10.5-or 11:1 comprestion

[2dsei]

goint to take my new head and get it planed 1o to 20 thousants and get it p&p get to compresstion up when i redo my engine how much do you think i can go with out the engine getting damanged

[A20A1]

well are you going to change your spark plugs... also are you getting any kind of engine (ignition/fuel) management?

I was thinking of doing 9.7:1 - 10.0:1

But rebuilding the engine isn't my thing.

[accordlxi2.0]

jesus 10.5:1

i'm sticking with my 9.6:1

[gfrg88]

isnt that guy versanick i think is his name running a b20 with 13:1 comp.???

[Deadhead]

I don't know, but i'd say if you have the money to go for higher compression, DO IT.

You get more power out of the motor and if you boost, you will get more hp for each pound of boost.

[b8er]

I don't know, but i'd say if you have the money to go for higher compression, DO IT.

You get more power out of the motor and if you boost, you will get more hp for each pound of boost.

i dont believe thats true, if you go boost you want low comp. high comp is for high reving all motor projects, im pretty sure once you start adding boost to high comp. your in for a BANG.

[2drSE-i]

yea high compression and boost can be run, but think about it. High compression off the bat, then add more pressure......pop like a balloon. like that google video, where the mustang blows the intake manifold off (lmao)

[b8er]

ah yes, i knew that hight comp. and boost was more prown to detination i just wasnt sure if its a streetable way to run boost, in my case i would much rater run low comp but i guess looking back at some dragserts we have had i feel like such a moron cause our last enginge was upwards of 11.5-1 running 20-25 psi boost, sorry guys, momentary laps of smartness ahah

[racerx]

if you want anything in the 10.0:1+ ratio range, you'll need to shave more then 0.010-0.020".

I would assume 0.030" would get you close to about 10.0:1, and you could probably safely go up to 0.035" and that would probably leave you at 10.5:1, but then again, why go that high if you're boosting?
you'll need all forged internals and a hella FM system to keep that thing under control. unless, of course, you want to rebuild it every 5000 miles...

[Hash_man_Se_i]

If you're going that high compression too, I would definately be rebuilding the bottom end too... Especially if its a high mileage motor, new bearings and such would definately be a good idea.

[AccordB20A]

ive just had head and block plained. not to increase compression but cause one was warped and the other had a narstey scratch. I really cant wait to see what this b20a of mine will perform like........

[Oldblueaccord]

goint to take my new head and get it planed 1o to 20 thousants and get it p&p get to compresstion up when i redo my engine how much do you think i can go with out the engine getting damanged

you will have to test assemble,mock up, the engine and check for piston to valve clearance. Most of the time clay in the piston and then check the thickness with mics. It would be debatable what clearance you would need. I would think .030 is ok but do some searches on some Honda specific sites for some more real numbers.

The other thing to remember is the timing belt will be come looser the more you shave off and I'm not sure how much the tensioner will take up.



There's a spec in the book for the max you cut from the head factory that is for a referance.

Also there is formulas that you can figure compression ratios with if you know all you dimensions. The cc of the conbusiton chambers would have to be measured since I never have found a "reliable " number on our head.


wp

[bobafett]

im curious what engine management u plan on using at 10.5 or 11:1

stock is 9.2 or 8.8 you are talking about a HUGE change in compression... tuning in a high compression motor is much more critical, so i hope you have a plan, other than just getting a high compression motor.

also worth mentioning is the fact that mike and daryl at openloop raised compression by welding inside the head, this would eliminate the need to shave or deck things as much.

[Ichiban]

Shaving the head and deck substantial amounts will retard cam timing as well. better have adjustable cam gear or some other way of compensating...

[w00tw00t111]

hey boba since the guys at open loop just welded inside the chamber, they wouldn't need to make any mods to the valvesprings or lifters right? One thing I was worried about was that if I decreased the squish area enough by a combo of hi comp pistons and skimming the deck/head that I would start getting some major valve lash. Just a question

[Ichiban]

do you mean valve lash or valve/piston interference? Valve lash won't be affected and any valve/piston interference means no-go. A20 valve lash is adjusted by a set screw on the rocker end, there are no lifters.

[bobafett]

^^ correct. but you are on the right track in assuming that increasing compression by welding the head will not affect head/block height and therefore not change the timing because of different dimensions. and your valvetrain should be unaffected by this mod

[88Accord-DX]

I'm new to this welding the head to raise compression, what & where is the welding at on the head?

[gfrg88]

yeah i have the same questions

[Ichiban]

some people call it a quench pad, on a 4 valve head it sorta resembles a cloverleaf, they fill the area around the edge of the chamber and between the valves.

[w00tw00t111]

Wow I feel pretty stupid. Oh well. So if you get a shop to P&P your head as well as increase the exhaust valve size and angle cut each valve would then welding the head make all the previous port work negligable? Why would welding the head be less safe then upping the compression ratio of the pistons? If I understand correctly upping the CR of the pistions is what causes the valve piston interference so if you are wanting to run 11-12.5 CR then wouldn't welding the head mean less headaches in getting the squish area at a safe level?

[w00tw00t111]

Well, besides the monetary objection I don't know why you wouldn't want to. I was talking to rjudgey and he explained to me that that's the aseries main limiting factor. That's where he found most of his power. And like I said if the shop wants in excess of 200 for each cylinder then unfortunetly I would have to go another route.

[bobafett]

yeah but we have 1 35mm exhaust valve per cylinder. and TWO 28?/33? mm intake valves. i think its fair to say we can get more air in than we can out...

again im not a flowbench master, but i thought i got the impression that exhaust side was restricting flow.

[bobafett]

thats true, we really cant FIT much bigger in there, but like ur sayin, there is plenty we can do to get that damn exhaust flowing

[bobafett]

oh yeah i knew that he had done it, also he mentioned that with lower CR and boost it would be a good idea to do that, and increase exhaust port size, so i guess i was on the right track for MY build, but definetly not for yours.