4HUNJYHQ

hi all, just wondering if anyone has tried or has any info on this chev 4/7 swap. I read about it on a yank forum. There was quite a bit of debate, main arguments for were smoother torque curve, better bearing life (apparently its an old flathead ford trick for a better balanced engine) and better fuel delivery under load (clearly cant be confirmed on a dyno) a number of the people on there argueing for were engine builders, and use it on dirt track motors because of the smoother torque and therefore better throttle control, and engine longetivity, and apparently nascar rules were restricted to original firing order because of this. obvious cam change (apparently crower amongst others offer one in their lineup), just wondering if anyone has had any real world experience with this

cheers, Andy

wabbit

I've seen heaps of debate on this one, but I've never seen any before and after testing done to confirm/deny it.

Most of the ones arguing for it were from the small block Chev stable.
incidently, a 4-7 swap in a small block chev gives it the same firing order as the Holden V8s.
Since the Holdens are a newer engine, I would assume the original designers were pro 4-7 swap

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greenhj

I know of a few holdens that have altered the cam to suit the chev firing order.

wabbit

well, there you go.

I've never heard of that happening.

kinda lends more weight to the fact that it's all just speculation, doesn't it?

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Move along, please

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allports

This is an old 1. Thats been going on in Top fuel for 20yrs and in prostock for 25yrs. Pro stock clain it to be worth 25hp.
Why would you change a 308 (nearly perfect) firing order to a chev???? Map it out on paper and you'll see.

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4HUNJYHQ

thanks for the the responses, the guys on this other forum were claiming up to 40hp on a 500 cube pro stock engine. Allports, is it worth trying on a mild 400 if im already doing a cam change or is it only really noticeable in highly strung engines?

cheers, Andy

allports

Yes it is as it eliminates the 5-7 fire which causes an issue. As well as the main bearing pounding in a high revving V8 Chev. Saves a KB as well due to the same issue. Also evens the exhaust pulses up a little.
You wont feel much under foot though.

__________________
If you plant a cucumber, you get a cucumber!
Two things are infinate,the universe & human stupidity, and Im not sure about the universe.
Albert Einstein
Without deviation from the norm, progress is not possible. Frank Zappa

4HUNJYHQ

well, im going to get a dyno reading as it is over the next couple of weeks, as soon as the car is back on the street. Then ill be getting a readout after my lpg goes on (asap after its on road again). Thats when ill be looking at the cam change (i will pull the heads and get them cc'd and flowed at same time) Im not sure what sort of specs to go with on the gas, getting differing reports, but i wanna keep it as a streeter, ill get it thrown on the dyno after the cam swap and maybe it can help someone make some sense if i keep similar cam specs. at this stage i dont intend to have it particularly high revving(6-6.5k max), it will be getting rollers with the cam though. If its likely to make the engine a lil bit more durable then its probably worth it imo

mrprem

Yeah I've done a fair bit of reading on this one. I doubt the 40hp claims of pro stock engine builders, everything I've read says a 1 or 2hp gain at most, it's more for the durability side of things. If I were putting a new cam in my engine I'd probably go the 4/7 swap just cos I was buying a new cam anyway but other than that I wouldn't bother, It would never show up under foot or in quarter mile times. Comp Cams does a range of 4/7 swap cams.

allports

All the major cam manufacturers make 4-7 swaps. Crower, Isky, Herberts, Comp, Crane etc. The reputed number for a Prostock was 20hp.

__________________
If you plant a cucumber, you get a cucumber!
Two things are infinate,the universe & human stupidity, and Im not sure about the universe.
Albert Einstein
Without deviation from the norm, progress is not possible. Frank Zappa

ColB

20 -40 hp in a NHRA prostocker is like 2hp in a street car. Seems about right. Not worth the swap IMO unless you're making 1500hp.

allports

Its still not a patch on the Buick firing order though.

__________________
If you plant a cucumber, you get a cucumber!
Two things are infinate,the universe & human stupidity, and Im not sure about the universe.
Albert Einstein
Without deviation from the norm, progress is not possible. Frank Zappa