Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by: KPower

How far can i push it on standard head bolts

Thread Tools
 
Search this Thread
 
Old 01-29-2016, 01:10 PM
  #1  
Junior Member
Thread Starter
 
sparkybean's Avatar
 
Join Date: Mar 2012
Posts: 110
Total Cats: 13
Default How far can i push it on standard head bolts

As above. Ive tried every combination of search term going - Best i found was in the DIY FAQ, which only says 'somewhere above 250hp'

I want to run somewhere between 250-275hp, and if i can get away with just rods then i will. I aint made of money.

Car is to be used on track.

Thanks.
sparkybean is offline  
Old 01-29-2016, 01:19 PM
  #2  
Senior Member
 
AlwaysBroken's Avatar
 
Join Date: Jun 2015
Location: TAMPA, FL
Posts: 817
Total Cats: 20
Default

Honestly that's probably going to be fine. Most people don't know where the upper limit is because going above 250whp safely requires opening the engine and spending 100 bucks on head studs when you put the head back is basically free. I was running 18 psi for over a decade, most of that time was on stock head bolts.

edit: I see you're just going to upgrade rods. I personally feel that you're pushing your luck going for 275whp on a track car with just rods. If your tune has any problems, you might have a bad time. If you lose a piston, a rod could go through a cylinder wall and you're going to be a few grand in the hole just to get the car running again.
AlwaysBroken is offline  
Old 01-29-2016, 02:52 PM
  #3  
Boost Czar
iTrader: (62)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 79,494
Total Cats: 4,080
Default

the rods are the weak link; they bend above ~250rwtq. you can just as easily kill forged pistons with bad tuning.
Braineack is offline  
Old 01-29-2016, 02:54 PM
  #4  
VladiTuned
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 35,821
Total Cats: 3,481
Default

275hp is like 250whp
You'd prob be ok with a stock engine at this point
18psi is offline  
Old 01-29-2016, 04:24 PM
  #5  
SADFab Destructive Testing Engineer
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 18,642
Total Cats: 1,866
Default

Rods will bend as low as 225 ft/lbs when driven hard on the track.

You tell us, i'm interested how long they hold up.
aidandj is offline  
Old 01-29-2016, 06:02 PM
  #6  
Junior Member
Thread Starter
 
sparkybean's Avatar
 
Join Date: Mar 2012
Posts: 110
Total Cats: 13
Default

Im fitting forged conrods. My question is about the head bolts. Wheres the limit?

Ta always broken. Im pretty confident about my abilities to tune, and have heard that stock pistons are good up to 300 without knock. Headgasket good to above 450 thnks to the head lifting thread. Only variable left is the head bolts atm
sparkybean is offline  
Old 01-29-2016, 06:07 PM
  #7  
SADFab Destructive Testing Engineer
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 18,642
Total Cats: 1,866
Default

You tell us. I'm interested in how long they hold up.
aidandj is offline  
Old 01-29-2016, 06:11 PM
  #8  
Elite Member
iTrader: (16)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 9,297
Total Cats: 477
Default

If you torque them correctly, they'll be fine. I ran mine around 350whp and it lifted the head, but I later discovered my torque wrench put them at 40 or 42 ft*lbs. I have head studs now, but wouldn't be afraid to run stock bolts to 400whp if you have a torque wrench that is verified to work correctly.
patsmx5 is offline  
Old 01-29-2016, 06:25 PM
  #9  
Junior Member
Thread Starter
 
sparkybean's Avatar
 
Join Date: Mar 2012
Posts: 110
Total Cats: 13
Default

Perfect, thanks. Waayy above what im going to be running then.

I did find, on my travels, a few posts hinting that the main bearing cap fasteners need changing at ~300hp. Not sure this is worth the worry though.

Otherwise, i dont think ive got any other parts to buy. Thank god. This '1 grand build' has cost almost triple that so far...

Last edited by sparkybean; 01-30-2016 at 06:59 AM.
sparkybean is offline  
Old 01-30-2016, 04:44 PM
  #10  
Elite Member
iTrader: (5)
 
Stealth97's Avatar
 
Join Date: Oct 2007
Location: Canton, Ga
Posts: 2,156
Total Cats: 66
Default

Originally Posted by sparkybean
Perfect, thanks. Waayy above what im going to be running then.

I did find, on my travels, a few posts hinting that the main bearing cap fasteners need changing at ~300hp. Not sure this is worth the worry though.

Otherwise, i dont think ive got any other parts to buy. Thank god. This '1 grand build' has cost almost triple that so far...
I had a budget of $1500. I think I'm $6k in..
Stealth97 is offline  
Old 01-30-2016, 06:57 PM
  #11  
Elite Member
iTrader: (6)
 
ryansmoneypit's Avatar
 
Join Date: Feb 2013
Location: A cave in Va
Posts: 3,395
Total Cats: 456
Default

I budgeted 2500. I'm at like 8 or 9 k. See a common theme here?
ryansmoneypit is offline  
Old 01-30-2016, 07:10 PM
  #12  
Senior Member
 
AlwaysBroken's Avatar
 
Join Date: Jun 2015
Location: TAMPA, FL
Posts: 817
Total Cats: 20
Default

I am actually within budget on the current build. Looks like I'll be in the 3000-3500 range including new pistons, refreshed head, new oil pump, harmonic balancer and clutch. I can't even imagine how much it would have been if I paid someone else to do it for me.

Extremely cheap engine builds don't make any sense to me, since there is a lot of small stuff that isn't part of your "list" of mods you are officially doing and it really eats into your budget. Timing belt, head gasket, bearings, etc all add up. On a 3k engine build, 500 bucks of nickel and diming doesn't really hurt that much. On a 1k engine build, it's half your budget. And then in another year or two, you're going to punch yourself because you had the engine open and you didn't take care of everything.
AlwaysBroken is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
BEAVIS
Build Threads
143
12-18-2019 10:52 PM
dvcn
Miata parts for sale/trade
10
02-09-2016 09:19 PM
btabor
ECUs and Tuning
9
01-30-2016 11:06 AM
theshdwconspracy
Engine Performance
5
01-23-2016 04:43 AM
zvehrs
General Miata Chat
3
01-12-2016 08:47 PM



Quick Reply: How far can i push it on standard head bolts



All times are GMT -4. The time now is 09:17 PM.