AGreen

The rotary I just finished blowing up made about 350 wheel horsepower. So let's just get this over with and I'll say now that in no way will I allow my car to hold a bigger engine with less power and more weight. There's potential here and I know I can tap it.

So my current status with this engine is that I have the block and crank at a machine shop getting bored/honed .030 over and it's getting forged aluminum flat top pistons. Based on bets, I have to make this work for under $2k. Sounds crazy, but I can sell my rotary stuff to make up for the losses. So far I am in for $1k. That includes:

Used TPI 350 (and 700r4) from an 88 trans am GTA
Megasquirt 2 version 3.0
SBC to 2nd gen Rx7 built-in cradle kit (allows for a smooth drop in)
700r4 to Rx7 diff driveshaft
Rx7 turbo differential
Sealed Power rebuild kit CMSHP760-300
Intercooler and piping (using the one I ran on the rotary)

So I'm within budget for now. I still need the turbo(s?) and some decent injectors, but I know how to wheel and deal for parts pretty good.

Now, for the BIG concern that I need help with. The flat tops are going to bump the compression ratio up to 9.8:1. That's assuming:
4.030 bore
3.48" stroke
0.019" deck clearance
0.039" compressed head gasket thickness
4.125" head gasket bore
64cc heads (stock)

I need to lower the compression ratio down a bit. I've done my research, but I'm sitting at a fork in the road right now. On one hand, I'm being told that double head gaskets are completely fine. People say they've used then for years and up to 20+ psi and never had a head gasket leak. I'm suspicious, and I feel rightfully so. On the other hand sits the option of larger cc heads. I have found a set of 191 heads for sale for $75 here locally. Some research says they're 76cc heads, some say 64. Some say the valves are 1.94/1.5 and some say 1.84/1.5. I'm still trying to figure out if they're even worth using? Are they one of the more "crack prone" sets of heads?

Here's another thing to consider. The majority of people are trying to build their SBC's for naturally aspirated power, so most of the forum banter I've been reading is about how poor everything breathes. The heads, the intake, the puny cam, etc. My train of thought is that I can make flow with pressure, so 90% of what I read on most SBC (especially TPI) subjects is essentially useless.

TL;DR:
Need to lower CR
191 heads are an option
I don't think the idea of doubling a head gasket is too smart
Are 191 heads a good, cheap option for my turbocharged application?

-Green

aliceempire

iTrader: (14)

Cool project. You may want to post this in the Power Adders board. Lotsa help there for such things. I was under the impression 191 heads were nearly identical to 193 heads which are 64cc heads but I wouldn't quote me on that. I would also think doubling head gaskets would be bad for quench. You might be able to find a good set of aftermarket 76cc heads second hand for relativly cheap,

Orr89RocZ

iTrader: (20)

1. Can you sell the flat tops and get a dish?

2. How much power you wish to make here?

3. Is air water intercooling or meth injection a possibility for you?

4. Is e85 available?

AGreen

1) Probably not. I'm pretty sure I'd never be able to sell them and get enough back to make it work out, even though they're brand new.
2) Over 400. That's the minimum goal. More is obviously better.
3) maybe, if it fits in the budget
4) I'll have to find out. Unfortunately, that will require some work to the fuel system to be able to handle e85. I remember looking in to that a while back and I think I would need to fun a new tank and lines or something.

I found a set of 993 heads. They should be 75 or 76cc as well. Any info on those?

And I'll give the power adders forum a shot. Thanks for the hint. This forum has been my go-to source for pretty much all of my searches. Lots of great stuff here.

Orr89RocZ

iTrader: (20)

400-500 whp i would leave it alone at 9.8 to one. Possibly look at grinding the chambers on your heads around spark plug boss area and deshroud the valve. That should remove a few cc from the chamber.

It will take a alittle bit of boost like that and get you the hp number you are after but will need good intercooling and be very cautious on the tune/timing. Keep cam somewhat mild in duration, not to much bigger than stock with stock
Throw a big rad in it and keep it cool as possible. 160 stat or even less if possible.

Meth injection would be ideal here. Cooling and octane it provides will keep engine safe.


Only other idea is 70+ cc chamber heads or aluminum heads. Or a .081 or thicker gasket to get overall piston to deck to over .100"

87hellbird

There is a guy on YouTube that ports the heads to allow more air around the valve, I'd look at that plus what orr said, as for injectors, I don't know if they will work but 8.1l vortec engine stock has 30# injectors and the marine one has 44#. For turbo, if you want it to spoil really fast for cheap, look at running twin Saab turboes only hard part will be getting headers or manifolds to bolt to them