7age using Honda rods???

[Mooro]

I was just brain-storming/day dreaming again and thinking about a 7age in my AW11 MR2. The main issue I have with them is the weak stock rods which general opinion seems to be that they are only good for 7500rpm max...This seems to be opposing the revy nature of the 4age head and does not sit right with me...I would like something that was capable of 8000 to 8500rpm reliably.

Anyway a guy who builds 7age race motors (way out of my league) mentioned that it maybe possible for budget application to use Honda rods with little to no machining involved. He couldn't remember the exact rod though so I was wondering if anyone had heard this and could shed some light on which Honda rods I would need?

Also are there any other rods from other engines which could potentially be used to save on the cost of billet rods?

[BeRad]

8500rpm + reliable = dreams....

"7age" rod specs would allow people to help you more.....

[Mooro]

By rod specs I presume you mean big end and small end diamters and lengths etc??? I don't know these but I was more aiming the question at people who had built 7age's or had researched them and had come across the same idea of using Honda rods.

In terms of 8000 to 8500 rpm reliably I don't think that is too far off the mark...definitely with stock 7afe rods but with something stronger I don't think it is unachievable. A stock blacktop redlines at 8200rpm and from what I can gather most people experienced with them seem to think 8500rpm is a safe limit. I know there is difference in piston speeds etc due to stroking etc etc but I don't think it is so great that 8000-8500rpm redline is unachievable. Most people who do 7age with stock prepped 7afe rods limit them to 7500rpm so I'm only looking for another 500 to 1000rpm???

[BeRad]

i was thinking more along the lines of the head, valve seats, springs etc wearing alot quicker than usual. although if the stock redline of the engine is 8200 i am wrong, sorry

[DX20VT]

A guy here I was talking too about 7A's had a N/A smallport version as a drift car an I think he used over 9000 on aftermarket rods etc etc.

[Forcefed6]

It is possible. I worked it all out for another person on Toymods a few weeks back from over that way.

To use the honda rod involves a custom set of pistons, and machining of the crank to make it work.

Brings it from a capacity of 17something cc upto 1868cc with the standard bore, or 1914cc with a 40thou over bore.

Crank needs offset grinding, and a bit more other work.

The honda rods are also really cheap. I can supply a set of SCAT H-beam rods for (with ARP bolts fitted) for around the $530 mark.

[Mooro]

It is possible. I worked it all out for another person on Toymods a few weeks back from over that way.

To use the honda rod involves a custom set of pistons, and machining of the crank to make it work.

Brings it from a capacity of 17something cc upto 1868cc with the standard bore, or 1914cc with a 40thou over bore.

Crank needs offset grinding, and a bit more other work.

The honda rods are also really cheap. I can supply a set of SCAT H-beam rods for (with ARP bolts fitted) for around the $530 mark.

Cheers for the info...do you know specifically which Honda engine they are from? 1.9L with blacktop head and 8500rpm would be nice

I guess all the work required on crank and buying custom pistons (not possible to use applicable Honda ones?) means it is still not a budget proposition?

[MRMOPARMAN]

i think 7afe rods are 137mm?

if ya download the corillo rod catalouge the honda B18a's have a rod length of 137mm. B18c's have a 138mm length.

other 7afe mesurments i have no idea.. will look into it though

[Mooro]

I found it in another thread the other day...I will see if I can find it again.

[Mooro]

For those interested I found the following dimensions for B18A/B rods,

Bore 81mm

stroke 89 mm

small end diameter 20.968 20.981 mm

big end diameter 48.00mm

rod length 137mm

So as mentioned above it wouldn't be possible to use them without getting custom pistons to overcome the 4.5mm extra length...it would result in a slightly better rod/stroke ratio but probably not a budget proposition

B16A rods are 134mm so I wonder if they could be made to work with stock 20V pistons, pending other dimensions (big end, small end) being workable? I guess the extra 1.5mm length would make the compression ratio very high. Using a 4age gasket (as opposed to 7afe) would recover about 0.6mm and maybe the 0.9mm could be recovered by some maching of combustion chamber and pistons??????

[DX20VT]

also the honda one's I looked at were a lot wider in the BE bearing width too.

[Mooro]

But the BE width is not really a weak point on the 7afe rods, so presumably (I may well be wrong here) you could potentially machine down the BE width of the Honda rods to suit the 7afe crank and still be as strong if not stronger than the 7afe rods. The only issue I can see is the BE cap bolting arrangement but if it is just one centrally located bolt each side then this shouldn't be a problem unless the bolts are massive.

[Mooro]

Obviously rod length is only one small part of the equation but some other possibilities I found with similar rod lengths

Datsun L16 - 133mm. I think these have a reputation for being tough little motors.
Honda B17a - 132. Good luck finding them though.
Mazda B6, BP - 132.9. Very common and again have a reputation for being very strong.

I guess my chances are slim but I'm going to look into the Mazda rods further as I reckon they would be a very good option if they can be made to work, they are plentiful and you can probably get them for nothing.

I'll add info here as I find it for the BP (1.8L) engine,
-Stock bore 83mm
-Stock stroke 85mm (so pretty similar to 7afe with an overbore)
-Stock rev limit is 7,200 rpm.
-Apparently the limit of the stock engines is ~8000rpm but I think this is more due to crank issues than rod strength plus I would bet that 20V pistons are lighter.
-I have attached a pic of the NA and turbo rods. The NA rod and bolts weigh 540gms whereas the turbo rod and bolts is 580gms...not sure how this compares to 7afe rods?
-Grr still can't find BE and SE diameters...

[wraith]

Sounds nice, but...
7A std stroke is 85.5mm, = mean piston speed of 4768 feet per min.
7A offset ground works out to be 90.5mm for 1868cc.
Which equates to a mean piston speed of 5047 feet per min.
I'm using FPM, because when I was looking at things like this the available data was in FPM. From memory, recommended max piston speed is about 4000FPM. OldCorollas knows a damn sight more than I do though, ask him.
Basically, with what you want to do, expect BANG a lot. These engines have conservative redlines for a reason...

cheers

Ash

EDIT- all calculations a preset 8500 RPM

[skiddz]

ive found they are a 132.5 rod length, any idea of the 7a v 20v pin height? in theory could you use a slightly shorter rod and a piston with a different pin height to acheive a decent (10-11.1)compression ratio?