corolla engine experts

[theboss]

Dear all,
I am building a stationary power solution and decided to go with toyota for their long standing reliability and cheaper availabitly. Aim is to start with "A" series engine and improve its low end power and torque because it will be comissioned at 1500 RPM. Because fuel used is natural gas its necessary to increase compression ratio for better efficiency. I determined that 7A (1.8l) engine with 4A (1.6L) heads should yeild me smaller combustion chamber thereby increasing compression ratio. Two characterstic very important for natural gas operation. My question to the experienced, is such a swap possible??

- Shall i source valves and cams of 7A onto 4A head as well??
- What are trouble areas i should look for in such swap??
- Volume of combustion chamber for both engines and types of pistons used. Overboring as offlimits as it will incurr an expense of purchasing retrofit over size pistons often hard to find. - Further improvment of low-end power in toyota engines.

[Piloter]

Aren't the F-series heads on the 4AFE and 7AFE essentially identical? The weak point of the 7A is supposedly the connecting rods, although many people have claimed to be putting down respectable power on a daily basis at high revs...

The non-North-American version of the 7AFE (Indian or Russian, can't recall) was the one that developed the most power, probably as it didn't have to comply with stricter emissions regulations. Also, a lot of non N-A engines had the TVIS style intake manifolds, to boost torque below 4,000 or so RPMs. Stock, the North American 7A develops peak torque at ~2,800 RPMs, and 1,500 is actually within the cold idle speed range. Cooling may be an issue, as may be various carbon buildups and potential condensation due to the low-RPM operation, however I have NO idea if the buildup would still be an issue with CNG as fuel. If you can find the pistons from a high-compression 4AGE (the smallport version), those should boost the CR to around 11.5:1 in the 7AFE without having to mill the head.

[94_Rolla_Guy]

The combustion chamber on the two heads are identical!!!

i would say the best way to bump the compression would be to use 4a-fe pistons in the 7a-fe block the 7a-fe pistons have a 12cc dish while the 4a-fe's have a 8cc dish i ran the math it will bump it to about 10.5:1 compression

Just watch out buying a second hand 7a-fe alot of them have issues with oil burning

[theboss]

well i need a CR of 12:1 atleast to beging with. Cooling is not a problem just install larger main pulley to spin coolant pump faster. Figired out 1500rpm wont put out much power even in a top tuned unit. Must start with 3.0 Inline six to beging with..costs costs costs..thats kills the purpose of DIY.

Second question:
How about building high compression 4A(1.6L) or 5A(1.5L)??? Atleast 12.0:1

[3S-GTE pRIZM]

you can use which ever head you want...thats not what makes the displacement difference...the 7afe Block is taller and bulkier than the 4afe block...and the problem with the 7afe motors is the rods...

[retiredat44]

you can always order custom pistons for the compression you desire. Though I have no clue if the crank is built for that high of compression.

[Buurin]

Maybe there's an easier way than using an A-series. I know there's a CNG version of 5S for Cali. You sure you can't use a turbo or blower here?

Sorry I'm pulling ?s outta my ass.

[dakmor]

A way to keep the engine cooler is to slow down the coolant. Keep at a set speed. When the engine makes it turn faster, the coolant has less time to draw heat. It's not blowing air, it's blowing a liquid. Get a new thermostat as well.

[94_Rolla_Guy]

two comment's Alot of cabs run on CNG and they don't have high comp engines..... they will actually run on either gasoline or CNG. so there's now way you NEED 12:1 I would guess its a efficency thing ....

one other thought is 4A-GE pistons i know some of the flat-top N/A pistons will do like 11.8:1 or something in a 7a-fe bottom end no one plays with compression ratio's so high because even our premium gas will detonate or knock at these compression ratio's

to help you with calculations.... the 7a/4a-fe heads are 32cc and 4a-ge heads are 36cc's if i remeber correctly

[theboss]

well guys im not in the United States of A otherwise I wouldnt be crying here. Yes CNG is cheap but not really in third world aka Pakistan. A lot of cars here work on CNG too without beefing compression but you see if i am to generate power then i tighten every nut and bolt with efficiency in mind. People run these engines with forced induction setups so I dont think it will run into problems with high compression. 12:1 may be a bit optimistic but least it should settle at 10.5-11.0.

Forced induction is big NO NO mainly for simplicity sake. Secondly natural gas aupply is at mere 5psi which means there is no room for some serious boost. Not building a commericla power plant with team of decidated engineers. Simplicity of set up is very important here.

Overboring may be the solution. Can some tell how much over boring in diameter 4A block can handle. Also what kind of piston they use and is it a interference engine or non?? A little bit of over bore and flat piston may be a solution here.

i would say the best way to bump the compression would be to use 4a-fe pistons in the 7a-fe block the 7a-fe pistons have a 12cc dish while the 4a-fe's have a 8cc dish i ran the math it will bump it to about 10.5:1 compression

What about flat top piston in 4A-FE?? Doing the maths it roughly it sets me in heaven at 11.7:1 without overboring or such. Using pistons with 4cc disk equates ration of 11.0:1. Ok what alternate pistons would fit in if flats were required. I have access to machine shop so can get around with slight modifications of pistons and such. Thinking to get a closer matching piston then gring a mm or two from top to match compression height.

Thanks to all who took time to respond.

[retiredat44]

maybe you should just try to shave (mill) the head about 6 thousandths of an inch (not sure in mm how much).. someone else maybe can say how much is safe.. you can pick up a little that way and it's safe.. don't go crazy though..

[theboss]

1/6000th of an inch..wtf..this is a microscope engine or what?? :P

I think im gonna go try flat or small dish volume pistons.

[retiredat44]

If you were here in the USA I would say get some new pistons made,, maybe for about $600.00 USD you can have a set made with higher compression.. my brother used to make pistons for dragters (8 liter engines) that were 1 liter in size, 18:1 compression, with domes the size of a regular big block sized piston.... maybe there is some company that sells them off the shelf for the Corolla.

[theboss]

Well thinking of going to junk yard pull few pistons and see what happens.

[lleroyb]

Have you looked at a dyno sheet for a 7AFE at 1500 rpm? You are in the range of a riding lawn mower engine. Onan make some reliabe flat twins. Kubota and Yanmar make some small diesels that might be converted to NG.

Lou