I have a set of domed pistons sitting around for a gsr block from my old build (n/a gsr). They are OTS 11.5:1 JE pistons and I have been contemplating trying a high compression turbo setup as a fun engine for the weekend drives. Before starting a new build, should I bother with the domed slugs ? Really just looking for throttle response and streetable power and since it will be on 91 octane, I won't bother to go past 10psi

Just want to trying something new and save a couple bucks at the same time. Should I expect a dangerous situation with the domes or spend the extra for some dished units ?

 

certiantly it can be done, and has been done quite a bit, some searching will reveal such setups. Really your main variable here is tuning. This type of engine will require the tune to be DEAD ON. your other issue will be quality of fuel. 91 is ok, but really 93 or even condisidering e85 might be a better option. Again, your location and fuel availability will be something you must condsider. colder plugs of course will be needed. What size turbo will you be running? if it were me, id prolly condsider something on the larger side, although you will be fighting the lag issue, but shouldnt be too bad as you have plenty of static compression to make up for it. 10psi seems reasonable, but again PSI isnt really the right unit to be condsidered here, more about power, and how fine you can walk the line between detonation and a super fun street car. Look around for some good tuners and get their advice. Best of luck.

 

I say the same thing, GSR heads have the smallest combustion chambers and domed pistons are really going to make it tight in there. I know someone who did a high compression B20VTEC on boost and he had to run 115 Octane race fuel to run 14 or 16PSI. Although im not sure how big his turbo was he made like 485WHP on the dyno. So it can be done but its going to require alot of fuel and a GREAT TUNE and proper octane. Why do you want to run 91? Do you only have 91 available in your area? Because down here we have 93.

 

Abudabi.... Do they have any honda tuners in the Middle East?

 

Yeah, the more I think about it, with something like this, Id really look into e85 if its available in your area. Wont cost much to modify your fuel system and well, ****, its cheaper anyway. (although you use more as comapred to gas) I think he will be fine as long as he gets a good tune.

 

Well e85 and over 91 octane is not an option anymore unless I decide to buy a drum and run unleaded VP fuel, which would be too costly for the setup. I am hoping to run 91 pump gas. I have considered a thicker HG, but I invite cam timing changes which I am trying to avoid. I will be tuning the setup myself and I've only tuned about 4 turbo hondas so I'm still not 100% comfortable doing this.

My other option is to rebuild with dished pistons which will end up costing alot of time and money. I intended on running the peakboost t3/to4e or the GT2860r. Don't have a set HP figure I want to see... I want a setup that is fun to drive and even more fun at the track.

 

91 will not suffice for this setup, unless you only want to run like 5-7psi. My best advice to you is to stay N/A for the time being. This is further supported by your lack of tuning experience. With 11:5.1 there is not room for error and you must be spot on with the tune. Stay N/A get some money saved up and go for a set of dished pistons, take it from there. All your asking for is trouble when you combine high compression+ low octane fuel+ inexpereinced tuner. Just my .02

 

You also need a hp target and a plan. without that, your project may never come to fruition

 

^^ That lines up with what i've been thinking. *damn*

I don't have a set horsepower goal per se. I figure anywhere around 250 for street driving and around 300 at the track would be a good start. The setup should make those figures easily under normal circumstances but I was interested in the power delivery of a hi comp turbo setup. I am thinking the power delivery would be alot more entertaining to drive and maybe even allow lower boost on the street. I do intend on trying a methanol spray setup as well.

Would a thicker headgasket make a marked difference ? Compression would still be around 10.5 and octane/tuning conditions stay the same.

 

you could sell your built na bottom end, and buy a stock ls or gsr bottom end, stock ls or gsr's can handle 300whp pretty eaisly. just a thought.

 

I've been getting alot of people talking about thicker headgaskets, but honestly not one of them has ever actually run one (haha). Been on the lookout for a stock B series block to consider switching over to. I'm a parts hoarder and don't really want to see the n/a block.

 

The dome on the pistons actually creates a lot of problems... I've tuned quite a few high compression setups, but some are GSR heads that are milled down a lot with flat top pistons and some are B16A heads with a dome piston. Both these motors end up around the came compression ratio. The flat tops always run more consistent and much easier to tune and makes more power on both race and pump fuel, yet the domed pistons always want the engine to run severely rich just to keep them from pinging.

A few of these motors came back to my engine builder over the years, and everytime we had these motors opened up, the tops of the piston domes are always shiny and very clean (no carbon) but the rest of the piston is pitch black. It really shows that a lot of heat builds up around the high point of the dome and much more prone to detonation and reaching the octane limits.

 

Long story short, forged 11.5:1 slugs won't get you much more than flattop OEM cast (p72's). Since there will be less chance for detonation, it will also be more forgiving with different gasoline, temps, etc, you'd see while driving on the road. The other end of the stick is that higher compression only makes more power per psi (marginal), not faster spool. Jeff Evans did a test regarding that.

300hp is about all you need for the street, unless you have some deathwish and proceed past 130mph on a public road. 300hp is enough to spin 3rd with most tires above 100 treadwear on decent asphault. Add in any gravel, cracks, etc, and it will spin at best, and go careening off the road at worst.