about 3000-4000 mi since '91. Motorracing activities
>Fast Fwd to 2010.. tired of lacking RPM. Purch LT1 intake to
mod and install. Still got it, unmodified.
>2010/2011 Figured out how I would get fresh air from
fwd of rad support, but decided I didn't want to mod the
car that much.
>Love EFI and always said I would mod a carb intake w/
inj bungs. (See where I'm goin' with this?)
>Early 2011 purch used aftermarket stinger (BB ) hood
>Later 2011 Started mods on EDELBROCK RPM AIRGAP for
inj bungs, fuel rails, old school oil fill tube and crankcase
vent, to use orig finned valvecovers.
>Thought I would just change intake and valve springs,
in the car, and see what I had.
>Looked at stock L-98 cam specs..."that ain't gonna work'
>Ordered a cam!
>Thought I would just poke a cam in that baby,
change intake and valve springs, in the car,
and see what I had.
>Thought again, pulled the motor, pulled the heads.
>early Sept 2012 Thought I would 'Fix the Quench'
'Just deck the block' ... oh yeah rings, bearings,
hone, budget? Still need guide plates, pushrods
and rockers.
>Then there was the SCR thing.
>9-20-2012 As of this moment the plan is to not deck
the block, finish checking the heads, cc them, reassemble
w whatever HG works the best for DCR.
Continue with 113 head work, while I enjoy driving my car.
Acquire a trash head and/or a good pair to prep.

Thanks to this forum, I knew going in the heads were the restriction.
I'm just looking for cost effective, seat of the pants performance,
with some hands on, old school hotrodding. (And a laptop to tune it)

I know I went about this bass ackwords, but the cam I mentioned
previously, fits nicely. Installed straight up, .039 HG, I think DCR
comes out 8.2 or 8.3. FWIW

Additional comments appreciated,
Cheers, Gary

Another wacky thought: how would 2.02 113 heads work on
top of a roller cam 327?

cv67

They would work good fully ported
Use 2.00 intakes the the larger exh valve.

Churchkey

Agree.

Will be using 113's on a .030 over 302 with a roller.

Be sure to check intake/head port match before final assembly.

Luck.

Crepitus

K..Port em. A setup like the TPIS cnc porting will get you to 250-260 cfm. But it will cost nearly as much as a decent aftermarket head. Cheep option; study up and port them your self. David Vizzard has a 113 porting article in his book how to "build max performance small block on a budget" You wont get to 260 cfm but you will improve on the stock 200cfm. The extrude o hone method that Greg Penn linked is interesting, I have no idea how expensive or effective it is.

troutster71

Thanks, already have. I can look into the inj bungs and see a bit of
a mismatch at the top of the ports. It would probably get worse if I
deck the block. Working on that.

GA