jaybuller

My setup is a 1983 cutlass. 3400 # race weight. Going with a th400 rear gears are 3.50 and im gonna go whatever stahl convertor matches my cam i choose but probably round 3800 to 4000.

Heres what i want: for drag strip max effort no class rules or anything more of a street race type setup.

The short block is a iron lq4 block with stock crank and forged rods and pistons(pistons have the big valve releifs for the L92s.) with l92s or 317s the compr. will be anywhere from 10:8.1 to 11:1.1 so compression will be good either way.

ill be running either a gmpp single plane or a victor Jr. with a carb.

nitrous will be a plate style 150 to 250 shot but no more than 300 ever.

What head would be better for my setup being mainly a trac car and a once in a great moon saturday night cruise car.

send my 317s in and have them ported or just go with a set of L92s?
I havent chose a cam cause im waiting on head selection also havnt bought an intake because of that reason. Im just not sure what head has the potential for a faster ET> basiccly i realize the stock l92s make more power but does the power under the curve with the cathedral port heads make up for the heads not making the most HP up top?

ZONES89RS

iTrader: (25)

If it was my choice with that combo and my money, L92 or Ls3 heads.

bitterman

Same here l92 head are great bang for the $$$

jaybuller

thanks for your opinions on the matter. I myself am leaning towards the L92 route because i built my last lq4 using 243 heads and it did good but always wanted to try out the LS3 heads. Im really looking for a high 500s low 600hp at the crank to get me where i want to be when on the giggle gas. i really want to break into the 5.8 5.9 area with this build on a 250 shot with my 3400 pound Gbody. ive been stuck at 6.2 in my cutlass for so long with the sbc setup and really want to break into the 5s!

speedtigger

iTrader: (16)

You might see if you can bump the compression up to about 11.5:1 or maybe even higher.

EastTnZ28

iTrader: (20)

Id go with the bigger valves. L92's

dogsballs

combine both of the above, LS3/L92 and compression.

stock casting will be fine.

matt93lsx

great question, i have heard everything from they are too big for a 370, to the deck height isnt thick enough for a large power adder etc. glad to hear some input on the l92s on a small ci motor. may just sway my 408 build plans, im not looking to outrun the world....just get in the 5s on gas which plenty of people on here have done on a budget

jaybuller

So y'all arnt having any issues running pump gas through a carb setup with over 11:1.1 on these? I would like to go as high as I can get away with while still being able to use the stuff at the pump. May be able to pull timing while on pump gas then mix in some race gas and turn it up? I don't know. I'll look into bumping it up over 11:5.1.

ZONES89RS

iTrader: (25)

Seen 12-12.5 on pump fuel.

dogsballs

can bleed off compression with a some smart choices on cam.

interesting question if you are talking about power adders as well

jgillen91

iTrader: (1)

I went l92/ls3 heads on my old combo. 3300 lbs 4.11 gears 4500 stall went 10.70's @126 on motor pump gas. Went 5.96 @116 on 250 shot.

370 lsx engine iron block

Bottom end-2005 lq4 block. 030 over 4.030" Racetec Forged Flat top Pistons .052 gm mls head gasket Scat forged 6.100" rods Stock Crank polished 24x Plasma moly rings gapped for nitrous Speedpro coated race bearings

Valve train heads, and cam Hydraulic roller cam speced by geoff at eps 235/251 duration at. 050" 623/631 lift 110+4 lsa Comp cams double roller timing set Ls7 lifters Comp cams hardened pushrods Ls3 rockers oem

Heads/ Intake-Ls3 heads ported by mike stark at cfm performance Indianapolis. Valve job, decked .040". See pic of flow sheet below. Ls3 hollow stem intake valves, Prc. 650 springs with titanium retainers. Stock ls3 rockers Victor jr intake port matched to heads with port work done to dividers done by cfm performance.

VLS1

Interested to know why you suggest this?

It is already well proven there is nothing to be gained by bumping compression with street spec cams/pump fuel combos. If anything all it will do is create headaches with being less forgiving for any tuning mishaps.

When someone beats Dave Mizell's 9.87 (10:1 motor) @ 2900LB race weight, by running more compression, then there may be something to it.

Running high static comp requires large duration camshaft (250+ @ .050") to see any real world gains, regardless of anything else.

dogsballs

all i know from my experience (talking 6 cars) with the square port heads is that increases in compression and use of fuels like e85 show much better gains (particularly at the track) than say running bigger cams on stock compression.

i can't explain why. could be flame front related in a smaller combustion chamber, could be due to the massive ports. they behave different to the cathedral head based motors, which like the massive cams.

06X6spdGTO

iTrader: (6)

My Gbody had no problem finding 10's once I got things Ironed out with the SBE...

With my new bullet I can say it will be 11.8-12.0 SCR...
Forged 370, 3150lb w/o driver

VLS1

I've worked for a successful performance and race engine builder previously, so have a pretty good understanding of the relationship of cam vs compression.

To put it simply, I will use Dave's combo again for an example.

Dave's motor, LQ4 dished piston with .030" off heads, works out to depending on piston/deck somewhere between 9.9 - 10:1 running a 239/247 cam for approximately 7.5 - 7.6:1 dynamic compression. In other words at the very safe end of pump gas range (7.5 - 8.5 dynamic)

Your engine from what I've read so far, LS2? Flat top with approx 2cc reliefs, .100" off heads for around 12:1 running 236/246? cam, resulting in dynamic comp of somewhere around 9 - 9.1:1 dynamic.

From what I have read your mph is very close, but with @ 300lb less weight, so theoretically your combo is making around 60 less HP.

Your dynamic comp is very high for a relatively small cam, and as I mentioned previously, a high static comp motor will generally run a lot more duration (250-260+ @ .050") which in turn brings the dynamic comp back to somewhere suitable. This is the main reason to run high static comp, to run more camshaft and move more air at higher rpm. Moving more air simply makes more power, the compression is not some miracle worker, it is simply bringing the dynamic into range with larger cams/heads etc.

dogsballs

i think we are talking similar things , maybe my wording could of been better.

i agree with what you are saying. different ways to achieve the same result.

my car was a mega budget build and came together with bits i had, would be interesting to see how it would go with a bigger cam.

VLS1

Absolutely it would be very interesting with a larger cam, I think doing this would be very beneficial with the high static compression ratio.

3pedals

iTrader: (3)

11:1 with a 235* intake lobe ran trouble free on the street for me on pump 91. I did not have to detune the timing to run the 91 octane either.

speedtigger

iTrader: (16)

Because more compression makes N/A cars go faster. This is not a "trendy" idea or a flight of fancy, but merely a cornerstone of racing since, well, the beginning of racing.

This is a vague general statement, but in my opinion it is factually untrue.

The limitation of increased compression is the ability of your combination and choice of fuel to handle the operating pressures. And, if you do enough reading of shared results of people who have pushed the envelope of pump gas compression with LS engines, you will find many, many examples of people venturing into the 12:1 compression ratio territory successfully.

So, take whatever lower compression N/A combo that you want to use as an example, pump it up to 11.5:1 and watch it make more power everywhere. It isn't a theory, it is historical fact.