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Discussion Starter · #1 ·
Im building an engine for a friend,a 383 stroker for his truck.He does'nt use this truck for towing or anything.He's looking for some strong power for the street.
383ci 10.7:1 cr
Aluminum 190cc heads 2.05/1.60
274H XE cam
1.6 Pro magnum roller rockers
Performer rpm intake
Speed demon 650cfm carb
50k Hei
the bottem end has:
5140 I-beam rods 6" bushed pins
5140 Forged crank
Hyperutectic pistons
Total seal gapless rings
Kings main/Rod bearings
4bolt main caps with ARP studs
Im wondering if this setup would be suitable for driving a few days a week?He has a 5spd Tremec trans in it.Also will this thing run premium pump fuel?Is this a good combo for what he's looking for?The truck is a 71' C10 lowered 4/6".
 

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go to the comp cams site
click on "charts and graphs" under Technical
click on dyno results
pick a cam chart shown
click on the chart

complete motor build spec's given, in your example, 274H cam idle vac=11Hg at 800rpms, carbs want 15Hg around town

you build a motor around the cam for the results you want
 

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Discussion Starter · #4 ·
So will 91 octane work?I know the newer corvettes run 11:1 everyday on the streets.I've looked at the comps dyno,but thier setup is far smaller than mines.Will this thing be a hassle to drive every now and then?He is really just looking for the power.
 

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bonzipenguins said:
So will 91 octane work?I know the newer corvettes run 11:1 everyday on the streets.I've looked at the comps dyno,but thier setup is far smaller than mines.Will this thing be a hassle to drive every now and then?He is really just looking for the power.

Newer Corvettes don't count. It's apples to onions.

It depends on what pistons you have.
Dished pistons will be a real challenge.
Reverse dome or flat top pistons with best squish might be OK.

Tuning will be critical on the razor's edge with 93.

If you are into the grooving thing, I would suggest grooving the pistons.

The famous engine builder Steve Henderson said many times,
"You can build a 420 hp engine with a fuel problem, or a 400 hp engine that will run on junk".
 

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i had an aluminum headed 383 with 11:1 with a 236 242 @.050 .520 lift hyd roller cam. It ran fine on 92 octane. It had 64cc heads with flat top JE pistons.

Adam
 

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Discussion Starter · #7 ·
im running hyperutectic Flat tops,with Gapless rings.So im a little confused because everyone is going back and forth.Will it run on pump gas?I am rejetting the carb and recurving the distributor at the local shop for this application.If my cr is too high what should I shoot for?
 

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In my experience, the motor will run on pump gas up to 11.0:1 with iron heads if you run a tight squish (0.035" to 0.040"), leaning to the tight side of that variance, jet the carb properly and limit ignition advance to 35-36 degrees total, in by 3,000. Of course the cam has to be matched up properly also with the correct intake closing point to limit cylinder pressure. I like to use KB's or other manufacturer's pistons that are made like KB's. Stock-type Chevy pistons are the worst because of the way the crown is recessed with a very narrow ring around the perimeter. It just doesn't make a real nice match with the underside of the head for a good squish. Even with a dished piston where you want less compression, the KB's have the dish offset to the chamber side so that you have a nice flat area to mate up with the underside of the head.
 

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Discussion Starter · #9 ·
sounds good,these heads have the heart shape chambers like vortecs I didnt know if it makes a difference I've heard that aluminum heads will run more compression,I believe these pistons are kb's.
 

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bonzi, your buddy wants a street car, go back to the comp cam charts and look at the 1500-3000rpms hp and tq and Hg values on all the cams
from their charts examples:
a 274 grind cam will be 11Hg at idle and make 225hp at 3,000
a 250 grind cam will be 19Hg at idle and make 225hp at 3,000

each full compression point can add "upto" 4% to the "peak rpms" hp for any motor size....doesn't usually add much to low rpm's performance, your adding 4% to a low hp and tq number at 1500- 3,000rpms
from the chart:
if their build had been 10.25, would be max 234fwhp at 3,000....6 additional fwhp doesn't do much on a 3,000lb car

for the street, max 10.0 so you can run more timing at low rpm's
 

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red65mustang said:
go to the comp cams site
click on "charts and graphs" under Technical
click on dyno results
pick a cam chart shown
click on the chart

complete motor build spec's given, in your example, 274H cam idle vac=11Hg at 800rpms, carbs want 15Hg around town

you build a motor around the cam for the results you want
Those charts are for 356 CI engines. You should have more vacuum when used on a 383. My 383, with that cam, has about 13" @ 800-900RPM.

BTW: +/- 10.3 CR and aluminum heads and runs on 89 octane.
 

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Remember. This guy is in Bakersfield. High summer temperatures and 91 octane gas. Not 93. At least not at the neighborhood Shell. Not saying it won't work, but there isn't a lot of margin at 10.7. You might want to take a close look at what's happening with your dynamic compression. With that big of a cam, you may get away with it. The cam seems a little large for a street 383 (to my taste, yours may vary) but going to a smaller cam might be the compression/fuel death knell. I'd like to hear a little more on the cam timing issues, dynamic compression, and probablilities of detonation from Xntrik. . . . . . . Perhaps using some camshaft timing tricks could help? ? ? ? ?

Pat
 

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Discussion Starter · #13 ·
So I might have to lower the compression a little?Is this really too much cam?It says 1800-up but in a 383 thats about 1500-up?
yeah he only put the compression so high because he wanted sound,and power.I told him in advance that compression might be a little high,He did'nt like the last motor I built for him.He said it was'nt mean enough.It was a 383 9.7:1,with a set of reworked vortec heads,268H xe cam and a rpm intake,I had put a 600cfm edelbrock on it.I honestly didnt see what was so bad with that setup it sounded great.But he said he wanted more sound.
 

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comp

CNC BLOCKS N/E said:
What the heck is 106 LDA.

Carl i think he ment LSA.. the "D" is right beside the "S" on the keyboard and maybe he fat fingered it???L.O.L.


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Everybody else,,, be really careful with blanket statements about running "X" compression on "Y" octane gas.... There are way to many factors to make a given combo work or not work... If the guy is on the site asking basic questions i doubt he is a pro at tuning an "one the edge" engine. It would be far better to err on the Conservative side, and know for sure there is going to be any burnt pistons..IMO..

One of the biggest issues for me over the years is,, time and time again I have herd the statement "I run 11.5 on 93 octane" then when you push the issue you come to find out they never checked the numbers and are going by magazine articles or advertised piston compression... My point is that there 11.5 engine really is 10.2......


Keith
 

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glen242,
yes I know the charts are 350's, but the charts are the best group I have found to show side by side all the relative effects and results for changing cam duration on a identical build (the 250H is a performer intake)

yes, change the bore/stroke ratio(350/383), change the heads(those are dart S/R), change whatever, the actual number will change but will follow the changes based on duration shown in the charts

the Hg at idle will only go down with use/abuse/miles on a stroker....start out with 11Hg-13Hg as max possible...... motor becomes a beeeeetch to tune after ??,??? miles
 

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Discussion Starter · #18 ·
I wasnt sure I have put bigger cams than this one in 350's,that were drove on the street.it says on the card it starts coming in at 1800 on a 350,so would'nt that be about 1500 on a 383?He's really not worried about having enough brake vacuum we will get a canister if it's not enough,And I have a friend at a wholesale fuels up here,they sell alcohal and high octane gas.Because they have a track up here.If it wont run he said he would mix fuels,but we just wanted to know if it would run on this setup comfortably?Is this setup really too big for the streets?
 
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